Reverse osmosis

Schematics of a reverse osmosis system (desalination) using a pressure exchanger.

1: Sea water inflow,

2: Fresh water flow (40%),

3: Concentrate flow (60%),

4: Sea water flow (60%),

5: Concentrate (drain),

A: Pump flow (40%),

B: Circulation pump,

C: Osmosis unit with membrane,

D: Pressure exchanger

Reverse osmosis (RO) is a membrane-technology filtration method that removes many types of

large molecules and ions from solutions by applying pressure to the solution when it is on one side of a

selective membrane. The result is that the solute is retained on the pressurized side of the membrane and

the pure solvent is allowed to pass to the other side. To be "selective," this membrane should not allow large

molecules or ions through the pores (holes), but should allow smaller components of the solution (such as

the solvent) to pass freely.

In the normal osmosis process, the solvent naturally moves from an area of low solute concentration (High

Water Potential), through a membrane, to an area of high solute concentration (Low Water Potential). The

movement of a pure solvent to equalize solute concentrations on each side of a membrane

generates osmotic pressure. Applying an external pressure to reverse the natural flow of pure solvent, thus,

is reverse osmosis. The process is similar to other membrane technology applications. However, there are

key differences between reverse osmosis and filtration. The predominant removal mechanism in membrane

filtration is straining, or size exclusion, so the process can theoretically achieve perfect exclusion of particles

regardless of operational parameters such as influent pressure and concentration. Reverse osmosis,

however, involves a diffusive mechanism so that separation efficiency is dependent on solute concentration,

pressure, and water flux rate.[1] Reverse osmosis is most commonly known for its use in drinking water

purificationfrom seawater, removing the salt and other substances from the water molecules.

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History

The process of osmosis through semipermeable membranes was first observed in 1748 by Jean-Antoine

Nollet. For the following 200 years, osmosis was only a phenomenon observed in the laboratory. In 1949,

the University of California at Los Angeles (UCLA) first investigated desalination of seawater using

semipermeable membranes. Researchers from both UCLA and theUniversity of Florida successfully

produced fresh water from seawater in the mid-1950s, but the flux was too low to be commercially

viable[2] until the discovery by Loeb and Sourirajan of techniques for making asymmetric membranes

characterized by an effectively thin "skin" layer supported atop a highly porous and much thicker substrate

region of the membrane. By the end of 2001, about 15,200 desalination plants were in operation or in the

planning stages worldwide.[1]

Process

A semipermeable membrane coil used indesalination

Osmosis is a natural process. When two liquids of different concentration are separated by a semipermeable

membrane, the fluid has a tendency to move from low to high solute concentrations for chemical potential

equilibrium.

Formally, reverse osmosis is the process of forcing a solvent from a region of high solute concentration

through a semipermeable membrane to a region of low solute concentration by applying a pressure in

excess of the osmotic pressure. The largest and most important application of reverse osmosis is the

separation of pure water from seawater and brackish waters; seawater or brackish water is pressurized

against one surface of the membrane, causing transport of salt-depleted water across the membrane and

emergence of potable drinking water from the low-pressure side.

The membranes used for reverse osmosis have a dense layer in the polymer matrix -- either the skin of an

asymmetric membrane or an interfacially polymerized layer within a thin-film-composite membrane -- where

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the separation occurs. In most cases, the membrane is designed to allow only water to pass through this

dense layer, while preventing the passage of solutes (such as salt ions). This process requires that a high

pressure be exerted on the high concentration side of the membrane, usually 2–17 bar (30–250 psi) for fresh

and brackish water, and 40–82 bar (600–1200 psi) for seawater, which has around 27 bar (390 psi)[3] natural

osmotic pressure that must be overcome. This process is best known for its use in desalination (removing

the salt and other minerals from sea water to get fresh water), but since the early 1970s it has also been

used to purify fresh water for medical, industrial, and domestic applications.

Osmosis describes how solvent moves between two solutions separated by a permeable membrane to

reduce concentration differences between the solutions. When two solutions with different concentrations of

a solute are mixed, the total amount of solutes in the two solutions will be equally distributed in the total

amount of solvent from the two solutions. Instead of mixing the two solutions together, they can be put in two

compartments where they are separated from each other by a semipermeable membrane. The

semipermeable membrane does not allow the solutes to move from one compartment to the other, but

allows the solvent to move. Since equilibrium cannot be achieved by the movement of solutes from the

compartment with high solute concentration to the one with low solute concentration, it is instead achieved

by the movement of the solvent from areas of low solute concentration to areas of high solute concentration.

When the solvent moves away from low concentration areas, it causes these areas to become more

concentrated. On the other side, when the solvent moves into areas of high concentration, solute

concentration will decrease. This process is termed osmosis. The tendency for solvent to flow through the

membrane can be expressed as "osmotic pressure", since it is analogous to flow caused by a pressure

differential. Osmosis is an example of diffusion.

In reverse osmosis, in a similar setup as that in osmosis, pressure is applied to the compartment with high

concentration. In this case, there are two forces influencing the movement of water: the pressure caused by

the difference in solute concentration between the two compartments (the osmotic pressure) and the

externally applied pressure.

Applications

Drinking water purification

Marines from Combat Logistics Battalion 31 operate ROWPUs for relief efforts after

the 2006 Southern Leyte mudslide

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Around the world, household drinking water purification systems, including a reverse osmosis step, are

commonly used for improving water for drinking and cooking.

Such systems typically include a number of steps:

a sediment filter to trap particles, including rust and calcium carbonate

optionally, a second sediment filter with smaller pores

an activated carbon filter to trap organic chemicals and chlorine, which will attack and degrade TFC

reverse osmosis membranes

a reverse osmosis (RO) filter, which is a thin film composite membrane (TFM or TFC)

optionally, a second carbon filter to capture those chemicals not removed by the RO membrane

optionally an ultra-violet lamp for sterilizing any microbes that may escape filtering by the reverse

osmosis membrane

In some systems, the carbon prefilter is omitted, and cellulose triacetate membrane (CTA) is used. The CTA

membrane is prone to rotting unless protected by chlorinated water, while the TFC membrane is prone to

breaking down under the influence of chlorine. In CTA systems, a carbon postfilter is needed to remove

chlorine from the final product, water.

Portable reverse osmosis (RO) water processors are sold for personal water purification in various locations.

To work effectively, the water feeding to these units should be under some pressure (40 pounds per square

inch (280 kPa) or greater is the norm).[citation needed] Portable RO water processors can be used by people who

live in rural areas without clean water, far away from the city's water pipes. Rural people filter river or ocean

water themselves, as the device is easy to use (saline water may need special membranes). Some travelers

on long boating, fishing, or island camping trips, or in countries where the local water supply is polluted or

substandard, use RO water processors coupled with one or more UV sterilizers. RO systems are also now

extensively used by marine aquarium enthusiasts. In the production of bottled mineral water, the water

passes through an RO water processor to remove pollutants and microorganisms. In European countries,

though, such processing of Natural Mineral Water (as defined by a European Directive[4]) is not allowed

under European law. In practice, a fraction of the living bacteria can and do pass through RO membranes

through minor imperfections, or bypass the membrane entirely through tiny leaks in surrounding seals. Thus,

complete RO systems may include additional water treatment stages that use ultraviolet light or ozone to

prevent microbiological contamination.

Membrane pore sizes can vary from 0.1 nanometres (3.9×10−9 in) to 5,000 nanometres (0.00020 in)

depending on filter type. "Particle filtration" removes particles of 1 micrometre (3.9×10−5 in) or

larger. Microfiltration removes particles of 50 nm or larger. "Ultrafiltration" removes particles of roughly 3 nm

or larger. "Nanofiltration" removes particles of 1 nm or larger. Reverse osmosis is in the final category of

membrane filtration, "hyperfiltration", and removes particles larger than 0.1 nm.

In the United States military, Reverse Osmosis Water Purification Units are used on the battlefield and in

training. Capacities range from 1,500 to 150,000 imperial gallons (6,800 to 680,000 l) per day, depending on

the need. The most common of these are the 600 and 3,000 gallons per hour units; both are able to purify

salt water and water contaminated with chemical, biological, radiological, and nuclear agents from the water.

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During 24-hour period, at normal operating parameters, one unit can produce 12,000 to 60,000 imperial

gallons (55,000 to 270,000 l) of water, with a required 4-hour maintenance window to check systems,

pumps, RO elements and the engine generator. A single ROWPU can sustain a force the size of a battalion,

or roughly 1,000 to 6,000 servicemembers.[citation needed]

Water and wastewater purification

Rain water collected from storm drains is purified with reverse osmosis water processors and used for

landscape irrigation and industrial cooling in Los Angeles and other cities, as a solution to the problem of

water shortages.

In industry, reverse osmosis removes minerals from boiler water at power plants. The water

is distilled multiple times. It must be as pure as possible so that it does not leave deposits on the machinery

or cause corrosion. The deposits inside or outside the boiler tubes may result in under-performance of the

boiler, bringing down its efficiency and resulting in poor steam production, hence poor power production at

turbine.

It is also used to clean effluent and brackish groundwater. The effluent in larger volumes (more than 500 cu.

meter per day) should be treated in an effluent treatment plant first, and then the clear effluent is subjected

to reverse osmosis system. Treatment cost is reduced significantly and membrane life of the RO system is

increased.[citation needed]

The process of reverse osmosis can be used for the production of deionized water.

RO process for water purification does not require thermal energy. Flow through RO system can be

regulated by a high pressure pump. The recovery of purified water depends upon various factors including

membrane sizes, membrane pore size, temperature, operating pressure and membrane surface area.

In 2002, Singapore announced that a process named NEWater would be a significant part of its future water

plans. It involves using reverse osmosis to treat domestic wastewater before discharging the NEWater back

into the reservoirs.

Food industry

In addition to desalination, reverse osmosis is a more economical operation for concentrating food liquids

(such as fruit juices) than conventional heat-treatment processes. Research has been done on concentration

of orange juice and tomato juice. Its advantages include a lower operating cost and the ability to avoid heat-

treatment processes, which makes it suitable for heat-sensitive substances like

the protein and enzymes found in most food products.

Reverse osmosis is extensively used in the dairy industry for the production of whey protein powders and for

the concentration of milk to reduce shipping costs. In whey applications, the whey (liquid remaining after

cheese manufacture) is concentrated with RO from 6% total solids to 10–20% total solids before UF

(ultrafiltration) processing. The UF retentate can then be used to make various whey powders,

including whey protein isolate used in bodybuilding formulations. Additionally, the UF permeate, which

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contains lactose, is concentrated by RO from 5% total solids to 18–22% total solids to reduce crystallization

and drying costs of the lactose powder.

Although use of the process was once avoided in the wine industry, it is now widely understood and used.

An estimated 60 reverse osmosis machines were in use in Bordeaux, France in 2002. Known users include

many of the elite classed growths (Kramer) such as Château Léoville-Las Cases in Bordeaux.[citation needed]

Maple syrup production

In 1946, some maple syrup producers started using reverse osmosis to remove water from sap before the

sap is boiled down to syrup. The use of reverse osmosis allows approximately 75-90% of the water to be

removed from the sap, reducing energy consumption and exposure of the syrup to high temperatures.

Microbial contamination and degradation of the membranes has to be monitored.

Hydrogen production

For small-scale production of hydrogen, reverse osmosis is sometimes used to prevent formation of minerals

on the surface of electrodes.

Reef aquariums

Many reef aquarium keepers use reverse osmosis systems for their artificial mixture of seawater. Ordinary

tap water can often contain excessive chlorine, chloramines, copper, nitrates, nitrites, phosphates, silicates,

or many other chemicals detrimental to the sensitive organisms in a reef environment. Contaminants such

as nitrogen compounds and phosphates can lead to excessive, and unwanted, algae growth. An effective

combination of both reverse osmosis and deionization (RO/DI) is the most popular among reef aquarium

keepers, and is preferred above other water purification processes due to the low cost of ownership and

minimal operating costs. Where chlorine and chloramines are found in the water, carbon filtration is needed

before the membrane, as the common residential membrane used by reef keepers does not cope with these

compounds.

Desalination

Areas that have either no or limited surface water or groundwater may choose to desalinate. Reverse

osmosis is a common method of desalination. Although, 85 percent of desalinated water is produced

in multistage flash plants.[5]

Large reverse osmosis and multistage flash desalination plants are used in the Middle East, especially Saudi

Arabia. The energy requirements of the plants are large, but electricity can be produced relatively cheaply

with the abundant oil reserves in the region. The desalination plants are often located adjacent to the power

plants, which reduces energy losses in transmission and allows waste heat to be used in the desalination

process of multistage flash plants, reducing the amount of energy needed to desalinate the water and

providing cooling for the power plant.

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Sea water reverse osmosis (SWRO) is a reverse osmosis desalination membrane process that has been

commercially used since the early 1970s. Its first practical use was demonstrated bySidney Loeb and

Srinivasa Sourirajan from UCLA in Coalinga, California. Because no heating or phase changes are needed,

energy requirements are low in comparison to other processes of desalination, but are still much higher than

those required for other forms of water supply (including reverse osmosis treatment of wastewater).[citation

needed]

The Ashkelon seawater reverse osmosis (SWRO) desalination plant in Israel is the largest in the world.[6]

[7] The project was developed as a BOT (Build-Operate-Transfer) by a consortium of three international

companies: Veolia water, IDE Technologies and Elran.[8]

The typical single-pass SWRO system consists of the following components:

Intake

Pretreatment

High pressure pump

Membrane assembly

Remineralisation and pH adjustment

Disinfection

Alarm/control panel

Pretreatment

Pretreatment is important when working with RO and nanofiltration (NF) membranes due to the nature of

their spiral wound design. The material is engineered in such a fashion as to allow only one-way flow

through the system. As such, the spiral wound design does not allow for backpulsing with water or air

agitation to scour its surface and remove solids. Since accumulated material cannot be removed from the

membrane surface systems, they are highly susceptible to fouling (loss of production capacity). Therefore,

pretreatment is a necessity for any RO or NF system. Pretreatment in SWRO systems has four major

components:

Screening of solids: Solids within the water must be removed and the water treated to prevent

fouling of the membranes by fine particle or biological growth, and reduce the risk of damage to high-

pressure pump components.

Cartridge filtration: Generally, string-wound polypropylene filters are used to remove particles of 1–5

µm diameter.

Dosing: Oxidizing biocides, such as chlorine, are added to kill bacteria, followed by bisulfite dosing to

deactivate the chlorine, which can destroy a thin-film composite membrane. There are

also biofouling inhibitors, which do not kill bacteria, but simply prevent them from growing slime on the

membrane surface and plant walls.

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Prefiltration pH adjustment: If the pH, hardness and the alkalinity in the feedwater result in a scaling

tendency when they are concentrated in the reject stream, acid is dosed to maintain carbonates in their

soluble carbonic acid form.

CO32– + H3O+ = HCO3

– + H2O

HCO3– + H3O+ = H2CO3 + H2O

Carbonic acid cannot combine with calcium to form calcium carbonate scale. Calcium carbonate

scaling tendency is estimated using the Langelier saturation index. Adding too much sulfuric

acid to control carbonate scales may result in calcium sulfate, barium sulfate or strontium sulfate

scale formation on the RO membrane.

Prefiltration antiscalants: Scale inhibitors (also known as antiscalants) prevent formation of all

scales compared to acid, which can only prevent formation of calcium carbonate and calcium

phosphate scales. In addition to inhibiting carbonate and phosphate scales, antiscalants inhibit

sulfate and fluoride scales, disperse colloids and metal oxides. Despite claims that antiscalants

can inhibit silica formation, there is no concrete evidence to prove that silica polymerization can

be inhibited by antiscalants. Antiscalants can control acid soluble scales at a fraction of the

dosage required to control the same scale using sulfuric acid.[9]

Some small scale desalination units use beach wells; they are usually drilled on the seashore

in close vicinity to the ocean. These intake facilities are relatively simple to build and the

seawater they collect is pretreated via slow filtration through the subsurface sand/seabed

formations in the area of source water extraction. Raw seawater collected using beach wells is

often of better quality in terms of solids, silt, oil and grease, natural organic contamination and

aquatic microorganisms, compared to open seawater intakes. Sometimes, beach intakes may

also yield source water of lower salinity.

High pressure pump

The pump supplies the pressure needed to push water through the membrane, even as the

membrane rejects the passage of salt through it. Typical pressures for brackish water range from

225 to 375 psi (15.5 to 26 bar, or 1.6 to 2.6 MPa). In the case of seawater, they range from 800 to

1,180 psi (55 to 81.5 bar or 6 to 8 MPa). This requires a large amount of energy.

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Membrane assembly

The layers of a membrane

The membrane assembly consists of a pressure vessel with a membrane that allows feedwater to

be pressed against it. The membrane must be strong enough to withstand whatever pressure is

applied against it. RO membranes are made in a variety of configurations, with the two most

common configurations being spiral-wound and hollow-fiber.

Remineralisation and pH adjustment

The desalinated water is very corrosive[citation needed] and is "stabilized" to protect downstream pipelines

and storages, usually by adding lime or caustic to prevent corrosion of concrete lined surfaces.

Liming material is used to adjust pH between 6.8 and 8.1 to meet the potable water specifications,

primarily for effective disinfection and for corrosion control.

Disinfection

Post-treatment consists of preparing the water for distribution after filtration. Reverse osmosis is an

effective barrier to pathogens, however post-treatment provides secondary protection against

compromised membranes and downstream problems. Disinfection by means of UV lamps

(sometimes called germicidal or bactericidal) may be employed to sterilize pathogens which

bypassed the reverse osmosis process. Chlorination or chloramination (chlorine and ammonia)

protects against pathogens which may have lodged in the distribution system downstream, such as

from new construction, backwash, compromised pipes, etc.[citation needed]

Disadvantages

Household reverse osmosis units use a lot of water because they have low back pressure. As a

result, they recover only 5 to 15 percent of the water entering the system. The remainder is

discharged as waste water. Because waste water carries with it the rejected contaminants, methods

to recover this water are not practical for household systems. Wastewater is typically connected to

the house drains and will add to the load on the household septic system. An RO unit delivering 5

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gallons of treated water per day may discharge anywhere between 20 and 90 gallons of waste water

per day.[10]

Large-scale industrial/municipal systems have a production efficiency typically 75% to 80%, or as

high as 90%, because they can generate the high pressure needed for more efficient reverse

osmosis filtration. On the other hand, as efficiency of waste-water rates increases in commercial

operations effective removal rates tend to become reduced, as evidenced by total dissolved

solids (TDS) counts.

Due to its fine membrane construction, reverse osmosis not only removes harmful contaminants that

may be present in the water, it also strips many of the good, healthy minerals from the water. A

number of peer-reviewed studies have looked at the long term health effects of

drinking demineralized water.[11] However, demineralized water can be remineralized and this

process has been done in instances when processing demineralized water for consumption. An

example of this process is Dasani, which adds sodium chloride (salt) and potassium chloride (salt)

to its water for "taste," according to the company.[12]

New developments

Prefiltration of high fouling waters with another, larger-pore membrane with less hydraulic energy

requirement, has been evaluated and sometimes used, since the 1970s. However, this means the

water passes through two membranes and is often repressurized, requiring more energy input in the

system, increasing the cost.

Other recent development work has focused on integrating RO with electrodialysis to improve

recovery of valuable deionized products or minimize concentrate volume requiring discharge or

disposal.

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Typical system

installation layout

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Acute RO loop

Types of Water Treatment Systems

 

Which Type of Water Treatment System Best Meets My Needs?

Descriptions of Four Main Types of  Water Treatment Systems

Commonly Asked Questions

Trouble Shooting Guide

Glossary

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Description of Four Main Types of Water Treatment Systems:

In an effort to help you identify your existing water treatment system or to help you choose the

new system which will best fit your needs, we have provided information about the following

four types of water purification and water filtration systems.

Distillation: Is the process in which a liquid such as water is converted by heating, into a vapor state,

and the vapor cooled and condensed to a liquid state and collected. It is the process of removing the

liquid (water) from its constituents or contaminants; as compared to other processes where

contaminants are removed from the water (liquid). Distilled water is water that has been purified by

passing through one or more evaporation –condensation cycles and contains essentially no dissolved

solids. See illustration

For additional information on distillation refer to frequently asked questions about distillation.

Reverse Osmosis: Is a process for the reduction of dissolved ions (such as salts) from water in which

pressure is employed to force liquid (water) through a semi-permeable membrane, which will transmit

the water but reject most other dissolved materials. When forced against the membrane surface, the

dissolved materials are repelled, while the water molecules are diffused through the membrane

molecule by molecule, forming purer water on the other side. Find out more on reverse osmosis

installation or learn more about RO systems.

How Salty is Your Water???

Salt Water is the general term for all water over 1,000 ppm (mg/L) total dissolved solids (TDS).

Water Type TDS (mg/L)

Fresh 

Brackish 

Highly Brackish 

Saline 

Sea Water 

Brine

<1,000 

1,000 – 5,000 

5,000 – 15,000

15,000 - 30,000 

30,000 – 40,000 

40,000 – 300,000+

For additional information on reverse osmosis refer our information page on Reverse Osmosis.

Ultraviolet: Sunlight has long since been known to kill micro-organisms. The rays from the sun contain

the UV *spectrum used in Ultraviolet Water Treatment Systems – although at much lower intensities. It

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is also referred to as either the Germicidal Spectrum or Frequency. The frequency used in killing micro-

organisms is 254 nanometers (nm). The UV lamps used are designed specifically to have the highest

amount of UV energy at this frequency. See illustration

*Spectrum an array of the components of an emission or wave separated and arranged in the order of

some varying characteristic (as wavelength, mass or energy).

Filtration: A process in which water passes through a water system that may include one or more

filters for the purpose of removing turbidity, taste, color, iron or odor. The design can be loose media

tank-type systems or cartridge devices. In general the process may include mechanical, adsorptive,

neutralizing and catalyst/oxidizing filters.

For additional information on filtration refer to frequently asked questions about filtration.

Under Counter Standard Reverse Osmosis System

Installation Guidelines

Your new reverse osmosis drinking water system processes, stores and dispenses water. It operates

on normal home water pressure between 40 –65 psi. The inlet water pressure, the water temperature

and the amount of TDS (total dissolved solids) affect the efficiency of the reverse osmosis system.

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In most cases your new reverses osmosis system will come with clear and concise installation

instructions. In the event you did not receive installation instructions, or if you are just interested in

knowing how a reverse osmosis system is installed, the following guide should prove to be very useful.

Keep in mind that there are many different types of reverse osmosis systems on the market and the

guidelines below may not apply to your specific system. Contact the manufacturer of your system for

product specific instructions.

Before beginning the installation, you should always check to make sure you have everything

necessary to complete the installation.

Your new system consists of the following items:

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- R.O Unit (1)

- Storage Tank (1)

- Faucet and Installation Kit (1)

Have on hand the following tools and materials during the installation process.

- Wrenches Sizes 7/16”, 9/16”, ½” & 5/8”

- Phillips Screw Driver- Drill With 3/8” Chuck

- Drill Bits Sizes ¼” or 1 1/8” For Air Gap faucet

PLEASE READ AND BECOME FAMILIAR WITH ALL INSTRUCTIONS AND PARTS BEFORE

STARTING THE INSTALLATION PROCESS

Step 1. Installation Location

Find a suitable location where the system can be installed. Make sure there is sufficient space under

the counter for proper installation. Locate the “cold” water shut off valve and sink drainpipe.

Step 2. Closing Cold Water Valve

Shut off the “cold” water supply under the sink or the location where the system will be installed. If the

existing “cold” water valve is inoperable, the water supply to the house must be shut off. Then, relieve

the line pressure by opening the “cold” water faucet. 

Step 3. Connecting To Cold Water Line

There are several options when connecting the reverse osmosis unit to the cold-water source. They

are:

3.1 Saddle valve (Standard) – Assemble saddle valve clamp on the “cold” water line. Turn the pipe

clamp adjustment plate to fit the contour of the pipe. (Small radius for 3/8” pipe, larger radius for 7/16”

through 5/8” pipe). Tighten bolt so saddle valve is firmly attached to feed water pipe (be careful not to

over tighten).

3.2 Ez adapter. (Optional) : Use some Teflon tape to prevent leaks. Assemble 90 degree needle valve

into the feed adapter.

** Flex line installation: Disconnect the flex line at the sink and install the feed adapter. Reconnect the

flex line to the adapter.

** Solid line installation: Disconnect the line at the sink cut off approximately ¾” off the line. Install the

feed adapter and reconnect line to the feed adapter.

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Step 4. Drain Line Connection: CAUTION: If the drain line pipe is badly corroded replace it.

At a point approximately six (6) inches above the trap, drill a 5/16” diameter bole through one wall of the

pipe. Attach the drain clamp; making sure that the hole in the clamp is aligned with the hole in the pipe.

Use a punch or drill bit to align the holes while tightening the clamp. Be careful not to over tighten the

clamp.

Step 5. Faucet Installation:

The faucet must be positioned with aesthetics, function and convenience in mind. An ample flat area is

required for the faucet base, so the base nut can be properly tightened. Conditions may exists which

eliminate the need to drill a hole in the sink.

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5a. A hole previously installed in the sink, covered by a chrome plate cover. Remove the cover and

mount the faucet.

5b. A spray hose that may not be functioning or needed. Remove the spray hose and plug the outlet

under the main faucet. If the sprayer uses a diverter at the base of the spout remove it, as the sprayer

diverter may pop up and shut the water off to the main faucet.

5c. If space is not available on the upper sink area, the faucet can be located in the counter top close to

the edge of the sink. Be careful to watch for obstructions below the counter such as drawers, cabinet

walls, support braces etc.. If the counter top is ceramic tile the method for drilling the faucet hole is the

same as for drilling a porcelain sink.

5d. The drilling process although not complicated, requires a certain amount of caution and preparation.

Porcelain enameled sinks can be chipped if care is not exercised when drilling the hole for the faucet

assembly. There are several ways of drilling the holes in to porcelain sinks without chipping; we have

found these two methods work very well.

D.1 Using a carbide grinding wheel, grind away the porcelain where the ¼” diameter hole is to be

drilled. Drill a ¼” diameter hole through the metal. This method results in a very clean and smooth hole.

D.2 Using a heavy duty variable speed drill and a carbide tip drill bit, carefully drill a ¼” diameter hole

through the porcelain and metal sink.

Caution: Do not allow metal chips to remain on the porcelain surface of the sink for any length

of time, the metal chips will stain the sink and be very difficult to remove.

5e. For stainless steel sinks, simply drill a ¼” diameter hole. Lightly file the edge of the hole to make

sure it is smooth and free of any burrs.

Step 6. Faucet Installation.

Once the hole has been drilled in the sink, the faucet stem may be inserted in the hole. Be sure the

faucet body, faucet base and the rubber faucet base washer are in place above the sink.

Install the star lock washer and nut on the faucet stem under the sink and tighten firmly while aligning

faucet in the desired direction. Once the faucet is installed, attach the ¼” tubing on to the bottom of the

faucet stem and tighten.

Note: Some states require the use of an air gap faucet. To assure compliance check you local plumbing

code. Locate the drain connection away from the garbage disposal to prevent potential contamination

and system fouling.

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Air gap faucet installation instructions:

Place the chrome washer and rubber washer on the base of the faucet. Slip the ¼” black line from the

system through the hole in the sink. From the topside of the sink, slip the ¼” black line from system

onto the barbed fitting located in the faucet base. The 3/8” black line from barb output is to be run as

straight down hill as possible to the drain clamp. Avoid low spots or loops. Place faucet into the hole of

the sink then from underneath sink, replace parts and tighten the hold down nut. Connect the ¼” blue

line to the threaded faucet stem.

Step 7. Unit Location

Place the system and the water storage tank in an area under the sink so they are out of the way. If the

system is to be hung on the wall be sure there is enough clearance from the cabinet floor to the bottom

of the filter housing sump, leave at least 3 inches. Drill two 1/8” pilot holes that match up to the

mounting holes in the systems bracket, mount the system to the cabinet wall.

Step 8. System hook up.

Remove any red caps from the end of the tubing. There may be water present in these lines if the

system was wet tested at the factory, so keep a towel handy to wipe up any water.

Note: color of lines may vary from manufacturer to manufacturer – we have attempted to use industry

standard colors in describing the system hook up procedures.

19

8A. Connect the units orange feed water line to the saddle valve or EZ adapter installed on the cold

water line. Use the plastic delrin sleeve that are provided in the installation kit and discard any brass

ferrules that may have been provided.

8B. Connect the black line from the unit directly to the drain clamp assembly. If an air gap faucet is

used see instruction listed under air gap faucet installation instructions.

8C. Connect the green line to the RO water storage tank.

8D. Connect the blue line from the unit to the faucet.

Note: Make sure all inserts, sleeves and ferrules provided in the installation kit are used.

THIS IS A GOOD TIME TO DOUBLE CHECK AND MAKE SURE ALL YOUR FITTINGS ARE TIGHT

AND THE TUBING IS SECURE IN THE FITTINGS.

Step 9. Starting Up the System

9A. Turn off the storage tank ball valve, this will ensure no water can enter the tank. Slowly turn on the cold water supply valve to the sink. If you have not already done so, open the valve of the cold-water self-piercing valve (turn counter clockwise to open). Check for any leaks around the valve. If any leaks are detected turn off cold water supply valve and make necessary repairs.

9B. Open the reverse osmosis faucet on the sink. You will hear a gurgling noise. This is normal air

being cleared from the system. It will take approximately 10-15 minutes before you actually see water

dripping from the reverse osmosis faucet. (Flip the faucet handle up to keep the faucet open during this

time.) The initial water dripping from the faucet may be black in color; this is the water flushing carbon

fines from the carbon post filters. Allow the water to drip from the faucet for 10-15 minutes then close

the faucet

9C. Now open the ball valve on the reverse osmosis storage tank, which will allow the tank to fill. This will take approximately 4-10 hours. During this period of time check all fittings for any leaks. If any leaks are found turn off cold-water line and make the necessary correction. Once the tank is full open the faucet and drain the system completely (until you are getting only a drip from the faucet). Shut the reverse osmosis faucet off and allow the system to re-fill.

9D. It is recommended on new installations that you drain the system 3 times prior to use.

9E. Make a daily check for any leaks during the first week after installation and check for leaks

occasionally thereafter.

If you have a refrigerator with an automatic water dispenser and/or icemaker and would like to use the water from your reverse osmosis system for theses applications you will find the following guideline very useful.

Hooking Up Your Reverse Osmosis System to Your Refrigerator

20

1. Install a Tee fitting on the tubing going from the post filter to the reverse osmosis faucet. Run a

¼” polypropylene tube up to 30’ from the reverse osmosis system and connect to the

refrigerator. Over a 30’ run use a tube larger than ¼” for best results. DO NOT USE COPPER.

Be sure you have the recommended water pressure to your ice- maker according to the

refrigerator manufacturer. This tube needs tube inserts on both ends. 

2. It is recommended to install a ball valve on the tube to the refrigerator for service and start up

purposes. Keep ball valve off until start up procedures is completed and reverse osmosis tank is

completely full and ready to drink. 

IMPORTANT: To avoid damaging the icemakers solenoid, Never turn icemaker on until you

have a full tank of water.

Filter and Membrane Changing Procedures: 

Recommended Filter Service Life and Filter Change Cycle

Sediment Pre-Filter – Change every 6-12 months more often in areas with very high turbidity in water.

Carbon Pre-Filter – Change every 6-12 months. This will help to ensure membrane life and quality.

Reverse Osmosis Membrane – Change the reverse osmosis membrane when the rejection rate falls

below 75%.

Carbon Post Filter – Change this filter every 6 – 12 months to insure quality water. Do not wait until

taste is a problem.

All reverse osmosis systems require some periodic maintenance to insure you are getting the same

water quality as when the system was new. There is no maintenance more important than timely filter

changes.

1. How to Change the Filters & Membrane 

It is important to ensure that when changing any filters or membrane on your drinking water system

appropriate sanitation and service procedures are used. The following step-by-step guideline will help

to ensure those sanitation and service procedures are met.

A. Be certain that only the proper filter cartridges are used for replacement.

B. The filter cartridges should remain in the original packaging until service to the system is performed.

C. The systems service area should be free from any dirt or dust.

21

D. The person performing the service MUST wash their hands with soap and water prior to performing

any of the service work.

E. NEVER RUN HOT WATER THROUGH THE SYSTEM!

FILTER Changes

Step 1. Turn off the water supply line valve to the reverse osmosis system. Close the ball valve on the

reverse osmosis storage tank. Open the reverse osmosis faucet and allow the pressure in the system

to bleed off.

Step 2. Place a shallow tray under the filter housing, to catch any water that may spill during the filter

changing process.

Step 3. Unscrew the filter housing and remove the used filter cartridge. (A special filter-housing wrench

is available)

Step 4. Carefully remove the O-ring and place it on a clean surface. Rinse out the filter housing using

warm water and a small amount of liquid soap. Be certain that all of the soap is thoroughly rinsed out of

the filter housing.

Step 5. Wipe the O-ring clean with a soft clean rag or towel and visually inspect for any nicks cuts or

abrasions that may cause the O-ring to improperly seat in the filter housings O-ring groove. If the O-ring

appears damaged replace it (O-rings are available from ESP)

Step 6. Lubricate the O-ring lightly with a silicon lubricant. Replace the O-ring in the O-ring filter-

housing groove. It is important to be sure the O-ring is properly seated in the groove as it provides the

watertight seal between the filter housing and the cap.

Step 7. Remove the new filter from the original plastic wrap. Measure the new filter to be sure it is the

proper length.

Step 8. Place the filter in the housing and carefully screw the filter housing back on to the cap of the

filter housing (hand tighten only).

Step 9. Turn the feed water supply valve on. Check for leaks.

Step 10. Open the reverse osmosis faucet and allow water to flow until the water is clear. Close faucet.

System is now ready for use.

MEMBRANE Changes (for standard replacement membranes)

22

Step 1. Turn off the water supply line valve to the reverse osmosis system. Close the ball valve on the

reverse osmosis storage tank. Open the reverse osmosis faucet and allow the pressure in the system

to bleed off.

Step 2. Disconnect tubing from membrane housing. Immediately label which tube came out of which

fitting.

Step 3. Unscrew membrane housing end cap and remove membrane. This may require needle- nose

pliers.

Step 4. Rinse and clean the inside of membrane housing with warm water.

Step 5. Insert new membrane in housing (o-ring end first) until you feel the o-rings seat into the

opposite end cap. To do so you may need to move the membrane in a slight circular motion to center

the membrane center tube. If the membrane is not properly seated untreated water will flow unrestricted

through the system.

Step 6. Replace and tighten the membrane housing screw cap. Reinstall the tubing you removed to the

appropriate fittings.

Step 7. Turn on the water supply line valve until you hear water entering the system. Check for any

leaks.

Step 8. Open feed water valve all the way. Allow filling until a steady drip flows from the reverse

osmosis faucet.

Step 9. Close reverse osmosis faucet.

Step 10. Open valve on storage tank. Check for any leaks. System is now ready for use.

 

TYPICAL REJECTION CHARACTERISTICS OF R.O.

MEMBRANES

Elements and the Percent R.O. Membranes will remove

 Sodium 

Sulfate 

Calcium

Potassium 

Nitrate 

Iron 

85 - 94%

96 - 98%

94 - 98% 

85 - 95% 

60 –75% 

94 – 98% 

95 – 98% 

23

Zinc 

Mercury

Selenium 

Phosphate 

Lead 

Arsenic

Magnesium

Nickel 

Fluoride 

Manganese 

Cadmium 

Barium 

Cyanide 

Chloride

95 – 98% 

94 – 96% 

96 – 98% 

95 – 98% 

92 – 96% 

94 – 98% 

96 – 98% 

85 - 92% 

94 – 98% 

95 – 98% 

95 – 98% 

84 – 92% 

85 – 92% 

% may vary based on membrane type water pressure, temperature & TDS

Does your RO membrane need to be replaced?

It is very difficult to guess when the membrane on a reverse osmosis drinking water unit needs to be

replaced. In most cases the membrane has a much longer life span than the other reverse osmosis

units filters. Since the membrane is the most expensive replacement component on the unit it makes

little sense to replace it before it is necessary.

To evaluate the performance of your reverse osmosis membrane, Environmental Safety Products

(ESP) offers free water sample testing. The process is easy. Simply contact us byemail to request a

membrane performance test kit. Be sure to include your name and complete mailing address with your

request. The kit will be mailed postage pre-paid. It will include two small (labeled) sample bottles,

sampling instructions and a return address envelope.

Here is the sampling process:

Bottle #1

1. Allow the reverse osmosis faucet to run for approximately 30 seconds.

2. Fill the plastic water sample bottle Labeled #1, making sure to leave approximately ½” of space

between the water level and the top of the bottle or cap.

3. Tighten lid to ensure the water sample bottle is well sealed.

4. Fill out the information card sheet that is provided.

5. Place the water sample AND the information sheet into the return package.

24

Bottle #2

1. Allow the water faucet at your kitchen sink (the unfiltered water) to run for approximately thirty

seconds.

2. Fill the plastic water sample bottle marked #2, making sure to leave approximately ½” of space

between the water level and the top of the bottle or cap.

3. Tighten the lid to ensure the water sample bottle is well sealed.

4. Place the water sample in the package with the bottle marked #1 (reverse osmosis water

sample).

Using the return address label provided place the correct amount of postage on the package, and mail

it back to ESP. Make sure you include your name, email address, and/or phone number in the package.

Upon receipt ESP will test both samples with a Conductivity Meter. Used to measure product water

quality in de-ionization & reverse osmosis system, this electronic instrument measures the electrical

conductance of a stream of water. Comparing the conductivity of your treated water to the conductivity

of your untreated water tells us the percentage of contaminate rejection being performed by your

reverse osmosis system. This percentage tells us how well the membrane is working. Once we have

the test results, we will contact you by email phone, or mail with the results. You can typically expect to

hear from us 5-7 days after you mail the samples until.

Portable Water Filtration Systems

PORTABLE WATER TREATMENT PRODUCTS - Options in Application and Technology

The range of portable water treatment products has expanded significantly over the last several years.

Much of this expansion is due to the increased variety of technologies and media available in the

market. These technologies have enabled manufactures to produce products with greater reduction

capabilities.

Although new technologies and media have enabled manufacturers to improve product performance

there has been little change in either the types of products or the basic applications. Water bottles,

gravity feed/pour through devices and hand held pump/filter units continue to be used to replace bottled

water, during outdoor recreational activities and travel and for emergency preparedness. In addition,

sometimes 'questionable' quality of bottled water and concerns about chemicals leached from plastic

containers has further increased the demand for this type of product.

PORTABLE WATER FILTRATION TECHNOLOGIES

25

There are multiple technologies and media currently used in portable water treatment devices, some

are common and some are new. Each is used to address a specific contaminant or water problem. In

many cases several of these technologies are used in conjunction with one another to create the end

product.

Spun Polypropylene is used as a filter to reduce sediment, dirt and turbidity that may be present in the

water source. It is also useful as a pre-filter to protect a secondary stage of treatment such as ceramic

filters, porous molded plastic, carbon block and/or membrane.

Porous Plastic technology can be applied in a variety of ways, contingent upon the finished

products micron rating; to reduce sediment, as a spacer between media layers, or as a method of

mechanically reducing cysts and bacteria. (I've explained micron rating in my article...we may have to

mix and match a bit.)

Granular Activated Carbon is used to improve taste and odor by reducing chlorine, industrial

chemicals and a multitude of organic contaminants. Additives to GAC may help to reduce lead, some

forms of heavy metals and additional contaminants. GAC can also be used as Pre and Post Filtration

for other technologies and as a method for removing chlorine or iodine after disinfection.

Carbon Blocks perform the same function as GAC. In addition, based upon micron rating, carbon

blocks have cyst and bacteria removal capabilities via mechanical filtration.

Ceramics will mechanically filter waterborne pathogens such as cysts and bacteria. Their effectiveness

in a given application is dependent upon choosing the right micron rating for the application. Various

micron ratings are available.

KDF is generally used to compliment other methods of treatment. It has a high capacity to remove

chlorine and selectivity for such contaminants as lead, arsenic, cadmium, mercury, calcium carbonate

and magnesium. In addition it is bacteriostatic.

Membranes are in use or are being evaluated for use in portable devices. Their sub-micron pore sizes

enable them to eliminate cysts, bacteria and in some cases viruses. Sediment pre-filtration is necessary

to protect the small pores from clogging.

Iodinated Resin has proven to be an excellent method of eliminating bacteria and virus from raw

water. Though effective, these resins have specific operating parameters. Use outside of these

parameters will negatively impact the products effectiveness. A post media is used in conjunction with

iodinated resin to eliminate the concern of iodine or iodide in the product water.

Ion Exchange Resins are used to remove selected contaminants. Resins are manufactured with this

selectivity in mind. For example, a specific ion exchange resin is produced to remove nitrates.

26

PORTABLE WATER DEVICES

Pour Through/Gravity Feed Units

These units vary widely in size. One of the smaller units is an 8 oz. inverted cup using carbon to

improve taste and odor. This unit has a 50 gallon capacity. An example of the larger unit would be a

terra cotta or stainless counter top unit using ceramics with media capable of reducing a multitude of

contaminants including cysts, bacteria, lead, chlorine and other heavy metals. The most versatile,

durable and portable of these large units is the Outback. This system breaks down for storage and

travel. It uses filters and chloro tabs to remove bacteria, cysts, virus, chlorine and organic matter. The

large units have a 2,500 gallon capacity and replaceable components. Many of the higher end products

have been tested to ANSI/NSF Standard 53 by credible independent laboratories.

Bottles

There are several portable bottle units on the market. There is a broad range of performance and price

- the higher price not necessarily indicative of higher levels of performance. Some bottles do their job

using a single filter. To achieve the same result others require that the filtration component be changed

once or even twice during a single use. The most common performance claims are those of improved

taste and odor. This is achieved using a simple carbon filter that fits inside the bottle. Other bottles are

capable of bacteria and cyst removal/reduction through the use of carbon blocks, porous molded plastic

or ceramics. Finally, in some cases the bottles can reduce viruses through the use of membrane and/or

iodinated resin. There are several bottles that offer replaceable filters while others have filters

permanently affixed to the unit, a straw or to the filter cap. One product actually opens from the bottom

of the bottle, allowing it to be used as a bottle and as a pour through/gravity feed unit in conjunction with

a larger container. Again, third party testing is a critical consideration when evaluating these products.

Pump/Filter Combinations

Pumps and pump/filter combinations usually use a technology such as Carbon blocks, ceramics,

porous plastic elements or membranes to effectively remove protozoan cysts and bacteria. It is

generally a good idea to incorporate some type of pre-filter to eliminate particulate that are larger than

the pore size that could cause premature clogging of the filter. These products are used primarily in the

outdoor specialty markets. Because this application may entail challenging a product with high levels of

contaminants in 'worst case conditions' the issue of performance testing becomes very important.

PRODUCT VERSATILITY

27

Many of the available portable products can be used in a multitude of applications. Within each product

type are individual products that are capable of producing potable water from non-potable raw water

sources, either by significantly reducing bacteria or cysts or sediment etc. They can also be used in

non-traditional ways, both inside and outside the home and in emergency or survival situations. A

sports bottle can be used to replace bottled water while at school, while traveling or during any

recreational activity. Some are designed specifically to filter water for babies while others can double as

gravity feed treatment/filtration devices to fill larger water containers. Some have capacities of as little

as 25 gallons and some have capacities as high as 200 gallons. Some remove only chlorine while

some have proven effective against bacteria, cysts and virus. Countertop gravity flow devices can

replace bottled water without the connection to the faucet. They can treat, filter and cool the water and

are easily emptied and moved. There are those that have the same range of performance

characteristics as sports bottles. Although their applications differ due to their size their capacity is

higher than that of a sports bottle. Combination pump/filter units are useful in both outdoor and

emergency situation where the user might need to capture water from streams, rivers, lakes, or other

suspect water sources.

TESTING

Though virtually all of the technologies used in portable filtration devices are also used in larger

(Counter top or Whole House) systems the amounts of media used are significantly smaller, hence the

portable systems generally have a much lower performance capacity. Many of the devices using

mechanical filtration have capacities similar to their larger counterparts. In the event that the product is

to be used as a water purifier and listed as such, the product must pass the stringent performance

evaluation required by the EPA. For all of these reasons it is critical to ensure that portable units have

been sufficiently tested and evaluated by an independent third-party laboratory and that the test results

support any claims made by the manufacturer and are available for general distribution to the buyer.

WHAT PORTABLE PRODUCT DO I CHOOSE?

Use the following process to weed out the good from the not so good.

Identify need:

What contaminant do you want to remove? What are the problems in water supply in question (chlorine,

lead, cysts, bacteria)?

Identify media or technology:

What technology is necessary to improve aesthetics and/or remove contaminants.

Identify application:28

Which type of product (or combination of products) will produce the water you need (bottle, gravity feed

system, etc). Once this is decided focus on products using this technology or media combination and

making claims to remove the contaminants you have identified.

Verify application given its operating parameters:

Make sure the product will work properly in the environment where you will use it. For example, a water

bottle using iodine to remove bacteria will not be effective when used in freezing temperatures by cross

country or downhill skiers. It only 'works' within a certain range of temperatures. Products may be

rendered less effective by a variety of conditions. These should be clearly stated in the operating

parameters furnished by the seller.

Verify the veracity of claims:

Ask the seller or the manufacturer to send you copies of third party tests done by reputable labs

showing the product can and has performed in accordance with claims.

Evaluate ease of use:

Will product meet claims and be easy to use in the environment of its intended use (outdoors, in an

emergency situation, etc.)

Evaluate capacity in terms of need:

Will the product produce enough potable water to meet the your needs in its intended application

Evaluate value versus price:

Don't assume that the higher price buys a 'better' product. Competing products often use identical

technology and differences in price can be the result of fancy packaging or presentation.

Producing Drinking Water Using Reverse Osmosis

Although Reverse Osmosis seems like a complex system it is really a simple and

straightforward water filtration process. And it's not a new process. High-pressure

(pump driven) reverse osmosis systemshave been used for years to desalinate*

water – to convert brackish or seawater to drinking water. Having a better

understanding of how a reverse osmosis system works will eliminate the mystery

and confusion you may feel when you look at a reverse osmosis system -- with

its many colored tubes and multitude of filters. Read on to enhance your

knowledge of residential reverse osmosis systems.

29

The most important points to remember:

All RO Systems work the same way.

Most RO (Reverse Osmosis) systems look alike.

All RO Systems have the same basic components.

The real difference is the quality of the filters and membranes inside the

RO.

 

How the Reverse Osmosis System Works?

Reverse Osmosis is a process in which dissolved inorganic solids (such as salts)

are removed from a solution (such as water). This is accomplished by household

water pressure pushing the tap water through a semi permeable membrane. The

30

membrane (which is about as thick as cellophane) allows only the water to pass

through, not the impurities or contaminates. These impurities and contaminates

are flushed down the drain.

For a definition of **Reverse Osmosis.

Ultimately, the factors that affect the performance of a Reverse Osmosis System

are:

Incoming water pressure

Water Temperature

Type and number of total dissolved solids (TDS) in the tap water

The quality of the filters and membranes used in the RO System (see

operating specs)

Diagram of a Reverse Osmosis Membrane:

 

What does a Reverse Osmosis System Remove?

A reverse osmosis membrane will remove impurities and particles larger than .001 microns.

31

 TYPICAL REJECTION CHARACTERISTICS OF R.O. MEMBRANES

Elements and the Percent R.O. Membranes will remove

 Sodium 

Sulfate 

Calcium

Potassium 

Nitrate 

Iron 

Zinc 

Mercury

Selenium 

Phosphate 

Lead 

Arsenic

Magnesium

Nickel 

Fluoride 

Manganese 

Cadmium 

Barium 

Cyanide 

85 - 94%

96 - 98%

94 - 98% 

85 - 95% 

60 –75% 

94 – 98% 

95 – 98% 

95 – 98% 

94 – 96% 

96 – 98% 

95 – 98% 

92 – 96% 

94 – 98% 

96 – 98% 

85 - 92% 

94 – 98% 

95 – 98% 

95 – 98% 

84 – 92% 

85 – 92% 

32

Chloride% may vary based on membrane type water pressure, temperature & TDS

 Basic components common to all Reverse Osmosis Systems:

1. Cold Water Line Valve:   Valve that fits onto the cold water supply line.

The valve has a tube that attaches to the inlet side of the RO pre filter. This

is the water source for the RO system. 

2. Pre-Filter (s):   Water from the cold water supply line enters the Reverse

Osmosis Pre Filter first. There may be more than one pre-filter used in a

Reverse Osmosis system. The most commonly used pre-filters are

sediment filters. These are used to remove sand silt, dirt and other

sediment. Additionally, carbon filters may be used to remove chlorine,

which can have a negative effect on TFC (thin film composite) & TFM (thin

film material) membranes. Carbon pre filters are not used if the RO system

contains a CTA (cellulose tri-acetate) membrane. 

3. Reverse Osmosis Membrane:   The Reverse Osmosis Membrane is the

heart of the system. The most commonly used is a spiral wound of which

there are two options: the CTA (cellulose tri-acetate), which is chlorine

tolerant, and the TFC/TFM (thin film composite/material), which is not

chlorine tolerant. 

4. Post filter (s):   After the water leaves the RO storage tank, but before

going to the RO faucet, the product water goes through the post filter (s).

The post filter (s) is generally carbon (either in granular or carbon block

form). Any remaining tastes and odors are removed from the product water

by post filtration.

5. Automatic Shut Off Valve (SOV):  To conserve water, the RO system has

an automatic shutoff valve. When the storage tank is full (this may vary

based upon the incoming water pressure) this valve stops any further water

from entering the membrane, thereby stopping water production. By

shutting off the flow this valve also stops water from flowing to the drain.

33

Once water is drawn from the RO drinking water faucet, the pressure in the

tank drops and the shut off valves opens, allowing water to flow to the

membrane and waste-water (water containing contaminants) to flow down

the drain. 

6. Check Valve:   A check valve is located in the outlet end of the RO

membrane housing. The check valve prevents the backward flow or

product water from the RO storage tank. A backward flow could rupture the

RO membrane.

7. Flow Restrictor:   Water flow through the RO membrane is regulated by a

flow control. There are many different styles of flow controls. This device

maintains the flow rate required to obtain the highest quality drinking water

(based on the gallon capacity of the membrane). It also helps maintain

pressure on the inlet side of the membrane. Without the flow control very

little drinking water would be produced because all the incoming tap water

would take the path of least resistance and simply flow down the drain line.

The flow control is located in the RO drain line tubing. 

8. Storage Tank:   The standard RO storage tank holds up to 2.5 gallons of

water. A bladder inside the tank keeps water pressurized in the tank when it

is full.

9. Faucet:   The RO unit uses its own faucet, which is usually installed on the

kitchen sink. In areas where required by plumbing codes an air-gap faucet

is generally used.

10. Drain line:   This line runs from the outlet end of the Reverse

Osmosis membrane housing to the drain. This line is used to dispose of the

impurities and contaminants found in the incoming water source (tap

water). The flow control is also installed in this line.

 

34

Diagram of a Reverse Osmosis System with Basic Components: 

 

Quality of RO Membranes and Filters – They're not all alike!

While one RO System may look just like the next in terms of design and

components, the quality of those components can be very different. These

differences can have a significant impact on the quality of the water the system

produces.

Here are some examples of questions you might ask and consequences

associated with "less than desirable" quality.35

Has the manufacturer used sound methods? What types of welds have

been used in these plastic products? Will they allow contaminated water to

bypass the filtration system? Will they allow the system to leak?

How has this filter or membrane been created? Will it allow the water to

'channel' and, in effect, bypass the removal component of this device?

What about the quality of the 'fill'? Are it's contents of a high enough

quality to produce the expected percentage of contaminant reduction?

Carbon quality, for instance, can have huge variances in reduction

capability, reduction capacity, and the sloughing of 'fines', which can

prematurely clog or foul the RO Membrane.

What are the manufacturer's controls on tolerances or variations in

specifications? If this component is rated as a 1-micron filter will it truly

filter out everything larger than 1 micron or will it only do the job 80% of the

time? And, what if it actually filters at a .5-micron rate? That will stop the

system from flowing -- clogging it and forcing filter replacement? If this is a

sediment filter and it fails the excess sediment will clog or foul the RO

Membrane.

And in general - Are the materials used in this product FDA or NSF

(National Safety Foundation) approved? If not, you might question their

quality or performance ability. 

So, it becomes clear that the quality of the components is the key

to an optimal functioning RO System.

Why and How To Increase the Gallon Per Day Capacity of A

Reverse Osmosis Systems

 

The main reason to change to a higher flow reverse osmosis membrane is to

improve the recovery rate which is to reduce the amount of time it takes to refill

the storage tank.  This insures that there is adequate water available during times

36

of heavy usage or when the reverses osmosis system may feed more than one

location such as an ice maker and a dispensing faucet.

 

Changing to a higher flow membrane has no effect on the quality of the water

your reverse osmosis system makes or the length of time the reverse osmosis

membrane will last.

 

The change to a higher capacity membrane is easy.  You simply replace your old

membrane with a new, higher capacity membrane, along with the correctly sized

drain line flow restrictor.  (Matching the membrane with the correctly sized drain

line flow restrictor is important to ensure the proper product to waste ratio is

meet.  A mis-matched combination will allow either excess water to flow to the

drain or cause premature fouling of the membrane.)  Most standard reverse

osmosis membrane housings will accommodate membranes ranging in

capacities from 10 – 150 gallons per day. 

Drinking Water Filter Buying Guide

How to Select a Drinking Water Treatment System

Step One - identify the contaminants in your water that need to be reduced or the

water conditions that need to be corrected. This is accomplished through a

comprehensive water quality test from a certified water testing laboratory. Our

mail in laboratory Water Test Kitsare certified in all states as an out of state

testing lab. Click here for the EPA list of State Offices that provide a directory of

State certified Laboratories for water quality testing. Community water treatment

systems must produce an annual Consumer Confidence Report (CCR) and

provide it to their customers. These reports indicate the condition of the drinking

water and any contaminants found. These reports are based on water leaving the

water treatment facility and will not determine the water condition at your faucet.

37

Distribution piping and home plumbing systems can alter the water quality

leaving the treatment facility. Click here for EPA Local Drinking Water

Information to read local water quality reports and other local water quality

information.

Step Two -  select an appropriate Drinking Water Treatment System based on the

results of the water quality testing. Not all treatment systems will remove all

contaminants or improve all water conditions. Some water quality problems may

require professional evaluation, design and installation of treatment systems.

Evaluate Countertop, Under-Counter and Whole House water treatment system

options to determine if these products meet your requirements for contaminant

removal. Each Drinking Water Treatment System has specific operating

parameters that are necessary for effective and safe operation. Make sure your

water quality and the household plumbing system meet these requirements when

selecting your water treatment system and that the daily output and flow rates

meet your needs.

Point of Use (POU) - water treatment applied at the point of water use. Usually

this is a single location application such as at the kitchen or bathroom sink for

water to be used for drinking and cooking.

Countertop Systems - these units sit on the counter and attach to the kitchen

faucet through hose connections leading to and from the treatment system.

Treated water may be delivered back at the faucet or through a spout at the

treatment unit. Another type of countertop unit uses a container that is filled with

tap water, which is then treated and pumped through the treatment unit and

treated water is delivered into a pitcher for use. This type of unit requires no

direct faucet connection.

Under Counter Systems - treatment systems under the counter require that

they be plumbed into the water supply line. If using a Reverse Osmosis (R.O.)

system, a drain connection is necessary and some R.O. units require a storage

38

tank. Under counter systems require a faucet be installed at the sink or

countertop for delivery of treated water.

Point of Entry (POE) - water treatment at the point where untreated water enters

the home. Locate the system after the water meter or pressure tank. Also called

"Whole House" water treatment. The purpose of this treatment option is to reduce

contaminants in water that will be distributed throughout the house. This can

have benefits for water using appliances such as washing machines and water

heaters and address contaminants that can not be removed from Point of Use

systems and Shower Filters. Household plumbing can be configured so that

certain water supply lines are treated and not others. For example, you may not

want to treat water going to outside faucets or used for lawn watering.

When evaluating any Water Treatment System, consider the following:

Certified Systems - Is the entire system or components tested and certified by

an independent third party to remove or reduce the specified water contaminants

and are safe for contact with drinking water? Click here to viewCertification

Standards for Water Treatment Systems.

Performance Data - Will the system remove the contaminants you are most

concerned about and are there any performance tests to demonstrate the

effectiveness of the treatment system at removing those specific contaminants? If

the system is reverse osmosis, will it produce enough water for your family?

Initial Cost - What is the cost of the installed system?

Operating Costs - What are the costs to replace the filter cartridges and how

often should they be replaced? Divide the cost of the replacement filter by the

recommended service life (in gallons of water filtered). This is the operating cost

per gallon for filtered water, excluding any electrical costs if applicable.

Step Three - install and maintain the Water Treatment System as required by the

equipment manufacturer. This will assure your system will consistently perform at 39

the level needed to meet your contaminant reduction goals. Regularly changing

the system filters and membrane cartridges and sanitizing the units and storage

tanks are necessary maintenance procedures to ensure safe, high quality water.

Drinking Water Treatment Technologies

Topics Covered

Mechanical Filtration Distillation

Adsorption Ion Exchange and Deionization

Reverse Osmosis Water Softening

Ozonation Aeration

Ultraviolet Light pH Modification & Acid Neutralization

Mechanical Filtration

This is the process of physically separating and removing suspended solids from a liquid by a physical

means, such as with filter media, rather than through a chemical process. Mechanical filtration can be

obtained through large whole house tank-type systems that hold loose media in layers or with

replaceable filter cartridges.

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Tank-Type Mechanical Filtration -  A large tank is

used to hold various layers of different media inside.

The systems are designed according to the filtration

requirements and contaminant removal needs.

Usually the filter medium includes substances such

as loose Activated Carbon, Copper-Zinc alloy,

Activated Alumina and various sands and gravels.

This media is layered and graded in particle size so

the least dense and coarsest material is at the inlet

water side and the more dense and finer material is

at the outlet side. These systems may be designed

for single use and disposed of when their service life

is complete or they may be serviceable and the

interior filter media can be replaced when the

capability and/or capacity is exhausted. Sometimes

these tank-type systems require backwashing,

whereby water is pumped in the opposite direction

as would normally occur through the treatment

system and is sent down a drain. This backwashing

process regenerates the media and removes

captured particles to allow for continued and

effective operation.

Some of the advantages of Tank-Type systems

over Cartridge-Type systems include:

Lower operating cost over time.

Less clogging with high turbidity and heavy

particulate water supplies.

Less servicing visits/requirements for

41

automatic/backwashing systems.

Cartridge-Type Mechanical Filtration - this option

utilizes fixed media and has most of the capabilities

of tank-type filtration. Due to the nature of the fixed

media used in Cartridge filtration, these systems can

go beyond the limits of tank-type systems that utilize

loose granular media. Mechanical filtration

cartridges are available for Surface Filtration or

Depth Filtration. Surface Filtration is more of a

straining process in which the filter medium is

designed to allow a certain size particle to pass

through and anything larger will be blocked. As the

larger particles are blocked, a layer develops on top

of the filter media to help with further filtration. These

type of filters clog easily and need more frequent

maintenance. Depth filtration media allows particles

of differing sizes to enter the filter and travel in

irregular pathways. A depth filter will have layers of

media to effectively screen out and capture smaller

and smaller particles as water travels through it.

Depth filters will have larger capacities and longer

service life. Cartridge filters are rated for particle

size based on two Industry standards.

1. Nominal Rating - the filter will remove 85% of

the particles at the rated size.

2. Absolute Rating - the filter will remove 99.9%

of the particles at the rated size.

Some of the advantages of Cartridge-Type

systems over Tank-Type systems include:

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Simple in-line plumbing installation or

connection to plumbing fixtures. No backwash

or wastewater connection issues.

Quick and easy servicing that can be done

without professional assistance.

Lower initial system and installation costs.

Greater versatility to handle a broad range of

particle sizes and flow rates.

Less space requirements. Most systems are

mounted on a wall or are installed under a sink

or placed on a countertop.

There is a variety of media used for mechanical filtration cartridges. Many

cartridges are dedicated to particle capture only. Other cartridges are

multifunctional and will integrate activated carbon to assist with additional

contaminant removal along with particle removal. The following list describes

several of the mechanical filtration cartridge types:

Pleated Cellulose -  the most inexpensive option made with a resin-coated paper. It has a

high surface area provided by the pleats. It works as a surface type filter and is good for dirt,

43

rust, scale and fine silt. The disadvantage of this filter type is it's vulnerability to cellulose eating

bacteria which will decompose the filter and make it ineffective. Requires frequent changes

and higher maintenance than depth filter types.

Pleated Synthetic Fabric - pleated media provides a high surface area. It is a surface type

filter and is good for clay, scale and fine silt. The synthetic material defends it from cellulose

eating bacteria. Requires frequent changes and higher maintenance than depth filter types.

String Wound Fiber - natural or synthetic yarns are tightly wound around a perforated core

creating built-up layers to form a depth type filter cartridge. Can meet the requirements for very

fine and course filtration.

Resin Bonded Filter - synthetic or cellulose fabric is rolled or cast into a preformed shape and

then treated with a polymer resin and cured. The cartridges are then machined to shape with

grooves added to increase surface area. Provides a broad range of particle filtration capability.

Spun Bonded Polypropylene - filters made primarily from synthetic fiber that are formed by

spun bonding the matted fibers onto a center core.

Ceramic - constructed from fired ceramic material and designed for use with very fine dirt,

sediment and other small contaminants including cysts. One advantage of this type of cartridge

is that they are cleanable with a cloth or brush. Wiping the exterior removes the outer layer of

media and exposes a new layer. The cartridge can then be put back in service until the filter

thickness is reduced to a specific value.

Multi-functional - these cartridge types incorporate activated carbon along with synthetic

fabric to act as both a mechanical filter and adsorptive filter to remove chlorine and other

contaminants such as organic chemicals. The configuration of these filters can be Activated

Carbon impregnated fabric or alternating layers of mechanical filtration media and Activated

Carbon to create a depth type filter. Activated Carbon does have mechanical filtration

capabilities because of its structure, but is a more expensive alternative as a mechanical filter

compared to non Activated Carbon options.

Adsorption Filtration

Adsorption is the process when liquid, gaseous and solid matter adheres to the surface or in

the pores of an adsorbent media. This is a process that holds particles to the adsorbent media

through physical and chemical forces. It is often confused with "Absorption", which is the

44

process of one substance penetrating into another substance. When the adsorbent media

forces are greater than the forces that keep the material in solution, then the materials will

adhere to the Adsorbent media surface. "Physical Adsorption" takes place when the surface

energy of a solid adsorbent material attracts a substance from a liquid. "Chemisorption" is the

process of attracting substances though a chemical ionic process and is discussed further

below under Ion Exchange. There are three key factors that impact the effectiveness of

Adsorption filtration:

Temperature - generally, the lower the temperature, the better the adsorption process. High

temperatures can cause "desorption" or the release of removed contaminants. This is why it is

recommended to connect Water Treatment Systems to cold water supply lines. The most

efficient temperature range for adsorption is 40° to 55°F.

pH - most nonpathogenic (not disease causing) organic contaminants in water are more

soluble in a more alkaline (higher pH) solution than in an acidic (low pH) solution allowing

better Adsorption. Substances such as Chlorine and Chloramine are more effectively removed

when the pH is below 7 (neutral pH).

Contact Time and Flow Rate - the amount of time water spends passing through an

adsorbent media has an impact on Adsorption. The longer the contact time, the greater the

effectiveness of Adsorption filtration. A Water Treatment System must take the flow rate of the

water into consideration to determine system effectiveness.

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There are several Adsorbent medias used in Water Treatment Systems and each media type

has specific characteristics and contaminant removal properties. The most common Adsorbent

medias follow:

Activated Carbon - this a product that has been "Activated" through a process in which temperatures

around 1300°F are applied to a carbonaceous substance in the absence of air to produce a carbonized

char. The next step is activating the carbonized char at 1500°F to 1800°F with steam, Carbon Dioxide or

acid to create a highly porous, clean and adsorbent material. Each teaspoon of Activated Carbon has the

equivalent surface area as a football field and one pound equals about 125 acres of surface area. The

most common carbon based substances used for Activated Carbon are Bituminous Coal and cellulose

based substances such as Wood or Coconut Shells. Depending on the base material and activation

methods used, the Activated Carbons will differ in their capabilities and can be selected for their

performance characteristics and contaminant removal effectiveness. Activated Carbon media is found in

primarily two forms:

1. Granular Activated Carbon (GAC) - this is Activated Carbon that has been broken into

small pieces and granules. It is common in tank-type Water Treatment systems as part

of the multi-media bed and is also used in cartridge form in a sealed container.

2. Carbon Block - most commonly used for cartridge type systems, this is a pressed block

media produced from a blend of finely crushed and powdered Activated Carbon and a

binder that is then molded and hardened or extruded to form the desired shape and

size. Often, specialized media will be added with the Activated Carbon to provide

customized contaminant removal performance. In general, carbon block exhibits faster

adsorption rates and 2- 4 times the adsorption capacity compared to GAC.

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Activated Alumina - a media that is produced by treating Aluminum oxide to become highly

porous and adsorptive. The mineral is first regenerated with a caustic solution of Sodium

Hydroxide and then followed by sulfuric acid neutralization. It has a surface area of over 22

acres per pound weight. It is a selective type Ion adsorbent (see below) and used to target

specific contaminants such as Fluoride, Selenium and Arsenic.

Reverse Osmosis

To understand how Reverse Osmosis (R.O.) works, you must first understand Osmosis and its

natural process. Water with dissolved solids in a less concentrated solution will naturally move

toward a more concentrated solution in an effort to dilute the more concentrated solution. This

is called Osmosis. In "Reverse Osmosis", the opposite happens, water from a more

concentrated solution of dissolved solids are forced to move toward the less concentrated

solution. This water movement of the different concentrations of dissolved solids occurs across

a "Semipermeable Membrane". This membrane is called semipermeable because it is

selective and allows some materials to pass through it (permeable) and prevents other

materials from moving across it. The force that causes the water to move in Reverse Osmosis

across the semipermeable membrane against the natural forces of Osmosis is provided by the

water pressure supplied to a Reverse Osmosis system. The solution with the higher

concentration of dissolved solids and contaminants is the feed water to the system supplied by

the home. The solution of less concentration of dissolved solids and removed contaminants is

the product water that has been treated for drinking.

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In a typical Reverse Osmosis System, the path of treated water in the home begins with a

connection to a cold water supply. Water passes through the Pre-Filters to remove any

contaminants that can effect the R.O. membrane. The water stream travels through the

membrane and is split into two paths, one path to become the Permeate (product) water and

the other water path is flushing the membrane of captured contaminants so it can continue to

perform effectively. The product water is sent to a storage tank to be used later or in the case

of a Tankless system, directly out the faucet. The water used to flush the membrane is called

the concentrate and is sent down the drain. The whole system is controlled by pressure limiting

and flow controls and automatic shutoff valves to ensure safe and effective operation. To fully

understand how a Reverse Osmosis system works, you will need to know the components of a

system and some terminology.

Total Dissolved Solids (TDS) - defined as the total weight of solid matter that is dissolved in

water. Dissolved solids can not be seen by the naked eye in water.  The measurement for TDS

is Parts per Million (ppm). A Reverse Osmosis system efficiency is measured by the amount of

TDS removed from the water. TDS can be easily monitored to determine when replacement of

the R.O. membrane is necessary or if a system is not functioning properly.

Pre-Filters - Reverse Osmosis membranes are sensitive to certain contaminants, such as

Chlorine and particulates. The cartridge filters located before the water passes through the

R.O. membrane are called "Pre-Filters" and treat the feed water so the membrane will not be

damaged and will function effectively. These Pre-Filters also provide additional contaminant

removal capability to a R.O. system as well as reduce Chlorine and particulate matter that can

harm and clog a membrane.

Membrane - the membrane functions to remove Total Dissolved Solids (TDS) down to a size

of chemical molecules and Ions (charged particles). It is usually made of layers of polymer

films that are spiral wound around a core with spacer screens between each layer. As the feed

water passes through the membrane, the layers have smaller and smaller pores, so the

resulting product water has been removed of most of the dissolved solids. Membranes act like

super mechanical filters to screen out particles larger than the pores of the membrane.

Membranes are designed to meet certain TDS rejection levels and operating conditions. In

general, a R.O. membrane can remove over 90% of TDS which can include salts, minerals,

metals, micro-organisms and some organic substances. Low molecular weight organics such

as Volatile Organic Chemicals (VOC's) require additional treatment for removal. It is important

to note that R.O. membranes reject different contaminants at different rejection levels. The two

most common R.O. membrane types are:

48

1. Cellulose Triacetate (CTA) - the material of this membrane type is subject to some

bacterial attack, it operates over a lower pH range, has a TDS rejection rate that

decreases as TDS increases, has excellent Chlorine resistance, has a lower operating

temperature and the Nitrate rejection is low.

2. Thin Film Composite (TFC) - this membrane has good bacteria resistance, operates

over a large pH range, has consistent high TDS rejection performance, higher operating

temperature and high nitrate rejection. It has poor resistance to chlorine and water must

have pre-treatment for Chlorine prior to reaching the membrane. It is the most common

membrane used in high quality R.O. systems.

Permeate - this is the supply water that has passed through the Reverse Osmosis membrane

to become treated water, also called product water.

Concentrate - the water that is diverted to flush the membrane of contaminants becomes the

concentrate water. This is the water that flows to the drain and is also called the "Reject

Water".

Post-Filter - a post filter is used after the product water leaves the R.O. membrane and before

the water travels to the storage tank or directly to the faucet. R.O. systems will use a Post-

Filter to remove additional contaminants not removed by previous stages in the system. Most

often this stage would be for organic chemical removal and contaminants that require specialty

media such as Lead or Arsenic.

Storage Tank - most water treatment systems need to produce a reasonable flow rate, about

0.5 to 0.75 Gallons per Minute (64 - 96 ounces per minute) at the faucet, to allow acceptable

filling of containers. Standard tank-type R.O. systems make drinking quality water at about 1-3

ounces per minute, therefore treated water is directed to a storage tank as it is produced until

the storage tank is full and the R.O. unit shuts off. When the faucet is opened, water flows from

49

the storage tank out the faucet. When the faucet is shut off, the R.O. system will replenish the

water level in the storage tank until full. Storage tanks have an air charged bladder that exerts

pressure on the water in the storage tank as the water fills the tank. This tank pressure is what

propels the water to the faucet when needed. Typical storage tank capacity is 2 - 4 gallons and

is affected by line pressure. The greater the water pressure, the more water storage capacity a

tank has because the water pressure must work against the storage tank bladder pressure.

Countertop R.O. Systems use a non-pressurized reservoir to hold the water.

Tankless R.O. System - the pressure in the storage tank used in most R.O. systems also

works against the R.O. membrane to some degree. As tank pressure increases the

backpressure on the system, the differential pressure across the membrane decreases and

reduces effectiveness and the treated water output rate of the system. Tankless R.O. systems

do not require a storage tank and therefore overcome some of the drawbacks of a traditional

R.O. system. Specialty high output membranes are used to produce treated water at a rate

that can be directly delivered to the faucet on demand.

Automatic Shut Off Control Valve - this device shuts off the the feed water to the membrane

when the R.O. system senses the storage tank is full. Usually this is done through pressure

monitoring. When the tank reaches about 2/3 of the incoming feed water pressure, the control

valve will shut off. When the tank is drained down to about 1/3 of the feed water pressure, the

control valve will open. This Automatic Shut Off Control Valve functions to conserve water by

preventing the continuing draining of concentrate "Reject Water" when the R.O. system

storage tank is full.

TDS Creep - when an R.O. system has not been in use for sometime, or if there is a low

differential pressure across the membrane, TDS will continue to permeate through the

membrane due to the natural process of Osmosis and the differential solution concentrations.

This may cause undesired contaminants to "Creep" across the membrane. Once the system is

back in operation, the membrane will be flushed and return to design performance levels.

Final "Polishing" Filter - this is the last stage in the water treatment process before the

treated water exits the faucet. Usually, water leaving a storage tank in a tank-type R.O system

or water leaving the final membrane in a tankless system will travel through a final filter to

remove any contaminants not removed from previous stages and to provide the highest quality

drinking water. Final taste and odor improvements are made at this stage.

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Drain Connection - the concentrate water that was derived from the flushing of the R.O.

membrane is directed down a drain line. The drain line is connected to the household waste

drain and in a typical undersink installation, this is usually the waste pipe from the kitchen sink.

The drain connector clamps around the waste drain pipe with a connection for the reject water

to flow from the R.O. System.

Air Gap Faucet - an Air Gap provides a clear vertical space in the R.O. system between the

drain line and the flood level rim of the sink, preventing the potential back-up of waste water in

the drain from contaminating the drinking water supply. The Uniform Plumbing Code requires

that there is no direct connection between the drinking water and the sewer wastes. Some

local plumbing codes across the country may not require an Air Gap as part of the R.O. system

and not all systems are sold with one. Having an Air Gap as part of a R.O. system is important

and recommended. The R.O. system is connected to a drain that can potentially back-up if a

plumbing problem materializes. The Air Gap component can take several forms, but the most

common is the integration with the faucet dispenser.

Booster Pump - a critical requirement for a R.O. system to operate effectively is water supply

pressure. In situations where the water supply pressure is below operating requirements, a

"Booster Pump" can be installed to increase the water supply pressure and improve the

performance of the Reverse Osmosis system.

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System Output - Reverse Osmosis systems are rated on water production output capability

and indicated as "Gallons per Day" (gpd). This can be confusing to a consumer as two types of

output are advertised for R.O. Systems.

1. R.O. Membrane Output - manufacturers provide output ratings for their R.O.

membrane cartridges. This is the tested performance of a membrane component

outside of a system installation in optimal conditions. Membrane "Gallons per Day"

output ratings are not achieved as a system output rating due to the fact the system is

working against differing water pressures from the water supply and storage tank as

well as restricted flow of the pre and post filter cartridges. This membrane rating should

only be used as a reference to determine what component is installed and to re-order

the correct membrane for a system. Since R.O. membranes are part of a R.O. system,

the membrane rating should not be used to compare R.O. systems. Only the tested

system performance will provide an indication of daily output of the R.O. system.

2. R.O. System Output - the average family uses 1-2 gallons of water per day per person

for cooking and drinking. Tested R.O. systems provide an indication of the average daily

output achieved by the system design. Consider the needs of your family when

determining the output requirements of your R.O. system. Many factors impact the

performance of a R.O. system such as water pressure, water temperature and amount

of TDS. Generally, the higher the rated output for a system, the faster the R.O. system

will produce treated product water.

Recovery Rate - this is a measure of a R.O. system's efficiency and is the percentage of feed

water that has traveled through the membrane to become permeate (product) water. The

higher the recovery rate, the more efficient the system. The formula for Recovery Rate is as

follows:

(Permeate in Gallons per Day ÷ Feed Water in Gallons per Day) x 100 = % Recovery Rate

Rejection Rate -  is the percentage of TDS that is rejected by a membrane in a R.O. System

and is also a measure of the system efficiency and performance. The higher the rejection rate,

the more efficient and effective the system. Rejection Rates can vary with different

contaminants that make up the TDS feed water. R.O. system performance data will include the

Rejection Rate of specific contaminants. The formula for Rejection Rate is as follows:

((Feed Water TDS in ppm - Permeate TDS in ppm) ÷ Feed Water TDS in ppm) x 100 = %

Rejection Rate

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There are several factors to consider when purchasing and using a Reverse Osmosis system.

No water treatment system can remove all contaminants in water and some treatment systems

have more critical operating requirements to be effective at contaminant removal. A Reverse

Osmosis system is more complicated that a mechanical type filtration system and incorporates

more specialized components. These systems should be installed where the supply water to

the system meets certain operating requirements as indicated by the R.O. system

manufacturer. Always consult the R.O. system manufacturer's operating requirements before

purchasing a R.O. system. The following are general guidelines to R.O. system

requirements,   

Quality of Supply Water - Reverse Osmosis systems require that the feed water meet certain

water quality requirements for the systems to operate effectively. If the supply water does not

meet these requirements, some type of pretreatment of the supply may be needed before the

water enters the R.O. system. Any pre-treatment of the supply water will depend on the water

quality problem. Some options can include a whole house "Point of Entry" system or filter

cartridges installed before the R.O. system. Unless a R.O. system is specifically designed to

be a microbiological filter, systems should be installed only on microbiologically safe water.

The following list describes several of the water quality requirements of a R.O. system.

pH - is a measure of the Acidity or Alkalinity of the water supply with 7.0 being neutral. Higher

numbers mean the water is Alkaline and lower numbers than 7.0 means the water is Acidic.

The recommended range for R.O. systems utilizing TFC membranes is pH 3 to 11.

Iron - as soluble iron in water is exposed to air, it will oxidize and precipitate out of solution to

become a solid in the form of Iron Hydroxide and/or Iron Oxide. These gelatinous substances

will "Foul" the R.O. membrane and reduce or prevent it from functioning effectively. The

recommended level for Iron in feed water should not exceed 0.2 ppm or mg/L.

Total Dissolved Solids (TDS) - the amount of suspended solids in the feed water will impact

the effectiveness of the R.O. system. The higher the concentration in the feed water the lower

the quality of the treated product water. A R.O. system recommendation is for TDS to not

exceed 1800 ppm.

Turbidity - is a measure of the amount of suspended matter in water. This suspended matter

blocks light rays and makes the water look cloudy. It is measured in Nephelometric Turbidity

Units (NTU) through the use of an instrument called a "Nephelometer", which uses a

53

photometric analysis to measure the light scattered by the suspended matter and generate a

value. Recommendation for R.O. systems is a NTU value below 5. 

Hardness - primarily the amount of dissolved compounds of calcium and magnesium.

Excessive hardness will not necessarily prevent the R.O. system from operating, but it will

shorten the life of the R.O. membrane. General recommendation for feed water hardness is

that it should not exceed 10 grains per gallon or 170ppm. There are five Hardness

classifications ranging from soft to very hard. The level of 170ppm falls into the fourth

classification of "Hard". 

Temperature of Feed Water - as water gets colder the viscosity increases making it thicker,

which slows down the production rate. Each R.O. system will have a recommended

temperature operating range and should never be allowed to freeze. In general, this range is

40°F to 100°F. Increasing the temperature of the supply water will not improve the quality of

the permeate (product water) or contaminant removal capability of the R.O. system, but it will

improve the rate of producing treated product water.

Water Pressure - critical to the operation of a Reverse Osmosis system is water pressure. In

general, the recommended operating pressure range is 40psi to 85psi. The concept of Reverse

Osmosis is based on the differential pressure across the membrane to overcome the natural

forces of Osmosis and drive high concentrations of dissolved solids from the feed water,

across the membrane, to lower concentrations of dissolved solids in the product water. Without

a high pressure difference across the membrane, the effectiveness and contaminant removal

capability will drop in a R.O. system. Another factor in storage tank-type R.O. systems is the

backpressure exerted by the air charged bladder in the storage tank. The higher the water line

pressure, the more it will overcome the storage tank pressure and the more water will be

stored in the tank. Operating at higher feed water pressures improves the quality of the

permeate (product) water. In situations where there is not enough water line pressure to

operate the R.O. system effectively, a booster pump can be installed to increase the water line

pressure to a level needed by the system.

The following is an example of how Temperature and Water Pressure have an impact on Reverse

Osmosis system performance. R.O systems may be rated at different Water Pressures and Water

Temperatures, so consult with the specific system specifications. Water Temperatures and Water

Pressures other than the rated manufacturer's values will impact treated water output (either increasing

or decreasing).

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Rated R.O. System

Performance

TFC Membrane 60psi, 77°F

Water Supply Pressure

40psi

Water Supply Temperature

50°F

Water Supply Pressure

60psi

Water Supply Temperature

65°F

Rated Output

15 gallons per day (gpd)

Pressure and Temperature

Adjusted Output

6.1 gallons per day (gpd)

Pressure and Temperature

Adjusted Output

12.4 gallons per day (gpd)

Ozonation

Ozone is a gas compound composed of three Oxygen atoms to make the molecule O3. The

naturally occurring element Oxygen exists as two atoms, O2. When energy is used to break

O2 bonds, single O1 Oxygen atoms form . These O1 atoms combine with O2 molecules to

form O3 Ozone. Ozonation is the process of feeding Ozone into a water source for disinfection

and to improve several water quality problems such as color and odor. The Ozone process

leaves no residual taste and odor as would occur in other disinfection options and adds no

chemicals to the water. Ozone has been used in community water treatment applications since

1906 and there are hundreds of water treatment plants in the US using Ozone today.

Ozone is unstable and will change back to Oxygen over time. Temperature, pH and water

quality all affect the time Ozone takes to revert back to Oxygen. The production and

introduction of Ozone into water must occur consecutively. Ozone's instability is due to the

weak bond from the third Oxygen atom and causes an oxidizing reaction with any oxidizable

substance. Oxidation is a chemical reaction to cause one substance to gain electrons and

another substance to release their electrons with the end result being a change in the structure

of the substances. This change in structure allows the substance to become deactivated or be

55

effectively treated or removed. Ozone is considered the most powerful Oxidizer available for

water treatment that can be used safely and a strong Disinfecting agent. Cyst organisms are

considered the most resistant to all disinfectants because of their protective shells and is

effectively treated, along with Bacteria and Viruses, with Ozone.

Ultraviolet Light

Ultraviolet Light (UV) is Radiation with wavelengths of energy shorter than the visible light spectrum

and longer than the X-ray wavelengths, about 265 nanometers. It is the invisible violet end of the light

spectrum. UV is used as a disinfectant to destroy Pathogens, which are organisms such as bacteria,

viruses or parasites that can cause disease. Water passes through a chamber in which an Ultraviolet light

source emits UV Radiation on the water. The UV source is similar to a fluorescent lamp, but it does not

have a phosphor coating on the inside of the tube that normally converts UV energy into visible light.

The UV radiation causes changes in the genetic material of the organism and inactivates it. However,

some bacteria are capable of repairing themselves and UV light is not effective at killing Giardia and

Cryptosporidium cysts because of the thick protective coats of these organisms.

UV treatment of water is automatic and adds no taste, odor or chemicals to the

water. For UV treatment to be effective, it must have a specific Radiation intensity

to provide the necessary penetration power to kill microorganisms. The design of

a UV treatment stage considers the UV source strength, water flow rate (contact

time) and surface area, There are several factors that can reduce the 56

effectiveness of UV treatment. Turbidity (suspended matter in water) and

impurities such as Iron can block UV rays from reaching microorganisms.

Hardness mineral deposits from the water can coat the chamber to reduce UV

effectiveness. Water should be pre-filtered before reaching the UV stage to

remove any potential contaminants that could decrease disinfection

effectiveness. UV light treatment should be monitored regularly and maintenance

can include removing the UV bulb four times a year to clean the lamp and UV

chamber to maintain UV intensity. The UV source will gradually lose strength

over time and most residential systems require annual replacement. The power

needed to operate the Ultraviolet light source can range from 10 to 30 watts.

Distillation

The process of separating the water from organic and inorganic matter using

evaporation and then condensation to capture the treated water is called

Distillation. The basis for the distillation process is the differences in volatilities of

chemical substances. Volatility is a measure of how fast an element or compound

evaporates. Low volatility means it will evaporate slowly, high volatility chemical

compounds will evaporate quickly. In the Distillation process, water is heated until

boiling to produce a water vapor. Dissolved solids and other contaminants with

boiling points higher than water (lower volatility) do not change to vapor. The

water vapor is captured in a chamber

where it cools and condenses to form liquid

water and is stored in a reservoir for use.

The impurities with the higher boiling points

than water are left behind in the boiling

chamber, so the condensed water has

lower mineral content and is of higher

quality.

Distillation is effective at removing

biological contaminants such as bacteria

57

and viruses. The prolonged boiling action at high temperature will kill microbes

and microorganisms. These dead organisms are not evaporated along with the

water and are left behind. Inorganic contaminants such as minerals are also left

in the boiling chamber and are not carried over during evaporation and

condensation. Volatile Organic Chemicals (VOC's) have lower boiling points than

water and can be carried over to the condensate side to contaminate the product

water. Some home distillers use an Activated Carbon stage to help with VOC

removal although water Distillers are not certified for removal of these

contaminants. While countertop water Distillers may remove several categories

of contaminants, they are certified for Total Dissolved Solids (TDS) removal only.

These are the suspended solids in water such as inorganic minerals.

Countertop home water distillers produce drinking water slowly with output at

about 1 gallon per 4.5 hours or about 5 gallons per day. With the average person

using 1 to 2 gallons of water per day for cooking and drinking, and a water

reservoir storage capacity of about 0.5 to 1 gallon, quality drinking water may be

in short supply. Using several plastic storage containers requires space and is

bulky. Transferring treated water to larger containers is inconvenient and may

require hand pumps for dispensing. Water Distillers require electricity and will not

operate during a power failure such as in an emergency situation when drinking

water is needed.

Distillers also require significant maintenance because of the residue left behind

when the water evaporates. Scale build-up in the boiling chamber can reduce the

efficiency of heat transfer to the water requiring more energy and longer

processing time. Maintenance recommendations include disassembly and

cleaning the boiler before each use and removing scale deposit build-up in the

boiling chamber with solutions and abrasion pads. The amount of maintenance is

dependent on source water quality and amount of dissolved solids. Distillers are

electrical appliances and the heating element may eventually need replacement

or the electrical controls may fail. The cost of using a water Distiller can be high.

58

Power consumption for typical home Distillers is about 750 watts and uses about

3 to 4 kilowatt hours of electricity per gallon. With electricity rates of $0.05 to

$0.15 per kWh, this translates to $0.15 to $0.60 per gallon for distilled water.

Additionally, water distillers use small carbon post-filters that must be replaced

about every few months at a cost of about $6 to $7 a piece.

Distillation units also get very hot and extra care needs to be taken in handling

and using these devices. The use of a home water Distiller will release hot steam

into a room and may make the room uncomfortable or increase cooling

requirements and costs. The lower boiling point Volatile Organic Compounds

(VOC's) in water vaporize first before water and are allowed to be released into

the surrounding room air through the gas vent. These VOC gases may create a

concern for Indoor Air Quality. VOC's can pose health risks and should not be

inhaled as a gas or ingested in drinking water. Consideration should also be

given to the fact that unnecessary electrical use contributes to greenhouse gas

emissions and environmental pollution. Countertop home water distillers are

certified to remove only Total Dissolved Solids (TDS). There are other water

treatment options available that are certified to treat TDS and additional water

contaminants that will require less maintenance and will operate at a lower cost

per gallon of treated drinking water.

Ion Exchange and Deionization

Ion Exchange occurs when an insoluble permanent solid medium, called the Ion

Exchanger, exchanges Ions with the solution surrounding the insoluble medium.

In a neutral atom that is neither negatively or positively charged, the negative

charges of the electrons revolving around a nucleus of an atom are balanced by

the positive charge of the protons in the nucleus. An Ion is an atom or group of

atoms that carry an electrical charge because they have lost or gained one or

more negatively charged electrons. "Cations" are positively charged Ions

because they have lost a negatively charged electron. "Anions" are negatively

charged Ions because they have gained a negatively charged electron.

59

Substances that become Ions often display different properties than the original

element from which it was formed.

Ion Exchange is used primarily to remove hardness minerals from water (water

softening), but has applications for a variety of water quality issues. As Ion

Exchange resin is depleted by giving off its Ions in exchange for obtaining the

desired Ions from substances in water, the resin must be "regenerated" to bring it

back to its fully Ionized form so the Ionic Exchange process can continue.

Regeneration is performed with a combination of backwashing the resin, which

cleans the resin and resets the resin configuration, and flooding the resin with a

regeneration solution that will bring the resin back to the correct chemical state.

The selection of the Ion Exchange resins and the "regenerant" used determine

the substances that will be exchanged in the water and the application.

How It Works - a molecule of Hydrochloric Acid (HCl) contains one Hydrogen

atom (H) and one Chloride (Cl) atom. When this molecule is forced to Ionize in

water, the two atoms split apart into a positively charged Hydrogen Cation (H+)

and a negatively charged Chloride Anion (Cl-). Once a substance separates into

its Ions, these Ions are now available to combine with other Ions with an opposite

charge, even if the other Ions are from a different type of molecule. For example,

if Sodium Hydroxide (NaOH) is added to water containing Ionized Hydrochloric

Acid, the result would be Sodium Chloride (table salt) and water as shown in this

example:

(H+ + CL-) +(Na+ +

OH-)

-

>Na+Cl- + H+OH-

Hydrochloric

Acid Ions+

Sodium

Hydroxide

-

>Table Salt + Water

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"Deionization" is a two phase Ion Exchange process that removes all ionized

minerals and salts, both organic and inorganic, from water. Positively charged

ions in a solution are removed first by a Cation exchange resin which exchanges

them for a chemically equivalent amount of Hydrogen Ions (H+). In the second

stage, negatively charged Ions are removed from the solution by an Anion

exchange resin and an equivalent amount of Hydroxide Ions (HO-) are released.

The Hydroxide and Hydrogen Ions produced by this process join to form water

molecules (H+ + HO- = H2O) while the mineral Ions are removed. This process is

also called "Demineralization" by Ion Exchange. It is not a common treatment

technique used in residential applications and does not remove microorganisms

or non-electrically charged substances such as synthetic organic chemicals

(pesticides, solvents, herbicides).

There are primarily two configurations of Ion Exchange water treatment

equipment:

Replaceable Cartridge Systems - for small applications such as Point of Use

(POU) drinking water at a single faucet, an in-line cartridge type unit can be used.

Larger cartridge type Point of Entry (POE) systems are available for "Whole

House" applications where the contaminant demand can be met by the system.

The cartridges can contain a mixed media bed with both Anion and Cation Ion

Exchange resin. When the media becomes exhausted and is no longer effective,

the cartridges are replaced. These units provide an economical and compact

alternative to water softeners for low sodium mineral free water.

61

Tank-Type Systems - for larger water flow rates and greater contaminant

removal, tank-type systems may be required. These configurations have one or

more 6' to 10" diameter portable tanks that use meters and electronic controls for

their effective operation. When the tank media becomes exhausted in about 6-10

years, the tanks are returned to a regeneration plant to reprocess the resin mix.

Generally, these systems are for industrial and commercial use and are

expensive to purchase and maintain.

The principles of Ion Exchange can be applied to water quality issues beyond

mineral removal with specific Ion Exchange resins. The following water quality

treatment examples demonstrate the versatility of the Ion Exchange process:

Dealkalization - the reduction of Alkalinity (high pH) in water.

Decolorization - the treatment of water discoloration referred to as "Tannins",

usually a yellowish tint, caused by microscopic, unsettleable particles.

Fluoride Removal - use of Activated Alumina as a selective Ion Exchange resin

to adsorb Fluoride.

Nitrate/Nitrite Removal - Anion Ion Exchange resin is used and is regenerated

with Sodium Chloride (NaCl) similar to a water softener.

Manganese & Iron Removal and pH Modification - a special Cation Exchange

resin is used to soften water, remove dissolved Iron and Manganese and modify

low-pH simultaneously.

Uranium Removal - found in water as Ion complexes, Uranium can be

effectively removed with Anion Exchange resins.

Water Softening

The treatment of water through Water Softening is the most common type of Ion

Exchange process. Water with hardness minerals, such as Calcium and

62

Magnesium, are passed through a bed of Cation Exchange media to exchange

the Calcium and Magnesium Ions in the water with Sodium or Potassium Ions

from the Ion Exchange resin. This effectively removes these hardness minerals

from the water, but increases the Sodium and Potassium levels of the water

leaving the treatment stage. The term "hardness" was originally applied to waters

that were hard to wash in because hardness minerals prevent soap from

lathering and produces an insoluble "curdy" precipitate in water. Dissolved

Calcium and Magnesium are also responsible for most scale (coating) build-up in

plumbing pipes and water heaters. Hard water in the home makes bathing and

laundry cleaning more difficult, leaves visible white chalky residue on plumbing

fixtures and can affect the life and efficiency of electrical appliances and water

heaters.

There are several Water Softener system configurations and some designs may

include more than one resin tank. Water Softener systems are primarily

composed of three components:

1. Pressure Vessel - this holds the bed of Cation Exchange resin and where

the actual water softening takes place.

63

2. Additional "Brine" Tank - to hold the regeneration material used to

regenerate the Ion Exchange resin and get it back to the necessary

chemical state to continue to perform the water softening function.

3. Controls - these are valves and water meters or timers usually located on

top of the pressure vessel that direct the flow of water and Sodium or

Potassium regeneration solution, called "Brine", during the regeneration

cycle.

Most Water Softening systems are automated to provide continuous and efficient

operation. Two classes of Automated Water Softeners are available

Demand Control Systems - these systems operate based on the demand for

regeneration and can also alter the amount of Brine solution needed to

regenerate the Ion Exchange resin. The system will either meter the amount of

water passing through it or have a sensor that registers when the softener is

nearing the end of its capacity and needs to be regenerated. These type of

systems are more efficient than Timer Control systems because the regeneration

cycle is based on the amount of use and the amount of Brine needed to replenish

the system. This can save money on regenerants, Sodium Chloride or Potassium

Chloride, as well as water and pumping costs.

Timer Control Systems - a time clock built into the system control is set for a

specific time period to regenerate the Ion Exchange resin. This is based on a

predetermined estimate of softened water usage and a predetermined estimate

of brine regenerant solution, whether it is needed or not.

Water hardness forming salts are measured in grains per gallon (gpg) or parts per million (ppm) and is

expressed in terms of equivalent quantities of Calcium Carbonate. This allows a common basis for

comparison of different hardness salts and compounds. 1 gpg = 17.1 ppm. In a water test report, total

hardness is the sum of Calcium and Magnesium Ions. The following is the industry standard for

classifying the levels of hardness:

64

Hardness

DesignationGrains per Gallon

Parts per Million

(mg/L)

Soft less than 1.0 less than 17.1

Slightly Hard 1.0 to 3.5 17.1 to 60

Moderately Hard 3.5 to 7.0 60 to 120

Hard 7.0 to 10.5 120 to 180

Very Hard 10.5 and over 180 and over

How It Works - water being treated for Hardness flows into a tank of Ion

Exchange Water Softening resin. The most common resin used for this

application is insoluble beads of polystyrene bonded with divinylbenzene that are

about 1/64" to 1/32" in size. This Ion Exchange resin is permanently negatively

charged and attract positively charged Ions (Cations). The Ion Exchange resin

holds positively charged monovalent (one+ charge) Sodium (Na+) or Potassium

(K+) Ions. When positively charged divalent (two++ charge) Calcium (Ca++) and

Magnesium (Mg++) Cations approach the Ion Exchange resin, a chemical

reaction occurs in which the Sodium or Potassium Ions on the Ion Exchange

resin are replaced by an equivalent quantity of Calcium and Magnesium Ions that

were in the water. There is a stronger attraction for divalent ions over monovalent

ions because of the greater positive charge, therefore the less attracted Sodium

and Potassium ions are released from the Ion Exchange resin and the more

attracted Calcium and Magnesium Ions are adsorbed in the Ion Exchange resin.

The less harmful Sodium or Potassium Ions have replaced the troublesome

hardness Ions in the water flowing through the home plumbing system. The

chemical reaction looks like this:

65

2RNA + Ca(HCO3)2 -> R2CA + 2NaHCO3

Sodium Ion

Exchange Resin+

Calcium

Bicarbonate in

Water

->Calcium Ion

Exchange Resin+

Sodium

Bicarbonate in

Water

R = Cation Exchange Resin

 

Fully Charged Resin   Ion Exchange & Exhausted Resin

When the Water Softener system determines the Ion Exchange resin is close to

"exhaustion" and will no longer be capable of capturing more Calcium and

Magnesium Ions from the water, a regeneration cycle is performed on the

system. The most common regenerate used is Sodium Chloride (table salt), but

Potassium Chloride can also be used. The advantage to Potassium Chloride is

that it does not increase the sodium level in the drinking water, which may be

important to individuals on a low sodium diet. Potassium Chloride is more costly

and usually a larger quantity is needed for regeneration compared to Sodium

Chloride. These regenerants are put into a storage tank of water to create a

highly concentrated regenerant solution called "Brine". Newer, more efficient

Water Softeners use about 3-7 lbs. of Sodium Chloride per cubic foot of resin for

regeneration, while older units can use 10-15 lbs. of salt per cubic foot of resin.

Water Softening systems are rated by removal capacity in grains. Average Ion

Exchange resin used for this purpose has a removal capacity of 30,000 grains 66

per cubic foot of resin. To determine when the Water Softener system will

become depleted and need regeneration, you would divide the capacity of the

system by the amount of grains per gallon of hardness that exists in the water.

For example, if your water had 6 gpg of hardness and your Water Softener

system capacity is 30,000 grains, you would have to regenerate the resin after

5,000 gallons (30,000 ÷ 6 = 5,000).

Systems can be designed as a "concurrent flow" or a "countercurrent flow" regeneration process. In the

concurrent flow, the Brine solution flows in the same direction as the water flow through the resin bed.

When the brine first enters the resin tank, it flows through a fresh water zone at the top. This mixing

with fresh water initially reduces the concentration of the Brine solution. This may cause the lower

levels of the resin bed to not fully regenerate and create a situation where hardness leakage can occur

when the system becomes operational. In the countercurrent flow, the Brine solution flows in the

opposite direction as the water flow through the resin bed. The advantage to the countercurrent flow

design is that the concentrated Brine solution immediately contacts the last portion of the resin bed first

for maximum regeneration. This ensures that when the unit is back in service, the water leaving the resin

bed passes through the most highly regenerated resin region last, ensuring maximum softening

effectiveness.

Source: Water

Quality Assoc.

Resin is fully

charged.

Hard water flows over

Ion Exchange media.

Hardness mineral Ions

are exchanged for

Sodium or Potassium

Ions.

Resin is exhausted.

Hardness minerals are

passing by the Resin.

Regeneration process

is needed.

Counter-flow

regeneration of Resin

with Brine solution.

Hardness minerals are

driven off the Resin.

Resin is fully

charged again ready

for use.

67

There are several steps in Water Softener regeneration:

Backflushing - water flows into the resin tank at a high flow rate to clean and flush out

particulates and suspended dirt that the resin may have filtered out. Backflushing also creates

a stirring and scrubbing action on the resin beads and expands the resin bed back to the

design state. The water used to backflush the resin bed is sent down the drain. This stage

prepares the resin for the regeneration step.

Regeneration - the brine solution is pumped into the resin bed at a very high concentration of

Sodium or Potassium Ions. This very high concentration forces the adsorbed Calcium and

Magnesium Ions to be released from the resin and be carried away to the drain. The Sodium or

Potassium Ions are then received by the Ion Exchange resin and the resin has been

regenerated and ready to begin the Water Softening process again.

Other Steps - depending on system design, there could be a quick rinse at the end of the

regeneration cycle to rid the system of any remaining high concentrations of brine solution.

Other steps can include a settling rinse to get the resin bed in a state to function optimally.

Brine Refill - this may be an automatic or manual process that is done when needed to get the

Brine solution back to a full level and at the necessary concentration in the Brine tank.

Aeration

The process of bringing water and air into contact with each other is called Aeration. This can

be accomplished by spraying or cascading the water into air or by injecting air into the water.

The primary purpose of Aeration for Water Treatment is for "Degasification" and

"Oxygenation". Aeration of water helps in the reduction of dissolved residual gases like Radon,

volatile organic chemicals (VOC's) and removal of some undesirable odors. It can also be

helpful with the chemical reduction of Ferrous Iron and Manganous Manganese.

68

There are two configurations of Aeration systems:

1. Open Gravity Aerators - used primarily for degasification such as for the removal of

dissolved gases such as VOC's and Carbon Dioxide, Hydrogen Sulfide (rotten egg

smell) and Radon. Iron and Manganese must be controlled in these systems or fouling

of the system can occur. For treating Radon and Methane gas, a fan must be

incorporated to expel the gas to the outside and away from the home and system.

These systems require that water be re-pumped to re-pressurize the water supply after

leaving the Aeration system.

2. Closed Pressure Aerators - oxygenation of the water is the primary purpose of these

systems. These treatment systems are under constant pressure and the line pressure

generated serves the distribution system. No re-pumping is needed. Due to the system

being under constant pressure, they are not well suited for the release of dissolved

gasses and VOC's. They are used to transform dissolved metals into precipitates that

can drop out of solution and be filtered.

pH Modification and Acid Neutralization

The pH scale determines how Acidic or Alkaline a solution is. The scale ranges from 1 to 14

with 7.0 being "Neutral". A pH below 7.0 is considered "Acidic" and a pH above 7.0 is

"Alkaline". Each single numerical increase or decrease represents a tenfold increase in Acidity

or Alkalinity. Acid is a substance that releases Hydrogen Ions (H+) when dissolved in solution

and the solution develops a higher concentration of Hydrogen Ions (H+) compared to Hydroxyl

Ions (OH-). An "Alkali" substance will cause a solution to become Alkaline and produce a

concentration of Hydroxyl Ions (OH-) that is greater than the Hydrogen Ions (H+).

69

One of the main reasons for the control of pH is to reduce corrosion. Low pH water has a

corrosive effect on metal surfaces such as Brass, Copper, Cadmium, Lead and Zinc and can

leave stains on plumbing fixtures. Water may become Acidic from the presence of Carbon

Dioxide (CO2) and the lack of alkalinity to offset the Acid. Carbon Dioxide may get into well

water from absorbing the CO2 released from decaying vegetation. The CO2 can combine with

water to form Carbonic Acid (H2CO3). Rainwater can also be Acidic (acid rain). High pH

Alkaline water, pH above 9.0, is also corrosive to metals such as Brass, Zinc, Aluminum and

Copper. Highly Alkaline water can cause drying of the skin when bathing, give water a "soda-

like" taste and cause scale to form on metal surfaces.

Treatment of low pH water is primarily done by passing the water through chemically reactive

media or feeding a liquid chemical solution into the stream of water. Calcite and Magnesia are

used as medias to reduce Acidity in water. Ion Exchange can be used with a weak Cation

Exchange resin to absorb the Carbonic Acid and also helps soften the water and remove Iron.

Soda Ash can be used in a chemical feeder application to reduce pH. High pH Alkaline water is

unusual in a residential environment and considered less critical. Treatment for high pH water

includes the use of chemical feed pumps to add acid-type solutions to the water. Ion Exchange

can also be used in a process called "Dealkalization".

REVERSE OSMOSIS is similar to the membrane filtration treatment process.

However there are key differences between reverse osmosis and filtration. The

predominant removal mechanism in membrane filtration is straining, or size exclusion,

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so the process can theoretically achieve perfect exclusion of particles regardless of

operational parameters such as influent pressure and concentration. RO (Reverse

Osmosis), however involves a diffusive mechanism so that separation efficiency is

dependent on influent solute concentration, pressure and water flux rate.[1] It works by

using pressure to force a solution through a membrane, retaining the solute on one side

and allowing the pure solvent to pass to the other side. This is the reverse of the

normal osmosis process, which is the natural movement of solvent from an area of low

solute concentration, through a membrane, to an area of high solute concentration

when no external pressure is applied.

How does reverse osmosis work?

To understand "reverse osmosis," it is probably best to start with normal osmosis.

According to Merriam-Webster's Collegiate Dictionary,osmosis is the "movement of a

solvent through a semipermeable membrane (as of a living cell) into a s olution of

higher solute concentration that tends to equalize the concentrations of solute on the

two sides of the membrane." That's a mouthful. To understand what it means, this

picture is helpful: 

On the left is a beaker filled with water, and a tube has been half-submerged in

the water. As you would expect, the water level in the tube is the same as the water

level in the beaker. In the middle figure, the end of the tube has been sealed with a

"semipermeable membrane" and the tube has been half-filled with a salty solution and

submerged. Initially, the level of the salt solution and the water are equal, but over time,

something unexpected happens -- the water in the tube actually rises. The rise is

attributed to "osmotic 

A semipermeable membrane is a membrane that will pass some atoms or molecules

but not others. Saran wrap is a membrane, but it is impermeable to almost everything

we commonly throw at it. The best common example of a semipermeable membrane

would be the lining of your intestines, or a cell wall. Gore-tex is another common

semipermeable membrane. Gore-tex fabric contains an extremely thin plastic film into

71

which billions of small poreshave been cut. The pores are big enough to let water

vapor through, but small enough to prevent liquid water from passing.

In the figure above, the membrane allows passage of water molecules but not salt

molecules. One way to understandosmotic pressure would be to think of the water

molecules on both sides of the membrane. They are in constantBrownian motion. On

the salty side, some of the pores get plugged with salt atoms, but on the pure-water

side that does not happen. Therefore, more water passes from the pure-water side to

the salty side, as there are more pores on the pure-water side for the water molecules

to pass through. The water on the salty side rises until one of two things occurs:

The salt concentration becomes the same on both sides of the membrane

(which isn't going to happen in this case since there is pure water on one side

and salty water on the other).

The water pressure rises as the height of the column of salty water rises, until

it is equal to the osmotic pressure. At that point, osmosis will stop.

Osmosis, by the way, is why drinking salty water (like ocean water) will kill you. When

you put salty water in your stomach, osmotic pressure begins drawing water out of your

body to try to dilute the salt in your stomach. Eventually, you dehydrate and die.

In reverse osmosis, the idea is to use the membrane to act like an extremely

fine filter to create drinkable water from salty (or otherwise contaminated) water. The

salty water is put on one side of the membrane and pressure is applied to stop, and

then reverse, the osmotic process. It generally takes a lot of pressure and is fairly slow,

but it works.

History

The process of osmosis through semipermeable membranes was first observed in 1748

by Jean Antoine Nollet. For the following 200 years, osmosis was only a phenomenon

observed in the laboratory. In 1949 the University of California at Los Angeles (UCLA)

first investigated desalination of seawater using semipermeable membranes.

Researchers from both UCLA and the University of Florida successfully produced

freshwater from seawater in the mid-1950s, but the flux was too low to be commercially

72

viable. The future of RO is promising. By the end of 2001, about 15,200 desalination

plants were in operation or in the planning stages worldwide

PROCESS

Formally, reverse osmosis is the process of forcing a solvent from a region of high

solute concentration through a semipermeable membrane to a region of low solute

concentration by applying a pressure in excess of the osmotic pressure.

The membranes used for reverse osmosis have a dense barrier layer in the polymer

matrix where most separation occurs. In most cases the membrane is designed to allow

only water to pass through this dense layer while preventing the passage of solutes

(such as salt ions). This process requires that a high pressure be exerted on the high

concentration side of the membrane, usually 2–17 bar (30–250 psi) for fresh and

brackish water, and 40–70 bar (600–1000 psi) for seawater, which has around 24 bar

(350 psi) natural osmotic pressure that must be overcome.

This process is best known for its use in desalination (removing the salt from sea

water to get fresh water), but since the early 1970s it has also been used to purify fresh

water for medical, industrial, and domestic applications.

Osmosis describes how solvent moves between two solutions separated by a

semipermeable membrane to reduce concentration differences between the solutions.

When two solutions with different concentrations of a solute are mixed, the total amount

of solutes in the two solutions will be equally distributed in the total amount of solvent

from the two solutions. Instead of mixing the two solutions together, they can be put in

two compartments where they are separated from each other by a semipermeable

membrane. The semipermeable membrane does not allow the solutes to move from

one compartment to the other, but allows the solvent to move. Since equilibrium cannot

be achieved by the movement of solutes from the compartment with high solute

concentration to the one with low solute concentration, it is instead achieved by the

movement of the solvent from areas of low solute concentration to areas of high solute

concentration. When the solvent moves away from low concentration areas, it causes

these areas to become more concentrated. On the other side, when the solvent moves

into areas of high concentration, solute concentration will decrease. This process is

73

termed osmosis. The tendency for solvent to flow through the membrane can be

expressed as "osmotic pressure", since it is analogous to flow caused by a pressure

differential. Osmosis is a great example of Diffusion.

In reverse osmosis, in a similar setup as that in osmosis, pressure is applied to the

compartment with high concentration. In this case, there are two forces influencing the

movement of water: the pressure caused by the difference in solute concentration

between the two compartments (the osmotic pressure) and the externally applied

pressure.

APPLICATIONS

Drinking water purification

Around the world, household drinking water purification systems, including a reverse

osmosis step, are commonly used for improving water for drinking and cooking.

Such systems typically include a number of steps:

a sediment filter to trap particles including rust and calcium carbonate

optionally a second sediment filter with smaller pores

an activated carbon filter to trap organic chemicals and chlorine, which will attack

and degrade TFC reverse osmosis membranes

a reverse osmosis (RO) filter which is a thin film composite membrane (TFM or

TFC)

optionally a second carbon filter to capture those chemicals not removed by the

RO membrane

optionally an ultra-violet lamp for disinfecting any microbes that may escape

filtering by the reverse osmosis membrane

In some systems, the carbon pre-filter is omitted and cellulose triacetate membrane

(CTA) is used. The CTA membrane is prone to rotting unless protected by chlorinated

water, while the TFC membrane is prone to breaking down under the influence of

chlorine. In CTA systems, a carbon post-filter is needed to remove chlorine from the

final product water.

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Portable reverse osmosis (RO) water processors are sold for personal water

purification in various locations. To work effectively, the water feeding to these units

should best be under some pressure (40 psi or greater is the norm). Portable RO water

processors can be used by people who live in rural areas without clean water, far away

from the city's water pipes. Rural people filter river or ocean water themselves, as the

device is easy to use (Saline water may need special membranes). Some travelers on

long boating trips, fishing, island camping, or in countries where the local water supply

is polluted or substandard, use RO water processors coupled with one or more UV

sterilizers. RO systems are also now extensively used by marine aquarium enthusiasts.

In the production of bottled mineral water, the water passes through an RO water

processor to remove pollutants and microorganisms. In European countries, though,

such processing of Natural Mineral Water (as defined by a European Directive) is not

allowed under European law. (In practice, a fraction of the living bacteria can and do

pass through RO membranes through minor imperfections, or bypass the membrane

entirely through tiny leaks in surrounding seals. Thus, complete RO systems may

include additional water treatment stages that use ultraviolet light or ozone to prevent

microbiological contamination.)

Membrane pore sizes can vary from .1 to 5,000 nanometers (nm) depending on filter

type. "Particle filtration" removes particles of 1,000 nm or larger. Microfiltration removes

particles of 50 nm or larger. "Ultrafiltration" removes particles of roughly 3 nm or larger.

"Nanofiltration" removes particles of 1 nm or larger. Reverse osmosis is in the final

category of membrane filtration, "Hyperfiltration", and removes particles larger than .1

nm.

In the United States military, R.O.W.P.U.'s (Reverse Osmosis Water Purification Unit,

pronounced "roh-poo") are used on the battlefield and in training. They come ranging

from 1500 GPD (gallons per day) to 150,000 GPD and bigger depending on the need.

The most common of these are the 600 GPH (gallons per hour) and the 3,000 GPH.

Both are able to purify salt water and water contaminated with N.B.C.

(Nuclear/Biological/Chemical) agents from the water. During a normal 24 hour period,

one unit can produce anywhere from 12,000 to 60,000 gallons of water, with a required

4 hour maintenance window to check systems, pumps, R.O. elements and the engine

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generator. A single ROWPU can sustain a force of a battalion size element or roughly

1,000 to 6,000 soldiers.

Water and wastewater purification

Rain water collected from storm drains is purified with reverse osmosis water

processors and used for landscape irrigation and industrial cooling in Los Angeles and

other cities, as a solution to the problem of water shortages.

In industry, reverse osmosis removes minerals from boiler water at power plants. The

water is boiled and condensed repeatedly. It must be as pure as possible so that it does

not leave deposits on the machinery or cause corrosion. It is also used to clean effluent

and brackish groundwater.

The process of reverse osmosis can be used for the production of deionized water.

In 2002, Singapore announced that a process named NEWater would be a significant

part of its future water plans. It involves using reverse osmosis to treat domestic

wastewater before discharging the NEWater back into the reservoirs.

Dialysis

Reverse osmosis is similar to the technique used in dialysis, which is used by people

with kidney failure. The kidneys filter the blood, removing waste products (e.g. urea)

and water, which is then excreted as urine. A dialysis machine mimics the function of

the kidneys. The blood passes from the body via a catheter to the dialysis machine,

across a filter.

Food Industry

In addition to desalination, reverse osmosis is a more economical operation for

concentrating food liquids (such as fruit juices) than conventional heat-treatment

processes. Research has been done on concentration of orange juice and tomato juice.

Its advantages include a low operating cost and the ability to avoid heat treatment

processes, which makes it suitable for heat-sensitive substances like

the protein and enzymes found in most food products.

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Reverse osmosis is extensively used in the dairy industry for the production of whey

protein powders and for the concentration of milk to reduce shipping costs. In whey

applications, the whey (liquid remaining after cheese manufacture) is pre-concentrated

with RO from 6% total solids to 10-20% total solids before UF (ultrafiltration)

processing. The UF retentate can then be used to make various whey powders

including WPI (whey protein isolate) used in bodybuilding formulations. Additionally, the

UF permeate, which contains lactose, is concentrated by RO from 5% total solids to

18–22% total solids to reduce crystallization and drying costs of the lactose powder.

Although use of the process was once frowned upon in the wine industry, it is now

widely understood and used. An estimated 60 reverse osmosis machines were in use

in Bordeaux, France in 2002. Known users include many of the elite classed growths

(Kramer) such as Château Léoville-Las Cases in Bordeaux.

Car Washing

Because of its lower mineral content, Reverse Osmosis water is often used in car

washes during the final vehicle rinse to prevent water spotting on the vehicle. Reverse

osmosis water displaces the mineral-heavy reclamation water (municipal water).

Reverse Osmosis water also enables the car wash operators to reduce the demands

on the vehicle drying equipment such as air blowers.

Maple Syrup Production

In 1946, some maple syrup producers started using reverse osmosis to remove water

from sap before being further boiled down to syrup. The use of reverse osmosis allows

approximately 54-42% of the water to be removed from the sap, reducing energy

consumption and exposure of the syrup to high temperatures. Microbial contamination

and degradation of the membranes has to be monitored.

Hydrogen production

For small scale production of hydrogen, reverse osmosis is sometimes used to prevent

formation of minerals on the surface of electrodes and to remove organics from drinking

water.

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Reef aquariums

Many reef aquarium keepers use reverse osmosis systems for their artificial mixture of

seawater. Ordinary tap water can often contain excessive chlorine, chloramines,

copper, nitrogen, phosphates, silicates, or many other chemicals detrimental to the

sensitive organisms in a reef environment. Contaminants such as nitrogen compounds

and phosphates can lead to excessive, and unwanted, algae growth. An effective

combination of both reverse osmosis and deionization (RO/DI) is the most popular

among reef aquarium keepers and is preferred above other water purification

processes due to the low cost of ownership and minimal running costs. (Where chlorine

and chloramines are found in the water, carbon filtration is needed before the

membrane, as the common residential membrane used by reef keepers does not cope

with these compounds.)

Desalination

Areas that have either no or limited surface water or groundwater may choose

to desalinate seawater or brackish water to obtain drinking water. Reverse osmosis is

the most common method of desalination, although 85 percent of desalinated water is

produced in multistage flash plants.[2]

Large reverse osmosis and multistage flash desalination plants are used in the Middle

East, especially Saudi Arabia. The energy requirements of the plants are large,

but electricity can be produced relatively cheaply with the abundant oil reserves in the

region. The desalination plants are often located adjacent to the power plants, which

reduces energy losses in transmission and allows waste heat to be used in the

desalination process of multistage flash plants, reducing the amount of energy needed

to desalinate the water and providing cooling for the power plant.

Sea Water Reverse Osmosis (SWRO) is a reverse osmosis desalination membrane

process that has been commercially used since the early 1970s. Its first practical use

was demonstrated by Sidney Loeb and Srinivasa Sourirajan

fromUCLA in Coalinga, California. Because no heating or phase changes are needed,

energy requirements are low in comparison to other processes of desalination, but are

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still much higher than those required for other forms of water supply (including reverse

osmosis treatment of wastewater).[citation needed]

The Ashkelon seawater reverse osmosis (SWRO) desalination plant in Israel is the

largest in the world.[3][4] The project was developed as a BOT (Build-Operate-Transfer)

by a consortium of three international companies: Veolia water, IDETechnologies and

Elran.[5]

The typical single pass SWRO system consists of the following components:

Intake

Pre-treatment

High-pressure pump

Membrane assembly

Remineralization and pH adjustment

Disinfection

Alarm/Control Panel

Pre-treatment

Pre-treatment is important when working with RO and nanofiltration (NF) membranes

due to the nature of their spiral wound design. The material is engineered in such a

fashion to allow only one way flow through the system. As such the spiral wound design

doesn't allow for backpulsing with water or air agitation to scour its surface and remove

solids. Since accumulated material cannot be removed from the membrane surface

systems they are highly susceptible to fouling (loss of production capacity). Therefore,

pretreatment is a necessity for any RO or NF system. Pretreatment in SWRO system

has four major components:

Screening of solids: Solids within the water must be removed and the water

treated to prevent fouling of the membranes by fine particle or biological growth, and

reduce the risk of damage to high-pressure pump components.

Cartridge filtration - Generally string-wound polypropylene filters that remove

between 1 - 5 micrometre sized particles.

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Dosing of oxidizing biocides such as chlorine to kill bacteria followed by bisulfite

dosing to deactivate the chlorine which can destroy a thin-film composite membrane.

There are also biofouling inhibitors which do not kill bacteria but simply prevent them

from growing slime on the membrane surface.

Prefiltration pH adjustment: If the pH, hardness and the alkalinity in the feedwater

result in a scaling tendency when they are concentrated in the reject stream, acid is

dosed to maintain carbonates in their soluble carbonic acid form.

CO3-2 + H3O+ = HCO3

- + H2O

HCO3- + H3O+ = H2CO3 + H2O

Carbonic acid cannot combine with calcium to form calcium carbonate

scale. Calcium Carbonate Scaling tendency is estimated using the Langelier

Saturation Index. Adding too much sulfuric acid to control carbonate scales

may result in calcium sulfate, barium sulfate or strontium sulfate scale

formation on the RO membrane.

Prefiltration Antiscalants: Scale inhibitors (also known as antiscalants)

prevent formation of all scales compared to acid which can only prevent

formation of calcium carbonate and calcium phosphate scales. In addition to

inhibiting carbonate and phosphate scales, antiscalants inhibit sulfate and

fluoride scales, disperse colloids and metal oxides and specialty products

exist to inhibit silica formation.

High pressure pump

The pump supplies the pressure needed to push water through the

membrane, even as the membrane rejects the passage of salt through it.

Typical pressures for brackish water range from 225 to 375 psi (15.5 to 26 bar,

or 1.6 to 2.6 MPa). In the case of seawater, they range from 800 to 1,180 psi

(55 to 81.5 bar or 6 to 8 MPa).

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Membrane assembly

The layers of a membrane.

The membrane assembly consists of a pressure vessel with a membrane that

allows feedwater to be pressed against it. The membrane must be strong

enough to withstand whatever pressure is applied against it. RO membranes

are made in a variety of configurations, with the two most common

configurations being spiral-wound and a hollow-fiber.

Remineralisation and pH adjustment

The desalinated water is very corrosive and is "stabilized" to protect

downstream pipelines and storages usually by adding lime or caustic to

prevent corrosion of concrete or cement lined surfaces. Liming material is used

in order to adjust pH at 6.8 to 8.1 to meet the potable water specifications,

primarily for effective disinfection and for corrosion control.

Disinfection

Post-treatment consists of stabilizing the water and preparing for distribution.

Desalination processes are very effective barriers to pathogenic organisms,

however disinfection is used to ensure a "safe" water supply. Disinfection

(sometimes called germicidal or bactericidal) is employed to sterilise any

bacteria protozoa and virus that have bypassed the desalination process into

the product water. Disinfection may be by means of ultraviolet radiation, using

UV lamps directly on the product, or by chlorination or chloramination (chlorine

and ammonia). In many countries either chlorination or chloramination is used

to provide a "residual" disinfection agent in the water supply system to protect

against infection of the water supply by contamination entering the system.

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Disadvantages

Household reverse osmosis units use a lot of water because they have low

back pressure. As a result, they recover only 5 to 15 percent of the water

entering the system. The remainder is discharged as waste water. Because

waste water carries with it the rejected contaminants, methods to recover this

water are not practical for household systems. Waste water is typically

connected to the house drains and will add to the load on the household septic

system. An RO unit delivering 5 gallons of treated water per day may discharge

40 to 90 gallons of waste water per day to the septic system.[6]

Large scale industrial/municipal systems have a production efficiency of closer

to 48% because they can generate the high pressure needed for RO filtration.

New developments

Prefiltration of high fouling waters with another, larger-pore membrane with

less hydraulic energy requirement, has been evaluated and sometimes used

since the 1970s. However, this means the water passes through two

membranes and is often repressurized, requiring more energy input in the

system, increasing the cost.

Other recent development work has focused on integrating RO

with electrodialysis in order to improve recovery of valuable deionized products

or minimize concentrate volume requiring discharge or disposal.

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