CHAPTER I

INTRODUCTION

1.1 GENERAL

Reverse Osmosis (RO) was invented in 1959 by Prof Reid of the University

of Florida, and was put into practical use by Sidney Loeb and Srinivasa

Sourirajan.

Reverse osmosis is a separation process that uses pressure to force a

solvent through a membrane that retains the solute on one side and

allows the pure solvent to pass to the other side. More formally, it is the

process of forcing a solvent from a region of high solute concentration

through a membrane to a region of low solute concentration by applying a

pressure in excess of the osmotic pressure. 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.

Figure 1.1 Reverse Osmosis Process

The membrane here is semi permeable, meaning it allows the passage of

solvent but not of solute. The membranes used for reverse osmosis have a

1

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.

Reverse Osmosis is the phenomenon of water flow through a semi

permeable membrane that blocks the transport of salts or other solutes through it.

It removes both dissolved organics and salts.

Reverse osmosis is used to reject bacteria, salts, sugars, proteins,

particles, dyes, and other constituents. Separation of ions with reverse osmosis is

aided by charged particles. This means that dissolved ions that carry a charge,

such as salts, are more likely to be rejected by the membrane .The larger the

charge and the particle, the more likely it will be rejected.

Figure 1.2 Reverse Osmosis Principle

Reverse Osmosis is for de-salination and purification of

brackish(other than sea water) and sea water for drinking and industrial use. This

can also be used for a variety of specialized membrane applications for chemical

recovery and waste water reclamation projects. The process achieves rejections

2

of 99.9% of viruses, bacteria and pyrogens. So now a days this reverse

osmosis is widely used in waste water treatment.

Figure 1.3 MOLECULE SIZE COMPARISON

1.2. CLEAN-IN-PLACE

CIP (Clean-in-Place) is a method of cleaning the interior surfaces of

pipes, vessels, process equipment, and associated fittings, without

disassembly . The closed systems were disassembled and cleaned manually.

The advent of CIP was a boon to industries that needed frequent internal

cleaning of their processes. Industries that rely heavily on CIP are those

requiring high levels of hygiene, and include: dairy, beverage, brewing, processed

3

foods, pharmaceutical, and cosmetics. The benefit to industries that use CIP is

that the cleaning is faster, less labour intensive and more repeatable, and poses

less of a chemical exposure risk to people. CIP started as a manual practice

involving a balance tank, centrifugal pump, and connection to the system being

cleaned. Since the 1950s, CIP has evolved to include fully automated systems

with programmable logic controllers, multiple balance tanks, sensors, valves, heat

exchangers, data acquisition and specially designed spray nozzle systems.

Simple, manually operated CIP systems can still be found in use today.

4

CHAPTER 2

LITERATURE REVIEW

1) Brackish water RO desalination plants installed by CSMCRI.

Base on the indigenous TFC membranes, CSMCRI has designed, fabricated and

installed several brackish water RO desalination plants having product water

capacities in the range 1000-5000 LPH to cater to the needs of rural community in

TN., Gujarat, W.B., and Rajasthan in the last few years. In this regard,

Department of Science and Technology, New Delhi has provided the financial

assistance while state Science & Technology Councils of different states have

provided the logistic support like site selection and infrastructure. The success of

RO desalination units has made considerable impact on decision making

authorities who are now more amenable to the idea of RO desalination of

providing water in problem villages. Before RO the water is sent to the cartridge

filter where 10 and 5 micron pore size is used. CSMCRI has also fabricated a

mobile desalination unit by mounting a small RO unit (500 LPH product water) on

a mobile van.

2) Characterization of foulants by autopsy of RO desalination membranes

F. H. Butt, F. Rahman and U. Baduruthamal

Research Institute, King Fahd University of Petroleum and Minerals, Box 1891,

Dhahran 31261, Saudi Arabia

Received 16 October 1996; accepted 21 July 1997.Available online 14 April 1998

A study was undertaken to identify various types of scales that were

responsible for shortening the useful life span of the membrane permeators in a 5

commercial reverse osmosis (RO) desalination plant. Compositions of the raw

and treated feed water and of the reject brine were determined using the

inductively coupled plasma (ICP) spectrometry and ion chromatography (IC).

Various scaling index calculations showed that the feed and brine were non-scale

forming with respect to CaCO3 (calcite), SrSO4, CaSO4.2H2O (gypsum), and silica

(SiO2). Two completely fouled membrane permeators, retired from stage 1 and

stage 2 of a commercial plant, were subjected to membrane autopsy using

scanning electron microscopy (SEM), X-ray diffractometry (XRD), optical

microscopy (OM), and energy dispersive x-ray florescence (XRF). The deposits

were predominantly amorphous in nature. The membrane autopsy showed that

CaCO3, SrSO4, and CaSO4.2H2O (gypsum) scales did not constitute a serious

problem in the plant. The advanced phosphonate+polyacrylate based scale

inhibitor had itself formed Ca phosphonate sludge, but the amount was quite

small. Though below saturation, silica is believed to have been precipitated due to

the catalyzing effect of trivalent Al3+ and Fe3+ ions. Iron fouling was the major

cause of reduced life span of the membranes and, to a lesser extent, calcium-

alumino-silicates

3) Fouling Development on Reverse Osmosis Membranes

Fouling is a major obstacle that prevents efficient

operation of reverse osmosis (RO) systems, causing deterioration of both the

quantity and quality of treated water, and consequently resulting in higher

treatment cost.

4) Chemical cleaning of reverse osmosis membranes

Fouling is the most important problem associated with the application of

membranes. A strategy for membrane regeneration is chemical cleaning of the

fouled membranes. One of the major applications of reverse osmosis

6

membranes is processing of water from different resources or for various

applications. This includes desalination or ion removal for makeup water for

boilers. In all cases fouling restricts membrane performance. In this work reverse

osmosis membranes were fouled with water. Chemical cleaning of the RO

membranes using acid, alkaline, surfactant and detergent solutions has been

discussed. Cleaning efficiency depends on the type of the cleaning agent and

its concentration. It has been shown that the efficiency increases with

increasing the concentration of the cleaning agent. Operating conditions such as

crossflow velocity, turbulence in the vicinity of the membrane surface,

temperature, pH and cleaning time also play a role in the cleaning process.

Optimum membrane cleaning requires in depth understanding of the

interactions between the foulants and the membrane as well as the

effect of the cleaning procedure on deposit removal and membrane

performance.

5) Membrane autopsy — a case study

L. Y. Dudley and E. G. Darton

Houseman Desalination Products, The Priory, Burnham, Slough SL1 7LS, UK

Received 31 May 1995; accepted 30 June 1995. Available online 11 December

1998.

This paper describes the authors' experiences of membrane autopsy

procedures to identify the cause of poor membrane performance at a European

power plant and the subsequent proposals made for improvement to the

operating, pretreatment and cleaning programmes. The reverse osmosis (RO)

system is a 2,500 m3/d unit producing water for cooling purposes. The 3-year-old

plant experienced continual output loss, which required the membranes to be

cleaned on a twice weekly basis, which increased to every 4 days in warm

weather. The autopsy objective was to carry out a destructive analysis on a fouled

membrane to identify the major causes of the fouling. These were identified as

7

being biological in nature with the significant presence of iron, which together

formed a biomass on the membrane surface.

CHAPTER 3

CONFIGUREURATIONS OF REVERSE OSMOSIS

3.1 GENERAL CONFIGUREURATIONS

3.1.1 FEED PRESSURE

The feed pressure is the most important parameter, which helps the

membrane to provide good efficiency. The pressure varies from 10kg/cm 2 to 28

kg/ cm 2. 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 which must be overcome.

3.1.2 PERMEATE PRESSURE

The permeate pressure is the output pressure of the membrane, it will be

lower than the feed pressure.

But the pressure difference between feed pressure and permeate

pressure should be less than 4.

P = feed pressure – permeate pressure = less than 4

3.1.3. FLOW RATE

The waste water which should be treated through the membrane is let in to

the membrane input. That is known as flow rate. This flow depends upon the

production of the industry. It may vary.

8

3.1.4. PERMEATE FLOW

The out let flow from the membrane is called permeate flow. This will be

lesser than the feed flow because of the filtration process done inside the

membrane and some amount is rejected.

3. 1.5 DIRECTION OF FLOW OF WATER:

The direction of water inside the membrane is in two types. They are

1) Cross - flow membrane filtration

In cross flow filtration, the feed is passed across the filter membrane

(tangentially to the filter membrane) at some pressure difference. Material which

is smaller than the membrane pore size passes through the membrane as

permeate or filtrate, and everything else is retained on the feed side of the

membrane as retentive.

In this the feed water direction and reject water flow will be in same

direction. The permeate water direction will be perpendicular to that.

Most probably spiral wound membrane has this filtration.

9

Figure 3.1 CROSS-FLOW MEMBRANE FILTRATION

2) Dead – end membrane filtration

This is a filtration technique in which all the fluid passes through the

membrane, and all particles larger than the pore size of the membrane are

retained at its surface. This means that the trapped particles start to build

up a "filter cake" on the surface of the membrane, which has an impact on

the efficiency of the filtration process.

Figure 3.2 DEAD-END MEBRANE FILTRATION

3. 1.6 TYPES OF MEMBRANE BASED ON SOURCE OF WATER

1) Brackish water membrane

2) Sea water membrane

The sea water membrane is used for treating the sea water only

having high TDS vale(more than 3500 mg/lt).

10

So the brackish membrane is used for treating the effluents of

municipal and industrial waste water.

3. 1.7 MEMBRANE MATERIALS

1. CTA (cellulose triacetate or CA),

2. Polyamides (TFC – Thin Film Composite)

Figure 3.3 TFC- POLYAMIDE WITH CARBOXYLATE GROUPS

The membrane material refers to the substance from which the

membrane itself is made. Normally, the membrane material is manufactured

from a synthetic polymer, although other forms, including ceramic

and metallic “membranes,” may be available. Currently, almost all

membranes manufactured for drinking water production are made of

polymeric material, since they are significantly less expensive than

membranes constructed of other materials. The material properties of the

membrane may significantly impact the design and operation of the

filtration system. For example, membranes constructed of polymers that

react with oxidants commonly used in drinking water treatment should not

be used with chlorinated feed water. Mechanical strength is another

consideration, since a membrane with greater strength can withstand

11

larger transmembrane pressure (TMP) levels allowing for greater operational

flexibility and the use of higher pressures with pressure-based direct

integrity testing Similarly, a membrane with bi-directional strength may

allow cleaning operations or integrity testing to be performed from either

the feed or the filtrate side of the membrane. Material properties influence

the exclusion characteristic of a membrane as well. A membrane with a

particular surface charge may achieve enhanced removal of particulate

or microbial contaminants of the opposite surface charge due to electrostatic

attraction. In addition, a membrane can be characterized as being

hydrophilic (i.e., water attracting) or hydrophobic (i.e., water repelling). These

terms describe the ease with which membranes can be wetted, as well as

the propensity of the material to resist fouling to some degree. MF membranes

may be constructed from a wide variety of materials, including cellulose

acetate (CA), polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN),

polypropylene (PP), polysulfone (PS), polyethersulfone (PES), or other polymers.

Each of these materials has different properties with respect to surface

charge, degree of hydrophobicity, pH and oxidant tolerance, strength, and

flexibility.

RO membranes are generally manufactured from cellulose acetate or

polyamide materials (and their respective derivatives), and there are various

advantages and disadvantages associated with each. While cellulose

membranes are susceptible to biodegradation and must be operated within

a relatively narrow pH range of about 4 to 8, they do have some resistance to

continuous low-level oxidant exposure. In general, for example, chlorine doses

of 0.5 mg/L or less may control biodegradation as well as biological fouling

without damaging the membrane. Polyamide (PA) membranes, by contrast, can

be used under a wide range of pH conditions and are not subject to

biodegradation. Although PA membranes have very limited tolerance for the

presence of strong oxidants, they are compatible with weaker oxidants such

as chloramines. PA membranes require significantly less pressure to operate and

have become the predominant material used for RO applications. A

characteristic that influences the performance of all membranes is the trans-

wall symmetry, a quality that describes the level of uniformity throughout the

12

cross-section of the membrane. There are three types of construction that are

commonly used in the production of membranes: symmetric, asymmetric

(including both skinned and graded density variations), and composite. Cross-

sectional diagrams of membranes with different trans-wall symmetry are material,

while composite membranes use different (i.e., heterogeneous) materials.

Symmetric membranes may be either homogeneous or heterogeneous. In a

symmetric membrane, the membrane is uniform in density or pore structure

throughout the cross-section, while in an asymmetric membrane there is a

change in the density of the membrane material across the cross sectional area.

Some asymmetric membranes have a graded construction, in which the porous

structure gradually decreases in density from the feed to the filtrate side of the

membrane. In other asymmetric membranes, there may be a distinct transition

between the dense filtration in layer (i.e., the skin) and the support structure. The

denser skinned layer is exposed to the feed water and acts as the primary

filtration barrier, while the thicker and more porous under structure serves

primarily as mechanical support. Some hollow fibres may be manufactured as

single- or double- skinned membranes, with the double skin providing filtration at

both the outer and inner walls of the fibres. Like the asymmetric skinned

membranes, composite membranes also have a thin, dense layer that serves as

the filtration barrier. However, in composite membranes the skin is a different

material than the porous substructure onto which it is cast. This surface layer is

designed to be thin so as to limit the resistance of the membrane to the flow of

water, which passes more freely through the porous substructure. NF and RO

membrane construction is typically either asymmetric or composite, while most

MF, UF, and MCF membranes are either symmetric or asymmetric

3. 1.8 TYPES OF MEMBRANES MODULE:

Membranes are never applied as one flat plate, because this large

surface often results in high investing costs. That is why systems are built densely

to enable a large membrane surface to be put in the smallest possible volume.

13

3. 1.8.1 TUBULAR MEMBRANES

Tubular membranes are not self-supporting membranes. They are located

on the inside of a tube, made of a special kind of material. This material is the

supporting layer for the membrane. Because the location of tubular membranes is

inside a tube, the flow in a tubular membrane is usually inside out. The main

cause for this is that the attachment of the membrane to the supporting layer is

very weak.

Tubular membranes have a diameter of about 5 to 15 mm. Because of the

size of the membrane surface, plugging of tubular membranes is not likely to

occur. A drawback of tubular membranes is that the packing density is low, which

results in high prises per module

.

Figure 3.4 Tubular membranes

14

3. 1.8.2 CAPILLARY MEMBRANES

With capillary membranes the membrane serves as a selective barrier,

which is sufficiently strong to resist filtration pressures. Because of this, the flow

through capillary membranes can be both inside out and outside in.

The diameter of capillary membranes is much smaller than that of tubular

membranes, namely 0.5 to 5 mm. Because of the smaller diameter the chances

plugging are much higher with a capillary membrane. A benefit is that the packing

density is much greater.

Figure 3.5 Capillary membranes

3. 1.8.3 HOLLOW FIBRE MEMBRANES

Hollow fibre membranes are membranes with a diameter of below 0.1 µm.

consequentially, the chances of plugging of a hollow fibre membrane are very

high. The membranes can only be used for the treatment of water with a low

15

suspended solids content. The packing density of a hollow fibre membrane is very

high. Hollow fibre membranes are nearly always used merely for nanofiltration

and Reverse Osmosis (RO). These membranes are mostly used for gas

separation and filtration.

Outside diameter: 0.5 – 2.0 mm Inside diameter: 0.3 – 1.0 mm Fiber wall thickness: 0.1 – 0.6 mm Fiber length: 1 – 2 meters

Figure 3.6 HOLLOW FIBRE MEMBRANE

3. 1.8.4 SPIRAL WOUND MEMBRANES

The design of spiral wound elements contains two layers of membrane

glued back to back onto a permeate collector fabric(permeate channel spacer).16

This membrane envelope is wrapped around a permeate empties from the

permeate channel spacer.

A plastic netting into the device and maintains the feed stream channel

spacing. It also promotes mixing of the feed stream to minimize concentration

polarization.

Spiral membranes consist of two layers of membrane, placed onto a

permeate collector fabric. This membrane envelope is wrapped around a centrally

placed permeate drain (see picture below). This causes the packing density of the

membranes to be higher. The feed channel is placed at moderate height, to

prevent plugging of the membrane unit.Spiral membranes are only used for nano

filtration and Reverse Osmosis (RO) applications.

Figure 3.7 Spiral wound membrane module

17

3. 1.8.5 DISK MEMBRANE MODULE

Figure 3.8 DISK MEMBRANE MODULE

3. 1.8.6 PLATE MEMBRANE MODULE

These type of membrane will be in flat.

Figure 3.9 PLATE MEMBRANE MODULE

3. 1.8.7 PILLOW-SHAPED MEMBRANES

Membranes that consist of flat plates are called pillow-shaped membranes.

The name pillow-shaped membrane comes from the pillow-like shape that two

18

membranes have when they are packed together in a membrane unit. Inside the

‘pillow’ is a supporting plate, which attends solidity. Within a module, multiple

pillows are placed with a certain distance between them, which depends on the

dissolved solids content of the wastewater. The water flows through the

membranes inside out. When treatment is done, the permeate is collected in the

space between the membranes, where it is carried away through drains.

3. 1.9 MEMBRANE SYSTEMS

The choice for a certain kind of membrane filtration system is determined

by a great number of aspects, such as the benefits of membrane filtration , costs,

risks of plugging of the membranes, packing density and cleaning opportunities.

The arrangement of the RO membranes in the vessels are termed as membrane

system arrangement.

Generally system of RO is many types .They are

1) Single module system:

Single module system retreats its own reject water along with feed water.

Figure 3.10 SINGLE MODULE SYSTEM

19

2) Single array system:

In this system the permeate and reject are collected separately and

the reject is not again taken as feed and treated.

Figure 3.11. SINGLE ARRAY SYSTEM

2) Multi array system

This system is twice of single array system, which takes first

system’s concentrate as feed for second system

20

Figure 3.12 MULTI ARRAY SYSTEM

4) Permeate staged system:

This system is differed from others, here first membrane’s permeate

is used as feed water to second membrane module and second membrane’s

concentrate is mixed with first membrane’s feed water.

Figure 3.13 PERMEATE STAGED SYSTEM

3. 1.10 SYSTEM COMPONENTS:

21

1) High pressure pump.

2) Pressure vessel

3) Shut down switches

4) D.C.S. system(control room)

5) Control instruments.

6) Tanks

7) Pressure gauges.

3. 1.11 SAMPLING METHODS

The two most common approaches for sampling are the grab and

composite methods.

1) Grab sampling involves the collection of one or more aliquots from the feed or

filtrate stream,

2) composite sampling involves collection of the entire process stream for

processing and subsequent analysis.

3. 1.12 FACTORS INFLUENCING R.O. PERFORMANCE

1) Flow rate

2) TDS value

3) Decrease in permeate flow and pressure

4) Scaling

5) Fouling (major problem caused)

6) Recovery of permeate

22

Table 3.1 FACTORS INFLUENCING MEMBRANE PERFORMANCE

INCREASING PERMEATE FLOW SALT PASSAGE

Effective pressure Increase Decrease

Temperature Increase Increase

Recovery Decrease Increase

Feed salt Decrease Increase

FOULING

Foreign materials which may be present in the feed water such as

hydrates of metal oxides, calcium precipitates, organic and biological mater. This

includes all kind of build–up of layers on the membrane surfaces. Inner surface of

the feed line tubing and the feed end scroll of the membrane element if it is

reddish brown, fouling by iron material may be considered.

Three kinds of fouling that reduces membrane performance

A membrane treatment system can be fouled by virtually anything present

in the water being fed to the unit. However, in common treatment systems such

as reverse osmosis, the fouling materials may be generally categorized as

inorganic, organic, or biological.

Inorganic compounds that cause fouling of membrane modules include

inorganic salts with low solubility. These may enter the treatment system in

particle form, or they may precipitate inside the system as a result of

concentration changes occurring in the feed water as permeate is recovered

through the membrane. The highest concentration of dissolved solids happens to

23

occur immediately adjacent to the surface of the membrane in the treatment

module.

If the feed water contains salts of low solubility, it is likely that these salts

will precipitate on the surface of the membrane to form scale. Salts such as

calcium carbonate (CaCO3) and calcium sulfate (CaSO4) are common in most

feed waters. Other salts such as barium sulfate (BaSO4), strontium sulfate

(SrSO4), and calcium fluoride (CaF2) also may be in solution. In many feed water

sources these salts are present at or near their solubility limits and will precipitate

as the concentration of the feed water increases in the system. Although this

precipitation can be controlled with proper pretreatment, fouling due to these salts

does occur frequently because of operator error or unknown changes in feed

water quality.

Metal hydroxides are other inorganic compounds that cause fouling. The

most common culprits are iron hydroxide, (Fe(OH3)) and aluminum hydroxide,

(Al(OH3)). As in the case of inorganic salts, these hydroxides may enter the

system as suspended particles or they may form inside the system. Unlike the

inorganic salts however, metal hydroxides do not deposit a hard crystalline scale

but rather a soft, gelatinous layer.

Clay, silt and other silica-based materials can cause fouling if the particles

are not removed in the pretreatment equipment located in the process train ahead

of the membrane treatment system. In some feed water sources clay occurs as

very finely divided (1 to 5 micron) particles. These small colloidal particles can be

very difficult to remove with conventional equipment. Silica may also enter the

membrane system in the dissolved or reactive form. This low molecular form of

silica will polymerize as the feed water concentration increases at the surface of

the membrane. The resulting solid silica deposit on the membrane can be

extremely difficult, if not impossible, to remove.

Organic compounds make up the second category of fouling materials. Surface

water sources like rivers and lakes may contain naturally occurring organics, for

example humic acids. Clarified water may contain residual polymers, and

24

wastewater influents may contain any number of organic compounds. The

mechanism behind organic fouling depends upon the size and chemical nature of

the specific substance causing fouling. High molecular weight compounds may

act more as particles and can plug the feed spacer in the membrane element.

This plugging may be worsened if inorganic particles, such as clays and metal

hydroxides, also are present.

Figure 3.14 FOULED MEMBRANE

Low molecular weight organics may foul the surface of the membrane

through chemical interaction. As an example, chlorinated phenols will adhere to

the surface of an RO membrane by means of hydrogen bonding. In this situation,

a small concentration of the chlorinated phenol in the feed water can cause a

large loss of flux in the treatment system.

Biological organisms also are troublesome because of their tendency to foul

membrane surfaces. Although they are technically organic, biological organisms

demand special consideration. In terms of fouling, the concern is primarily with

single cell organisms. These include bacteria, algae and fungi. Of these, bacteria

25

cause the majority of problems in membrane water treatment systems for a

variety of reasons.

First, many types of bacteria can adapt to the environment inside the

membrane modules. Unfortunately, a great number of these species are found in

typical feed waters, particularly water from a surface source, such as a river or

lake.

Second, since the bacteria are rejected by the membrane, they end up on

its surface. While their presence there is bad enough, their food, consisting of

organic matter, also is being concentrated at the membrane surface. When

bacteria are placed in a liveable environment with sufficient food, they multiply

rapidly. This means that even more bacteria end up on the membrane surface.

Finally, bacteria have a number of defence mechanisms. Several have

small hair like appendages, called fimbriae, which stick out from all sides of the

cell. These allow the bacteria to attach themselves, and remain attached, to the

surface of the membrane or to the feed spacers. In addition, bacteria secrete a

mucous capsule, or slime, which coats the cell and protects them from any harsh

elements entering their environment.

TABLE 3.2. THICKNESS OF FOULANT VS EFFICIENCY LOSS

Thickness of foulant materials on

membrane surface

Percentage loss of efficiency

0.4 mm 4%

0.8mm 8%

3. 1.13 BENEFITS OF MEMBRANE FILTRATION

• Osmosis offers a unique advantage that it is a process that can take place while

26

temperatures are low. Therefore, this enables the treatment of heat-sensitive

matter. That is why these applications are widely used for food production.

• It is a process that does not require much energy and thus, energy costs are

low. The process just requires energy to pump liquids through the membrane.

This is far too low when compared to the total amount of energy required for a

technique such as evaporation.

• The process can easily be expanded.

• Process management of membrane filtration systems is simple.

Membrane filtration systems can be managed in both dead-end flow as

well as cross-flow. The purpose of the optimization of the membrane techniques

is the achievement of the highest possible production for a long period of time,

with acceptable pollution levels.

27

CHAPTER 4

CONFIGURATIONS OF MFL RO PLANT

4.1 GENERAL

The project work was done at Madras Fertilizers Limited in Manali, Chennai.

M.F.L. was incorporated on dec. 8, 1966 as a joint venture between GOI

AND AMOCO India incorporated of U.S.A. (AMOCO) in accordance with the

fertilizer formation agreement executed on 14.5.1966 with equity contribution of

51% and 49% respectively.

About 1000 employees are at present working in the company.

The company has a very good relationship with public and farmers. So the

feed back given by the formers are updated at every moment

The company produces the following products:

1. UREA

2. NPK-complex

3. NK-mixture

4. MOP-IMPORTED

5. DAP-IMPORTED

28

4.2 WATER NEEDS OF MFL

Water is vital material for the production of fertilizers. Approximately

630 m3/hr of water is processed every day at R.O. Plant. The potable water is

supplied by Chennai Metro Water Supply and Sewage Board(CMWSSB).

The boiler and feed water for fertilizer production is taken from the treated

sewage water from MFL’s treatment plants.

CMWSSB supplies water for fertilizer production. Due to increase in

population and scarcity at summer seasons the supply of raw water was

restricted.

In order to eliminate raw water shortage and to reduce the cost of raw

water the Tertiary treatment plant and R.O. plants were installed in the year

1993/94.

The sewage water is taken from Kodungaiyur sewage treatment plant.

Owned by CMWSSB and supplied to M.F.L. Tertiary treatment plant and R.O.

plant. Which reduces the raw water cost/consumption.

After 1995 the full need of water is being supplied by R.O. Plant.

The primary treated sewage water is being bought for Rs. 9/m3

(approximately) and taken to tertiary treatment plant. After tertiary treatment of the

sewage the cost is Rs. 56/m3 (approximately).Then the T.T.P. water is supplied

to R.O. plant.

The R.O. plant production is then taken to the Demineralisation plant and

stored and then to the boilers as feed water.

29

Figure 4.1 REVERSE OSMOSIS PLANT DIAGRAM

1.Pilot plant 2. R.F. sump 3. Roughing filters 4. Filtered water storage tank

5. Chlorine retention tank 6. Dual media filters 7. Cartridge filters 8. Hp

pumps 9. Membrane stack 10. Blended storage tank 11.Settlement tank

12.Backwash tank13.Chlorine storage tank &Injection tank 14.Chemical

dosing tank 5.Digital control system room 16.Tertiary treated water storage

pond

30

4.3 DETAILS OF RO PLANT IN MFL

4.3.1 MULTI ARRAY SYSTEM.

In MFL multiple array system is being used. Three trains operates in

parallel, each designed to produce 120 m3/hr of permeate. Each of the three

trains will be a three staged system with the reject from each stage forming the

feed of the following stage.

The product water from the three stages are combined to form the train

product(permeate) stream.

1) 3 trains

2) Each have 4 banks

3) Each banks are named as A, B,C,D.

4) A,B,C banks have 10 vessels each and D bank has 7 vessels.

5) Each vessel houses 6 membranes connected in series (8”

diameter and 1m long, RO membranes).

Table 4.1 TRAIN AND ITS COMPONENTS

BANK No. OF VESSELS No. OF MEMBRANES

A1& A2 5+5=10 60

B1& B2 5+5=10 60

C1& C2 5+5=10 60

D 7 42

Total No. Of membranes 222

31

Figure 4.2 MULTIPLE ARRAY SYSTEM AND BANK ARRANGEMENT

Each trains are designed to operate with a permeate recovery of 75% and at this

recovery it is anticipated to give the efficiency of 95% at ambient temperature.

32

4.3.2. SPECIFICATIONS OF R.O. PLANT

Feed water supply : 160 m3/hr/train.

Permeate water flow : 120 m3/hr/train.

Reject water flow : 40 m3/hr/train.

Feed water pressure : 16 kg/cm2 g.

P : less than 4.

R.O. membrane material type: T.F.C Spiral wounded brackish water membrane.

Size of a membrane : 8” dia.

: 40” long.

Feed temperature : not more than 40 o c

Percentage recovery : 75 % (Permeate)

Percentage recovery = permeate flow x 100/ feed flow

Dimensions of pressure : 200 mm dia.

vessels : 6 m long.

MOC of pressure vessels : GRP.

Thin film composite R.O. membrane give excellent performance for a wide

variety of application including low pressure tap water use, single – pass sea

water & brackish water desalination, chemical processing and waste

treatment. This membrane exhibits excellent performance in terms of flux, salt

rejection and microbial resistance.

R.O. element can operate over a pH range of 2 to 11, are resistant to

compaction and are suitable for temperature upto 45 o c.

Salt rejection 99.5% and flux – 24 l/m2hr

33

4.3.3 PROBLEMS FACED BY R.O. PLANT

The main problem is caused by fouling and scaling. Because the sewage

water contains more organic matter, microbes and dissolved organic solids.

These will accumulate on the surface of the semi permeable membrane.

The foreign materials which may be present in the feed water such as

hydrates of metal oxides, calcium precipitates, organic and biological matters.The

term includes the build up of all kinds of layers on the membrane surfaces,

including scaling.

Inner surface of the feed line tubing and the feed end scroll of the

membrane element, if it is reddish brown fouling by iron content.

Biological fouling (or) organic material is often shinny or gelatinous.

Due to the increase in accumulation of these particles day by day the

efficiency of the membrane will be slowly decreased. After some years the

efficiency will be very much low. The pressure difference ( P ) will be

increased to 4 and above. It leads to failure of membrane by wear and tear of

brine seal and membrane.

Figure 4.3. FOULED MEMBRANE PHOTO(unrolled)

34

4.3.4 . MAINTENANCE OF RO ELEMENT

The R.O. element are frequently washed by chemicals, so as to keep the

membrane surfaces clean and face of deposits.

Table: 4.2 RO WASH PROCEDURES

Chemical

concentration

Quantity of

permeate

Solution

concentration for

circulation

Wash

sequence Duration

HCl 33% 4000 lts 0.5% ACD 30 min.

HCl 33% 4000 lts 0.5% BCD 30 min.

HCl 33% 4000 lts 0.5% A 4 hrs

HCl 33% 4000 lts 0.5% B 4 hrs

HCl 33% 4000 lts 0.5% C 4 hrs

HCl 33% 4000 lts 0.5% D 4 hrs

HCHO 37% 1700 lts 1.0%(60 kgs) ACD 8 hrs

HCHO 37% 1700 lts 1.0%(60 kgs) BCD 8 hrs

All banks are flushed with permeate

SLS(85 %)+

EDTA(98%)

1700 lts 0.2%(3.5 kgs+

3.5kgs)

ACD/BCD30 min

each

do do do A 2hrs

do do do B 2hrs

do do do C 2hrs

do do do D 2hrs

SLS + EDTA Soaking 12 hrs

35

Chemical

concentration

Quantity of

permeate

Solution

concentration for

circulation

Wash

sequenceDuration

NaOH (10-11 pH ) 500 lts A 30 min

NaOH (10-11 pH ) 500 lts B 30 min

NaOH (10-11 pH ) 500 lts C 30 min

NaOH (10-11 pH ) 500 lts D 30 min

Total wash hours 80 hrs

.

The R.O. elements are washed when any one of the following conditions arrives:

1) Permeate flow reduction

2) P change

3) Increase in Salt passage

Acid wash:

0.5% HCl is being used to wash the membrane for the acid wash.

Alkaline wash:

NaOH is used for alkaline wash.

Acid wash is desirable for removing organic and inorganic salts like

CaCO3, CaSO4 and BaSO4.

Alkaline wash is desirable for removing silica, biofilms and organic matters.

These leads to foul the membrane. These results with low efficiency, recovery

change and increase in P, decrease in salt passage.

36

CHAPTER 5

MATERIALS AND METHODS

5.1 SOURCE

After identifying the solution the same membrane was performed to treat

the tertiary treated waste water.

5.2 SAMPLE COLLECTION AND ANALYSIS

The inlet water and out let water of the membrane were taken. These

samples were analysed at Laboratory in Madras Fertilizers Limited, Manali.

5.3 ANALYSIS OF THE VARIUOS PARAMETERS

The following parameters of the samples were analysed.

5.3.1 COLOUR:

After the collection of the sample the colour of the sample was noted.

5.3.2 pH Value:

The pH value was found by pH meter.

5.3.3 CHLORIDES:

Procedure:

100 ml of sample was taken in two flasks, 1 ml of potassium chromate

indicator is added in each flask. The liquid is literate with N 35.5 silver

nitrate solution from burette drop with constant stirring unit there is a

37

permanent change from yellow to brick red. The volume of titrant is recoded as

‘A’ml. The above procedure is repeated for distilled water to obtain ‘B’ ml.

Quantity of chlorides present

in the sample = ((A-B)XNX35450)/Volume of sample mg/l.

N : Normality of AgNO 3

5.3.4 SULPHATES:

Procedure:

20 ml of the sample was taken in a beaker. 10 ml of 2N HCl

acid was added to it and heated till it was boiled. At the time of boiling 30

ml of barium chloride solution was added. The solution is filtered in the

beaker through wattman after No. 42. The barium Chloride react with

sulphate present in the sample in the presence of HCl and barium sulphate

was allowed to settle. The filtered sulphate was taken in the weighed

crucible and was placed in the muffle furnace till got charged. Then it was

weighed (W2). The difference between the weight of empty crucible and weight

W2 gives the amount of sulphate present in the sample .

mg of residue X molecular weight of BaSO4

Amount of sulphate =

Volume of samples

5.3.5 TOTAL DISSOLVED SOLIDS:

Total Dissolved Solids

20 ml of the sample was filtered through No. 42 wattman filter paper and it

was cooled in a weighed crucible. It is heated in the water bath and evaporated to

dryness in the oven for one hour, then the container was weighed and the

38

increased weight was noted down. The increased weight is known as dissolved

solids present in the 20 ml of sample.

mg of residue present in the filter paper

Total Dissolved solids = X1000 in mg/l

ml of sample taken

5.3.6 TOTAL HARDNESS:

Procedure

Standardisation of EDTA with standard Hardwater

20 ml of standard hard water was taken in a clean conical flask. 5 ml of

ammonia buffer solution was added and a pinch of Erichrome Black–T indicator

was added and it was titrated against EDTA solution which was taken in the

burette. At the end point wine red colour changes to blue. The volume was noted

(V1).

Estimation of hardness

20 ml of sample was taken in a clean conical flask. 5 ml of ammonia buffer

solution and a pinch of Erichrome black – T were added and titrated against

EDTA solution. The end point was just the change from wine red to blue colour.

The volume was noted (V2).

1ml of standard hard water = 1 mg of CaCO3

20 ml of standard hard water = V1ml of EDTA

1 ml of EDTA = 20/V1 mg of CaCO3

20 ml of sample water = V2 ml of EDTA

Therefore total hardness of sample = (20 X V2) / (V1X 20) X 1000 mg/l.

39

5.3.7 CALCIUM HARDNESS:

Take 50 ml sample add 1N NaOH solution followed by pattern reading

indicator then titrate vs EDTA solution.

End point : pink to blue colour.

Calcium Hardness = Titrant volume X Normality of EDTA X equivalent weight

volume of sample taken

5.3.8. LOSS OF IGNITION (LOI):

Take 1 gram sample make it to dry at 105o c. After drying keep the

crucible at 500 o c in muffle furnace for half an hour. Weight difference is the

loss of ignition.

LOI = weight difference X 100

weight of the sample

5.3.9. TOTAL IRON :

Take definite volume of sample add conc. HCl followed by Hydroxyl

Ammonium Hydrochloride solution. Reduce the volume to 5 ml by drying over hot

plate. Then cool it add Ammonium Acetate buffer followed by 1,10-

orthophenonthroline indicator. Then take the absorption at 510 nm, run a

standard and blank along with the sample.

Take the absorbance using spectrophotometer.

Total Iron = Sample OD X Std. Conc. X 1000

40

(Std. OD X Volume of sample taken)

5.3.10. PHOSPHATES:

Take the definite volume of sample add Conc. HNO3 and H2 SO4 then

keep it for fuming. After fuming over, cool it then add phenolphthalein followed

by sodium hydroxide solution. Then add Ammonium Molybdenum solution

followed by stannous chloride solution. Take the absorbance at 690 nm, in

spectrophotometer. Run a standard and blank along with the sample.

Phosphate = Sample OD X Std. Conc. X 1000

( Std. OD X Volume of sample taken)

5.3.11. SILICA:

If the sample is turbid filter it through wattman 42 filter paper take

the definite volume of filtered sample add 1:1 HCl and Ammonium Molybdate

solution followed by oralic acid. Take the Absorbance at 410nm using

Spectrophotometer. Run a blank and standard along with the sample.

Silica = Sample OD X Std. Conc. X 1000

(Std. OD X Volume of sample taken)

5.3.12. TURBIDITY:

Calibrate the Nephelo turbidity metre using standard solution. Now

shake the sample well and find out the turbidity using Nepheloturbidity metre.

41

5.3.13. OIL AND GREASE:

Take a definite volume of sample ( in a separate funnel) add small

volume of concentrate HCl followed by Petroleum Ether(W1). Shake well. Discard

the bottom layer. Collect the upper layer and dry it in a weighed beaker (W2).

Weight difference ( W1- W2) is the oil and grease.

42

CHAPTER 6

RESULTS AND DISCUSSION

6.1 MEMBRANE AUTOPSY

6.1.1. MEMBRANE SELECTION

Old used membrane was selected in wet condition. Its last performance

was noted. The efficiency of the old membrane was less than 70%.The same

membrane was opened. Then it was unsealed and the brine seal removed.

Then it was unrolled carefully and one membrane sheet was selected

to cut.

Figure 6.1 MEMBRANE SELECTION

It was marked 0.5 m x0.5 m area in one membrane sheet.

In the same way the other membrane sheets were marked. They

were cut as the mark. They were spreaded over a white sheet and

43

then the membrane was scrapped without damaging the membrane

surface. The sample collection was grab sample.

Membrane specifications:

Pore size of the membrane : 0.01 µm.

Feed rate : 8 m3 / hr

Diameter of the membrane : 8 inches.

Length of the membrane : 40 inches.

Type of membrane : Brackish water membrane(spiral wound).

Feed pressure : 16 kg /cm 2 g.

Percentage recovery : 75% (permeate)

Membrane maintenance washes:

The membrane is washed by the following chemicals, when ever there is

a change in p (feed pressure – permeate pressure), efficiency, flow rate,

recovery and time period.

1) 0.5% HCl wash

2) 1.0% HCHO wash

3) 0.2% (SLS+ EDTA) wash

4) NaOH (10-11 pH ) wash

The efficiency of the membrane will be slowly decreased through out the

operation period due to accumulation of particles over the membrane surface.

After some period there will be no change in efficiency, between pre and post

wash of these chemicals mentioned above. This may occur inbetween the life

time of the membrane mentioned by the manufacturer or after the life time. This

depends on the pre-treatment and solids presented in the feed water of reverse

44

osmosis membrane. So it is considered as the membrane should be discarded

and disposed or removed from the vessel and new membrane shall be installed.

. Figure 6.2 PHOTO OF UNROLLED MEMBRANE

45

Figure 6.3 PHOTO OF FOULED MEMBRANE

The Figure. 6.3 shows the film of the deposited particles. The scrapped materials

were collected from membrane surface in wet condition and they were analysed.

TABLE 6.1 INGREDIENTS OF SAMPLE (SCRAPPED MATERIAL)

Sl.

No.PARAMETERS RESULTS(mg/l)

1 Total hardness as CaCO3 352

2 Calcium hardness as CaCO3 264

3 Loss Of Ignition(LOI) 99.26%

4 Total Iron 10.10

5 Phosphates 7.18

6 Sulphates 795

7 Silica 45.0

8 Chlorides 556

9 Total Dissolved Solids 5300

10 Turbidity(NTU) 30.0

11 Total Organic Compounds 440

46

As per the results, the Loss Of Ignition is 99.26%. So the organic compound

materials are high as foulant materials which were deposited throughout the

period of membrane, which were not washed out by ordinary wash.

6.1.2 METHODOLOGY

The membrane wash was done by 0.5% of HCl. By overcoming this the

deposition and accumulation on the membrane seen. Another used old

membrane was selected which was same batch and same efficiency while

disposed. So now 0.6%, 0.75%, 1.0% HCl solutions were tried over the old

membrane. 0.6 & 0.75% of HCl gives no improvement in removing the

depositions. 1.0% HCl (washed for 5 min) removes the deposition easily without

any stress. The analysis of 1% HCl washed solution is given below.

TABLE 6.2 HCL WASH SAMPLE

Sl. No. Parameters Results(mg/l)

1 Total hardness as CaCO3 220

2 Calcium hardness as CaCO3 120

3 Loss Of Ignition 96%

4 Total Iron 9.77

5 Phosphates 1.77

6 Sulphates 285

7 Silica 40.0

8 Chlorides 920

9 Total Dissolved Solids 1440

10 Sodium EDTA 1983

11 Total Organic Compounds 360

12 SLS(Sodium Laurel Sulphate) 1525

47

13 Oil & grease 10.0

6.2 RESULTS:

After the autopsy and washing by 1 % HCl the same

membrane’s removal efficiency was checked. The 75% recovery of permeate

water was set.

The collected samples were tested to find the amount of

pollutants available in both feed and permeate water of reverse osmosis

membrane. So the efficiency of the membrane could be easily found.

Table 6.3 MEMBRANE PERFORMANCE AT STARTING STAGE.

Sl.

No.Parameters Feed mg/l Permeate mg/l

Efficiency

%

1 Na 420 56 86

2 Ca 64 12.8 83.2

3 Cl 620.3 75.4 86.3

4 TDS 1348.5 210 84.4

5 pH 7.4 7.3 -

6 Total hardness 340 60.7 82.3

7 Sulphates 230 17.5 76.08

48

8 Total iron 13.4 2.7 79.8

The overall efficiency was 82.58 %.

Then the membrane was experimented for more than 100hrs and the performance and efficiency was found out. It is tabulated below.

Table 6.4 MEMBRANE PERFORMANCE AFTER 100hrs

Sl.

No.Parameters Feed mg/l

Permeate

mg/l

Efficiency

%

1 Na 385 60.45 84.3

2 Ca 72.3 11.56 83

3 Cl 630.5 87.0 86.2

4 TDS 1403.5 227.36 83.8

5 pH 7.2 7.1 -

6 Total hardness 365.3 55.8 84.7

7 Sulphates 276 60.16 78.2

8 Total iron 12.7 2.6162 79.4

Now the overall efficiency was 82.9%.

So from the above results, the efficiency was maintained throughout

the experimented time period. So 1 % HCl wash may be adopted followed by high

pH and detergent washes.

49

CHAPTER 7

CONCLUSION

From the above project study it can be seen that the major foulants

are iron and fouling. More over Loss Of Ignition (LOI)of pre and post

cleaning is found to be more than 95% which clearly indicates the presents of

fouling to a greater extent.

Owing to the reason the source of feed water is treated sewage,

hence it is concluded that one of the methods of membrane maintenance

is to adopt membrane cleaning with 1% HCl using Cleaning In Place(CIP)

followed by high pH and detergent washes.

50

BIBILIOGRAPHY

1.N.Manivasakam, “Industrial Effluents Origin, Characteristics, Effects, Analysis

and Teatment”, 1987.

2.Evaluation of Membrane Processes and their Role in Wastewater Reclamation,

Final Report of Contract for US Department of interior OWRT,David Argo and

Martin Rigby, November 30,1981.

3. “Analysis of Water and Waste Water”,BIS Publication (1993),New Delhi

4. Wesley Eckenfelder Jr. W (2000), “Industrial Water Pollution Control” Tata

McGraw Hill Publishing Co.Ltd, New Delhi.

5. Metcalf and Eddy (1979), “Waste Water Engineering Treatment and Disposal”.

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6. Nemerow N.L (1978), “Industrial Water Pollution”, Wesely Publishing Company

Inc., USA.

7. Control of Fouling of Reverse Osmosis Membranes When Operating on

51

polluted Surface Water, J.E.beckman, E.Bevage, J.ECurver, I.Nusbaum, and

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11. S.K.Garg (1986), Volume – I, “Environmental Engineering and Pollution

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12. Study and Experiments in Waste water Reclamation by Reverse osmosis, I.

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52

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53