ENVIRONMENTAL ENGINEERING

343Lecture 5:

Water Quality

Philadelphia UniversityFaculty of Engineering

Department of Civil EngineeringFirst Semester, 2013/2014

Water quality parameters - qualitatively reflect the effect of various impurities on the intended use of water

Standard Methods for the Examination of Water and Wastewater- Standard analytical test procedures which provide quantitative measurements of these parameters

WATER QUALITY REQUIREMENTS

Water quality parameters - qualitatively reflect the effect of various impurities on the intended use of water

Standard Methods for the Examination of Water and Wastewater- Standard analytical test procedures which provide quantitative measurements of these parameters

WATER QUALITY REQUIREMENTS

Water quality requirements vary according to proposed use of the water. Water unsuitable for one use may be satisfactory for another. These are set by the user. It represents a known or assume need and are based on prior experience of the user.

Water Quality Standards are set by a governmental agency and represent a statutory requirement

WATER QUALITY REQUIREMENTS

In-Stream standards – Streams have minimum quality standards based on its use. Wastewater discharged from human activities together with the geology and natural characteristics of the watershed.

Potable-water Standards – EPA ; WHO addresses turbidity, SS taste, odor, moderate dissolved inorganic; absence of organics, toxic substances and pathogens

Wastewater effluent standards- e.g. EPA standards for the discharge of wastewater. – require secondary treatment. Industrial wastewater must be pretreated to become compatible with receiving domestic WW.

WATER QUALITY REQUIREMENTS

Physical water-quality parameters

Chemical water-quality parameters

Biological water-quality parameters

Water quality requirements 

TOPICS

PHYSICAL WATER-QUALITY PARAMETERS

Parameters:• Suspended Solids• Turbidity• Colour• Taste• Odor• Temperature

SOLIDS(IMPURITIES) TYPES OF SOLIDS

1. Dissolved Solids (in Liquid) cannot be removed from liquid without accomplishing a phase change such as distillation, precipitation, adsorption, extraction or high pressure membrane

2. Suspended solids (filterable solids) those solids that can be filtered by a glass fiber filter disc can be removed from water by physical methods such as sedimentation, filtration and centrifugation.

3. Colloidal particles1. Size in range between dissolved substances and

suspended particles2. Can be removed by high-force centrifugation or

filtration – very small pore size3. Measured by turbidity

Seldom found in groundwaters due to the natural filtering capacity of soils

1.0 SUSPENDED SOLIDS

Suspended Solids

Immiscible liquids-Oils-Grease

Source- Surface waters; Domestic WW

and Industrial WW

Organic-Plant Fiber-Biological Solids (Agal

Cells; Bacteria;)

Source – Surface Waters; Domestic WW;

Industrial WW

Inorganic-Clay-Silt

Source – Surface Waters; Domestic

WW; Industrial WW

Sources of Suspended Solids

SUSPENDED- LARGER THAN MOLECULAR SIZE SUPPORTED BY BUOYANT AND VISCOUS FORCESDISSOLVED-MOLECULES OR IONS HELD BY MOLECULAR STRUCTURE OF WATERCOLLOIDS- TECHNICALLY SUSPENDED BUT EXHIBITS CHARACTERISTICS OF DISSOLVEDDifference Between Dissolved, Suspensions and Colloidal Solutions Property Dissolved Suspensions Colloidal Solutions

Particle size Less than 10 - 6 mm Greater than 10 -

3 mm

Between 10 - 6 and 10 - 3

mm

Visibility of

particles

Invisible to naked eye not

visible under powerful

microscope

Easily visible

Invisible to naked eye.

Visible under powerful

microscope.

Sedimentation of

particles Do not settle down

Settle down due

to gravity

Settle down under high

centrifugation

Filtration through

filter power No residue is formed

Residue is

formed No residue is formed

Water Pollution – The presence in water of

impurities in such quantity and of such nature as to impair the use of the water for a stated purpose

Water quality is predicted on the intended use

SOLID  Measured in mg/L Sources (s):

Inorganic compounds such as clay, sand Organic compounds such plant fibre, human

wast Effects (s):

Aesthetics Adsorption point/centre for chemical and micro-

organism Health aspect

2- TURBIDITY

Turbidity: The presence of suspended material such as clay, silt, finely divided organic mater, and other particulate material in water

The unit of measure is a Turbidity Unit (TU) or Nephlometric Turbidity Unit (NTU)

It’s a measure of the cloudinessRiver values range from 2 to 200mg/L of SiO2The EU drinking water upper limit is 10mg/L with

a guideline value of 1mg/L

3-COLOR Color in water is caused by dissolved

minerals, dyes or humic acids (decomposition of lignin) from plants. Apparent Color: Color that is partly due to

suspended solids (SS) True Color (water treatment): Color that is

contributed by dissolved solids (DS) after removal of SS

Color itself is not usually undesirable from the stand point of health- it indicates that water needs appropriate treatment

4- ODOR Many organic and inorganic chemicals are

odorous including algae and other organisms H2S – hydrogen sulfide sometimes present in

ground water and wastewater. Threshold odor is determined by diluting a

sample with odor –free water until the last perceptible odor is detectable (dilution factor)

Like odor, may be due to decaying micro-organisms or algae or due to high conc. of salts such as Ca & Mg

5-TASTE

6- TEMPERATURE One of the most important parameters in natural

surface waters. It influences the number and type of microorganism

species present and their rate of activities; affect most chemical reactions; affect solubility of gases e.g oxygen decrease with

increase temp. Conc of O2 around 8mg/L @ 25 degree Celsius

In WWTP, T above 36oC, the aerobic MO population tends to be less effective as WW purifiers

In rivers, as increased water temp reduces the amount of oxygen in water, thereby making river less desirable for fish, particularly salmonoids.

CHEMICAL WATER QUALITY PARAMETERSParameters

TDS Alkalinity Hardness Metals Nutrients pH

1- ALKALINITY Alkalinity measures the buffering capacity of

the water against changes in pH; measuring the amount of acid needed to lower the pH in a water sample to a specific endpoint (4.5).

Water that has a high alkalinity can accept large doses of acids or bases without altering the pH significantly.

Waters with low alkalinity, such as rainwater or distilled water, can experience a drop in the pH with only a minor addition of an acid or base.

Alkalinity is expressed as mg (CaCO3)/L

ALKALINITY In water the only significant contribution to

alkalinity are carbonate species and free H+ and OH_

Acid base reaction H2CO3 H+ +HCO3

HCO3- H+ + CO3

2-

2- HARDNESS Measure of “multivalent” cations in water

such as Ca2+,Mg2+, Fe2+, Mn3+ Ca2+ and Mn2+are very important

Source (s): natural mineral on earth

effect (s): excessive soap usage (a waste !) precipitate form on hardware precipitate in pipe – temperature and pH increases

HARDNESSTotal Hardness The sum of the divalent metallic cations (Ca & Mg).

These cations reacts with soap to form precipitate and with other ions present in water to form scale in boilers.

Measured as mg CaCO3/L Two kinds of hardness:

carbonate hardness; temporary in characteristics, precipitated through boiling

non-carbonate hardness- chloride and sulfate; permanent in characteristic, eliminated through chemical softness / ion exchange

WT goal is to provide water with a hardness of less in the range of 75 to 120mg/L as CaCO3 by using softener

3-NUTRIENTS: Two nutrients are essential for the growth of organisms:

Nitrogen Phosphorus Both are indictors of water pollution

I-Nitrogen (N)Source (s) Elements for protein, chlorophyll and biological

compounds Decomposition of compounds animals and human wastes, chemicals (fertilizers)Effect (s)

NO3- poisoning to human specially babies below than 6month old and animals

NO3-> NO2-(in acidic condition) – will substitute O2 in blood vessel

Nitrogen; Exist in a form of “inorganic”, and “organic nitrogen

Measured by TKN “total Kjeldahl Nitrogen; is a measure of the total organic and ammonia nitrogen.

NUTRIENTS

NUTRIENTSII-Phosphorus (P)Exist in a form of “inorganic”, and “organic

phosphate”.Source (s):

readily present in soil fertilizers human wastes (“organic phosphate” domestic wastes (element in detergent)

effects (s) Cellular activity and aquatic plants > 0.2 mg/L – disturb coagulation processes in

water treatment plants

4-IONS – ANIONS AND CATIONSMajor Ions (conc. In mg/L) such as Ca, Mg,

Na, K, SO2, Cl, NO3, HCO3Minor Ions: Conc in µg/L such as Al, Cu,

Fe, MnSource (s):

Minerals readily available from nature Effect (s):

Colour, odour, taste and turbidityDeteriorate health (at high concentration)

4-IONS – ANIONS AND CATIONS

Metals – non toxic and toxic Heavy metals: such as As, Ba, Cd, Cr, Pb, Hg, Se,

AgSource (s)

human activities such as mining and industries

Effect (s): dangerous disease such as cancer, abortion

and deformation in newborn baby

5- PH The negative log of the hydrogen ion

concentration pH of most mineral waters is 6 to 9 If pH is out side the range 6 – 9, it might kill off

the active microbiological population including the aquatics organisms

pH is important in ensuring proper chemical treatment

ELECTRICAL CONDUCTIVITY/ CONDUCTIVITY It is a measure of the ability of an aqueous

solution to carry an electric current by the movement of ions.

The higher the numbers of ions, the higher magnitude of conductivity

Pure water has 0.05µS/cm (microsiemens/cm)

Sea water has about 40000 µS/cm Groundwater 200-1500

6-DISSOLVED OXYGENOne of the most important measures of water quality is dissolved oxygen. Oxygen, although poorly soluble in water, is fundamental to aquatic life. Without free dissolved oxygen, streams and lakes become uninhabitable to aerobic organisms, including fish and most invertebrates. It is found that the concentration of DISSOLVED OXYGEN in water is SMALLDissolved oxygen is inversely proportional to temperature, andthe maximum amount of oxygen that can be dissolved in water at 0°C is 14.6 mg/L to 7.6 at 30C.

DISSOLVED OXYGEN Dissolved oxygen in water is consumed by the

oxidation of dissolved ammonia (NH3)and ammonium ion (NH4+)to form the nitrate ion (NO3

⎯).NH3(aq) + 2O2(aq) + OH NO3-(aq) + 2H2O(aq)

The most common substance oxidized by oxygen in water is ORGANIC MATTER OF BIOLOGICAL ORIGIN

Such organic matter (such as dead plant material like polymerized carbohydrate below), is oxidised by dissolved oxygen. e.g. CH2O+O2(aq) CO2(g) + H2O(aq)

DISSOLVED OXYGEN Under oxygen free (anaerobic) conditions

dissolved organic matter will decompose if appropriate bacteria are present:

2CH2O CH4+ CO2

Such anaerobic conditions are common in SWAMPS and at the bottom of deep lakes

The Methane (CH4) produced in this process bubbles up towards the surface of the swamps and is the reason that methane used to be known as ‘marsh 'or ‘swamp 'gas

ORGANIC SUBSTANCES The main element of organic compounds is

Carbon. Organic substances may be

Natural occurring organic substances includes protein, lipids, carbohydrates and plant pigments

Synthetic organic chemicals Pesticides and agrochemicals Surface active agent including emulsifier, wetting

agent, foams, detergents Halogenated hydrocarbons ( CHCl3, CHBr3, CHCl2Br,

etc Over 120 toxic organic compounds listed on the

USEPA Priority Pollutant List including pesticides and solvents

ANALYSIS OF ORGANIC SUBSTANCES

Various parameters are used as a measure of the organic strength of wastewater: BOD –Biochemical oxygen demand COD –Chemical oxygen demand  TOC –Total organic carbon VSS –Volatile suspended solid

BIOCHEMICAL OXYGEN DEMAND (BOD)The quantity of oxygen utilized by a mixed

population of micro organisms to biologically degrade the organic matter in the wastewater under aerobic condition.

BOD is the most important parameter in water pollution control.

it is used a measure of organic pollution as a basis for estimating the oxygen

Needed for biological processes, as and indicator of process performance

Expressed in milligrams of oxygen required per liter of wastewater (mg/L).

BIOCHEMICAL OXYGEN DEMAND

BOD : BOD5: is the amount of dissolved oxygen used up from the water by microorganisms as they break down organic material at 20C over a 5-day periods. BOD5 for Rivers if > 5 mg/L, they considered

polluted BOD For MWW range 150-1000mg/L

CHEMICAL OXYGEN DEMAND (COD)

COD- Determine the amount of oxygen needed to oxidize

the organics in a water or wastewater using a strong oxidizing chemical agent- Potassium dichromate rather than using micro-organisms as in BOD

It measures the total organic carbon with the exception of some aromatics such as benzene which are not oxidized in the reaction.

Indirectly measure amount of organic matter in the water sample

Faster determination of oxygen demand in a water sample, than BOD

It takes shorter time ( 2hrs) compared to 5 days for BOD5

The EU upper limit of 125mg/L for treated wastewaters prior to discharge to rivers

RELATION BETWEEN COD AND BOD COD > BOD COD ~ ultimate BOD COD/BOD ~ 2, biodegradable organic COD >> BOD, non-biodegradable organic

TOTAL ORGANIC CARBON- TOC TOC- : measures all carbon as CO2 in mg/L Inorganic carbon ( HCO3, CO2, CO3, etc) must

be removed prior test by acidifying and aerating the sample.

Theoretically the COD is 2.66 times greater than TOC

BIOLOGICAL WATER-QUALITY PARAMETERSthe three most significant microbial groups are

the bacteria, fungi, and protozoa.  Bacteria have the primary role of decomposing

wastewater compounds, forming settleable solids, and at times are the source of operational problems. 

Fungi are significant since many operational problems are caused by members of this group. 

Protozoa are microorganisms that play a key role as predators and help control the bacterial populations. 

COMPOSITION OF WW RECALL

99.9 % Water

0.1% Solids

Solids are divided into Organic and inorganic

solids

Inorganic(30%)

Organic (70%)

Suspended Organics

(Colloidal –protein)

Dissolved Organics

(Carbohydrates)

Dissolved Inorganics

(metals, salts,P,N)

Suspended Inorganics

(Grit)

Secondary Treatment

Dissolved Organics and Suspended

Organics

Primary Treatment

60% SS; 30% BOD and Grit

Tertiary Treatme

nt

Composition of WW

Suspended Solids

Biodegradable Organics Pathogens

Body waste, food waste rags, paper,

biological cells

Soluble organics Bacteria, virus etc.

Protein )40-60%( – amino

acids

Carbohydrates 25-50% - sugars

starch, cellulose

Lipids )10%(- fats, oils and

grease

Contain Carbon – exert an oxygen demand

TYPICAL COMPOSITION OF UNTREATED DOMESTIC WASTEWATER [METCALF AND EDDY, 1991].

Concentration (mg/lt.)

Contaminants Weak Medium StrongTotal Solids (TS) 350 720 1200

Total Dissolved Solid (TDS) 250 500 850Suspended Solid (SS) 100 220 350

Settleable Solid 5 10 20Biological Oxygen Demand (BOD5) 110 220 400

Total Organic Carbon (TOC) 80 160 290Chemical Oxygen Demand (COD) 250 500 1000

Nitrogen (total as N) 20 40 85Organic 8 15 35

Free ammonia 12 25 50Nitrites 0 0 0Nitrates 0 0 0

Phosphorous (total as P) 4 8 15Chlorides 30 50 100Sulfate 20 30 50

Alkalinity (as CaCO3) 50 100 200Grease 50 100 150

Total coliform (no/100 ml) 106-107 107-108 107-109