bte3620wk3-4

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WATER QUALITY MANAGEMENT

WATER POLLUTANTS AND THEIR SOURCES

TYPES OF POLLUTANTS

Non ± point sources : This is made up of pollutants from Agricultural runoff and urban

runoff( stormwater drainage). This ischaracterized by multiple discharge points.

Point sources : This is made up of pollutants fromdomestic sewage and industrial waste collectedby a pipe network or channels and conveyed to a

single point for discharge . In general point source pollution can be reducedor eliminated through waste minimization andproper wastewater treatment prior to discharge toa natural water source

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Major water pollutant categories and principal

sources of pollutants

Pollutant category Point Sources Non-Point SourcesDomestic

sewage

Industrial

Wastes

Agric. runoff Urban runoff

Oxygen-demanding

materialX X X X

Nutrients X X X XPathogens X X X XSuspended solids

/sedimentsX X X X

Salts X X XToxic metals X XToxic organic chemicals X XHeat X 2

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Major water pollutant categories and principal

sour ces of pollutants� Oxygen ± demanding material: Any material that can be oxidized in the

receiving water using dissolved molecular oxygen. ± Sources : Food residue , human waste , food processing , paper

industry, farm inputs e. g fertilizer, pesticide, herbicides.

± Effects : Threat to aquatic and human life.

� Nutrients :

± Source : Nitrogen and phosphorous fertilizers, food ± processingwastes, detergents etc.

± Effect : Excessive nutrients leads to upset in the food web (chain) e .g excessive growth of algae , water hyacinth etc.

� Pathogenic Organisms : Bacterial, viruses and protozoa excreted bydiseased persons or animals

± Effect : Makes water unsafe for drinking , fishing , swimming. Certainshell fish become toxic.

� Suspended solids / sedimentation: Organic and inorganic particles inwaste water discharged into a receiving water.

± Effects : Organic suspended solids exert oxygen ± demand,

� Reduces the usefulness of water

± Sources : Soil erosion due to logging ,strip mining , constructionactivities, discharge of industrial waste , destruction of aquatic life dueto sediment deposits.

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Major water pollutant categories and

principal sources of pollutants� Salts :

± Make up of the total dissolved solids (TDS) in water .

± Sources : Discharge from industries, excessive use of fertilizers ( inorganic ) in farming.

± Effects :Damage to aquatic and plant life. Makes water

unsuitable for water supplies,� Toxic metals and toxic organic compounds :

± Sources : Urban runoff, agricultural runoff ± use of farm inputse . g pesticides, herbicides etc ,industrial waste water discharges e . g. electroplating , electronics.

± Effects : Toxicity in the food chain, Toxic to human even in

small quantities.� Heat :

± Sources : Industrial processes, power plants etc

± Effect : increases rate of oxygen depletion, reduces aquatic lifeof fish.

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WATER QUALITY MANAGEMENT IN

RIVERS� Objective :

± To control the discharge of pollutants so thatwater quality is not degraded to an unacceptablelevel.

� Impact of pollution on water : ± Factors :

� Volume and speed of the flowing water .

� The depth of water in the channel

� Type of bottom, surrounding vegetation etc� Climate of the region.

� Land use patterns.

� Mineral content of the watershed.

�Type of aquatic life in the river. 5

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EFFECTS OF NUTRIENTS ON WATER

QUALITY IN RIVERS� Effects of Nitrogen :

± In high concentrations, NH3-N is toxic to fish.

± NH3, in low concentrations, and NO3 serve as

nutrients for excessive growth of algae ± The conversion of NH4+ to NO3- consumes

large quantities of dissolved oxygen.

� Effects of Phosphorus :

± Serves as a vital nutrient for algae growth. ± Increase in oxygen demand by dead algae

(made up of organic matter).

± Over taxing of the Dissolved oxygen (DO)supply of the water leading to fish death.

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Management Strategy for control of

excessive nutrients

� Removal of nitrogen and / or phosphorus from waste

water before discharge using tertiary treatment.

� Reduction in the use of substances or industrial

process or producing nitrogen and phosphoruscontaining materials.

� Waste minimization through recycling, conversion ,

technology modification etc.

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BIOCHEMICAL OXYGEN DEMAND (BOD)� Definition: The amount of oxygen required to oxidize a substance to

carbon dioxide and water by microorganisms.

� When a water sample is placed in a closed container and inoculated

with bacteria, the oxygen consumption follows the pattern shown

below:

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BIOCHEMICAL OXYGEN DEMAND (BOD)

contd.

� BOD can be described mathematically as a first order reaction asfollows:

degradedcompletely beenhaswastewhen the possiblenconsumptiooxygenmaximumthei.e.BODultimate

organicsof nconsumptioin theusedoxygenof amount

mg/L)(,at timeremainingchemicalsorganictheof equivalentoxygen(mg/L),at timeorganicsof equivalentoxygen

ln

)daysnconstant(iratereaction

remainingchemicalsorganictheof equivalentoxygen

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BIOCHEMICAL OXYGEN DEMAND (BOD)contd.

� Oxygen depletion:

± Related to the ultimate BOD and the rate constant

(k)

± The ultimate BOD increase in direct proportion to

the concentration of degradable organic matter.

± The rate constant is dependent on the following:

± The nature of the waste

� The ability of the organisms in the system to use

the waste

� The temperature

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BIOCHEMICAL OXYGEN DEMAND

(BOD)contd.- Temperature

� The temperature

± T= temperature of interest , 0C

± kT= BOD rate constant at the

temperature of interest ( in days-1

) ± K20= BOD rate constant

determined at 200 C ( in days-1)

± = Temperature coefficient. For

typical domestic wastewater this

varies from 1.135 for 4 0C to 20 0C

And 1.056 for 20 0C to 300C

20

20 )( !

T

T k k U

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contd.

� Nature of the Waste.� There are thousands of naturally occurring organic compounds, and

not all of them can be degraded;

� Simple sugars and starches are rapidly degraded and will thereforehave a very large BOD rate constant.

� Cellulose (for example, toilet paper) degrades much more slowly

� Compounds such as the higher molecular weight polycyclic aromatichydrocarbons, highly chlorinated compounds such as DDT, PCBs,caffeine, or many of the estrogenic compounds used 'in birth controlpills are almost undegradaable in the BOD test or in conventionalwastewater treatment. In some cases,

� Many of the phenolic compounds are actually toxic to themicroorganisms, killing them so that little or no degradation of the

waste can occur.� The BOD rate. constant for a complex waste depends very much oil

the relative proportions of the various components.

� The lower rate constants for treated sewage compared with rawsewage result from the fact that easily degradable organics are morecompletely removed than less readily degradable organics duringwastewater treatment.

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contd.� Ability of Organisms to Use Waste.� Any given microorganism is limited in its ability to use organic compounds.

� Many organic compounds can be degraded by only a small group of microorganisms.

� In a natural environment receiving a continuous discharge of organic waste,

that population of organisms that can most efficiently use this waste willpredominate.

� However, the culture used to inoculate the sample used in the BOD test maycontain only a very small number of organisms that can degrade the particular organic compounds in the waste.

� This problem is especially common when analyzing industrial wastes.

� The result is that the BOD rate constant would be lower in the laboratory test

than in the natural water.� To avoid this undesirable outcome the BOD test should be conducted with

organisms that have been acclimated to the waste so that the rate constantdetermined in the laboratory is comparable to that in the river.

� Acclimated means that the organisms have had time to adapt their metabolisms to the waste or that organisms that can use the waste have beengiven the chance to predominate in the culture.

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contd.� Temperature.

� Most biological processes speed up as the temperature increases and

slows down as the temperature drops.

� Because oxygen use is caused by the metabolism of microorganisms, the

rate of its use is similarly affected by temperature.

� Ideally, the BOD rate constant should be experimentally determined for

the temperature of the receiving water.

� There are two difficulties with this ideal.

± Often the temperature of the receiving water changes throughout the

year. -a large number of tests would be required to define k. ± An additional difficulty is the task of comparing data from various

locations having different temperatures.

� Laboratory testing is therefore done at a standard temperature of 200 C,

and the BOD rate constant is adjusted to the temperature of the receiving

water using the following expression:.

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LABORATORY MEASUREMENT OF

BIOCHEMICAL OXYGEN DEMAND

� Standard BOD Test: the standard BOD test is outlinedwith emphasis placed on the reason for each step rather than the details.

� Step 1.

� A special 300 mL BOD bottle (Figure 8-3) is completelyfilled with a sample of water that has been appropriatelydiluted and inoculated with microorganisms.

� Samples require dilution because the only oxygen

available to the organisms is dissolved in the water.� The most oxygen that can dissolve is about 9 mg/L so

the BOD of the diluted sample should be between 2 and

6 mg/L.

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LABORATORY MEASUREMENT OF BIOCHEMICAL

OXYGEN DEMAND...

Standard BOD Test (contd.) Step1...

� Samples are diluted with a special dilution water that contains a of the trace elements required for bacterial metabolism so thatdegradation of the organic matter is not limited by lack of bacterialgrowth.

� The dilution water also contains an inoculum of microorganisms sothat all samples tested on a given day contain approximately thesame type and number of microorganisms.

� The ratio of undiluted to diluted sample is called the sample size,usually expressed as a percentage:

Sample size (%) = Volume of undiluted sample x 100

� Volume of diluted sample� The inverse relationship is called the dilution factor .

� Dilution factor, P = Volume of wastewater sample

� Volume of wastewater plus dilution water

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Standard BOD Test (contd.) Step 1...

� The appropriate sample size to use can be

determined by dividing 4 mg/L (the midpoint of

the desired range of diluted BOD) by the

estimated BOD concentration in the samplebeing tested.

� A convenient volume of undiluted sample is

then chosen to approximate this sample size.

� The bottle is then stoppered to exclude air

bubbles.

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Standard BOD Test (contd.) Step 2

� Step 2.

� Blank samples containing only the

inoculated dilution water are also placed inBOD bottles and stoppered.

� Blanks are required to estimate the

amount of oxygen consumed by the added

inoculum in the absence of the sample.

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Standard BOD Test (contd.) Step 3

� Step3.

� The stoppered BOD bottles containing diluted samples and blanksare incubated in the dark at 200C for the desired number of days.

� The samples are incubated in the dark to prevent photosynthesis

from adding oxygen to the water and invalidating the oxygenconsumption results.

� For most purposes, a standard time of 5 days is used.

� To determine the ultimate BOD and the BOD rate constant,additional times are used.

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Standard BOD Test (contd.)

� Step 4.

� After the desired number of days has elapsed, the samples andblanks are removed from the incubator and the dissolved oxygenconcentration in each bottle is measured.

� The BOD of the undiluted sample is then calculated using the

following equation:

� DOb,t = dissolved oxygen concentration in blank (blank) after t daysof incubation (in mg/ L)

� DOs,t = dissolved oxygen concentration in sample after t days of

incubation (in mg/L)� P = dilution factor

P

DO DO BOD

t st b

t

)( ,, !

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Standard BOD Test (contd.) Step 3...

� Note:� The preceding equation is valid only when the BOD of the seedwater or the dilution water is negligible.

� If the BOD of the dilution or seed water is significant, then thefollowing equation must be used.

� P = dilution factor

� Dos,i = the initial DO of the sample

� DOb,i = the initial DO of the blank (seed) control

� DOb,t = dissolved oxygen concentration in blank (blank) after t daysof incubation (in mg/ L)

� DOs,t = dissolved oxygen concentration in sample after t days of

incubation (in mg/L� f = ratio of seed in diluted sample to seed in seed control = (% seed

in diluted sample)./(% seed in seed control) = (volume of seed indiluted sample)/volume of seed in seed control)

P

f DO DO DO DO

BOD

t bibt si s

t

)()( ,,,, !

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Standard BOD Test (contd.)

� Notes:

� The preceding equation is valid only when the BOD of the seedwater or the dilution water is negligible.

� If the BOD of the dilution or seed water is significant, then thefollowing equation must be used.

� DOb,t = the initial DO of the sample� DOb,i = the initial DO of the blank (seed) control

� f = ratio of seed in diluted sample to seed in seed control = (% seedin diluted sample)./(% seed in seed control) = (volume of seed indiluted sample)/volume of seed in seed control)

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Types of Oxygen Demand

� Nitrogen Oxidation

� Many organic compounds, such as proteins, also contain nitrogen thatcan be oxidized with the consumption of molecular oxygen.

� Because the mechanisms and rates of nitrogen are distinctly differentfrom those of carbon oxidation, the two processes must be consideredseparately.

� Oxygen consumption due to oxidation of carbon is called carbonaceousBOD (CBOD), and that due to nitrogen oxidation is called nitrogenous

BOD (NBOD).� The organisms that oxidize the carbon in organic compounds to obtain

energy cannot oxidize the nitrogen in these compounds.

� The nitrogen is released into the surrounding water as ammonia (NH3).

� At normal pH values, this ammonia is actually in the form of theammonium. cation (NH+4).

� The ammonia released from organic compounds, plus that from other

source such as industrial wastes and agricultural runoff (i.e., fertilizers),is oxidized to nitrate (NO ± 3) by a special group of nitrifying bacteria astheir source of energy in a process called nitrification.

� The rate at which the NBOD is exerted depends heavily on the number of nitrifying organisms present.

� Few of these organisms occur in untreated sewage, but theconcentration is high in a well-treated effluent.

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NITROGEN OXIDATION� When samples of untreated and treated

sewage are subjected to the BOD test,oxygen consumption follows the pattern

shown in Figure� In the case of untreated sewage, the

NBOD is exerted after much of the CBODhas been exerted.

� The lag is due to the time it takes for thenitrifying bacteria to reach a sufficientpopulation for the amount of NBODexertion to be significant compared with

that of the CBOD.� In the case of the treated sewage, a higher

population of nitrifying organisms in thesample reduces the lag time. Oncenitrification begins, however, the NBODcan be described by Equation with a BODrate constant comparable to that for theCBOD of a well-treated effluent (k = 0.80

to 0.20 day').� Because the lag before the nitrogenous

BOD is highly variable, BOD5 values areoften difficult to interpret.

� When measurement of only carbonaceousBOD is desired, chemical inhibitors areadded to stop the nitrification process.

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NITROGEN OXIDATION...

� Total Kjeldahl nitrogen(TKN) is a measure of the totalorganic and ammonia nitrogen in wastewater.

� TKN gives a measure of the availability of nitrogen for building cells, as well as the potential nitrogenous oxygendemand that will have to be satisfied.

� The overall reaction for ammonia oxidation is:

) N.molmole)(14g1(

)mol.Ogmoles)(32(2

utilizednitrogenof grams

usedoxygenof grams

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1-

12

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ionnitrificat24

!!

p

N BOD

H O H N OO N H

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CHEMICAL OXYGEN DEMAND(COD)

� COD test

± This is used to determine the oxygen equivalent of the

organic matter that can be oxidized by a strong chemical

oxidizing agent eg. Potassium dichromate in an acid

medium. ± In general the COD of a waste will be greater than the BOD5

because more compounds can be oxidized chemically than

can be oxidized biologically.

± BOD5 is typically less than ultimate BOD( which is less than

COD) except for totally biodegradable waste.

± The COD test can be conducted in about and hour

± The result can be correlated with BOD5 which can be used

to aid in the operation and control of the wastewater

treatment plant.

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Effects of BOD input into Rivers� DO Sag Curve

� The concentration of dissolved oxygen in ariver is an indicator of the general health of the river.

� All rivers have some capacity for self-purification.

� As long as the discharge of oxygen-demanding wastes is well within theself-purification capacity, the DO level willremain high, and a diverse population of

plants and animals, including game fish, canbe found.

� As the amount of waste increases, theself-purification capacity can be exceeded,causing detrimental changes in plant andanimal life.

� The stream loses its ability to cleanse itself,and the DO level decrease,

� When the DO drops below about 4 to 5 mg/L

most game fish will have been driven out.� If the DO is completely removed, fish and

other higher animals are killed or driven out,and, extremely noxious conditions result.

� The water becomes blackish andfoul-smelling as the sewage and deadanimal life decompose under anaerobicconditions (i.e., without oxygen).

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Effects of BOD input into Rivers (contd.)

� One of the major tools of water quality management in rivers isassessing the capability of streamto absorb a waste load.

� This is done by determining theprofile of DO concentration

downstream from a wastedischarge.

� This profile is called the DO sagcurve because the DOconcentration dips asoxygen-demanding materials areoxidized and then rises againfurther downstream as theoxygen, is replenished from theatmosphere and photosynthesis.

� The biota of the stream are often areflection of the dissolved oxygenconditions in the stream.

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� Mass-balance for BOD and DO Mixing.� Mass of DO in wastewater = QWDOW

� Mass of DO in river = Qr DOr

� Where QW = volumetric flow rate of wastewater( m3/s)

� Qr = volumetric flow rate of the river (m3/s)

� DOW=dissolved oxygen concentration in the wastewater( g/m3)� DOr = dissolved oxygen concentration in the river(g/m3)

� The mass of DO in the river after mixing equals the sum of the mass fluxes.� Mass of DO after mixing =QWDOW + Qr DOr

� For ultimate BOD,

� Mass of BOD after mixing = QWLW+Qr Lr

� LW = ultimate BOD of the wastewater (mg/L)

� Lr = ultimate BOD of the river (mg/L0

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� The concentration of DO and BOD

after mixing are the respective

masses per unit time divided by

the total flow rate( i.e. sum of river

flow and wastewater flows)

� La is the initial ultimate BOD after

mixing.

r

r r W W a

r W

r r W W

QQW

LQ LQ L

QQ

DOQ DOQ DO

!

!

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Receiving Water Quality Standards (from INWQS)parameter units CLASSES

I IIA IIB III IV VDO mg/L 7 5-7 5-7 3-5 <3 <1

COD mg/L 10 25 25 50 100 >100

BOD mg/L 1 3 3 6 12 >12

Total

dissolved

solids

mg/L 500 1000 - - 4000 -

Total

suspended

solids

mg/L 25 50 50 150 300 >300

Faecal

coliformcounts/

100ml

10 100 400 5000 5000 -

Total

coliform

counts/

100ml

100 5000 5000 5000 5000 >50000

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Receiving Water Quality Standards (from INWQS)

Class

USESI

Represents water bodies of excellent quality. Standards sets for the conservation of natural

environment in its undisturbed state. Water bodies such as those in the national park areas,

fountain heads, inland and in undisturbed areas come under this category where strictly no

discharges of any kind is permitted. Water bodies in this category meets the most stringent

requirements for human health and aquatic life protection.

II

Represents water bodies of good quality. Most existing raw water supply sources come under

this category. In practice, no body contact activity is allowed in this water for the prevention of probable human pathogens. There is a need to introduce another class for water bodies not

used for water supply but similar quality which may be referred to as Class IIB. The

determination of Class IIB standards is based on criteria for recreational use and protection of

sensitive aquatic species

IIIIs defined with the primary objectives of protecting common and moderately tolerant aquatic

species of economic value. Water under this classification may be used for water supply with

extensive/advanced treatment. This class of water is also defined to suit livestock drinking

needs.

IVDefined water required for major agricultural activities which may not cover minor application to

sensitive crops

VRepresent other water which do not meet any of the above uses

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Environmental quality Regulations, 1979

(Sewage and Industrial Effluents)

Maximum Effluent Parameter Limits Standards A and B

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