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Lecture 11

Dr.Vandana

Environmental Pollution Control ETZ C362 1

Wastewater Sampling and Analysis

Chapter 8

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Summary of Lecture 10

Environmental Pollution Control ETZ C362 2

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Potential uses of fresh water

Agriculture

Industrial

Household/ domestic

Power generation

Recreational

Reasons of Water stress

Population growth

Expansion of business activity

Rapid urbanization

Climate Change

Pollution

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Classification of waste water by their origin

1. Domestic waste waterWater discharged from residential and commercial

establishments. The pollutants in domestic waste water arise from

residential and commercial cleaning operations, laundry, food preparation,

body cleaning functions and body excretions.2. Industrial waste waterDischarged from manufacturing plants where water

is used for various processes and also for washing and rinsing of equipment,

rooms etc.

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Types of Water pollutants and their effects

Water pollutants can be classified into nine categories

1. Oxygen demanding waters

2. Disease causing agents3. Synthetic organic compounds

4. Plant nutrients

5. Inorganic chemicals and minerals

6. Sediments

7. Radioactive substances

8. Thermal discharges9. oil

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Process which affects which affects dissolved oxygen (DO) content in water

are reaeration, photosynthesis, respiration and oxidation of wastes.

Reaeration is the process by which O2transfer takes place from atmosphere to

water.

The rate of reaeration depends on the rate of absorption through the air-water

interface & on the rate of dispersion within the body of water beneath the

surface.

The transfer rate can be expressed as N= KL( CS- CL)

Cs- DO level of saturation

CL- actual concentration DO in waterKL- liquid phase mass transfer rate coefficient

N- mass flux of O2 across unit area of the surface in unit time

DO2deficit , CS- CL

Oxygen demanding waste

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Photosynthesis

In presence of solar radiation, green plants utilize CO2 and

inorganic nutrients present in the water to synthesize organic

materials & liberate O2.

DO level in day is comparatively higher than night.

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Effects of other pollutants

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Inorganic chemicals and Minerals

Inorganic acids

Inorganic salts

Metal and metal compounds

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Chapter 8: Waste Water Sampling and Analysis

Sampling can be two types : grab sample and composite sample

Grab samples: Shows only the prevailing conditions at the time of

sampling and are useful in determining the effects of extreme

conditions of the waste.

Composite sample can be obtained by collecting individual samples at

frequent intervals and mixing them together.

Sampling

Methods of Analysis -Determination of Organic matter

Dissolved Oxygen (DO)

Determined by Winklers method

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Biochemical Oxygen Demand (BOD) measure of the oxygen

utilized by microorganisms during the oxidation of organic

materials)

Chemical Oxygen Demand (COD)

Total Organic Carbon (TOC)

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Determination of Inorganic Matters

Nitrogen

Phosphorus Trace elements

Alkalinity

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Nitrogen

Important nitrogen containing chemical species in waste water systems are

ammonia, organic nitrogen, nitrite and nitrate.

Ammonia (NH3) containing nitrogen & organic nitrogen combindly called

Kjeldahl Nitrogen and which contribute ~ 99% of the total nitrogen indomestic waste water.

All form of nitrogen can be measured analytically by colorimetric

techniques.

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Determination of Kjeldahl Nitrogen

The method comprise with digestion of nitrogensample with sulfuric acid and catalyst, whichdecomposes the organic substance by oxidation toliberate the reduced nitrogen as ammonium sulfate.

Chemical decomposition of the sample is completewhen the medium has become clear and colorless.

The solution is then distilled with sodium hydroxidewhich converts the ammonium salt to ammonia. Theamount of ammonia present (hence the amount of

nitrogen present in the sample) is determined byseveral methods like back titration using boric acid andsodium carbonate or using Nessler reagent (potassiummercuric iodide).

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MAJOR REACTIONS

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The standard technique used for the determination of ammonia

is the Nessler method.

The neutralized sample is distilled to separate the ammonia

from interfering substances.

The ammonia in the distillate is reacted withNesslersreagent

(K2HgI4) and produces a yellowish-brown colloidal dispersion.

The colour intensity is directly proportional to the amount of

NH3 present and can be estimated photometrically.

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Another method is the phenol hypochlorite method.

Ammonia is treated with phenol and hypochlorite in

the presence of a catalyst to produce the blue colored

indophenol solution. The intensity of colour is proportional to the

ammonia concentration.

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Determination of nitrogen present as nitrite is based on the

diazotization of sulphanilic acid with nitrite followed by its

combination with N-(1-napthyl)-ethylenediamine

dihydrochloride to form a purple azodye.

The intensity of the colour is directly proportional to the nitrite

concentration.

Nitrogen present as nitrate can be analyzed by reducing it to

nitrite or ammonia which is determined by Cd reduction

method.

In Cd reduction method ,the nitrates are quantitatively reduced

by Cd to nitrite.

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The nitrite formed is measured by the diazotization method.

This method gives the sum of the nitrite and nitrate nitrogen,

a separate analysis of the nitrite is required.

Nitrates can be reduced to nitrites with Zn under controlledconditions and the nitirtes determined colorimetrically.

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Phosphorus

P exists in waste water as orthophosphate,

polyphosphate and organic phosphate

Orthophosphate is determined by colorimetric method.The sample is treated with ammonium molybdate under

acid conditions to form molybdophosphoric acid which is

then reduced by V/SnCl2 when a colour complex is

formed. The intensity of the colour is proportional to the

phosphate concentration in the solution.

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Polyphosphates are first hydrolyzed to orthophosphate in

acidic medium and then analyzed.

The amount of polyphosphate is obtained by subtracting the

amount of orthophosphate originally present in the samplefrom the result.

Organic P is first oxidized to phosphate ion & then analyzed.

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Trace elements

Major trace elements are: Cr, Pd, Zn and Cd

Trace elements are determined by AAS & colorimetry.

Dithiozone is the colorimetric reagent used for the

determination of Cd, Pb and Zn.

Acid digestion is required to eliminate the interference fromcyanide,nitrite, sulphide, sulphite etc.

These metals give a red/pink coloured complex which can be

extracted in a suitable solvent. The colour intensity is determined by a colorimeter or

spectrophotometer.

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Cr determination involves oxidation of the metal to the hexavalent state and its

reaction with diphenylcarbazide in acidic medium and a red-violet product is

formed and its intensity can be measured photometrically.

Atomic Absorption Spectrometry

Quite rapid, highly selective and

automated for monitoring effluent

streams.

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Alkalinity Reason: Presence of bicarbonates, carbonates and hydroxides of metal ions

such as Ca, Mg, Na and K.

Measured by titrating the sample with a standard acid.

If the pH of the original sample is higher than 8.3, the titration is carriedout using phenolphthalein indicator until it becomes colourless and this end

point is known as phenolphthalein alkalinity or bicarbonate equivalencepoint.

Bicarbonates are present in the original sample along with hydroxides andcarbonates and in such cases the sample is titrated with methyl orange

indicator.

Determination of alkalinity is important in water softening, chemicaltreatment of waste water, corrosion control and in removal of ammonia byair stripping.

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Physical Characteristics

Suspended solids

important in the analysis of waste waters.

The suspended matter contained in domestic waste waters and inmany industrial wastes is largely organic and responsible for asignificant portion of the oxygen demand.

Major parameter used to evaluate the quality of domestic andindustrial wastes.

Total solids in waste waters refers to the matter that remains asresidue after evaporation and drying at 103 to 1050C.

It can be classified as filterable solids and suspended solids.

Filterable solidsAble to pass through a specified filter and consistof colloidal and dissolved solids.

Colloidal solids10-3to 10-6mm

Dissolved solids- 10-6mm (exist as molecules and ions in solution).

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Suspended solids They are retained on the filter and theirminimum diameter is about 1microm.

Of the suspended solids, the settelable solids are those which

settle in a cone-shaped container in a definite time period. Classification of suspended solids on the basis of their

volatility at 6000C- volatile suspended solids(VSS) (organic

matter that is oxidised at this temp.) and fixed suspended

solids or non-volatile suspended solids (NVSS) (inorganic

fraction that remains as ash).

The suspended solids concentration can be measured by

gravimetric methods.

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Colour and Odour

Colour may be organic or mineral origin

Organic sources include algae, tannis, humic compounds etc.

Inorganic sources are Fe and Mn compounds, chemicals anddyes from various industries etc.

Odours in water are caused by algae and decaying vegetation

and also some inorganic substances like mercaptans,amines

and sulphides.

The odour causing substances are present in very small

quantities and are often complex. So its difficult to isolate and

identify them.

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The standard test method is the threshold dilution method in

which the odour bearing sample is diluted with oduor free

water , until a dilution is obtained which has a barely

perceptible odour.

The result is expressed in terms of the threshold odournumber (TO) which is given by

TO = ml of sample + ml of odour-free water/ ml of sample.

TO is a function of temperature, the test temp. should be

reported in all cases.

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Colour is measured by comparison with known standards.

Suspended matter in water can interfere with the measurement of colour.

The sample is centrifuged to separate the solids and analysis is made on

the clear portion.

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Bacteriological Measurements

The most popular method is based on determining the

content of indicator organisms in it and the principal

indicator organisms used are the coliform group of bacteria.

The coliform bacteria has the ability to ferment lactose or

lauryl tryptose broth and produce gas. This we can use as asimple test to check the presence of coliform group.

Two general method used to obtain the number density of

coliform organisms in the test sample are membrane filter

technique and the most probable technique (MPT).

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Membrane filter technique: A known volume of the watersample is passed through the filter that has a very small pore

size. The coliform bacteria are captured by the filter and the

filter is exposed to nutrients which promote the growth of

coliform while inhibiting that of other organisms.

After incubation (2448hrs), the number of coliform colonies

is counted and their density is determined. The coliform

colonies appear pinkish in colour and their count is made with

the aid of an optical device.The coliform density is reported interms of total colifroms per 100ml.

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The most probable number (MPN) of organisms is a statistical estimate of

their density and is based on the examination of a number of portions of

different sizes giving +ve orve results for coliforms .

t u

N1, N2, N3sizes of portions examined

P,r,tno.of portions of respective sizes giving +ve results a- constant for any particular set of conditions

q,s,uno. of portions of respective sizes givingve results and therefore may be omitted for computing

conc. Of coliforms/ml

Y- probability of occurrence of a particular result

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Limitations

Coliform often grow in treatment facilities or water bodies and the tests can reveal

high populations even though pathogens are far less likely to multiply under the

same environmental conditions.

Some viruses and several organisms may survive for longer periods than coliforms,

and reduction of coliforms to low concentrations or even to zero may not always

indicate that the water is safe.

The MPN is that value of which gives a maximum value of Y.

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Here the MPN is

0.47 per ml at

which aY is

maximum or we

can say that the

MPN per 100ml

is 47.

U= 3

0.48

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Water quality standards

Water quality standards are to ensure the water quality in a

resource is suitable for the proposed use.

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Chapter 9 : Wastewater Treatment

Objectives:

Basic processes of water treatment

Advanced wastewater treatment

Recovery of materials from process effluents

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Treatment

Physical

Biological

Chemical

Screening, Sedimentation,

floatation and filtration

Precipitation, Coagulation anddisinfections

Biofiltration and Activated

Sludge Process

Physical &

Chemical

Air stripping, Carbon

adsorption, Oxidation and

reduction, Ion exchange, andmembrane Processes

Purpose of waste water treatment

Remove the contaminants from water so that the treated water can meet the

acceptable quality standards

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BITS Pilani, Pilani CampusET ZC362: Environmental Pollution Control

Another classification of waste water treatment processes

Primary Treatment

Removes identifiable suspended solids and floating matter

Secondary Treatment

Also known as biological treatment (organic matter that is soluble or in thecolloidal form is removed

Tertiary Treatment

Also known as advanced waste treatment (may involve physical, chemical orbiological processes)

Pretreatment

Primary Treatment Process

FlotationSedimentation

Discrete Settling Flocculent Settling Zone Settling

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Primary Treatment

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Pretreatment To remove large floating and suspended solids .Also include flow measurement

and prechlorination to prevent odours.

Consist of screening and grit removal.

Fixed bar screens are the most common types screens used in domestic waste

water treatment facilities.

Bar Screen

- catches large objects

such as bricks, bottles,pieces of wood, etc.

Pretreatment

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Is used to remove large floating and suspended solids. This process consists of

screening and then grit removal

Screening

Manuallyraked bar screen

Mechanically-raked bar screen

Apertures in the

range of 25-

50mm

Openings

ranging

from 5-40

mm

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The screening process produces objectionable screenings whichmust be disposed of in a satisfactory manner.

Methods of disposal include burial, incineration, grinding and

digestion.

To avoid the disposal problems, a device known as a comminutorcan be used instead of the screens.

The comminutor grinds large solids which can then be handled in

the sedimentation tank.

After screening, the waste water enters a grit chamber for the

removal of inorganic grit, consisting of sand, gravel, cinders and

pebbles.

Alternative of Screening

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Comminuter

Grit Chamber

After screening, the wastewater enters into a grit chamber for the removal of inorganicgrit, consisting of sand, gravel and pebbles. These chambers are generally designed

as long chambers and the velocities of waste flow is reduced to 3 cm/sec, whichallows settling of the grit material. The grit can be removed by scrappers.

Grit chambers are provided to protect pumps from abrasion and to reduce theformation of heavy deposits in pipes and channels.

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Grit chambers are provided to protect pumps from abrasion and

to reduce the formation of heavy deposits in pipes and channels.

Two types of grit chambers: horizontal flow and aerated.

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Wastewater Treatment

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Preliminary Treatment

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Sedimentation

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The settleable solids are removed by gravitational settling under

quiescent conditions.

The sludge formed at the bottom of the tank is removed either

by vacuum suction or by raking it to a discharge point at the

bottom of the tank for withdrawal. The clear liquid produced is known as the overflow and it should

contain no readily settleable matter.

The sedimentation may be carried out in rectangular horizontal

flow, circular radial flow or vertical flow basins.

SedimentationThe solids are removed by gravitational settling The sludge formed at the bottom of

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The solids are removed by gravitational settling. The sludge formed at the bottom ofthe tank is removed as underflow either by vacuum suction or by raking it to adischarge point

Equipments

Rectangular Horizontal flow

Sludge Scrapper It conveys the overflow from the chamber to the outlet section

It prevents the sludge to go out with the overflow

It helps to come out the sludge pushing the settle solids into a sludge hopper.

Circular radial flow

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Circular radial flow

Over flow is collected at weirs. A rotary

sludge scrapper (rotate as a fan) forces

the settle sludge down into a central

hopper

Vertical flow

It is used for small scale operation. A

sludge blanket (filter for small particles is

maintained in the lower part of the tank

through which the suspension rises.

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Flotation

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Used in place of sedimentation, for treating industrial waste

waters containing finely divided suspended solids and oily

matter.

This technique is used in paper industry to recover fine fibres

from the screened effluent and in the oil industry for theclarification of oil bearing waste.

Also used for treating effluents from tannery, metal finishing,

coldrolling, and pharmaceutical industries.

Particles of density close to that of water are very difficult tosettle in normal sedimentation tanks and take a long time for

separation.

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The separation can be speeded up by aerating the effluent

whereby the air bubbles are attached to the suspended

matter.

This has the effect of increasing the buoyancy of the particles,

as a result particles float to the surface.

To aid the flotation process , chemical coagulants such as

aluminium and ferric salts or polymer coagulant-aids are used.

Two types of flotation : Dispersed air flotation and dissolved

air flotation.

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In dispersed air flotation, air is introduced directly into the

liquid through a revolving impeller or through diffusers.

This technique is not a favored tech. in the treatment of

municipal waste waters.

In dissolved air flotation, air is brought into contact with the

waste water at a pressure of several atmosphere when air is

dissolved.

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baffleDissolved air flotation system without recycle

Dissolved air flotation system with recycle

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