water treatment and management

7/29/2019 Water Treatment and Management

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WaterWaste water is mainly result of Anthropogenic activities.

Origin of waste water:

1) Domestic waste water2) Industrial waste water3) Muncipal Waste water

Domestic waste water is that which discharge from residential and commercial complex

is.

Human waste, usually from lavatories: (faces, used toilet paper, wipes, urine,other bodily fluids) also known as black water

Washing water (personal, clothes, floors, dishes, etc.) also known as grey water orsullage

Rainfall collected on roofs, yards, hard-standings, etc. (traces of oils and fuel butgenerally clean)

Surplus manufactured liquids from domestic sources (drinks, cooking oil,pesticides, lubricating oil, paint, cleaning liquids, etc.)

Muncipal Waste water

In urbanized areas, municipal wastewaters (mainly sewage) generally are conveyed to a

point of treatment through sewers. Sewers carry some level of flow during all hours ofthe day and night.

Groundwater infiltrated into sewerage. Urban rainfall run-off from roads, car-parks, roofs, side-walks or pavements

(contains oils, animal faces, litter, fuel residues, rubber residues, metals from

vehicle exhausts etc)

Industrial waste:-

Industrial site drainage (silt, sand, alkali, oil, chemical) Industrial cooling waters (biocides, heat, slimes, silt) Industrial process waters Organic - bio-degradable - includes waste from abattoirs and creameries and ice-

cream manufacture.

Organic - non bio-degradable or difficult to treat - for example Pharmaceutical orPesticide manufacturing

Solids and Emulsions - e.g. Paper manufacturing, food stuffs, lubricating andhydraulic oil manufacture

agricultural drainage - direct and diffuse

Waste water constituents:

Suspended solids can cause sludge deposits and anaerobic conditions in theenvironment, eg. sand, grit, metal particles, ceramics, etc.
http://en.wikipedia.org/wiki/Human_wastehttp://en.wikipedia.org/wiki/Lavatoryhttp://en.wikipedia.org/wiki/Human_f%C3%A6ceshttp://en.wikipedia.org/wiki/Toilet_paperhttp://en.wikipedia.org/wiki/Urinehttp://en.wikipedia.org/wiki/Blackwater_%28waste%29http://en.wikipedia.org/wiki/Greywaterhttp://en.wikipedia.org/wiki/Sullagehttp://en.wikipedia.org/wiki/Oilhttp://en.wikipedia.org/wiki/Fuelhttp://en.wikipedia.org/wiki/Pesticidehttp://en.wikipedia.org/wiki/Lubricanthttp://en.wikipedia.org/wiki/Painthttp://en.wikipedia.org/wiki/Groundwaterhttp://en.wikipedia.org/wiki/Rainfallhttp://en.wikipedia.org/wiki/Roadhttp://en.wikipedia.org/wiki/Litterhttp://en.wikipedia.org/wiki/Rubberhttp://en.wikipedia.org/wiki/Metalhttp://en.wikipedia.org/wiki/Exhausthttp://en.wikipedia.org/wiki/Industryhttp://en.wikipedia.org/wiki/Abattoirhttp://en.wikipedia.org/wiki/Creameryhttp://en.wikipedia.org/wiki/Ice-creamhttp://en.wikipedia.org/wiki/Ice-creamhttp://en.wikipedia.org/wiki/Pharmaceuticalhttp://en.wikipedia.org/wiki/Pesticidehttp://en.wikipedia.org/wiki/Solidshttp://en.wikipedia.org/wiki/Emulsionhttp://en.wikipedia.org/wiki/Paperhttp://en.wikipedia.org/wiki/Oilhttp://en.wikipedia.org/wiki/Agriculturehttp://en.wikipedia.org/wiki/Sandhttp://en.wikipedia.org/wiki/Ceramichttp://en.wikipedia.org/wiki/Ceramichttp://en.wikipedia.org/wiki/Sandhttp://en.wikipedia.org/wiki/Agriculturehttp://en.wikipedia.org/wiki/Oilhttp://en.wikipedia.org/wiki/Paperhttp://en.wikipedia.org/wiki/Emulsionhttp://en.wikipedia.org/wiki/Solidshttp://en.wikipedia.org/wiki/Pesticidehttp://en.wikipedia.org/wiki/Pharmaceuticalhttp://en.wikipedia.org/wiki/Ice-creamhttp://en.wikipedia.org/wiki/Ice-creamhttp://en.wikipedia.org/wiki/Creameryhttp://en.wikipedia.org/wiki/Abattoirhttp://en.wikipedia.org/wiki/Industryhttp://en.wikipedia.org/wiki/Exhausthttp://en.wikipedia.org/wiki/Metalhttp://en.wikipedia.org/wiki/Rubberhttp://en.wikipedia.org/wiki/Litterhttp://en.wikipedia.org/wiki/Roadhttp://en.wikipedia.org/wiki/Rainfallhttp://en.wikipedia.org/wiki/Groundwaterhttp://en.wikipedia.org/wiki/Painthttp://en.wikipedia.org/wiki/Lubricanthttp://en.wikipedia.org/wiki/Pesticidehttp://en.wikipedia.org/wiki/Fuelhttp://en.wikipedia.org/wiki/Oilhttp://en.wikipedia.org/wiki/Sullagehttp://en.wikipedia.org/wiki/Greywaterhttp://en.wikipedia.org/wiki/Blackwater_%28waste%29http://en.wikipedia.org/wiki/Urinehttp://en.wikipedia.org/wiki/Toilet_paperhttp://en.wikipedia.org/wiki/Human_f%C3%A6ceshttp://en.wikipedia.org/wiki/Lavatoryhttp://en.wikipedia.org/wiki/Human_waste


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Biodegradable organics can cause anaerobic conditions in the environment &Composed principally of proteins, carbohydrates, and fats, biodegradable organicsare measured most common in terms of BOD (biochemical oxygen demand) and

COD (chemical oxygen demand). If discharged untreated to the environment,

their biological stabilization can lead to the depletion of natural oxygen resources

and to the development of septic conditions

Pathogenstransmit disease, eg. bacteria, viruses, prions and parasitic worms Nutrientscan cause Eutrophication Heavy metalstoxicity to biota and humans Refractory organicstoxicity to biota and humans Dissolved solidsinterfere with reuse, eg. ammonia, road-salt, sea-salt, cyanide,

hydrogen sulfide, thiocyanates, thiosulfates, etc

Emulsions such as paints, adhesives, mayonnaise, hair colorants, emulsified oils,etc.

Toxins such as pesticides, poisons, herbicides, etc.

Water Pollutants & their Effects

Oxygen demanding Waste:1. Dissolved Oxygen:

Dissolved Oxygen is essential for sustaining the plant and animal life inaquatic system.

The difference between the saturation concentration and the concentrationof oxygen actually present in water at given time is called as oxygen

deficit (D). D = CSCL.

When the oxygen level falls below the saturation value, oxygen from theatmosphere diffuses into the water body, at the rate proportional to Deficit.

This is known as Reaeration.

During day time the aquatic plants, while undergoing Photosynthesis,gives out Oxygen, hence the concentration of DO increases, During night

the Plants as well as microorganisms compete for Oxygen, thus decreasingthe concentration of oxygen.

When the oxygen demanding waste enter the aquatic system causing itsdeoxygenation, since the dissolved oxygen is consumed in theirbreakdown by microorganisms, hence the organic substance are said to

exert demand on availability of dissolved oxygen.
http://en.wikipedia.org/wiki/Virushttp://en.wikipedia.org/wiki/Prionhttp://en.wikipedia.org/wiki/Parasitehttp://en.wikipedia.org/wiki/Ammoniahttp://en.wikipedia.org/wiki/Cyanidehttp://en.wikipedia.org/wiki/Hydrogen_sulfidehttp://en.wikipedia.org/wiki/Thiocyanatehttp://en.wikipedia.org/wiki/Thiosulfatehttp://en.wikipedia.org/wiki/Emulsionhttp://en.wikipedia.org/wiki/Painthttp://en.wikipedia.org/wiki/Adhesivehttp://en.wikipedia.org/wiki/Mayonnaisehttp://en.wikipedia.org/wiki/Hairhttp://en.wikipedia.org/wiki/Toxinshttp://en.wikipedia.org/wiki/Pesticidehttp://en.wikipedia.org/wiki/Poisonhttp://en.wikipedia.org/wiki/Herbicidehttp://en.wikipedia.org/wiki/Herbicidehttp://en.wikipedia.org/wiki/Poisonhttp://en.wikipedia.org/wiki/Pesticidehttp://en.wikipedia.org/wiki/Toxinshttp://en.wikipedia.org/wiki/Hairhttp://en.wikipedia.org/wiki/Mayonnaisehttp://en.wikipedia.org/wiki/Adhesivehttp://en.wikipedia.org/wiki/Painthttp://en.wikipedia.org/wiki/Emulsionhttp://en.wikipedia.org/wiki/Thiosulfatehttp://en.wikipedia.org/wiki/Thiocyanatehttp://en.wikipedia.org/wiki/Hydrogen_sulfidehttp://en.wikipedia.org/wiki/Cyanidehttp://en.wikipedia.org/wiki/Ammoniahttp://en.wikipedia.org/wiki/Parasitehttp://en.wikipedia.org/wiki/Prionhttp://en.wikipedia.org/wiki/Virus


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Pollution results when the oxygen demand exceeds the oxygenavailability.

The discharge of waste into the water body results in the depletion ofdissolved oxygen level as they are oxidized by the bacteria. This process isopposed by reaeration which replaces oxygen. The simultaneous action of

deoxygenation and reaeration produces what is called as Oxygen Sag

Curve.

The sag curve initially drops as the depletion of Oxygen in waste water isfaster that reaeration. At the point where the DO level is minimum, therate of reaeration becomes equal to the rate of deoxygenation, and the DO

level begins to increase and return to normal.

DC is critical concentration of dissolved oxygen, corresponding to Criticaltime. Critical time is the time at critical point when the conditions will beat its worst. The DO level will be minimum and if it reaches zero, then

anaerobic conditions may prevail leading to death of aerobic aquaticinhabitants.

Oxygen Sag Curve

2. Biological Oxygen Demand: Biological Oxygen Demand is a measure of the oxygen utilized by micro

organisms during the oxidation of organic materials.

It is the most widely known measure for assessing the water pollutionpotential of a given organic waste.

Time

DO

DODC

Saturation value


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The demand for oxygen is directly proportional to the amount of organicwaste that has to be broken down. BOD is direct measure of oxygenrequirements and indirect measure of Biodegradable organic matter.

Drinking water has BOD of less than 1 ppm (mg/lt), water with BOD = 5ppm has doubtful purity.

When the waste water contains carbonaceous as well as nitrogeneousmaterials than we get two stage BOD. During the first stage thecarbonaceous materials are broken down into CO2 and H2O and NH3.

The nitrifying bacteria oxidizes NH3 to nitrites and then to nitrates. Hence

the second hump, as the nitrifying bacteria exerts additional oxygendemand.

3. Disease Causing Agents: Pathogens are the disease causing micro organisms, carried by the water

bodies coming from sewage, farms, industries, etc.

Some of these bacteria are water borne, responsible for disease likecholera, typhoid, dysentery, etc. Polio viruses and infectious hepatitis

viruses are also part of the sewage water.

4. Synthetic Organic Compounds: These include pesticides, synthetic organic chemicals and detergents.

These compounds are not biodegradable and hence may persists for longperiods.

These are of greater concerns, as these compounds are accumulative toxicpoisons and may ultimately reach the objectionable levels in water bodies.

TIME

BO

D

Carbonaceous Stage

Nitrification Stage


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The polyphosphate builders released from detergents are the majorproblem as they contribute to increased phosphate levels in water streamwhich eventually acts as nutrients for aquatic life, thus posing the trouble

of eutrophication.

5.

Plant Nutrients: In waste water the nutrients are present in abundance in the form ofphosphates, nitrates, ammonia or combined organic nitrogen.

When unusually high levels of nutrients are present in water bodies, itleads to excess growth of algae. This produces green slime layer over the

surface of water body and subsequently leads to eutrophication.

This layer also reduces light penetration and restricts atmosphericreoxygenation of water.

The excess algal growth can result in clogging of filter in the treatmentplants.

If high concentration of nitrates is present in the drinking water, thesenitrates are converted into nitrites in the intestine by bacterial action.

When these enter the blood stream, it becomes attached to hemoglobin,

forming a complex called methaemoglobin. As a result oxygen carryingcapacity of the blood is reduced.

6. Inorganic Chemicals: Inorganic acids are the major source of water pollution. Acids can cause

corrosion of metals and concrete and is fatal to fish.

Cadmium, discharged with effluents from pigment, textile, electroplatingindustries, etc. and be lethal to aquatic plants and animals even at the

concentrations of 0.1 ppm. The permissible level in drinking water is 0.01

ppm.

Lead is a cumulative poison and concentrates preliminary in the bones.Permissible limits in drinking water are 0.05 ppm.

Mercury is the most toxic aquatic pollutant. Its permissible levels are0.002 ppm.

Silver is also cumulative poison and can cause discoloration of skin inhumans. Its permissible limit in drinking water is 0.05ppm.

7. Thermal Discharges: An increase in temperatures of water bodies decreases the oxygen

saturation percentage and lowers the DO levels.


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The hot layer, which itself holds less oxygen, prevents the reoxygenationof cooler layers below it, thus the DO levels falls rapidly.

The metabolic activity of microorganisms increases with temperature atthe rate which is double for every 10 0 C increase in temperature. Thusincrease in temperature causes decrease in oxygen available and an

increase in oxygen consumption.

Impact of Discharge on Natural Cycles

The impact on cycles in the receiving water varies based on the following factors:

1. Degree and type of treatmentWastewater receiving only Primary Treatment will have a greater negative impact

on the receiving stream than wastewater receiving Primary and SecondaryTreatment.

2. Discharge flow rateA greater volume of flow will carry a greater mass of pollutants to the receivingstream.

3. Discharge characteristicsThe more pollutants that are removed during treatment, the lesser the impact onthe receiving stream.

4. Dilution in receiving streamRelates to discharge flow rategenerally, the greater the dilution with the

receiving stream, the lesser the impact of the discharge.

5. Ambient quality of receiving streamCharacteristics of the stream before discharge is introduced will impact on theamount of additional pollutants the stream can receive and still regenerate itself.

6. Amount of mixing of discharge with receiving streamMixing affects dilution of the discharge. Generally, better mixing of the discharge

with the receiving stream will prevent localized impacts from a concentrated

discharge.7. Use of receiving stream

Some uses (e.g., recreation or drinking water source) will require that the

wastewater meet stricter discharge limits, requiring a higher degree of treatment.

Determination of Organic matter:

Dissolved Oxygen:Procedure:

It is based on the reaction of dissolved oxygen with manganese Ions to form aprecipitate of manganese dioxide.


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The manganese dioxide is then treated with iodine ions when iodine is liberated inan amount chemically equivalent to the original dissolved oxygen.

The liberating iodine is determined, by titrating it with sodium thiosulfate.

The presence of nitrites and iron in the solution can interfere with original DOdetermination. This is eliminated by use of azide, permanganate and the alum to

remove nitrite, iron and suspended solids respectively.

Biological Oxygen Demand:

Procedure: Two standard 300 ml BOD bottles are filled completely with the waste water of

which the BOD is to be measured and the bottles are sealed.

The waste water may have high oxygen demand to deplete all the dissolvedoxygen in the sample before the end of 5 days, thus interfering with the test.

Hence the sample is diluted to a large extent with high purity water, the dilutingwater is made up of deionized water, appropriate nutrients, phosphate buffer, trace

elements and seeding organisms (usually small amount of sewage water).

A blank titration is carried out on diluting water, which is subtracted from theresults of the actual waste water.

DO content of one bottle is determined immediately. The other bottle is incubated at 20 C for 5 days in total darkness, after which its

oxygen content is measured.

The difference between the two DO values is the amount of oxygen that isconsumed by microorganisms during the 5 Day.

Incubation of 5 days @ 20 C is required for complete breakdown of carbonaceousmatter. The oxygen demand for nitrifying bacteria is assumed to be negligible, as

the nitrification is very slow.

Chemical Oxygen demand:

In COD the oxidizing bacteria of BOD test are replaced by a strong oxidizingagent under acidic conditions.

The COD test does not distinguish between organic matter that are biodegradableand those that are not, hence gives the measure of total oxidizable organic matterin sample.


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COD test is valuable for wastes where BOD test is not applicable due to presenceof toxic substance, low oxidizing rates, presence of algae in the waste water.

BOD / COD ratio are indicators of degree of biodegradability of the waste. Ratiosof 0.8 or higher indicate wastes that are highly positive to biological treatment,

where as ratios lower than 0.8 indicate that the waste are not favaourable tobiological treatment.

Procedure: Waste water sample is mixed with excess with an excess of potassium dichromate

and sulfuric acid and the mixture is heated under total reflux conditions for 2

hours. Chlorine interference can be eliminated by adding mercuric sulfate to thesample prior to the addition of other reagents.

During digestion the chemically oxidizable organic material reduces astoichiometrically equivalent amount of dichromate, the remaining dichromate is

titrated with standard ferrous ammonium sulfate solution.

The amount of potassium dichromate reduced gives a measure of amount ofoxidizable organic material.

Chlorine and nitrites present in the waste interferes with the COD tests by oxidizing and

thereby reducing dichromate, resulting in inorganic COD, which makes the resulterroneous.

Total Organic carbon (TOC):

It is oxidation of total carbon (organic as well as inorganic carbon) present in thewaste sample, measure by NDIR.

TOC can be performed in short span of time and hence offers valuable support toCOD and BOD results. Empirical correlation between TOC, COD and BOD, for a

specific plant, can be estimated and established and it possible to obtain a

tentative estimate of the plant performance quickly.

Suspended Solids:

The determination of suspended matter is extremely important, as it contributes tosignificant oxygen demand since majority of the suspended solids are organic in

nature.

Two types of suspended solids: 1) filterable solids and 2) suspended solids. Filterable solids are those, that pass through filter media and consists of colloidal

and dissolved solids.

Suspended solids are retained by the filter media and their min diameter is 1micron.


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The suspended solids are treated at 600 C, the organic matter is oxidized at thistemperature is known as Volatile suspended solids (VSS) and the inorganic

remains as ash is termed as Non Volatile Suspended Solids (NVSS)

In Actual analysis, the waste water is evaporated and at the temperatures of 105110 C and the residue is dried and weighed. The residue weight is the TSS.

Alkalinity: Alkalinity is due to presence of bicarbonates, carbonates and hydroxides of

Calcium, magnesium, sodium and potassium.

Determination of total alkalinity is important parameter for water softening,chemical treatment of waste water, corrosion control, etc.

It is measured by titrating the sample against the standard (N/50) sulfuric acid. If the pH of the sample is > than 8.3 than phenolphthalein indicator is used for

titration until the solution becomes colorless, which gives the bicarbonatealkalinity. The titration is further carried on, now using methyl orange indicator,

which gives colour change from yellow to red. This gives total alkalinity.

Drinking water standards:

Parameters Acceptable limit (ppm)

Turbidity 10 NTU

Taste and odour Acceptable

pH 6.58.5TDS 10001500

DO > 6 ppmBOD < 2 ppm

Hardness (CaCO3) 200250

Chlorides 250Sulfates 150

Fluorides 0.81.5

Nitrates 45Iron 0.1

Zinc 5

Hg and Phenol 0.001 each

Polynuclear aromatichydrocarbons

0.001


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TREATMENTPROCESS

PROCESS DESCRIPTION

Preliminary Treatment

Screening Removes rags, sticks, and other debris; protects pumping equipment

Degritting Removes settleable inorganic grit

Pre-Aeration Adds oxygen to the wastewater to reduce odors

Flow Metering andSampling

Measures and records flows; sample wastewater for analyses ofcomponents

Primary Treatment

Sedimentation andFlotation

Removes settleable organic and inorganic particles and floating debrissuch as fats, oils, and greases

Secondary TreatmentBiological Treatment Removes dissolved and remaining colloidal organic matter; can convert

ammonia-nitrogen to nitrate-nitrogen

Sedimentation Separates biomass and chemical precipitates from treated wastewater

Tertiary (Advanced)Treatment

Chemical PhosphorusRemoval

Adds chemical to form precipitate with phosphorus for removal in thesecondary clarifiers

Biological NutrientRemoval

Removes nitrogen and phosphorus using specialized microorganisms

Multimedia Filtration Removes additional suspended solids (beyond that obtained by simplesettling) using gravity or pressure filters

Disinfection

Disinfection Kills pathogenic organisms

Solids Treatment

Digestion Stabilizes remaining organic matter; results in overall net reduction in solids

Disposal Moves stabilized solids from plant to farmland for recycling or to landfill


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PRIMARY TREATMENT

Primary treatment comprises of pretreatment and sedimentation step.

1) PRIMARY TREATMENT

Waste water is pretreated to remove large floating and suspended solids whichcould interfere with normal operation of subsequent treatment process. Pretreatment sometimes also involve chlorination to prevent any odour that mayemanate during subsequent process.

Pretreatment consists of screening and grit removala) screening:

Screen of different shapes and sizes are used depending on the type of solid to beremoved.

Screens are either manually or mechanically cleaned. Bar screens are the most commonly used screens, they are either manually raked

or mechanically raked. They are parallel metal bars having aperture size of 20 60 mm for coarsescreening and 1020 mm for fine screening.

Screening produces material that must be disposed off in satisfactory manner thatmay include incineration, burial, grinding or digestion.

Removes or reduces size of solids which may interfere with downstreamprocesses.

Designed to remove floating material and larger suspended solids. Generates head loass.

Screenings Disposal

Screenings material is very offensive.

Stinks. Attracts vermin and flies. May contain organic material. Disposal in accordance with environmental regulations or permit requirements. Generally landfilled.


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b) Grit Chamber:

Grit is the heavier mineral matter found in wastewater. Sand, cinders, eggshells, etc. Will not decompose.

Causes excessive wear on pumps and other mechanical equipment. Can clog pipes or accumulate in tanks and digesters. Should be removed as soon as possible after reaching plant. Grit Chambers are generally long chambers, with very low inlet velocity of waste

water so as to facilitate the settling of grit. The grit can be removed by scrapping.

Grit consists of sand, gravel, cinders and pebbles. Grit chambers are preceded by screens Grit chambers are provided to protect pumps from abrasion and to reduce the

formation of heavy deposits in pipes and channels.

When comminutors are used than it is preceded by Grit Chamber.

Grit Disposal

Disposal in accordance with environmental regulations or permit requirements. Generally landfilled

c) Comminutors:

Comminutor is the device used to avoid disposal problems faced by screening. It replaces screening Cuts and shreds retained material to approximately size. Material not removed from flow. Material removed by sedimentation later in the treatment process. Comminutors grind larger solids which can later be handled by sedimentation

tanks.


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2) SEDIMENTATION

Settle able solids are removed by gravity settling under quiescent conditions. The sludge is formed at the bottom of the tank and is removed by vacuum suction

or by raking it to the discharge point at the bottom of the tank for withdrawal. The clear liquid known as overflow is removed from top. It should not contain

readily settleable particles.

Minimum time spend by the liquid in settling tank is 23 hrs. Three types of flow is possible in the settling tank:

o Rectangular horizontal Flow: Feed is introduced at one end along thewidth of the tank and the overflow is collected at the surface across theother end. An endless conveyor scrapper is used to scrape the floating

material and pushes it into sludge trough/hopper.

o Circular radial Flow: Feed is introduced through a centre well and theclarified effluent is collected at the weirs along the periphery of the tank.

Sludge removal occurs by the help of rotary sludge scrapper which forces

the settled down the sloping bottom into the central hopper, from where itis withdrawal. Often used in large ETPs.

o Vertical Flow: feed enters at a point along the bottom and the clarifiedeffluent is collected at top. A sludge blanket is maintained in the lowerpart of the tank through which suspension rises. It is important to bleed the

sludge timely so as maintain the desired blanket.

SETTLING THEORY

Discrete Particle and flocculent particle behaviour are the two particles behaviour that

occurs in sedimentation tanks.

The discrete particle behaviour, particles do not interfere with one another theirshape, size and mass remains constant during settling.

In flocculent settling the particles agglomerate during the settling and do notposses constant characteristics. The settling of particles in suspension depends on

the concentration and the flocculating properties.

Discrete Settling: Sedimentation of particles from suspentions is unhindered by the

presence of other settling particles and is function only of the properties of the fluid anf


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the particle under consideration. In discrete settling all particles having velocities greater

than terminal velocity of the critical particles will settle, where as the particles havingvelocities lower than the terminal velocity of the critical particle will not settle.

The critical particle is the one that enters at the top of settling zone and settles with

velocity (Vt) just sufficient enough to reach the bottom of the sludge zone.

Terminal settling velocity of the slowest settling particle that could be completelyremoved in an ideal settling tank depends on the flow rate of entering waste stream and

the surface area of the sedimentation tank and not on the depth of the tank.

Flocculent Settling: It occurs when settling velocities of particles increases due to

coalescence with other particles. Coalescence increases with increase in bed depth and

overflow. This phenomenon is clearly observed in primary clarifiers.

Zone Settling: It occurs when suspension is dense and the particles are so closely placed

that the velocity field of fluid displaced by the adjacent particles during settling overlap.

There is upward displacement of fluid with the reduction in the settling velocities of the

particles. (hindering effect). It occurs at very high concentrations where the suspensiontends to settle with distinct interface between the settling solids and the clear liquid above

it. (zone settling). This type of settling is observed in activated sludge process. 4 zonesare clearly observable: Initially the solid concentration is uniform, but with time a clear

liquid forms at top and an interface develops.

Zone A: Clear Liquid. Zone B: Uniform Concentration: Hindered settling condition occur in this

zone.

Zone C: Transient Zone: The velocity decreases due to high concentrationof solids.

Zone D: Sludge : The main mechanism is compressive settling as thesolids are supported mechanically by the particles beneath them.

Ultimately only two zones remain viz clarified liquid and sludge.

Coagulation & FlocculationWhat are Colloids?

Small particles (0.001 to 1 m) Usually negatively charged Particles repel so suspension is considered stable

1. Very small particles causing turbidity do not settle due to gravitational forces.2. This colloids are minute, charged particles (usually negatively charged), exhibit

Brownian motion and are held in suspension.3. Colloids are stable, hence if this destabilization is removed and smaller particlesare made to combine with the bigger mass by addition of coagulant like alum or

Iron salts, settling will take place easily, quickly and readily in the sedimentation

tank.

What is Coagulation?

Charge neutralization is the commonly termed as coagulation.


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What is Flocculation?

Building of larger flocs from the smaller particles is called as flocculationflocculation is a "process of contact and adhesion whereby the particles of a dispersion

form larger-size clusters". Flocculation is synonymous with agglomeration and

coagulation.

Many flocculants are multivalent cations such as aluminum, iron, calcium or magnesium.These positively charged molecules interact with negatively charged particles and

molecules to reduce the barriers to aggregation. In addition, many of these chemicals,

under appropriate pH and other conditions such as temperature and salinity, react withwater to form insoluble hydroxides which, upon precipitating, link together to form long

chains or meshes, physically trapping small particles into the larger floc.

Examples of coagulants: Alum: Al2(SO4)3.14H2O Ferric chloride: FeCl3 Ferric sulfate: FeSO4

PolyelectrolytesReaction with coagulants:

Al2(SO4)314H2O 2Al3++ 3SO42-+ 14H2O 2Al3+ + colloids neutralize surface charge 2Al3+ + 6HCO3- 2Al(OH)3(s) + 6CO2If insufficient bicarbonate is available:

Al2(SO4)314H2O 2Al(OH)3(s) + 3H2SO4-+ 14H2Oo Optimum pH: 5.5 to 6.5o Operating pH: 5 to 8

Steps of Coagulation:

Addition of Coagulants Neutralization of particles. Aggregation and Binding

Factors influencing coagulation:

pH of water: pH of water is important for selecting a coagulant, Alum works inslightly alkaline pH (6 - 8), whereas iron salts are effective in pH (5 9).

High Temperatures: At higher temperatures, viscosity of water (resistance tosettling) decreases, hence flocs settle better.

Turbidity: More the turbidity more is the removal. Addition of activated Silica / polyelectrolyte: Addition of activated Silica or

polyelectrolyte (having characteristics of polymer and electrolysis) aid the processof coagulation.

Floatation:

Used for Industrial wastewater treatment containing finely divided particles oroily matter.

Particles of density close to water are difficult to settle and takes longer time forsettling.


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In floatation separation is brought about by introducing fine gas bubbles into theliquid phase.

The bubbles attach to the particulate matter and the buoyant force of thecombined particle and gas bubbles is great enough to cause particles to rise to the

surface.

The advantage of floatation over sedimentation is that, very small or lightparticles that settle slowly can be easily removed in a short span of time.

Used in paper industry, oil industry, metal finishing industry , pharmaceuticalindustry.

To aid in the floatation process, chemical coagulants are added like aluminiumand ferric salts or polymer coagulants.

This chemical increase the flocculent structure so that they can easily entrap airbubbles

Types of Floation:

1) Dissolved air floatation2)

Dispersed air floatation3) Vacuum Floatation

Dissolved Air Floatation:

Air is dissolved in waste water under a pressure of several atmospheres, followedby release of pressure to atmospheric level.

In small tanks the entire flow is held in retention tank under pressure for severalminutes to allow time for the air to dissolve.

It is then admitted through a pressure reducing valve to a floatation tank, wherethe air comes out of solution in form of minute bubbles through the entire volumeof liquid.

In some larger units portion of clear effluent is recycled, pressurized and semisaturated with air with the result that air comes out of solution at the entrance of

the tank

Dispersed Air Floatation:

In this system, air bubbles are formed by introducing the gas phase directly intothe liquid phase through a revolving impeller or through diffusers.

Disadvantage of this process, it causes turbulance which breaks up fragile flocs.Vacuum Floatation:

It consists of saturating the waste water with either direct aeration or dissolved airfloatation.

Partial vacuum is applied which causes the dissolved air to come out of solutionas minute bubbles.

The bubbles and the attached minute particles rise to the surface to form a blanketwhich is removed by skimming mechanism.


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SECONDARY TREATMENT:

Why secondary treatment?

Dissolved impurities are removed. The organic matter that exerts high demand for oxygen must be reduced further so

that the effluent is rendered suitable for the discharge into water bodies.

Provide BOD removal beyond what is achieved in primary treatment removal of soluble BOD additional removal of suspended solids

Microorganisms stabilizes the waste matter. Convert colloidal and dissolved carbonaceous organic matter into various gases

and cell tissue known as protoplasm.

Density of protoplasm is higher than water, it can be easily removed by settling. Two methods:

Aerobic Process Anaerobic Process

Biological or secondary treatment is very similar in concept to naturalbiodegradation of organic matter by aerobic bacteria. In biological treatment plantthe oxygen supplied to the bacteria is consumed under controlled conditions so

that most of the BOD is removed in treatment plant rather than in watercourse.

Aerobic Process:

Wide spectrum of organic matter could be oxidized. Gives very stable end products The end product includes CO2, Water and new cell tissues. Capable of high growth rates thus generates large amount of biological sludge. Suitable for waste water containing BOD5 less than 700 mg/l

Anaerobic Process:

This process does not require oxygen for breaking the organic matter. Complex organic compounds are broken down and converted to low molecular

weights fatty acids by acid formers (acetic and propionic acids).

Methanogenic bacteria convert the organic acid into methane gas and CO2. Cell production is very low, hence low sludge formation. Generally used to stabilize the sludge produced in aerobic process and waste

water with BOD more than 700 mg/l.

Basic Ingredients for Secondary treatment:

High density of microorganisms (keep organisms in system) Good contact between organisms and wastes (provide mixing) Provide high levels of oxygen (aeration) Favorable temperature, pH, nutrients (design and operation) No toxic chemicals present (control industrial inputs)


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Classification of Micro organisms

Nutritional Requirements: On the basis of chemical form of carbon required,microorganisms are classified as

Autotrophic: organisms that use CO2 or HCO3- as their sole source of carbon. Heterotrophic: organisms that use carbon from organic compounds.

Energy Requirements: On the basis of energy source required, microorganisms areclassified as

Phototrophs: organisms that use light as their energy source. Chemotrophs: organisms that employ oxidation-reduction reactions to provide

energy. They are further classified on the basis of chemical compounds oxidized

(i.e., electron donor)

Chemoorganotrophs: Organisms that use complex organic molecules as theirelectron donor.

Chemoautotrophs: Organisms that use simple inorganic molecules such ashydrogen sulfide or ammonia as their electron donor.

Temperature Range: On the basis of temperature range within which they can proliferate,

microorganisms are classified as Psychrophilic: organisms whose growth is optimum within 15 to 30C. Mesophilic: organisms whose growth is optimum within 30 to 45C. Thermophilic: organisms whose growth is optimum within 45 to 70C.

Oxygen Requirements: On the basis of oxygen requirement microorganisms are classified

as

Aerobes: organisms that use molecular oxygen as electron acceptor. Anaerobes: organisms that use some molecule other than molecular oxygen as

electron acceptor.

Facultative organisms : organisms that can use either molecular oxygen or someother chemical compound as electron acceptor.

Microorganism Growth:

LAG Phase: The bacteria initially acclimatize to their new surroundings and starts

synthesizing new cells.

Need to regenerate pools of essential nutrients before growth can resume. LOG GROWTH Phase:

The bacteria cell divide exponentially depending upon their ability toprocess food and their generation time.

Cells in optimum growth state, divide repeatedly by binary fission atmaximal rate

STATIONARY Phase: As the food becomes exhausted the log growth phase tapers off. The population remains constant as a result of balance between growth of

new cells and death of old cells.

DEATH Phase: As the limitation of food supply increases, bacterial death rate increases

the production of new cells.


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Types of Secondary treatment:

Dispersed Growthsuspended organisms Activated sludge Oxidation ditches/ponds Aerated lagoons, stabilization ponds Fixed Growthattached organisms Trickling filters Rotating Biological Contactors (RBCs)

Activated Sludge Process:Activated sludge consists of sludge particles, teeming with living organisms, produced in

either raw or settled wastewater by the growth of organisms (which include bacteria) in

aeration tanks where dissolved oxygen is present.

The Activated Sludge Process is one of several biological wastewater treatment alternatives

in Secondary Treatment. When Activated Sludge is added to wastewater, the organisms inthis mixed liquor quickly decompose the wastes in the wastewater being treated. After a

required period of aeration and agitation in the aeration tank, the mixed liquor usually flows

to a separate tank called a clarifier where the activated sludge is allowed to settle out and the

remaining liquid is discharged as effluent. The settled sludge is either disposed of as waste

activated sludge or reused in the aeration tank as return activated sludge. Some sludge must

always be returned to the aeration tanks to maintain an adequate population of organisms.


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Process uses microorganisms to speed up decomposition of wastes. Food is known as Biochemical Oxygen Demand (BOD). Organism mass is called Mixed Liquor Volatile Suspended Solids (MLVSS).

When wastewater is added to activated sludge: Microorganisms feed and grow on waste particles in the wastewater. As organisms grow and reproduce, waste is removed and wastewater is partially

cleaned.

Organisms need a balance of food (BOD) and oxygen. BOD is inherent in thewastewater and oxygen is added by aeration equipment.

The balance of food to organism mass is known as F/M ratio, food tomicroorganism ratio. An appropriate F/M ratio is necessary to obtain proper

performance from the activated sludge process.

Oxidation and removal of soluble or suspended solids is the result of the activatedsludge process in waste treatment.

This treatment takes place in a few hours in an aeration tank. Stabilized soluble or suspended solids occur when organisms partially oxidizesolids.

Organism activity forms carbon dioxide, water, sulfate, and nitrate compounds. Remaining solids are changed to a form that can be settled and removed as sludge

during sedimentation.

F/M Impact:

Low F/M (low rate of wasting) starved organisms more complete degradation larger, more costly aeration tanks more O2 required higher power costs (to supply O2) less sludge to handle

High F/M (high rate of wasting) organisms are saturated with food low treatment efficiency More sludge

Aeration Types:

Conventional Systems Tapered aeration Step aeration Complete mix system

Oxidation Ditches

Continuous channel extended aeration process. Usually no primary settling.


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Mixing and aeration provided by brush rotor assemblies. Organic loading, Mixed Liquor Suspended Solids (MLSS)2000 to 6000 mg/L.

Trickling Filters:

Good adaptability to handle peak shock loads Ability to function satisfactorily after a short period of time Affected by weather Used mainly for milk processing, paper, pharma and domestic waste water. Rotating distribution arm sprays primary effluent over circular bed of rock or

other coarse media, 13 m in depth.

Air circulates in pores between rocks Biofilm develops on rocks and micro-organisms degrade waste materials as

they flow past

As the microorganisms utilize the organic matter, the thickness of the biofilmincreases, it is no longer supported by solid and gets detached from the surface.

This process is known as sloughing. The sloughs are removed in settling tank thatfollows the filter

Not a true filtering or sieving process Material only provides surface on which bacteria to grow Can use plastic media

lighter - can get deeper beds (up to 12 m) reduced space requirement larger surface area for growth greater void ratios (better air flow) less prone to plugging by accumulating slime


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Abnormal ConditionsPonding

Results from a loss of open area in media bed.Causes

Excessive organic loading. Lack of primary clarification. Improper media selection. Accumulated fibrous material filling media voids.

Odors

Aerobic processno serious odors should exist.


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Foul odors indicate anaerobic conditions.Filter Fly

Tiny, gnat-sized fly (psychoda). Most frequently found in low-rate filters.

Control Increase recirculation rate. Apply approved insecticides. Flood filter. Results in poor effluent quality. Should be carefully monitored. Apply chlorine dose.

Sloughing

Excessive film loss is an indication that there are problems with the biologicalactivity within the filter media.

Rotating Biological Contactors:

A fixed film system similar to trickling filters.

A Rotating Biolgoical Contactor (RBC), is a secondary biological treatment process

which utilizes a rotating shaft surrounded by plastic media discs. RBCs utilize a fixed

film media system similar to a trickling filter. The microbial growth is passed through thewastewater, however, while the wastewater is passed through the microbial growth in a

trickling filter. Biological growth attaches to the media discs and form a slime layer over

the discs. The rotation of the shaft alternately exposed the biomass with the wastewater

and then with the oxygen in the atmosphere. RBCs are typically preceded by preliminarytreatment processes such as screening and grit removal as well as primary treatment such

as primary settling.

RBCs are typically followed by secondary settling tanks and disinfection.

Media Media is moved through wastewater. Rotating shaft surrounded by plastic discs called media. Slime grows on plastic media. As media drum rotates, media is alternately submerged in wastewater and

exposed to air. Consists of series of closely spaced discs mounted on a horizontal shaft androtated while ~40% of each disc is submerged in wastewater

Discs: light-weight plastic Slime is 1-3 mm in thickness on disc


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Appearance of Media

A gray, shaggy appearing biological slime is indicative of a system designed strictly forBOD removal. A brown, thinner, less shaggy biological slime is indicative of a nitrifying

system.

Sloughing :Sloughing is the term used to refer to the process in which excess microbrial growth

separates from the media and is washed to the secondary clarifiers with the treated

wastewater.The excess slime will settle out in the secondary clarifiers and be removed from the

system.

Covered

Generally covered for reasons relating to climatic conditions. Protect slime from freezing. Prevent rain from washing slime from media.

Avoid exposure to sunlighto Prevents growth of algae.o Prevents deterioration of media.

Provides some protection for operators from sun, rain, snow, wind, etc. duringmaintenance.


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LOW TECH SOLUTIONS/ ADVANCED BIOLOGICAL TREATMENT:

The terms, treatment ponds and treatment lagoons, are used interchangeably.There are three basic classifications, or types, of ponds utilized for wastewater

treatment. These include aerobic, anaerobic, and facultative ponds.

Aerobic Ponds contain dissolved oxygen (DO) throughout the entire depth of thepond all the time. Treatment is accomplished through the stabilization of organic

wastes by aerobic bacteria and algae.

Dissolved oxygen can be introduced into a pond through several means. Algae, like other plants, emit dissolved oxygen as a by-product of

photosynthesis..

Wind, blowing across the surface of a pond, will cause oxygen to be absorbed intothe water.

Mechanical aeration devices agitate the water surface to cause spray and waves sothat oxygen can be absorbed from the air. Some mechanical devices include

paddle wheels, mixers, and rotating brushes.

Diffused aeration utilizes a blower system to discharge air into the water. The airstream is broken into fine bubbles; the smaller the bubbles, the greater the oxygen

transfer.

Anaerobic Ponds function without dissolved oxygen (DO) throughout any of itsdepth. Treatment is accomplished by anaerobic bacteria at the bottom of the pond,

which ferment the sludge. Anaerobic ponds have a depth of eight (8) to twenty (20) feet, and a typical

detention time of 20 to 50 days. These ponds are ideal for pretreating strong

industrial wastewater, such as that from food processing functions.

A deep sludge blanket covers the bottom of these ponds, while a scum layercovers the surface. The scum layer is important to the pond because:

It helps to minimize offensive odors It blocks transfer of DO through surface contact It helps insulate the pond or lagoon to ensure ideal conditions for sludge

fermentation.

Facultative Ponds contain a supernatant (upper) layer that is aerobic, and lowerlayers that are anaerobic.

Facultative ponds typically range from three (3) to eight (8) feet in depth.5 Thedetention time can be as short as 25 days or as long as 180 days.6 The primary

operational problem with facultative ponds is that the presence of algae in the

effluent results in high total suspended solids.

Advantages of Ponds

Compared to conventional treatment processes, ponds and lagoons offer manyadvantages for smaller installations. Treatment ponds and lagoons:

1. Are economical to operate2. Are capable of handling high flows3. Are adaptable to changing loads


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Have an increased potential design life Serve as wildlife habitat Consume little energy. Disadvantages of Ponds

There are a few disadvantages to ponds and lagoons. The facilities:1. May cause odors2. Require large land areas3. Are affected by climactic conditions4. May have high suspended solids levels in effluent5. Might contaminate groundwater.

Do not have the daily sludge wasting that a conventional system has. After 5 - 10years of operation sludge has built up and needs removed. Lagoon operators

should put aside a portion of their budget each year for sludge removal, even

though actual removal may be only once every 5 years. Removal of sludge from a

lagoon requires quite a bit of time and labor, especially when compared to a

conventional system

Chemical Oxidation

Chemical oxidants such as Chlorine, Ozone and Hydrogen peroxide are used forremoving organic materials that are resistant to biological or other treatment

processes.

Widely used as disinfectants Chlorine inactivates the bacteria present in waste water before it is discharged to

receiving streams.

When added to water chlorine forms hypochlorous acid (HOCl). Waste waternormally contains ammonia, thus hypochlorous acid reacts with it forming

monochloramine, dichloramine and trichloramine.

This choramines are stable and can be removed easily. Chlorine is also used to oxidize cyanide to CO2 and NOx. It is carried out in the

alkaline pH (~8.5) to prevent generation of poisonous Hydrogen cyanide gas

Ozone is the powerful oxidizing agent and disinfectant used in substitute forchlorine.

It is useful for removal of color, taste and odor. Advantage of ozone is, it leaves no undesirable byproducts such as organic

chlorides.

Effective in oxidation of many organic materials including pesticides, surfactants,cyanides and phenols.

SLUDGE TREATMENT & DISPOSAL

Handling and disposal of sludge from waste water treatment plant is a bigproblem and costs around 50 % of cost of treatment plant.

Primary treatment sludge contains around 5% solids Secondary treatment (activated sludge) contains ~ 1% solids.


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Trickling filters contains ~ 2% solids. Volume reduction is the most economical method. Sludge also needs to be stabilized (to stop biological activity)

Characteristics of Sludge:

Primary sludge contains organic matter as well as inorganic matter Secondary sludge contains bacterial biomass

High level of plant nutrients. Enhanced level of toxic metals like mercury, lead, cadmium, arsenic, zinc,

copper, chromium.

Pathogens POPs.

Treatment & Disposal Methods:

Steps in sludge removal are:

Concentration:

Digestion Conditioning Dewatering Oxidation Ultimate Disposal

Concentration: The purpose of concentration is remove water and reduce the volume of sludge. Common methods employed for this are gravity settling / floatation. Gravity settlers concentrate the sludge to 5 9% solids whereas floatation

concentrates the sludge to 45% solids.

Sludge is concentrated to reduce the volume as far as possible so that sludge canbe handled more effectively.

Digestion:

The sludge is stabilized by digestion after thickening. Digestion is done either under aerobic or anaerobic conditions. In anaerobic digestions (most common method) the organic content of the sludge

is decomposed to give methane and CO2 at the same time bound water is released

from the sludge.

Properly digested sludge is black in color and has a faint smell and is stable. Raw sludge is fed to active digestion zone and gas lifts the sludge particles and

other materials which forms supernatant layer on top of digestion zone.

The gas is collected at top and the digested sludge is withdrawn from bottom. Normal detention period in standard digester varies from 3070 days. In aerobic digestion the sludge is aerated in an open tank for about 20 days. During the process substantial portion of sludge is oxidized reducing the solid

content by ~30%.


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Conditioning: The sludge after stabilizing is conditioned to improve its dewatering

characteristics.

Conditioning is carried out by adding chemicals like iron salts, alum, lime andpolyelectrolyte.

These chemicals bind the sludge particles together and encourage the release ofabsorbed water.

Sometimes sludge is heated under pressure, this breaks down the gel structure ofthe sludge and water is released.

This treatment has advantage of sterilizing the sludge, also allowing theoxidization of sludge thus completely stabilizing it.

Dewatering:

Dewatering is done for efficient handling of sludge. Methods employed are centrifugation and filtration. In centrifugation the solid cake from bowl is conveyed by screw conveyor to the

oxidation treatment.

Drying beds are also used, it consists of filtering medium on which sludge isapplied and dewatering takes place by combination of evaporation and drainage.

Heat drying is the modern technique used in application where the sludge needs tobe incinerated or when it is a saleable commodity.

Oxidation:

Final oxidation is carried out to remove bacteria and reduce the volume of sludge. Incineration is common technique used (either in furnace or fluidized bed dryer).

It results in oxidation of sludge and vaporization of moisture. The dried sludge is

finally disposed. Wet oxidation is also used in which sludge is ground, mixed with air and

subjected to high temperature and high pressure in a reactor.

The mixture of gas liquid and ash leaves the reactorUltimate Disposal: Wet sludge is sprayed on croplands/ fields where it works as fertilizer or fertilizer

base.


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Dried sludge is used as landfill or soil conditioner.Methods of Ultimate disposal:

Land fill

Sea Dumping


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Agriculture land application


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Sylviculture and Forestry application


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Land reclaimation

Incineration with energy recovery


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Gasification

water treatment and management

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