Anuradha Children's Club

8/2/2019 Anuradha Children's Club

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WATER TREATMENT

water cycle1 - hydrologic cycle journey of waterRaw water - surface water - impurities - suspended, dissolved andcolloidal solids, bacteria, colouring and odour inducing agents and

organic matter.

As of 2006, waterborne diseases are estimated to cause 1.8 milliondeaths each year.

These deaths are attributable to inadequate public sanitation systemsand it is clear that proper sewarage need to be installed.


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Table 1: Contaminants and pollutants present in thedomestic waste water2

S.No. Constituent Overallconcentration

in mg/L

1. Total nitrogen 20-82

2. Total phosphorus 10-20

3. Suspended solids 150-320

4. Total dissolved solids 300-900

5. BOD 100-300

6. COD 300-1000

The treatment of water depends on the factors such as quantity andquality of raw water and required standards of purified water.

Standards of water quality


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Table 2: Drinking water standard

Parameter Standard

Physical Parameters

Colour 10 to 20 (Platinum-cobalt scale)

Odour 0 to 4 Po value

Temperature 10C to 15.6CTurbidity 5 to 10 ppm

Taste No objectionable taste

Chemical Parameters

pH 6.5 to 8

Hardness 7.5 to 115 ppm (CaCO3 equivalent)Total Solids < 500 ppm

Chlorides < 200 ppm

Iron and Manganese < 0.30 ppm

Dissolved oxygen 5 to 6 ppm

Lead 0.10 ppm

Arsenic 0.05 ppm

sulphate < 20 ppm

BOD Nil

Biological Parameters

B-coli No B-coli in 100ml

M.P.N.(Most Probable

Number)

One number in 100ml


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Equalization:

Industrial wastewater treatment processes - undesirable wastes are

sometimes produced over short periods of time - "slugs" - suchwastes would damage a biological treatment process - wastes aresometimes held, mixed with other wastewaters, and gradually released,thus eliminating "shocks" to the treatment plant.

Air or steam stripping:

Process of transfer of dissolved contaminants from liquid phase intovapour steam

Concentration gradient between liquid and gas phases is important.

Volatile contaminants with low water solubility are removed under

normal atmospheric conditions

Hot or live steam is used instead of air to remove the semi-volatilecontaminants in steam stripping procedures


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II. Chemical Treatment

Chlorination: oxidizing chemical

Cl2 + H2O H+ + Cl- + HOCl (1)

Hypochlorous acid (HOCl) is the prime disinfecting agent

Ozonation :More effective against cysts and viruses than chlorine Advantages - no taste or odour problems Disinfective power of ozone is limited by its relatively low solubility in water.

Neutralization:Addition of acid or base to adjust pH levels back to neutrality.

Ca(OH)2 Ca2+ (aq) + 2OH (causing pH change) (2)


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Adsorption:

Treatment by activated carbon is mostly due to adsorption or absorption.When a chemical species is adhered to the surface of a solid - adsorption.

When partial chemical bonds are formed between adsorbed species or when

the absorbate got into the channels of the solids - absorption.

Porous material with high ratios of surface area to unit weight up to 100 acresper pound.

Activated carbon -affinity to organic materials such as solvents used inprinting inks and common coatings.

To absorb colored organic particulates to inorganic metal ions.

Water filter - ceramic elements are filled with ahigh grade silvered granulated activated carbon(GAC).

The GAC reduces pesticides, chemicals,chlorine, tastes and odours, while leaving thenaturally occurring minerals found in the waterunaffected.


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Chemical oxidation and reduction:Toxic chemical compound is converted into lesser toxic compounds. Toxic organic compounds - phenols, pesticides and amines. Calcium hypochlorite, ozone and hydrogen peroxide - typical oxidisingagents, Sulphur dioxide (SO2) and sodium borohydride (NaBH4) - reducing

agents.

Ion Exchange:To remove hardness, iron and manganese salts in drinking watersupplies.Certain natural and synthetic materials - to exchange one of their ions. Naturally occuring minerals - aluminium silicate minerals - zeolites.

Synthetic ion-exchange resins - composed of organic polymer withattached functional groups

SO3 H+

(strongly acidic cation exchange resins), or COO H+ (weakly acidic cation exchange resins or -N+(CH3)3OH (strongly basic anion exchange resins)

2 Res-SO3 H+ + Ca2+ (Res-SO3 )2Ca

2+ + 2H+ (4)

(here Res represents resin phase)


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Reverse Osmosis:

Figure 4: Normal and Reverse Osmosis Process:

Reverse osmosis4 - pressure is applied to the region of higher

concentration to force water molecules to diffuse into the region oflesser concentration across semipermeable membrane (Figure 4).

Pure water is extracted from concentrated wastewater in this process.Cellulose acetate and ployamides are the common membranematerials

Electrodialysis:Uses ion-selective membranes and an electrical potential differenceto separate anions and cations in solution.

When the electrodialysis is running, the direct current field affects the

flow of dissociated salt components in water solution.


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CM cation exchange membrane, D diluate chamber, e1,e2 electrode chambers, AM

anion exchange membrane, K concentrate chamberFigure 5: Electrodialysis (reproduced from ref.5)

Cations moving towards the cathode pass through the cation exchangemembranes and cannot go through the anion exchange membranes.

Anions drawn to the anode pass through the anion exchange

membrane but stop at the cation exchange membranes.

Using the right combination of anion exchange and cation exchangemembranes we can separate the ions in the inlet solution and create adesalted flow called diluate, and concentrated flow called concentrate.


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III. Biological treatment methods:

Method use microorganisms, mostly bacteria, in thebiochemical decomposition of wastewaters to stable end

products - carbon dioxide, water and other end products.

Biological treatment - aerobic and anaerobic methods - basedon availability of dissolved oxygen.


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Table 3: Treatment systems used to remove the major contaminants

Contaminant Treatment system Classification

Suspended solids Screening and comminution

Sedimentation

FlotationFiltration

Coagulation / sedimentation

Land treatment

P

PP

P

C / P

P

Biodegradable

organics

Activated sludge

Trickling filters

Rotating biological

contactors

Aerated lagoons

Oxidation ponds

Intermittent sand filtration

Land treatment

Physical / Chemical

B

B

B

B

B

P / B

B / C / PP / C

Pathogens Chlorination

Ozonation

Land treatment

C

C

P


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Nutrients:

Nitrogen

Suspended-growth nitrification

and denitrification

Fixed-film nitrification and

denitrification

Ammonia stripping

Ion exchangeBreakpoint Chlorination

Land treatment

B

B

C/P

CC

B /C / P

Phosphorus Metal salt coagulation /

Sedimentation

Lime coagulation / sedimentation

Biological / chemical phosphorusremoval

Land treatment

C / P

C / P

B / C

C / P

Refractory organics Carbon adsorption

Tertiary ozonation

Land treatment systems

P

C

P

Heavy metals Chemical precipitationIon exchange

Land treatment

CC

C / P

Dissolved inorganic

solids

Ion exchange

Reverse osmosis

Electrodialysis

C

P

C

B = biological, C = Chemical, P = physical


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Sewage water treatment:

The wastewater treatment mainly involves three stages:

primary treatment, secondary treatment and tertiary treatment.7

Primary Treatment:

Screening for the removal of floating objects in a chamber

comprising parallel arranged steel bars

Wastewater is allowed flow into a grit chamber for a short timefor the proper settling of heavy materials such as sand and grits.

Sewage wastewater moves into a primary settling tank which is

also known as sedimentation basin to enable the gradualsettlement of suspended solid substances by gravitational force.

Primary treatment is aimed to remove 60% of suspendedsolids and 40% of BOD.

2 S d T t t


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2.Secondary Treatment

Trickling filter, activated sludge process and oxidation ponds called lagoonsare the important procedures involved in the secondary treatment.

Trickling filter: - called sprinkling filters Consists of an aerobic revolving sprinkler that is suspended over a bed of

porous material.

When the sewage water passes through the porous bed, various types ofmicrobes such as bacteria, fungi and protozoan are absorbed in the aerobicfilter medium.

Treated sewage is aerated by the circulation of air through the porous bed.The sewage is recirculated repeatedly till the sufficient BOD reduction is

achieved.

Figure 7: A typical diagram of a trickling filter8,9


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B. Activated Sludge Process (ASP):

Oxygen is required by bacteria and other types of microorganismspresent in the system to live, grow, and multiply in order to

consume the dissolved organic "food", or pollutants in the waste.

After several hours in a large holding tank, the water is separatedfrom the sludge of bacteria and discharged from the system.

ASP involves a biological andaerobic treatment for wastewater9

After primary settling, the wastewater is carried to an aeration tank.

The aeration of wastes is doneeither by diffused compressed air

or by mechanical stirring.


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Activated sludge is returned to the treatment process - remainderis disposed of by one of several accepted methods.

Clear, colourless and odourless effluent is obtained from anactivated sludge. This process reduces the BOD by 85% to 90%.

C. Oxidation ponds:

The shallow artificial pond for the biological treatment ofwastewater is called oxidation pond.

Wastewater - algal and bacterial action at high temperature

Oxidation ponds provide aerobic medium at the surface andanaerobic medium at the bottom layer.

Aerobic bacteria degrade the organic matter in the sewage by

utilising atmosphere O2.

The algae utilise the CO2 released by the aerobic bacteria for thephotosynthetic purposes.

The sewage waste is being detained in the oxidation ponds for

about 10-30 days.

3 Tertiary Treatment: advanced treatment


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3. Tertiary Treatment: advanced treatment

Primary objective:

(i) reduction of Nitrogen (N2) and Phosphorus (P) contents in the

effluent wastewater.

(ii) reducing the eutrophication and BOD in the wastewater.

Nitrogen Removal:

Ammonium ion - oxidized to nitrate by bacteria like nitrobacter andnitrosomonas - in a process called nitrification.

2NH4+ + 3O2 2NO2

- + 2H2O + 4H+

2NO2- + O2 2NO3

-

nitrosomonas

nitrobacter

Once the ammonia has been oxidized to nitrate, it may bereduced by anaerobic bacteria such as pseudomonas,micrococcus, serratia and achromobactor.

(5)

(6)


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6NO3- + 2CH3OH 6NO2

- + 2CO2 + 4H2O

6NO2- + 3CH3OH

3N2 +3CO2 + 3H2O + 6OH-

Nitrogen gas is released to the atmosphere and thus removed from thewater.

Ammonium ion can be converted to volatile NH3 by adding lime to increasethe pH, after which the pH is lowered again by CO2 injection to reprecipitate thelime.11

Finally, the remaining organic compounds can be filtered out with activatedcharcoal, and disinfectant can be added to produce quite pure water.

NH4+

(aq) + OH (aq) NH3(g) + H2O (10)

This denitrification requires a source of carbohydrate10 and methanol is

often used for that purpose.

4NO3-(aq) + 5 CH2O 2N2(g) + 4HCO3

-(aq) + CO2 + 3H2Odenitrifyingbacteria (7)

(8)

(9)


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An alternative approach that does not involve pH modification is toremove ammonium ions from the neutral solution by ion exchangeusing the natural ion exchanger clinoptilolite or syntheticexchangers.

More complete removal of ammonium nitrogen is effected bysubsequent chlorination, to form mono-, di-, and trichloroamines.

Hypochlorous acid is the effective chlorinating species under

treatment conditions.

NH4+

(aq) + HOCl(aq) NH2Cl(aq) + H3O+(aq) (11)NH2Cl(aq) + HOCl(aq) NHCl2(aq) + H2O (12)HOCl(aq) + NHCl2(aq) NCl3(aq) + H2O (13)

In the presence of carbon adsorption filters the chloramines undergo

a heterogenous surface reaction that produces nitrogen gas as oneof the products.


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Phosphorus Removal:

Phosphorus appears in water as orthophosphate (PO43-),

polyphosphate (P2O7), and organically bound phosphorus.

Microbes utilize phosphorus during cell synthesis and energytransport.

As a result, 10 to 30 percent of all influent phosphorus is removedduring secondary biological treatment.

This process is called Enhanced Biological Phosphorus Removal.

When the biomass enriched in these bacteria is separated fromthe treated water, these biosolids have a high fertilizer value.


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Al3+ + PO43-

5Ca(OH)2 + 3HPO42- Ca2OH(PO4)3 + 3H2O + 6OH

-

AlPO4

Phosphorus removal - achieved by chemical precipitation,usually with salts of iron (e.g. ferric chloride), aluminium (e.g.alum), or lime.

This may lead to excessive sludge productions as hydroxidesprecipitates

With lime, phosphate is removed as insoluble mineralhydroxyapetite Ca5(PO4)3(OH) (eqn.15).

Phosphorous, which is removed in the form of a phosphaterich sludge, may be land filled or resold for use in fertilizer.

(14)

(15)


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Secondary effluent

BOD = 25 mg/l

PO43 = 25 mg/l

NH4+

= 20 mg /l

Lime =

Ca(OH)2

addition

Phosphate removal

Lime + PO43

Ca5(PO4)3(OH)Excess OH

from lime pH

= 11

Lime

sludge

Recycled lime

CaO + H2O Ca(OH)2

NH3

Air

Furnace

Ca sludge + heat CaO

Recarbonation, lime

precipitation,

neutralization

H2CO3 + Ca2+ + 2OH

CaCO3 + H2O

CO2 CaCO3

sludge

Activated

charcoal

Chlorine

Ammonia stripping

NH4+ + OH NH3 + H2O

Final effluent

BOD < 1mg/l

PO43 = 0.2 - 1 mg/l

NH4+ = 0.31.5 mg /l as N2

pH = 7

Organic

removal

Figure 9: Tertiary treatment of municipal waste water 11


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Process Flow Diagram for a typical large-scale treatment plant9

Figure 10: Overall Water Treatment Plant

Sludge Digestion:

The sewage sludge is large in bulk and contains putresciblesubstances and living organisms.

Sludge is an excellent soil conditioner and it can be used as a fertilizeron farmland. However, it needs additional treatment to make it suitable.

This treatment is called Sludge digestion and takes place in large,

enclosed tanks.


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The main objective of sludge digestion is to break the organic matterof the sludge into liquid and simple compounds which are stable andunfoul in nature.

Digestion significantly reduces the sludge quantity. This processremoves abut 99.8% coli forms.

A by-product of the sludge digestion process is methane gas. Thiscan be burned to produce electricity.

Anaerobic digestion of sludge is given by the following equation(16)10

The electricity can be used to heat more sludge or to provide heatand light for the treatment works.

Sometimes more energy is produced than the required. The surplusis sold to the electricity companies.

2 CH2O CH4(g) + CO2(g)

.


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References:

1. http://earthguide.ucsd.edu/earthguide/diagrams/watercycle/2. P.Anandan, R. Kumaravelan, Principles of Environmental Engineering, Scitech

Publications (India) Pvt.Ltd., Ed., 2004.3. A. Ifthikarudeen, K. Pandian, S. Krishnan, Principles of Environmental Science and

Engineering, Sooraj Publications, Ed., 2005.4. http://www.science.uwaterloo.ca/cchieh/cact/applychem/watertreatment.html5. http://www.mega.cz/electrodialysis.html6. http://www.scribd.com/doc/7019099/Treatment-Process-Flow-sheets7. http://www.pub.gov.sg/prodcts/usedwater/pages/WasteWaterTreatmentProcess.aspx8. http://tristate.apogee.net/et/ewtwtkf.asp9. http://en.wikipedia.or/wiki/Sewage treatment10. Gary W. vanLoon, Stephen J. Duffy, Enviromental Chemistry- A Global Perspective,

Oxford University Press, 2003.11. Thomas G. Spiro, William M. Stigliani, Chemistry of the Environment, second edition,

Prentice-Hall of India Pvt.Lt.,

12. Further Reference:13. http://water.me.vccs.edu/courses/ENV149/methods.htm14. http://www.cyber-nook.com/water/Solutions.html15. http://www.college.ucla.edu/webproject/micro7/studentprojects7/Rader/asludge2.htm

Exercise:


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Exercise:

2. Prepare a water filtration column by cutting off the bottom of a cleanempty 2-liter plastic bottle.

3. Remove and discard the bottle label.4. Cut two pieces of cheesecloth. Layer the two squares one on top of

the other.5. Use the layered squares to cover the mouth of the bottle where the

cap is normally attached.6. Secure the cheesecloth over the mouth of the bottle with a rubberband.

7. Invert the bottle (mouth pointing down) and mount it in a ring standwith an empty, large, clear, colourless container beneath it to collectfiltered liquid.

1. Preparation of solution:Measure 4 cups of tap water into a large clear,

colourless container. Add the following itemsto the water and then stir thoroughly with a

large spoon:1/2 teaspoon of the rusty metal object1/2 teaspoon soil2 or 3 small leaves1 tablespoon household vinegar1 tablespoon cooking oil.


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8. Place 2 cups of activated charcoal into the water filtration column (thislayer will fill the neck and shoulders of the bottle).

9. Place 2 cups of sand into the water filtration column as the next layer.

10. Place 2 cups of gravel into the water filtration column as the final layer.

11. Place 3-4 cups of tap water onto the layer of gravel so the water passesthrough the column and cleans out any small particles of dirt andcharcoal. Discard the water that drains into the collection container.

12. Measure and pour 3 cups of the unfiltered water from step 1 into thecolumn, pouring it onto the layer of gravel.Observe the water as it passes through the filter. Place a sheet of whitepaper under the container of filtered water.Observe and record the properties of the filtered water. Using pH paper,measure and record its pH.

13. Compare its appearance with the water that remains from step 1.Measure how much filtered water was collected. Is it the same volume

that you placed into the filter?

Be Safe: Do NOT consume any of the water in this Activity, includingthe filtered water. Harmful contaminants may remain.


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SOLID WASTE TREATMENTINTRODUCTION:

Ever-increasing population - changing lifestyles, extensive use of

disposable articles in day to day life, lack of awareness, lack ofinfrastructural facilities for proper treatment and disposal of garbage - majorproblems the Indian cities are facing.

As per the Municipal Solid Waste Rules, 2000, municipal bodies will beresponsible for providing necessary infrastructure and manpower forsegregation, transportation, storage, processing and disposal of municipal

solid waste.

NIMBY (Not In My Backyard) attitude of common man has made the task ofthe municipal bodies more difficult with respect to waste storage.

Several studies conducted by environmental and technical institutions like

NEERI indicate that over 100,000 metric tonnes of garbage are generated inthe Indian cities per day.

Only about 50%-80% of this waste gets collected for disposal on thedumping grounds. Remaining waste is left on the streets which eventuallyenters the drains, gutters etc.


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These studies have also indicated that municipal solid waste is likely toreach 125,000 MT per day by the year 2030 considering the changing urbanconsumption pattern and increase in per capita income.

There are different categories of waste generated, each take their own time

to degenerate (as given in the Table 1).1

Table 1: Categories of waste generated and their own timetaken to degenerate1

Type of litterApproximate time it takes

to degenerate the litter

Organic waste such as

vegetable and fruit peels,

leftover foodstuff, etc.

A week or two

Paper 10-30 days

Cotton cloth 2-5 months

Wood 10-15 years

Woolen items 1 year

Tin, aluminium, and other

metal items such as cans100-500 years

Plastic bags One million year

Glass bottles Undetermined

SOLID WASTES s non mo s ith the ord ref se


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SOLID WASTES - synonymous with the word refuse

The wastes generated and discarded from human and animal activities that arenormally solid are called as solid wastes.2

Components

garbage rubbish

Animal and plant residue combustiblenon-combustible

Trash white goods rubble

Refrigerators,air conditioners

Construction anddemolition debris,

rock fragments

Types of Solid Wastes depending on their source

Household waste is generally classified as municipal solid waste (MSW) Industrial waste as hazardous waste

Biomedical waste or hospital waste as infectious waste.


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Municipal Solid Waste

Organic

fraction

Segregated at source

Inert

debris

Hazardous

waste

Biological

treatment

Incineration

Composting, vermicomposting, biogas,

landfill gas

Combustibles

Packaging

material,

paper

Non

combustibles

Glass,

Metal

Fuel

pallets

Recyclable

dry waste

Low grade

construction,

paving of

roads

Hospital

Waste

Planned according

to the specific

requirement

Others

Recycling

industries

Figure 1: Segregation of municipal solid waste3

Segregation of municipal solid wasteMunicipal waste - generated in ever increasing volumes in

the urban areas.


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Solid waste characteristics:

Fundamental functions of solid waste management:

Collection, processing and disposal

To effectively implement these functions, solid wastes may be characterised asto their rates of generation, as well as to their physical and chemicalcharacteristics.

Chemical properties of Municipal Solid Wastes:

Accurate information on the chemical composition of the components of MSWis important for a number of reasons.

Composition of landfill leachate is directly affected by MSW composition.

Composition must be known for evaluating alternative MSW processing and

recovery options.

If solid wastes are to be used as a fuel, some important properties4 todetermine include ultimate analysis, proximate analysis, energy content, andparticle size distribution.


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Ultimate Analysis of solid waste components:

Defined as its total elemental analysis, i.e., the percentage of Carbon,Hydrogen, Oxygen, Nitrogen, Sulphur, and ash in a sample.

Due to concerns over emissions of chlorinated compounds, duringcombustion, the determination of halogens is often included in an ultimateanalysis.

The percent values of C, H, N, S and chlorine are measured directly by

established procedures.

The Oxygen value is calculated by subtracting the other components,including ash and moisture, from 100%.

The results of Ultimate analysis are typically used to characterise thechemical composition of the organic fraction of MSW.

Such a determination is essential for combustion. The data are also used todefine the proper mix of MSW materials to achieve suitable nutrient ration(e.g., C/N) for biological conversion processes such as composting.


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Data on the ultimate analysis of individual combustible materials arepresented in Table 2.

Table 2: Ultimate Analysis of the combustible components in MSW.

Component % by wt (dry basis)

C H O N S Ash

Organic

Paper 43.5 6.0 44.0 0.3 0.2 6.0

Plastics 60.0 7.2 22.8 - - 10.0

Foodwastes 48.0 6.4 37.6 2.6 0.4 5.0

Yard wastes 47.8 6.0 38.0 3.4 0.3 4.5

Textiles 55.0 6.6 31.2 4.6 0.15 2.5

Rubber 78.0 10.0 - 2.0 - 10.0

Wood 49.5 6.0 42.7 0.2 0.1 1.5

Inorganic

Glass 0.5 0.1 0.4


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The ash fraction is the residual remaining after combustion and isprimarily inorganic.

Ash may exit an incinerator and enter the atmosphere via the flue, or, itmay be retained within the solid waste residue.

Ash from unprocessed, unsorted MSW typically contains a much highercontent of potentially toxic metals such as Cadmium (Cd), Lead (Pb), andMercury (Hg).

A number of non-toxic metals also occur, such as iron, copper,magnesium, calcium, and sodium.

Material Percentage byweight

Metals 16

Combustibles 4.0

Ferrous metal 18.3

Non-Ferrous metal 2.7

Glass 26.2

Ceramics 8.3

Mineral, ash, other 24.1

Table 3: Composition of a sample of MSW Ash.


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Proximate Analysis of MSW:

Used to estimate the capability of MSW as a fuel.

Proximate analysis includes the following tests.

Moisture content, determined by loss of moisture afterheating at 105 C for 1h.

Volatile combustible matter, the additional loss of weightafter ignition at 950 C for 7 min in a recovered crucible(oxygen is excluded). Fixed Carbon, the combustible residue left after volatilematter is removed. (Ignition at 600 to 900 C). Ash, the weight of residue after combustion in an open

crucible.

Proximate analysis data for the combustible components of MSWand bulk samples of MSW are presented in Table 4.


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Waste Type Moisture Volatile FixedCarbon

Non

combustable

(ash)Food mixed 70.0 21 3.6 5.0

Paper mixed 10.2 76 8.4 5.4

Plastics

mixed0.2 96 2 2

Polyethylene 0.2 98


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The energy content of solid waste is the heat of combustion released whenthe waste is burned.

Two types of heats of combustion: Higher heat of combustion and

Lower heat of combustion.

Higher heat of combustion includes the heat of vaporization of water, whilelower heat of combustion does not include the heat of vaporization of water.

Energy content of MSW are based on the results of bomb calorimeter tests.

The energy stored within the chemical bonds of a material is known as theheat of combustion. This heat is released when the material is burned.

The heat generated by the combustion of a material in a calorimeter may bedetermined by measuring the temperature rise that occurs upon its

combustion. U = CvT / M

Where U is the heat value (cal/g) of the unknown material, T the rise intemperature (C) from thermogram, M the mass (g) of unknown material,and Cv the heat capacity (cal / C) of the calorimeter (measured by usingstandardised material).


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Fusion point of Ash:Provides information on its physical behaviour under high temperatures, i.e.,softening and melting.Temperature at which the ash from waste combustion forms clinker by fusion

and agglomeration.Fusion temperatures are often measured under both reducing and oxidizingconditions.Typical fusion temperatures for clinker formation from MSW range from 1100 to1200 C.

Content of Nutrients and other substrates:In applications where the organic fraction of MSW is used as feedstock for

compost or biological conversion into methane, ethanol, information on theessential nutrients in the waste materials is important.

The organic fraction of most MSW can be classified according to their relativedegree of biodegradability as follows:

Sugars Starches and organic acids Proteins and amino acids Hemicellulose Cellulose and lignocellulose Lignin Fats, oils, and waxes.


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Physical properties of MSW:Density:

The most important use of the knowledge of the density of solid waste is the

determination of its compacted volume. For better control of operation, it iseasier just to weigh things than to measure volumes. By knowledge of thecompacted density, the volume of landfill space requirement can be calculatedeasily. Compacted volume is also required to size vehicles used to collect solidwastes.

Densities of solid waste may be expressed on an as-compacted or as-

discarded basis. The ratio of the as-compacted density c to the as-discardeddensity d is called the compaction ratio r, orr = c/ d

Moisture content:The moisture content of solid wastes is useful for estimating heat content,

landfill sizing, and transport requirements. Moisture content is expressed eitheras a percentage of the wet weight or as a percentage of the dry weight of the

material. The wet-weight method is more commonly used and is expressed asfollows:

M = (w-d) / w 100where M is the moisture content (%), w the initial weight of sample asdelivered and d the weight of the sample after drying at 105C.

Particle size distribution:


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The distribution of solid waste components is important forimproving the rate of chemical reactions.

Smaller particle sizes provide greater surface area - rapid reaction

with microorganisms in a compost pile, or more rapid combustion inan incinerator (Table 5).

Important consideration in the recovery of materials, for example,with the use of processing equipment such as trommel screen or amagnetic separator.

Table 5: Typical particle size distribution of MSW

Component Size range (mm) Typical (mm)

Food 0-200 100

Paper and

Cardboard100-500 350

Plastics 0-400 200Glass 0-200 100

Metals 0-200 100

Clothing and

textiles0-300 150

Ashes, dust 0-100 25


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Field capacity:

Field capacity may defined as the total amount of moisture retained bymixed solids against the force of gravity.

Hydraulic Conductivity of compacted waste:

The hydraulic conductivity, designated as K, of compacted waste

strongly influences the movement of liquids (especially leachate) andgases in a land fill.

Dense materials such as sludges tend to resist rainfall infiltration andpromote runoff from landfill cell.

In contrast, paper and yard waste, by virtue of having large particles and

therefore large void space, exhibit little resistance to rainfall infiltration.

PROCESSING OF SOLID WASTES


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PROCESSING OF SOLID WASTESPurpose of Processing(i) to improve the efficiency of solid waste management systems,(ii) to recover the usable materials for reuses and

(iii) to recover conversion products and energy.5,2

In almost all solid waste management systems, the

reduction of volume is an important factor.

Collection vehicles with compaction mechanismsare used for the collection of solid wastes (Figure 2).

To increase the useful life of landfills, wastes usually

are compacted before being covered.

Stationary and movable type of compactionequipments are used for the process of compaction

Waste processing Techniques:1. Mechanical volume and size reduction:a. Compaction (Mechanical volume reduction):


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b. Shredding ( size reduction):

Objective - to obtain a final product of uniformreduced size in comparison to its original form.

Size reduction does not imply volumereduction.

The total volume after shredding may be higherthan that of before shredding in somesituations.

2. Component separation

Air separation:Used to separate lighter materials (usually organic)from heavier (usually inorganic) ones.

The lighter material may include plastics, paper, paper products andother organic materials.

Application of size is that, the shredded wastes can be disposedoff in land fills without using daily cover.

Used in systems designed to recover materials and energy fromsolid wastes.


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Magnetic separation:

Method of recovering ferrous scrap from shredded solid wastes

When wastes are mass-fired in incinerators, the magnetic separator isused to remove the ferrous material from the incinerator residue.

Screening:

common form of separating solid wastes - depending on their size by theuse of one or more screening surfaces.

Used before and after shredding and after air separation of wastes invarious applications dealing with both light and heavy fraction materials.

Other separation techniques:

Hand-sorting or previewing: Previewing of the waste stream and manualremoval of large sized materials is necessary, prior to most types ofseparation or size reduction techniques.

Prevent damage or stoppage of equipment such as shredders or screens, due to items such as rugs, pillows, mattresses, large metallic or plasticobjects, wood or other construction materials, paint cans, etc.


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Inertial separation: Inertial methods rely on ballistic or gravity separation principles toseparate shredded solid wastes into light ( i.e., organic) and heavy ( i.e.,

inorganic) particles.

Flotation: Glass rich feedstock is immersed in water in a soluble tank.

Glass chips, rocks, bricks, bones and dense plastic materials that sink tothe bottom are removed with belt scrappers for further processing.

Light organic and other materials that float are skimmed from thesurface. These materials are taken to landfill sites or to incinerators forenergy recovery.

Chemical adhesives (flocculants) are also used to improve the capture of

light organic and fine inorganic materials.

Optical sorting: Used to separate glass from the waste stream - can be accomplished byidentification of the transparent properties of glass to sort it from opaquematerials (e.g., stones, ceramics, bottle caps, corks. Etc.,) in the wastestream.


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TECHNOLOGIES AVAILABLE FOR PROCESSING, TREATMENT, ANDDISPOSAL OF SOLID WASTE

The main technological options available for processing/ treatment anddisposal of MSW are composting, vermi-composting, anaerobic

digestion/biomethanation, incineration, gasification and pyrolysis, plasmapyrolysis, production of Refuse Derived Fuel (RDF), also known aspelletization and sanitary landfilling/landfill gas recovery.6,7

The choice of technology has to be made based on the waste, quality, andlocal conditions.

The best compromise would be to choose the technology, which (1) haslowest life cycle cost, (2) needs least land area, (3) causes practically no airand land pollution, (4) produces more power with less waste, and (5) causesmaximum volume reduction.

3. Drying and DewateringShredded waste material is pre-dried to decrease its weight by

removing the amount of moisture. If there is any need for incineration of

sludge from treatment plants, then dewatering is essential.


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There was a tendency to use these well-proven technology for wasteto-energy conversion.

As described in Figure 4, MSW without segregation could be usedeither in sanitary landfill or mass burning to produce power.

However, after mechanical segregation, an energy-rich fuel called RDF

(refuse derived fuel) is obtained, which can be used to produce powereither through biochemical or thermal rout.

In biochemical rout, only anaerobic digestion has been usedcommercially while in the case of thermal rout, both pyrolysis and RDFburning have been used successfully for commercial purposes.


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Municipal

solid waste

Sanitary

land fill Mass burning

Mechanical

segregation

Ferrous

Aluminium

Glass

Refuse derived

fuel

Anaerobic

digestionHydrolysis /

FermentationPyrolysis

Ethanol Oil, gas andCHAR Steam

Biochemical

conversionThermal

conversion

RDF burning

Methane

Figure 4: Options for energy production from MSW (municipal solid waste)7


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1. Composting:

Composting is the decomposition of organic matter by microorganism inwarm, moist, aerobic and anaerobic environment.

Composting is suitable for organic biodegradable fraction of MSW, yard (orgarden) waste/waste containing high proportion of lignocelluloses materials,which do not readily degrade under anaerobic conditions, waste fromslaughterhouse and dairy waste.

The overall composting process6 can be explained as follows:

organic matter + O2+ aerobic bacteria CO2 + NH3 + H2O + other endproducts + energy

Compost is the end product of the composting process. This finishedproduct, which looks like soil, is high in carbon and nitrogen and is an

excellent medium for growing plants.

Composting is an environmentally sound and beneficial means of recyclingorganic materials and not a means of waste disposal.


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2. Vermi Composting

Vermi-compost is the natural organic manure produced from the excreta ofearthworms fed on scientifically semi-decomposed organic waste.

It is, however, to be ensured that toxic material does not enter the chain

which if present could kill the earthworms.

3. Biogasification:

It originates from bacteria in the process of bio-degradation of organicmaterial under anaerobic (without air) conditions.

The natural generation of biogas is an important part of the biogeochemicalcarbon cycle.

Biogas is a mixture of gases composed of

methane (CH4) 40-70% vol%,carbondioxide (CO2) 30-60 vol%,other gases 1-5 vol% including - hydrogen (H2) 0-1 vol% and

hydrogen sulphide (H2S) 0-3 vol%.6


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.

.

In the absence of oxygen, anaerobic bacteria decompose organic matter asfollows:

Organic matter + anerobic bacteria CH4 + CO2 + H2S + NH3 + Otherend products + Energy.

Methanogens (methane producing bacteria) are the last link in a chain ofmicroorganism, which degrade organic materials and return thedecomposition products to the environment. In this process, biogas isgenerated, which is a source of renewable energy.

Anaerobic processing of organic material is a two-stage process, wherelarge organic polymers are fermented into short-chain volatile fatty acids.

These acids are then converted into methane and carbon dioxide.

The metabolic stages in biogasification are illustrated in Figure 5.


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In biogasification process both the organic polymers fermentation process andacid conversion occur at the same time, in a single-phase system

Biogasification process is particularly suitable for wet substrates, such assludges or foodwaste, which present difficulties in composting, as the lack ofstructural material restricts air circulation.

e etabo c stages b ogas cat o a e ust ated gu e 5

Complex

organic carbon

Monomers

Organic acids

Acetic acid

H2 +CO2

CH4 + CO2

Hydrolysis

Acidogenesis

Acetogenesis

Methanogenesis

4 Incineration


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4. IncinerationIncineration is a waste treatment technology that

involves the combustion of organic materials and/orsubstances. Incineration and other high temperaturewaste treatment systems are described as thermal

treatment.

This process converts the waste into incinerator bottomash, flue gases, particulates, and heat, which can in turnbe used to generate electric power.

The flue gases are cleaned of pollutants before they are dispersed in theatmosphere

Incinerators reduce the volume of the original waste by 95-96 %, dependingupon composition and degree of recovery of materials such as metals fromthe ash for recycling.

Incineration has particularly strong benefits for the treatment of certainwaste types in niche areas such as clinical wastes and certain hazardouswastes where pathogens and toxins can be destroyed by high temperatures.


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5. Pyrolysis/Gasification, Plasma Pyrolysis Vitrification (PPV)/Plasma ArcProcess:

Pyrolysis gasification processes are established for homogenous

organic matter like wood, pulp, etc., while plasma pyrolysis vitrification is arelatively new technology for disposal of particularly hazardous wastes,radioactive wastes, etc.

Toxic materials get encapsulated in vitreous mass, which is relativelymuch safer to handle than incinerator/gasifier ash. In all these processes,besides net energy recovery, proper destruction of the waste is alsoensured.

This process produces fuel gas/fuel oil, which replace fossil fuels andcompared to incineration, atmospheric pollution can be controlled at theplant level.

NO and SO gas emissions do not occur in normal operations due to thelack of oxygen in the system.

C b H tHigh- and moderate Low-molecular


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Carbonaceous

solidsHeat molecular weigth

organic liquids (tars

and oils, some

aromatics)

+ Char +

Organic

liquidsheat

Aromatic

organics +

NH3 + H2S +

COS + HCN

HCN

Low-molecular

weight organic

liquids

Char + CH4 +

H2 + H2O +

CO + CO2

Amounts depend on

nitrogen and sulphurcontent in feed stock

weigth organic

liquids (many

organic acids

and aromatics)

Figure 6: Pyrolysis and gasification reactions.8

6. Sanitary Landfills and Landfill Gas Recovery

Sanitary landfill is the scientific dumping of municipal solid waste due towhich the maturity of the waste material is achieved faster and hence gascollection starts even during the landfill procedure.

Its main advantage is that it is the least cost option for waste disposal


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Hazardous waste

Industrial and hospital waste is considered hazardous as they may

contain toxic substances.Certain types of household waste are also hazardous.

Hazardous wastes are toxic, corrosive, highly inflammable, or explosiveand react when exposed to certain things e.g. gases. India generatesaround 7 million tonnes of hazardous wastes every year, most of which isconcentrated in four states: Andhra Pradesh, Bihar, Uttar Pradesh, andTamil Nadu.

Household wastes that can be categorized as hazardous waste includeold batteries, shoe polish, paint tins, old medicines, and medicine bottles.

The different types of symbols used to designate the hazards and

recycling of waste is presented in Table 6.9

Its main advantage is that it is the least cost option for waste disposaland has the potential for the recovery of landfill gas as a source of energy,with net environmental gains if organic wastes are landfilled.

The gas after necessary cleaning can be utilized for power generation or

as domestic fuel for direct thermal applications.

Table 6: Common hazard and recyle symbols.


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Name SymbolName Symbol

Toxic sign

Non-ionizing

radiation sign

Caution sign

Biohazard sign

Radiation sign

Warning sign

Ionizing radiation sign

High voltage sign

Chemical weapon

symbol

Laser hazard sign

Optical radiation

Recycle arrow

In the industrial sector the major generators of hazardous waste are the
http://en.wikipedia.org/wiki/Skull_and_crossboneshttp://en.wikipedia.org/wiki/Non-ionizing_radiationhttp://en.wikipedia.org/wiki/Non-ionizing_radiationhttp://en.wikipedia.org/wiki/Biological_hazardhttp://en.wikipedia.org/wiki/Radiationhttp://en.wikipedia.org/wiki/Warning_signhttp://en.wikipedia.org/wiki/Ionizing_radiationhttp://en.wikipedia.org/wiki/High_voltagehttp://en.wikipedia.org/wiki/Chemical_warfarehttp://en.wikipedia.org/wiki/Laserhttp://en.wikipedia.org/wiki/Laserhttp://en.wikipedia.org/wiki/Chemical_warfarehttp://en.wikipedia.org/wiki/High_voltagehttp://en.wikipedia.org/wiki/Ionizing_radiationhttp://en.wikipedia.org/wiki/Warning_signhttp://en.wikipedia.org/wiki/Radiationhttp://en.wikipedia.org/wiki/Biological_hazardhttp://en.wikipedia.org/wiki/Non-ionizing_radiationhttp://en.wikipedia.org/wiki/Non-ionizing_radiationhttp://en.wikipedia.org/wiki/Non-ionizing_radiationhttp://en.wikipedia.org/wiki/Non-ionizing_radiationhttp://en.wikipedia.org/wiki/Skull_and_crossbones


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In the industrial sector, the major generators of hazardous waste are themetal, chemical, paper, pesticide, dye, refining, and rubber goods industries.Direct exposure to chemicals in hazardous waste such as mercury and

cyanide can be fatal.

Biomedical waste or Hospital waste

Hospital waste is generated during the diagnosis,treatment, or immunization of human beings or animals orin research activities in these fields or in the productionor testing of biologicals.

It may include wastes like sharps, soiled waste,disposables, anatomical waste, cultures, discardedmedicines, chemical wastes, etc.

These are in the form of disposable syringes, swabs, bandages, body fluids,human excreta, etc. The chemicals include formaldehyde and phenols, which

are used as disinfectants, and mercury, which is used in thermometers orequipment that measure blood pressure.

These waste is highly infectious and can be a serious threat to human healthif not managed in a scientific and discriminate manner. It has been roughlyestimated that of the 4 kg of waste generated in a hospital at least 1 kg wouldbe infected.


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Surveys carried out by various agencies show that the health care

establishments in India are not giving due attention to their wastemanagement.

After the notification of the Bio-medical Waste (Handling andManagement) Rules, 1998, these establishments are slowlystreamlining the process of waste segregation, collection, treatment,

and disposal.

Many of the larger hospitals have either installed the treatmentfacilities or are in the process of doing so.

The Rules have defined and stipulated ten categories of biomedicalwastes generated by hospitals on a daily basis and clearly specified

the methods and means of safe disposal (Table 7).


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Table 7: Categories, Disposal mode and Colour adopted for different types ofbiomedical wastes2

Category

of Waste

Type of Waste Examples Type of

Treatment

Mode of Disposal Colour Type of

Container

I Human Anatomical

Waste

Human tissues, organs, body parts. Incineration Deep burial Yellow Plastic Bags

II Animal Waste Animal tissues, organs, body parts,

carcasses, bleeding parts, fluid, blood,

waste generated by veterinary hospitals,

colleges, discharge from hospitals,

animal houses.

Incineration Deep burial Yellow Plastic Bags

III Microbiology and

biotechnological

wastes

Wastes from laboratory cultures, stocks

or specimen of micro organisms live or

attenuated vaccines, human and animal

cell cultures used in research and

infectious agents from research and

industrial laboratories

Autoclaving /

Microwaving

Incineration Yellow Plastic Bags

Red Plastic

Bag

Disinfected

container

IV Waste Sharps Used and unused needles, syringes,

scalpels, blades, glass, etc.

Autoclaving /

Microwaving /

Chemical

disinfection

Shredding Blue/White

translucent

Puncture

proof

container/

Plastic Bag


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V DiscardedMedicine &

Cytotoxic drug

Outdated, contaminated and

discarded medicinesIncineration Secured Land fill Black Plastic Bag

VI Soiled Wastes Items contaminated with body fluidsand blood including cotton, dressings,

soiled plaster casts, bedding, etc.

Autoclaving /Microwaving /

Chemical

disinfection

Shredding Yellow Plastic Bags

Red Plastic

Bag

Disinfected

container

VII Solid Wastes Wastes generated from disposableitems other than the waste sharps such

as tubing, catheters, intravenous sets,

etc.

Autoclaving /

Microwaving /

Chemical

disinfection

Land fill Red PlasticBag

Disinfected

container

Blue/White

translucentPuncture

proof

container/

Plastic Bag

VIII Liquid Wastes Waste generated from laboratory andwashing, cleaning, house keeping and

disinfecting activities

Chemical

disinfection

drains

Discharge into drains - -

IX Incineration Ash Ash from incineration of anybiomedical waste

- Municipal Land fill Black Plastic Bag

X Chemical Wastes Chemicals used in production ofbiological, chemicals used in

disinfecting, as insecticides, etc

Chemical

disinfectionSecured land fills for

solids and discharge

into drains forliquids.

Black Plastic Bag


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WASTE MINIMISATIONMore benefits can be achieved from the better use and disposal of

wastes. Four types of waste management to be employed are10

Refuse

Reuse Recycle Reduce

In India, some municipal areas have banned the use of plastics and theyseem to have achieved success.

For example, today one will not see a single piece of plastic in theentire district of Ladakh where the local authorities imposed a ban onplastics in 1998.1

One positive note is that in many large cities, shops have begunpacking items in reusable or biodegradable bags. Certain biodegradableitems can also be composted and reused.

If one follows the waste trucks flying on the roads of Chennai, onecould end up in Perungudi, almost at the heart of the city, where a largewaste dump is maintained, or at Kodungaiyur, on the outskirts.11

The Perungudi dump yard receives more than 1,400 tonnes per day ofsolid waste.


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One visit to Perungudi establishes the fact that the site is a large

producer of dioxins and other poisonous gases, and that it could be agood place to set up a facility making chemical weapons for a large army.

From the 800 tonnes of solid waste collected in Coimbatore city perday, it was possible to generate eight mega watts of power resulting in700 lakh units of electricity production annually.

The annual income from electricity would be about Rs. 21 crore. Inaddition to power generation, equal amount of income could also begenerated through manure production from slurry coming out of biogasplants.

The maintenance of waste to power generation project through

anaerobic digestion (biogas plant) could be economical, if maintained bythe local youth groups like Self-Help Groups.


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What you can do to reduce solid waste?Carry your own cloth or jute bag when you go shopping.

Say no to all plastic bags as far as possible.Reduce the use of paper bags also.

Reuse the soft drinks polybottles for storing water.Segregate the waste in the house - keep two garbage bins and see to it

that the biodegradable and the nonbiodegradable is put into separate binsand dispose off separately.

Dig a compost pit in your garden and put all the biodegradables into it.

See to it that all garbage is thrown into the municipal bin as the collectionis generally done from there.

When you go out do not throw paper and other wrappings or even leftoverfood here and there, make sure that it is put in the correct place, that is into

a dustbinAs far as possible try to sell all the recyclable items that are not required

to the Kabariwala (person who trades in waste)


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References:1. http://edugreen.teri.res.in/explore/solwaste/types.htm

2. P. Anandan, R. Kumaravelan, Principles of Environmental Engineering,Scitech Publications (India) Pvt.Ltd., Ed., 2004.h

3. http://edugreen.teri.res.in/explore/solwaste/wastemgt.htm4. John Pichtel, Waste Management Practices, Taylor and Francis, 2005.5. T. V. Ramachandra, Management of Municipal Solid Waste, Capital Publishing

Company, 2006.6. P.U. Asnani, Solid waste management in India Infrastructure Report 2006,

Urban Infrastructure.7. Sudhir Kumar, Technology options for municipal solid waste-to-energy

project, Times (TERI Information Monitor on Environmental Science) 5(1): 111, 2000.

8. Vincent Cavaseno and the staff of chemical engineering, Industrialwastewater and solid waste engineering, McGraw-Hill Publications Co.,

New York,N.Y. 1980.9. http://en.wikipedia.org/wiki/Hazaed_symbol10. http://edugreen.teri.res.in/explore/solwaste/what.htm

11. http://www.hinduonnet.com/businessline/2001/06/13/stories/04136708.htm

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