DISPOSAL OF SOLID
WASTES
Dr.Pracheth.R.
Outline
• Importance
• Solid waste
• Sources of refuse
• Storage
• Collection
• Methods of disposal
Importance
• Public health engineers, sanitarians
• Health hazard
• Advice- camp sanitation, natural disasters
Solid wastes
• Garbage (food wastes)
• Rubbish (paper, plastics, wood, metal, throwaway containers, glass)
• Demolition products (bricks, masonry, pipes)
• Sewage treatment residue
• Dead animals, manure
• No night soil
• Per-capita daily output :0.25-2.5kg
Health hazard
• Decomposes, fly breeding
• Attracts rodents
• Pathogens
• Water, soil pollution
• Unsightly appearance, nuisance- bad odours
Sources of refuse
• Street refuse
• Market refuse
• Stable litter
• Industrial refuse
• Domestic refuse:
 ash, rubbish, garbage
Residue from fire –cooking, heating
Sources of refuse
• Garbage:
 Waste matter- preparation, cooking,
consumption of food
Waste food, vegetable peelings
Quick removal, disposal : ferments on storage
Storage
• First consideration
• Galvanized steel dust bin with close fitting cover
• Paper sack
Storage
• Public bins :
Large number of people
 Not covered
Concrete platform : 2-3 inches above ground
level
Handled, emptied mechanically : lorries
Collection
• House- house: best
• Dump – public bins
• Refuse dispersed all along street
• Refuse collection vehicles
• Mechanical transport
• Dustless refuse collector
Methods of disposal
• Dumping
• Controlled tipping
• Incineration
• Composting
• Manure pits
• Burial
Dumping
• Refuse dumped in low lying areas
• Bacterial action- decreases in volume –humus
• Kolkata
• Drawbacks:
 Flies, rodents
Nuisance: odour, unsightly appearance
Loose refuse : dispersed by wind
Drainage from dumps : pollution- surface,
ground water.
Controlled tipping (Sanitary landfill)
• Most satisfactory : land available
• Material placed in trench/other prepared area :
compacted and covered with earth at end of
working day
• Modified sanitary landfill :
 Compacted and covered once a week
Trench method
• Level ground available
• 2-3 m deep, 4-12 m wide
• Refuse compacted, covered with earth
Ramp method
• Terrain is moderately sloping
• Excavation done to secure covering material
Area method
• For filling land, depressions, disused quarries,
clay pits
• Refuse: deposited, packed, consolidated in
uniform layers up to 2-2.5 m deep
• Each layer sealed on exposed surface with mud
cover
• Sealing: prevents fly, rodent infestation, nuisance
of smell, dust
Mechanism controlled tipping
• Chemical, bacteriological, physiological changes
in buried refuse
• Temperature : rises 60 degree C within 7 days :
kills all pathogens : decomposition
• 2-3 weeks to cool down
• Complete decomposition: 4-6 months : into an
innocuous mass
Incineration
• Land unavailable
• Hospital refuse
• Industrialized countries
• India : fine ash
• Manure
Flow diagram- incinerator
Composting
• Combined disposal of refuse and night soil or
sludge
• Organic matter breaks down under bacterial
action : stable humus like material “ Compost”
• CO2, H2O, heat
• Heat : 60 degree C : several days – destroys egg,
larvae of flies, weeds, pathogens
• Compost : few/no pathogens, good soil builder
Bangalore Method ( Hot
fermentation)
• Indian Council of Agricultural Research
• Trenches : 90 cm deep
• 1.5 to 2 m broad
• 4.5 to 10 m long, depends on amount of refuse,
night soil
• Depths >90 cm : slow decomposition
• Location: not less than 800 m from city limits
Composting procedure
• Layer of refuse : 15 cm thick: at bottom of
trench
• Over this, night soil : 5cm thick
• Alternate layers of refuse and night soil – 15cm:
5cm – till heap rises to 30 cm above ground level
• Top layer of refuse : at least 25 cm thick
• Heap covered with excavated earth
Contd…
• Within 7 days : heat generated in compost mass
by bacterial action
• Heat stays : 2-3 weeks- decomposes refuse and
night soil , destroys pathogens
• At end of 4-6 months : decomposition is
complete , manure formed
Mechanical composting ( Aerobic
method)
• Compost manufactured on large scale by
processing raw materials and turning out a
finished product
• Refuse first cleared : rags, bones, metal, glass,
items interfering with grinding
• Pulverised : reduce size of particles < 2inches
• Pulverised refuse : then mixed with sewage,
sludge/ night soil in a rotating machine,
incubated
Contd…
• Completed in 4-6 weeks
• Developed countries : Holland, Germany
• India : Delhi, Nagpur, Hyderabad, Chennai Pune
Manure pits
• Rural areas
• Thrown around house : soil pollution
• Garbage, cattle dung, straw , leaves dumped into
manure pits, covered with earth after each days
dumping
• Two such pits needed : one is close, other use
• 5-6 months : converted to manure
Diagram – manure pit
Burial
• Small camps
• Trench : excavated
• At end of each day: refuse covered with 20- 30
cm earth
• When level of trench is 40 cm from ground level
: trench filled with earth and compacted, new
trench dug out
• 4-6 months : contents can be taken out, used in
fields.
Public education
• People : little interest
• Pamphlets, newspapers, films
Economics and finance
• For efficient refuse disposal : heavy capital
outlay
• Industrialized countries : upto 20%
International cooperation
• International Solid Wastes and Public Cleansing
Association- 1970: improve sanitary services
• WHO International Reference Centre : collect,
evaluate, spread information
Outline
• Sewage
• Sullage
• Health aspects
• Composition
• Aim of purification
• Modern sewage treatment plant
• Other methods of sewage treatment
Sewage
• Waste water- community – solid and liquid
excreta, derived from houses, street, factories,
industries
Sullage
• Waste water- no human excreta
• Kitchens, bathrooms
Amount of sewage depends
• Habits of people
• Time of day
Health aspects
• Nuisance, unsightliness, unpleasant odour
• Breeding- flies, mosquitoes
• Soil pollution, water supply
• Food contamination
• Increase- enteric, helminthic diseases
Composition
• 99.9% water
• Solids- 0.1%:
• Avg adult: 100 gm/ day
Aim of purification
• Aim: stabilize organic matter- disposed off safely
• Convert sewage- EFFLUENT- disposed off-rivers,
sea, lands
Strength of sewage
• BOD: Amt of O2 absorbed by sample –sewagespecified period : 5 days at 20 degree C for
aerobic destruction/ use of organic matter by
living organisms
• More than equal 300: strong
• 100: weak
• Natural water:1
• Untreated domestic sewage: 100
Decomposition of organic
matter
• Aerobic process:
Most efficient- reduce organic matter
Requires continuous supply of O2
Organic matter broken: CO2, water, ammonia,
nitrates, nitrites by bacteria action
Contd…
• Anaerobic process:
Sewage highly concentrated, plenty solids
Methane, ammonia, CO2, H2
Slower, more complex
MODERN SEWAGE TREATMENT
PLANT
• Purification: action of aerobic, anaerobic
bacteria
• Primary: solids separated- screening,
sedimentation, anaerobic digestion
• Secondary: aerobic oxidation
Primary treatment
• Screening
• Grit chamber
• Primary sedimentation
Screening
• Pass through metal screen
• Intercepts floating objects- wood pieces, rags,
garbage mass, dead animals
• Prevent obstruction
• Vertical bars
• Screenings removed : mechanically, manually,
disposed- burial
Grit chamber
• Long narrow, detention: 30 s- 1min
• Allow settlement- heavier solids- sand, gravelpermit organic matter to pass through
• Grit: collects at bottom, periodically removed;
disposed- dumping
Primary sedimentation
• Primary sedimentation tank
• Rectangular
• Sewage- slowly, 6-8 hrs
• Purification: sedimentation- suspended matter
• 50-70%: settle down- gravity
• 30-40% organisms- reduced
Contd…
• Organic matter settle down: SLUDGEmechanically removed, without disturbing
• Microbes- attack- complex organic solids:
ammonia
• Fat and grease- rise to surface : SCUM: removed
time to time , disposed off
Secondary treatment
• Effluent- contains proportion: organic matter,
living organisms
• High demand for O2: pollution
 Trickling filter method
Activated sludge process
Trickling filter method
• Bed of crushed stones
• Effluent- sprinkled uniformly on surface of bedby using revolving device
• Device: has hollow pipes- each have row of holes
• Pipes keep rotating, sprinkling effluent in a thin
film on filter
Contd…
• Over surface and down through filter: complex,
biological growth- algae, fungi, protozoa,
bacteria: ZOOGLEAL LAYER
• Effluent goes through filter: oxidized by bacteria
in zoogleal layer
• Action: biological; filter-misnomer
Contd..
• Advantage: efficient – purifying sewage
• Layer: grows, dies
• Dead matter sloughs off: break away, washed
down filter: HUMUS (light, green flocculent
material)
• Oxidized sewage: let into secondary
sedimentation tanks
Activated sludge process
• Aeration tank
• Effluent from primary sedimention tank mixed
sludge drawn from final settling tank:
Mixture: aeration- 6- 8 hrs
 Mechanical agitation
Forcing compressed air continuously from
bottom aeration tank- DIFFUSE AERATION
Contd..
• Organic matter- oxidised to CO2, nitrates, wateraerobic bacteria in activated sludge
• Typhoid, cholera organisms destroyed
• Let into secondary sedimentation tank
• Less space, more skill
Sludge digestion
• Digestion:
Incubated under favourable temp, pH- anearobic
auto digestion- complex solids broken into water,
CO2, methane, ammonia
Volume- reduced
3-4 weeks- sludge digested
Residue- inoffensive, manure
Sludge digestion tanks
Contd..
 Sea disposal
Land: composting with town refuse
Effluent disposal
• By dilution:
Water sources- rivers, streams- disposal by
dilution
Effluent dissolved in water, impurities oxidised
by dissolved O2 in water
• Disposal on land: irrigation purpose
Okhla sewage treatment plant
Summary
Thanks