Disposal of Waste
Dr Abhay Nirgude
Professor & Head
Specific Learning Objectives
• Define sewage & Sullage
• Enumerate various methods of solid waste
disposal.
• Discuss functioning of Modern sewage
treatment plant.
• Write the uses of Biogas plant
Disposal of Waste
Solid waste
Sewage Disposal
Liquid waste disposal
Solid waste
• Health Hazards due to solid waste :1. It decomposes and favours fly breeding.
2. It attracts rodents and vermin.
3. Act as medium for transmission of pathogens to man’s food.
4. Water and soil pollution.
5. Unsightly appearance, nuisance and bad odours.
Sources of Refuse
1. Street refuse
2. Market refuse
3. Stable litter
4. Industrial refuse
5. Domestic refuse ( ash, rubbish and garbage)
Solid waste
 Storage
 Collection
Methods of Disposal
1.
2.
3.
4.
5.
6.
Dumping
Controlled Tipping or Sanitary Land-fill.
Incineration
Composting
Manure pits
Burial.
Composting
Bangalore Method(Anaerobic)
• Trenches :• 3 feet Deep
• 5-8 feet broad
• 15-30 feet long
• From 800m from city limits
• Alternate layers of refuse
(15 cm) and night soil (5cm)
• Top layer covered by
excavated earth
• 4-6 months decomposition
is complete by anaerobic
digestion.
Mechanical Composting ( Aerobic)
• Refuse cleared of
salvageable materials.
• Pulverised in Pulverising
equipment.
• Reduction of particle size to
2 inches.
• Mixed with sewage and
incubated.
• Time :- 4-6 weeks.
Excreta Disposal
Transmission of Faecal-born diseases
Sanitation barrier
Septic Tank
Treatment of household sewage.
• Design Features :1.
Capacity :- 2 & ½ -5 c.ft/Person.
2.
Length :- Twice the breadth.
3.
Depth :- 1.5-2 meter
4.
Liquid depth :- 1.2 meter.
5.
Air space :- 30cm.
6.
Bottom :-
7.
Inlet & Outlet :-
8.
Retention Period :- 24 hours.
Septic Tank
Working of A Septic Tank
• Solid settle down in the tank to form “ Sludge”.
• Grease and fat rise to form “Scum”.
• Sludge undergo anaerobic digestion
• Effluent :- Liquid that passes out of the outlet pipe.
• Effluent undergoes Aerobic Oxidation.
Operation & Maintenance
• Avoid use of soap & disinfectants to clean septic tank.
• Desludging of the septic tank to be done at least once a year.
• New septic tank is filled with water till outlet level and ripe
sludge added to provide right type of bacteria.
Aim of the sewage Purification
• Aim :- Stabilize organic mater to dispose off
safely.
• Test of Organic content of the sewage
1. Biochemical Oxygen Demand ( BOD) :2. Chemical Oxygen Demand (COD ) :3. Suspended Solids :-
Biochemical Oxygen Demand ( BOD)
• “Amount of oxygen absorbed by a sample of sewage during a
specified period ( 5 days), at a specified temperature ( 20 deg
C.) for the aerobic destruction or use of organic matter by
living organism.”
• Value :- Range from 1mg/L to 300mg/L.
• Strong Sewage :- BOD is 300mg/L.
• Weak Sewage :- BOD is 100mg/L.
Chemical Oxygen Demand (COD )
• “ Measures the oxygen equivalent of that portion of the
organic matter in a sample which is susceptible to oxidation
by a strong chemical oxidiser.”
• If wastes contain toxic substances, this test may be the only
practical method for determining the organic load.
Suspended Solids
• Amount of suspended solids in a domestic sewage may vary
from 100 to 500 P.P.M. (mg/l).
• Weak Sewage :- 100mg/l suspended solids
• Strong Sewage :- 500mg/l suspended solids
Modern Sewage Treatment
• Primary Treatment
1. Screening
2. Grit Chamber
3. Primary Sedimentation
• Secondary Treatment
• Trickling Filter Method
• Activated Sludge
Process.
• Secondary
Sedimentation
• Sludge digestion
• Disposal of Effluent.
Design
Activated Sludge Process
Other Methods of Sewage Disposal
1. Sea outfall
2. River Outfall
3. Land treatment
4. Oxidation pond
5. Oxidation Ditches
Oxidation Pond or
waste Stabilization Pond
Sokage Pit
Sokage Pit
Biogas Plant
Biogas Plant layout