Transcript Solid waste and disposal methods

Sources of solid waste
• Residential
• Commercial
• Institutional
• Construction and demolition
Municipal solid waste (MSW)
• Municipal services
• Treatment plant sites
• Industrial
• Agricultural
• Biomedical waste
Industrial solid waste
Agricultural waste
Hospital waste
Solid waste and disposal methods
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Municipal Waste
Food waste
fruit or vegetable residues (garbage) decompose rapidly
Rubbbish
Combustible or non combustible solid wastes excluding food wastes or
other putrescible materials. Combustible rubbish includes paper,
cardboard, plastics,rubber etc. Non combustible rubbish includes
glass, crokery, tin cans etc
Ashes and residues
Materials remaining from the burning of wood, coal and other
combustible wastes
Demolition and
construction wastes
Wastes from razed buildings and other structures are classified as
demolition waste. Wastes from the construction and repairing of
residential, commercial and industrial buildings and similar structures
are classified as construction wastes
Special wastes
Wastes such as street sweepings, roadside litter, dead animals and
abandoned vehicles are classified as special wastes
Treatment Plant Wastes
The solid and semisolid wastes from water, wastewater and industrial
treatment facilities
Nature of Industrial solid waste
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Hazardous and Non-hazardous waste
• Characteristics - Hazardous
– Corrosivity
– Flammability
– reactivity
– Toxicity
• Catagories
– Chemicals
– Biological
– Radioactive
– Explosives
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Disposal of refuse
Land filling
Incineration
Disposal into sea
Composting
Disposal by land filling
In this method refuse is carried out and dumped into low lying area
• Disposal by land filling
• In this method refuse is carried out and dumped into low lying area
• The refuse is filled up or dumped in layers of 1.5 m or so and each such layer is
covered by good earth of atleast 20 cm thickness so that the refuse is not directly
exposed. If the thickness of land filling is large filling shall be done in layers and
each layer should be compacted by the movement of bull dozers, trucks etc.
• Insecticides like D.D.T etc. should be sprayed on the layers to prevent breeding of
mosquitoes and flies. A final cover of about 1 m of earth is laid and compacted at
the top of the filled up land.
• The waste is stabilized by aerobic as well as anaerobic processes
• The entire process can be stabilized into five distinct phases
• During first phase aerobic bacteria will deplete the available oxygen to effect the
oxidation of organic matter. As a result temperature in the fill increases
• In the second phase anaerobic and facultative bacteria develop to decompose the
organic matter and in third phase methanogenic bacteria develop to cause evolution
of methane.
• In the fourth phase methanogenic activity get stabilized
• In the fifth stage methanogenic activity subsides representing depletion of organic
matter and ultimately the system returns to aerobic conditions
Sanitary landfills
• The refuse get stabilized in a period of 2 to 12 months and settles down
by 20-40% of its original height. The filling of land can be utilized for
developing some green land, park or recreational spot.
• Advantages
• This method is simple and economical. No costly equipment is
required
• Separation of different kinds of refuse as required in incineration
method is also not required
• There are no residues or byproducts left and hence no further disposal
required
• Low lying water logged areas and quarry pits can be easily reclaimed
and put to better use.
• Disadvantages
• Unavailability of land in future
• The dumped garbage may contain harmful and carcinogenic non
biodegradable substances such as plastics, medicines, paints,
insecticides etc.During winter season the excess water may seep out
through the area as a colored liquid called Leachate. This may contain
organic compounds like chlorinated hydrocarbons, benzene, toluene,
xylene etc.is likely to seep to contaminate the ground water leading to
diseases like cholera, typhoid,etc.
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Disposal by compositing
Biological method of decomposing solid waste
Under aerobic or anaerobic condition or both
Final end product is manure
In aerobic composting process because it involves piling
up of refuse and its regular turning either manually or by
mechanically devices so as to ensure sufficient supply of
air
• The process starts with mesophilic bacteria which oxidize
the organic matter to carbon dioxide and liberate heat. The
temperature rises to 45oC and at this point thermophillic
bacteria take over and continue the decomposition. During
this phase the temperature rises to about 60oC. After about
3 weeks the compost is stabilized and this is shown by
appreciable fall in temperature. The final compost should
have earthy smell and dark brown color.
• Moisture content is a critical factor in aerobic composting
process. A moisture content of about 55% should be
established so that the biological activity may proceed at
an optimum rate.
Composting
Invessel
Composting has 3 phases:
Mesophilic
Thermophilic
(pseudomonads) (Bacillus, then
Thermus)
Cooling/maturation
(Bacillus, pseudomonads,
others)
What chemical and physical factors
are important in a compost pile?
• temperature
• C/N ratio: the ratio of carbon to nitrogen
• nutrients: usually plenty in the organic
residues
• oxygen
• pH
• moisture: optimal is 50-60%
• particle size
Temperature
• A result of microbial action – energy is
produced
• Too cool – decomposition will be too slow
• Too hot – beneficial microbes will die
• Do need temperature to be at or above
55oC for part of the time to destroy human
and plant pathogens
C/N ratio (carbon/nitrogen) –
why is it important?
•Carbon acts both as an energy source and the basic
chemical building block.
•Nitrogen is needed to make both amino acids and
nucleic acids.
•If nitrogen is limiting , microbial population will be
small and long time for decomposition
•Ideal ratio for composting = 30:1
C/N ratio (carbon/nitrogen)
• High C/N items:
• Low C/N items:
– Dead leaves
– Straw
– Wood chips or sawdust
– Bark
– mixed paper
– Newspaper
– Corrugated cardboard
– Vegetable scraps
– Coffee grounds
– Grass clippings
– Manure
Most microbes can tolerate a pH
range of 5.5 - 8.5
• Initially, a lowered pH favors the growth of
fungi
– More breakdown of lignin and cellulose
• If pH drops too low, even fungi are
affected
– Decomposition slows or stops!
• Aeration – providing oxygen – returns the
pH to an acceptable range
Moisture
• Most rapid decomposition takes place in
thin film of water on surfaces of organic
particles.
• Too little – poor bacterial activity
• Too much – anaerobic pockets and odor,
nutrient leaching, slower decomposition
• Ideal: 50-60%;
Particle size
Large – prevents compaction;
allows oxygen flow and aeration.
Less surface area
Small – more surface area
for more microbes = faster
decomposition. Can compact.
• Disposal by incineration
• Burning of refuse at high temperature in furnaces called incinerators
• Separation of combustible matter from incombustible will reduce the
load on incinerators
• The left out ashes and clinkers (fused masses of incombustible
materials) have to be disposed by land filing or for other use. Clinker
can be used as aggregate for making low grade concrete and ashes can
be used for bricks
• The heat prodced can be used in the form of steam power for running
turbines to generate electricity
• The maximum temperature in the combustion chamber should be
sufficient (> 670oC). If steam is to be generated then a temperature of
10000C is required in the combustion chamber.
• Merits
• Ensures complete destruction of pathogenic bacteria
• No odor trouble
• Requires less space for refuse disposal
• Some cost can be recovered by selling power
• Demerits
• Costly method and require a technical know how
• Solid waste to be burnt should have high calorific value
SW Management elements
• Incineration..
– Heat recovery through boilers - efficiency – 70%
– Amount of steam produced varies from 1.0 to 3.5 kg/kg of
MSW
– Four basic unit operations
• Preparation (auxillary fuel) and transportation of waste to
incinerator
• Combustion of organic waste into flue gases
• Heat transfer from flue gases
• Exhaust of cooled flue gases with pollutants through for
APCDs for removal of pollutants
SW Management elements
• Incineration..
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Heat recovery efficiency – 70%
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Amount of steam produced varies from 1.0 to 3.5 kg/kg of MSW
Properties of solid waste
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Physical
– Density
– Weight per unit volume (kg/m3)
– Varies with
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Waste constituents
Degree of compaction
State of decomposition
Depth of waste
Season
Length of storage time
– Examples (mass/density)– food wastes (19.6/288); paper (19.6/81.7);
Glass (3.4/194) – Uncompacted waste
Properties of solid waste
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Physical
– Moisture content
– Percentage of wet weight of material
– Important role in
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Compaction
Decomposition
Leaching of inorganic components
And use in incineration
– Examples – food waste (50-80%); plastics (1-4%); construction
combustibles (4-15%)
– .
Properties of solid waste
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Physical
– Particle size and distribution
– Important for
• recovery
• & compaction of wastes
– Field Capacity
– Moisture retained in a waste after gravitational pull
– Excess – forms leachate
– Leachate – transport of contaminants to ground water table
– Varies with compaction pressure and state of decomposition
– Typical uncompacted waste – 50-60%
Properties of solid waste
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Chemical
– Proximate analysis
– Includes four tests –
• loss of moisture at 105 deg.C for 1 hour;
• Volatile combustion matter
• Fixed carbon
• Ash
Type
Moisture
Volatiles
Carbon
Ash
Mixed food
70
21
4
5
Mixed paper
10
75
9
6
Residential
MSW
21
52
7
20
Properties of solid waste
– Elemental Analysis (also called ultimate analysis)
– Determination of carbon, hydrogen, oxygen, nitrogen, sulphur and ash
– Used to characterize waste in terms of organic matter
Type
C
H
O
N
S
Ash
Mixed food
73
11
15
.4
.1
rest
Mixed
paper
43
`5.8
44
.3
.2
rest
Refuse
driven fuel
44
7
38
.7
<.1
rest