Solid Waste ManagementSolid Waste Management

What is solid waste?- Solid waste is an useless, unwanted or discarded material.

- It consists of part of raw materials, intermediate product or finished product which has got no commercial value.

- As defined by federal law, “solid waste may be solid, liquid or semiliquid, generated from industries, muncipalities, businesses or home”.

- It includes discarded article that is worn out, broaken, packaging or organic wastes or toxic substance produced as a by product of some industrial process.

What is Solid Waste Management?- Solid waste management involves management of activities

associated with generation, storage, collection, transfer and transport, processing and disposal of solid waste which is environmentally compatible, adopting principles of economy, aesthetics, energy and conservation.

- Solid waste management involves four steps :

a) Generation & composition of waste.

b) Collection of waste.

c) Transportation of waste.

d) Disposal of waste.

From where does the waste comes from?- The major sources are mining (75%), Agriculture

(12%),Industries (9 %), Muncipalties (3%) & Sewage sludge (1 %).

- The composition of each type varies from location to location.

Solid Waste Disposal Practices.

If waste is either not reused directly or recycled, there are only three places where the waste can be disposed :

1) Into or onto the land (Landfills)

2) Into the air (Incineration)

3) Into the water (Ocean dumping)

Land disposal of waste :Open dumping cost is low

Sanitary landfills cost is more

According to Resource Conservation & Recovery Act (oct

1976), open dumps are prohibited & directed to develop a

complaince schedule to convert open dumps into sanitary

landfills.

New federal regulations require landfills to be upgraded to meet more strict standards to protect ground water aquifers and other environmental and health factors.

Incineration :

- A common method employed in areas with concentrated populations, where land availability is a problem.

- A method employed for disposal of toxic waste and waste from hospitals.

- Coupling of waste incineration with energy recovery is getting increased attention.

Ocean dumping :

-For many years, this is practiced as an inexpensive & convenient method of waste disposal. But now, as per Marine Protection & Sancturies Act (1972), permit has to be obtained for ocean dumping.

Disposal on Land :

- Suitable for flat land.

- Trench of 2 m deep & 2 – 5 m wide is cut.

- The excavated soil is used to cover the trench.

Trench method

- Quitable in areas where natural depressions exist.

- Waste is put in depressions & compacted.

- A layer of earth is put on the top.

Area method

- Modification of trench & area method.

- A ramp of about 15 m wide, 30 m long & of suitable height is created .

- At the end refuse is compacted along with soil cover so that it becames a part of ramp.

Ramp method

Sanitary landfilling is defined as “method of disposing of

refuse on land without creating nuisance or hazards to

public health or safety, by utilizing the principles of

engineering to confine the refuse to the smallest practical

area, to cover it with a layer of earth at the conclusion of

each day’s operation or at such more frequent intervals as

may be necessary”.

Incineration is defined as a controlled combustion process

for burning solid, liquid or gaseous combustible wastes to

gases & residues containing non-combustible material.

CO2, water vapour, ash & non-combustibles are the end

products.

TTT & O are essential for satisfactory incineration.

Selectional view of a retort multi-chamber incinerator

A Compost Heap. Compost heaps may be age-scale operations or backyard projects. The critical mix sludge organic matter, oxygen and decomposers.

Composers feast on the organic matter and break it down in presence of oxygen into simpler, partly degraded organic mineral components. Compost may then be used as a conditioner.

POWER FOR HANDLING

MATERIAL

RECLPTION OF RAW REFUSE

POWER

SEPARATION & SALVAGE (Removal of plastics, metals, glass

etc

POWER

POWER

POWER

PRETREAIMENT OF COMPOSTABLE MATTER-SIZE REDUCTION, SCREENING ETC.

CONTROLLEO DECOMPOSITION

MARKET PREPARATION

MATURATION

SALVAGED MATERIAL FOR RECYCLE AND

DISPOSAL

Flow chart for a mechanical compost plant

Comparison of Contamination Potentials for Three Types of Disposal

Effects of Ocean Effect of Land Effects of Contaminants Disposal Disposal incineration Pathogens Contamination of No problem if Destroyed by (bacteria, shellfish sludge is stabilized; incineration viruses, and should not apply parasites) sludge on crops grown for raw consumption Metals Mostly nontoxic as Absorpt on of cad- Metals in air a result of chemical mium, zinc, nickel, emissions and changes after and copper poten- ash. dumping tially toxic to plant growth, potential hazard to human health from eating crops contaminated with cadmium Organic Bioconcentration Potential absorption Largely degraded chemicals by fish, a potential by cattle grazing on by incineration, health hazard land where sludge possible formation has been spread, of suspected potential ground carcinogens water contamination by smaller more soluble compounds

Processing methods for the futureProcessing methods for the future1) Pyrolysis : It is the process of heating refuse in a nearly

oxygen-free environment to produce oil, gas and/or char as an end product.

- A ton of solid waste processed in this manner yields energy approximately equivalent of about one barrel of oil.

- It is an endothermic reaction and is carried out at temperatures between 500 – 1000oC.

-The end products have high calorific value and energy recovery can be from 37 to 62%.

2) Biogas production : When solid wastes with a large proportion of organic matter is subjected to anaerobic decomposition, a gaseous mixture (CH4 & CO2) know as biogas can be produced.

- The gas production ranges from 0.29 m3/kg of vs added/day to 0.13 m3/kg of vs added/day in different seasons.

- The sludge has good manurial value (NPK :: 1.6 : 0.85 : 0.93).

- Satisfactory detention period is of about 25 days.

- Methane, thus produced is also a commercially recoverable fuel.

- Los Angeles and california use verted gas from sanitary landfills to proide electricity to 350 and 1,000 homes respectively.

3) Refuse derived fuel systems (RDF system) : In this method, combustibles are separated from non-combustibles.

- The combustibles are then shredded and burned in industrial boilers as a primary fuel or as a supplement to fossil fuels.

- In US, RDF is used to supplement other fuel sources in a ratio of 20% RDF to 80% fossil fuel.

- This method besides reducing cost also helps in reducing the sulphorous emissions.

4) Conversion of SW to protein :

- Laboratory investigations conducted at Louisana State Univ. USA, showed that under aerobic conditions, it is possible to convert the insoluble cellulose contained in muncipal waste by using cellulolytic bacteria.

- The bacteria are then harvested from media to use as protein.

- The process involves size reduction followed by mild allcaline oxidation treatment before aerobic oxidation.

- The single cell protein (SCP0, thus produced has a crude protein content of 50 6 % and has been successfully tested on animals.

- How ever, the process has yet to be tested on full scale basis.

5) Bioconversion : The decomposition of sw can be accelerated artificially by using an aerobic digeoter. Producing end products CH4 & CO2.

- The results can be obtained within a week.- A demonstration Bioconversion plant is in operation in

Florida, since 1978.6) Co-disposal : - An emerging technology cost led as thermal co-disposal.- it involves simultaneous disposal of solid waste and sewage

sludge.- It involves the use of energy from burning solid waste to dry

the sludge to a point at which it will burn without supplemental fuel or in combination with more refuse.

- This method is suggested, because sludge due to its volume & presence of persistant chemicals such as heavy metals, creates problem is disposal and also use of such sludge as fertilizer is questioned moreover, because of its high water content, it can not be burned easily.

7) Other methods : Due to high paper content in the waste from developed countries, a method has been envolved to hydropulp the waste and recover paper fiber from refuse.

- This method is used at Ohio.