16568045 methods of waste disposal

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WASTE MANAGEMENT

Waste managementis the collection, transport, processing, recyclingor disposal

of waste materials. The term usually relates to materials produced by human

activity, and is generally undertaken to reduce their effect on health, the

environment or aesthetics. Waste management is also carried out to recover

resources from it. Waste management can involve solid, liquid, gaseous or

radioactivesubstances, with different methods and fields of expertise for each.

Waste management practices differ for developed and developing nations, for

urban and rural areas, and for residential and industrial, producers. Managementfor non-haardous residential and institutional waste in metropolitan areas is

usually the responsibility of local governmentauthorities, while management for

non-haardous commercial and industrial waste is usually the responsibility of the

generator.

!olid Waste "isposal, disposal of normally solid or semisolid materials, resulting

from human and animal activities, that are useless, unwanted, or haardous. !olid

wastes typically may be classified as follows#

Garbage:decomposable wastes from food

Rubbish:non decomposable wastes, either combustible $such as paper, wood, and

cloth% or noncombustible $such as metal, glass, and ceramics%

Ashes:residues of the combustion of solid fuels

Large wastes:demolition and construction debris and trees

Dead animals

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Sewage-treatment solids: material retained on sewage-treatment screens, settled

solids, and biomass sludge

Industrial wastes:such materials as chemicals, paints, and sand

Mining wastes:slag heaps and coal refuse piles

Agricultural wastes:farm animal manure and crop residues.

WASTE MANAGEMENT METHODS

Waste management methods vary widely between areas for many reasons,

including type of waste material, nearby land uses, and the area available.

DISPOSAL METHODS

1. LANDFILL

"isposing of waste in a landfill involves burying waste to dispose it off, and this

remains a common practice in most countries. &andfills were often established in

abandoned or unused quarries, miningvoids orborrow pits. ' properly-designed

and well-managed landfill can be a hygienic and relatively inexpensive method of

disposing of waste materials. (lder, poorly-designed or poorly-managed landfills

can create a number of adverse environmental impacts such as wind-blown litter,

attraction of vermin, and generation of liquid leachate. 'nother common byproduct

of landfills is gas $mostly composed of methane and carbon dioxide%, which is

produced as organic waste breaks down anaerobically. This gas can create odor

problems, kill surface vegetation, and is a greenhouse gas.

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!anitary landfill is the cheapest satisfactory means of disposal, but only if suitable

land is within economic range of the source of the wastes) typically, collection and

transportation account for *+ percent of the total cost of solid waste management.

n a modern landfill, refuse is spread in thin layers, each of which is compacted by

a bulldoer before the next is spread. When about m $about / ft% of refuse hasbeen laid down, it is covered by a thin layer of clean earth, which also is

compacted. 0ollution of surface and groundwater is minimied by lining and

contouring the fill, compacting and planting the cover, selecting proper soil,

diverting upland drainage, and placing wastes in sites not sub1ect to flooding or

high groundwater levels. 2ases are generated in landfills through anaerobic

decomposition of organic solid waste. f a significant amount of methane is

present, it may be explosive) proper venting eliminates this problem.



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2. INCINERATION

ncineration is a disposal method that involves combustion of waste material.

ncineration and other high temperature waste treatment systems are sometimes

described as 3thermal treatment3. ncinerators convert waste materials into heat,

gas, steam, and ash.

ncineration is carried out both on a small scale by individuals and on a large scale

by industry. t is used to dispose of solid, liquid and gaseous waste. t is recognied

as a practical method of disposing of certain haardous wastematerials $such as

biological medical waste%. ncineration is a controversial method of waste disposal,due to issues such as emission of gaseouspollutants.

ncineration is common in countries such as 4apanwhere land is more scarce, as

these facilities generally do not require as much area as landfills. waste-to-energy

$Wt5% or energy-from-waste $5fW% are broad terms for facilities that burn waste in

a furnace or boiler to generate heat, steam and6or electricity. 7ombustion in an

incinerator is not always perfect and there have been concerns about micro-

pollutants in gaseous emissions from incinerator stacks. 0articular concern has

focused on some very persistent organics such as dioxinswhich may be created

within the incinerator and which may have serious environmental consequences in

the area immediately around the incinerator. (n the other hand this method

produces heat that can be used as energy.

3. RECYCLING METHODS

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The process of extracting resources or value from waste is generally referred to as

recycling, meaning to recover or reuse the material. There are a number of different

methods by which waste material is recycled# the raw materials may be extracted

and reprocessed, or the calorific content of the waste may be converted to

electricity. 8ew methods of recycling are being developed continuously, and are

described briefly below.

PHYSICAL REPROCESSING

The popular meaning of 9recycling: in most developed countries refers to the

widespread collection and reuse of everyday waste materials such as empty

beverage containers. These are collected and sorted into common types so that theraw materials from which the items are made can be reprocessed into new

products. Material for recycling may be collected separately from general waste

using dedicated bins and collection vehicles, or sorted directly from mixed waste

streams.



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The most common consumer products recycled include aluminumbeverage cans,

steel food and aerosol cans, ;"05 and 05T bottles, glass bottles and 1ars,

paperboard cartons, newspapers, magaines, and cardboard. (ther types of plastic

$0


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'n example of waste management through composting is the 2reen =in 0rogram

in Toronto, 7anada, where household organic waste $such as kitchen scraps and

plant cuttings% are collected in a dedicated container and then composted.

ENERGY RECOERY

The energy content of waste products can be harnessed directly by using them as a

direct combustion fuel, or indirectly by processing them into another type of fuel.

>ecycling through thermal treatment ranges from using waste as a fuel source for

cooking or heating, to fuel forboilersto generate steam and electricity in a turbine.

0yrolysisand gasificationare two related forms of thermal treatment where waste

materials are heated to high temperatures with limited oxygen availability. The

process typically occurs in a sealed vessel under highpressure. 0yrolysis of solid

waste converts the material into solid, liquid and gas products. The liquid and gas

can be burnt to produce energy or refined into other products. The solid residue

$char% can be further refined into products such as activated carbon. 2asification

and advanced 0lasma arc gasificationare used to convert organic materials directly

into a synthetic gas $syngas% composed of carbon monoxideand hydrogen. The gas

is then burnt to produce electricity and steam.

!. COMPOSTING

7omposting operations of solid wastes include preparing refuse and degrading

organic matter by aerobic microorganisms. >efuse is presorted, to remove

materials that might have salvage value or cannot be composted, and is ground up

to improve the efficiency of the decomposition process. The refuse is placed in

long piles on the ground or deposited in mechanical systems, where it is degraded

biologically to a humus with a total nitrogen, phosphorus, and potassium content of

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16568045 methods of waste disposal

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