Incineration, the combustion of organic material such as waste with
energy recovery, is the most common Waste to Energy implementation.
Incinerators reduce the volume of the original waste by 95-96 percent,
depending upon composition and degree of recovery of materials such as
metals from the ash for recycling
Incinerators have electric efficiencies of 14-28%. In order to
avoid losing the rest of the energy, it can be used for e.g. district
heating (cogeneration). The total efficiencies of cogeneration
incinerators are typically higher than 80% (based on the lower heating
value of the waste).
The method of using incineration to convert municipal solid waste
(MSW) to energy is a relatively old method of Waste to Energy
production. Incineration generally entails burning waste (residual MSW,
commercial, industrial and RDF) to boil water which powers steam
generators that make electric energy and heat to be used in homes,
businesses, institutions and industries. One problem associated with
incinerating Municipal Solid Waste to make electrical energy, is the
potential for pollutants to enter the atmosphere with the flue gases
from the boiler. These pollutants can be acidic and in the 1980s were
reported to cause environmental damage by turning rain into acid rain.
In thermal Waste to Energy technologies, nearly all of the carbon
content in the waste is emitted as carbon dioxide (CO2) to the
atmosphere (when including final combustion of the products from
pyrolysis and gasification; except when producing bio-char for
fertilizer). Municipal solid waste (MSW) contain approximately the same
mass fraction of carbon as CO2 itself (27%), so treatment of 1 metric
ton (1.1 short tons) of MSW produce approximately 1 metric ton (1.1
short tons) of CO2.
In the event that the waste is landfilled, 1 metric ton (1.1 short
tons) of MSW would produce approximately 62 cubic metres (2,200 cu ft)
methane via the anaerobic decomposition of the biodegradable part of the
waste. This amount of methane has more than twice the global warming
potential than the 1 metric ton (1.1 short tons) of CO2, which would
have been produced by combustion. In some countries, large amounts of
landfill gas are collected, but still the global warming potential of
the landfill gas emitted to atmosphere In addition, nearly all
biodegradable waste is biomass. That is, it has biological origin. This
material has been formed by plants using atmospheric CO2 typically
within the last growing season. If these plants are regrown the CO2
emitted from their combustion will be taken out from the atmosphere once
more.
Another very dangerous chemical found in the solid waste is Dioxin.
Dioxins are environmental pollutants. They belong to the so-called
“dirty dozen” - a group of dangerous chemicals known as persistent
organic pollutants (POPs). Dioxins are of concern because of their
highly toxic potential. Experiments have shown they affect a number of
organs and systems. Once dioxins enter the body, they last a long time
because of their chemical stability and their ability to be absorbed by
fat tissue, where they are then stored in the body.
The chemical name for dioxin is: 2,3,7,8- tetrachlorodibenzo para
dioxin (TCDD). The name "dioxins" is often used for the family of
structurally and chemically related polychlorinated dibenzo para dioxins
(PCDDs) and polychlorinated dibenzofurans (PCDFs). Certain dioxin-like
polychlorinated biphenyls (PCBs) with similar toxic properties are also
included under the term “dioxins”. Some 419 types of dioxin-related
compounds have been identified but only about 30 of these are considered
to have significant toxicity, with TCDD being the most toxic.In terms
of dioxin release into the environment, uncontrolled waste incinerators
(solid waste and hospital waste) are often the worst culprit dioxin
disturbs the endocrine balance in the reproductive systems of women in
particular. Endometriosis, spontaneous abortion and complicated
pregnancies may result from dioxin poisoning in women.
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