(best examples and good practices) on household organic waste ...

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2.2 Anaerobic Digestion (AD)
2.2.1.Introduction
Anaerobic digestion can be defined as the biological process during which the
complex organic matter is decomposed by anaerobic microorganisms due to
the absence of oxygen. Anaerobic microorganisms degrade the organic matter
producing mainly CO2,CH4 water <strong>and</strong> stabilized organic matter (digestate).
During the process CH4 can be collected <strong>and</strong> used as an energy source. (
Balkwaste, 2010)
Anaerobic digestion (AD) is typically employed in many wastewater treatment
facilities for sludge degradation <strong>and</strong> stabilization, <strong>and</strong> it is the principal
biological process occurring in l<strong>and</strong>fills. Internationally, AD has been used for
decades, primarily in rural areas, for the production of biogas for use as a
cooking <strong>and</strong> lighting fuel. Nowadays, AD is used for the production of thermal
energy that heats water (circulated with water pipes) to proper temperatures
for the drying of organic material such as sludge <strong>and</strong> kitchen waste. Also many
small scale (household) anaerobic digesters are operational in China <strong>and</strong> India
for waste treatment <strong>and</strong> gas production. In the recent decades, Europe has
developed large-scale centralized systems for municipal solid waste treatment
with electricity generation as a co-product. (EPA., 2008)
2.2.2 The applications of the AD process in the Society
Anaerobic digestion of animal manure, manure is maybe the most common
utilization of AD-technologies. There are several million low technology
installations in Asia providing biogas for cooking <strong>and</strong> lighting <strong>and</strong> many more
AD plants in Europe <strong>and</strong> North America. (EPA., 2008)
The AD process is applied to countries with large animal manure quantities per
year <strong>and</strong> they have strict rules for the quality of the final stabilized product.
There are two main concepts of manure based biogas production: the large
scale, co-digestion plant <strong>and</strong> the small farm scale biogas plant. (Al Seadi., 2003)
Another AD application is the treatment of primary <strong>and</strong> secondary sludge
resulted from the aerobic treatment of municipal wastewater which is common
to many modern countries especially in the European Union. The system is
widely utilized in thous<strong>and</strong>s of installations in the industrialized world <strong>and</strong>
connects with the municipal wastewater treatment systems. The anaerobic
digestion process is used to stabilize <strong>and</strong> reduce the final amount of sludge. The
digestate is used as a fertilizer on agricultural l<strong>and</strong>, dried <strong>and</strong> incinerated or
l<strong>and</strong>filled. Especially the biogas which is produced is mainly used as a
wastewater treatment plant energy source (partly).Though in order for a