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

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Figure 10.: AD basic process description
(Southern Energy Network., 2009)
For the dilution, a wide range of different kind of water sources may be used
such as clean water, sewage sludge, or re-circulated liquid from the digester
effluent. In order for the temperature in the digesting vessel to be maintained
inside the vessel, a heat exchanger is usually required. The final product
(biogas) obtained this way is scrubbed to obtain pipeline quality gas. In case of
residue treatment, the effluent from the digester is dewatered, <strong>and</strong> the liquid
recycled for use in the dilution of incoming feed. The biosolids finally are been
composted. (EPA., 2008)
Digesters range in complexity from simple, empty cylindrical cans with no
moving parts to fully automated <strong>and</strong> integrated industrial facilities. The
simplest are easy to design <strong>and</strong> maintain, but require consistent monitoring
<strong>and</strong> are less efficient. The most complex, on the other h<strong>and</strong>, are designed to
detect subtle changes in conditions, such as may occur with small changes in
feedstock feed rate, concentration, <strong>and</strong> quality. (Buekens.,2005)