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

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Process flexibility is one of the advantages of multi-stage systems. However,
this flexibility also increases cost <strong>and</strong> complexity by requiring additional
reactors, material h<strong>and</strong>ling <strong>and</strong> process control systems. On the opposite end
of the spectrum, batch or sequential batch systems aim to reduce complexity
<strong>and</strong> material h<strong>and</strong>ling requirements. As opposed to continuous wet <strong>and</strong> dry
systems, the feedstock does not need to be carefully metered into a batch
reactor, thereby eliminating the need for complex material h<strong>and</strong>ling
equipment. The primary disadvantage of batch digesters is uneven gas
production <strong>and</strong> lack of stability in the microbial population. To surmount these
issues, batch systems can also be combined with multi-stage configurations.
Batch Reactors: are loaded with feedstock, subjected to reaction, <strong>and</strong> then are
discharged <strong>and</strong> loaded with a new batch. Substrate is sealed in the digester for
the complete retention time. When unmixed, the content of the digester
stratifies into layers of gas, scum, supernatant, an active layer, <strong>and</strong> stabilized
solids at the bottom. Retention times range from 30-60 days, with typically an
organic loading rate between 0.5 <strong>and</strong> 1.6 kg TVS/m 3 reactor volume/day. There
are three types of batch systems (Figure 12.):
Figure 12.: The (3) types of batch reactors systems
(EPA., 2008)
‣ Single stage batch
‣ Sequential batch system
‣ Up flow Anaerobic Sludge Blanket reactor
The single-stage batch system involves re-circulating the leachate to the top of
the same reactor. An example of such a system is the Biocel process in Lelystad,