II.
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Contact reactor
Another way to solve the problem of escaping bacteria is the contact digester. The
contact system uses a digester tank similar to a complete mix reactor, but the solids in the
effluent are piped back into the influent entering the digester tank. This means (1) the
bacteria tends to stay in the reactor rather than simply being pumped out, and (2) the solid
matter goes through the reactor several times, so that the solids retention time (SRT) ends
up being several times the hydraulic retention time (HRT). [9]
This increases the
methane yield from a given feedstock.
Acid Phased Reactor
This reactor type splits the digestion into two tanks, the first for acid formation and the
second for methane formation. Methane-forming bacteria are slower to grow than the
other bacterial populations, so whereas a single tank requires a large volume to allow the
methanogens to regenerate, the phased approach allows a reduced size for the first tank.
[9]
Temperature Phased Reactor
This reactor arrangement consists of a thermophilic reactor followed by a mesophilic reactor.
The first reactor destroys the pathogens and rapidly digests part of the feedstock, while the
second reactor deals with the odour in the first reactor’s effluent and further digests the material.
[9].