Startup of an anaerobic single stage digester with a fixed wheat straw bed

The most common form of technology for energy utilization via anaerobic treatment is slurry digestion with
a low solids contents, such as sewage sludge or manure.
Process control and maintenance are relatively simple, but costs involved with liquid handling and heating
favour large, centralised plants. Raising the solids content of a digester to 30% significantly improves the
economy of anaerobic digestion, increasing the methane production per volume unit reactor, and avoiding
the handling and heating of large volumes of process water.
One simple and potentially cheap method of high-solids reactor implementation is a single stage fixed bed
reactor, with a solid substrate as the bed and a recycled leachate stream One potential problem with this design is an initial organic acid production during reactor startup, which originates from the easily degradable substrate. A low initial loading rate gives a safer but prolonged startup, and decreases gas production in this period. The choice of substrate strongly influences the probability of clogging. A more careful choice of carrier material allows quicker startup, and reduces the risk of clogging. The material
should degrade slowly, to avoid overload during startup, and have a rigid structure in order to avoid clogging.
This bed can then be fed from the top with more easily degradable substrate, e.g. crop residue. In this study, we
demonstrate startup of a single stage wheat straw (low biodegradability) reactor in a fixed bed.