Biomedical Engineering Reference
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Hydrogenotrophes
Acetoclasts
Figure10.2
Themethanisationofbiowaste
Many of these have been based more on landfill gas (LFG) generation than truly
representative anaerobic bioreactors, which does lead to some confusion at times.
However, it is generally accepted that the linked, interdependent curves for cel-
lulose decomposition and gas evolution can be broadly characterised as having
five principal stages, outlined below.
•
Stage I
- Peak biowaste cellulose loadings; dissolved oxygen levels fall to
zero; nitrogen, and carbon dioxide tend to atmospheric levels.
•
Stage II
- Carbon dioxide, hydrogen and free fatty acids levels peak; nitrogen
levels fall to around 10%; cellulose begins to be broken down.
•
Stage III
- Carbon dioxide decreases and plateaus, to hold at around 40%;
methane production commences and achieves steady state at around 60%; free
fatty acids decrease to minimum levels; cellulose breakdown continues at a
linear rate with respect to time; nitrogen levels fall to near zero.
•
Stage IV
- Carbon dioxide and methane continue in steady state at c. 40%
and c. 60% respectively; cellulose component reduces steadily.
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