1. There are four key biological/ chemical
reaction stages of anaerobic digestion:
- Hydrolysis
- Acidogenesis
- Acetogenesis
- Methanogenesis
2. Almost any organic matter can be
digested anaerobically. Not all will produce enough biogas to be
viable though.
3. Anaerobic digestion occurs in nature at
all temperatures, but below 10 degrees centigrade the rate
of biogas
production is so slow that running a biogas process is usually considered not
viable, for
any form of biogas generation system.
4. There are two temperature ranges over
which the many micro-organisms which produce biogas
work most efficiently.
These are known as the:
- Mesophilic
- Thermophilic
Temperature ranges, with the optimum
temperature usually considered to be at the top of the range.
5. The process is truly ancient:
- Fermentation for the production of alcohol was known to the Ancient Egyptians and is recorded as far back as 2,000 BC.
- The methane producing stage of anaerobic digestion is performed by a type of micro-organism known as archaea. It's not a bacteria. In fact in comes from a distinctly different branch of the phylogenetic tree of life to bacteria.
Benefits of Anaerobic Digestion
a) Environmental Benefits
- Reduces carbon emissions and can contribute to national renewable energy targets
- Only biogas (and some carbon dioxide) is taken out, so valuable nutrients are recycled back into the soil
- Digestate may also be used as a feedstock for other biofuel production and for innovative fibre building materials
- AD creates skilled ‘green’ jobs and contributes to growth in the local economy
- When used in conjunction with segregated municipal waste collection, it reduces waste sent to landfill
- Sanitizes waste output providing a reduced public health hazard/ reduces pollution risk.
b) Benefits to Those That Own and Operate AD Plants
- Landfill taxation costs reduced, transportation costs can be less
- Owning an AD plant lends authority to the owner organizations green credentials
- Possible government incentive payments available
- Secures a reliable long-term waste disposal route for the plant owners own waste
- Potential for truly profitable sales of outputs.
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