Page last updated 30/08/2018
Chapter 4 How Biogas works
The making of biogas (methane and carbon dioxide) from
food materials is an anaerobic microbiological process,
involving a symbiotic population of microbes (bacteria and
archaea). The process requires the right conditions, such as
pH, temperature, retention time, the chemical and physical
nature of the feed, and moisture content. There are several
ways in which an anaerobic digester can be run, such as in
batch, continuous or semi-continuous modes. Different
approaches to the process include using stirred tanks (CSTR),
plug flow, upflow sludge blanket (UASB), anaerobic filters and
baffled reactors. There are also different ways to pre-process
the feed including chopping and pre-digestion using flooded
pre-digesters and leach beds. The quality of the feed material
can be monitored using different parameters, such as TS
(Total Solids), VS (Volatile Solids), COD (Chemical Oxygen
Demand), BOD (Biological Oxygen Demand), batch or semi-
continuous tests. The process can be mathematically
modelled. (72 references).
http://dx.doi.org/10.3362/9781780448497.004
The value of anaerobic digestion to produce compost has
received little interest until recent years. Biogas effluent
slurry, or bio-slurry, is increasingly seen as having value, not
only as a fertilizer, but also in reducing crop disease and
acting as a soil conditioner. Its use has lasting effects on the
soil. The ways in which it is processed affect the value of the
product: composting and vermi-composting increase its
usefulness. The benefits of bio-slurry are shown by the
results from many practical examples. (33 references).
http://dx.doi.org/10.3362/9781780448497.005
From the wide range of biogas digester designs, only a few
meet the criteria for use in the programmes in Asia which
have been made in large numbers. The floating drum system
was developed in India, but has largely been replaced by
fixed dome systems. Fixed dome systems were developed in
China and the two main approaches are to use a dome made
from brick or concrete. There are several aspects that are
common to both fixed dome designs: such as how the dome
is sealed, how reservoir pits are made, the covers over
reservoir pits and inlet pits. Various attempts have been
made to adapt such plants for climates that have lower
ambient temperatures. (21 references).
http://dx.doi.org/10.3362/9781780448497.006
Note: clicking on a dx.doi link gives a list of references in that
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Small-scale Rural Biogas Programmes
Chapter Abstracts - 2