FEATURE
Demystifying anaerobic
digesters of agricultural waste
By Nita Karume
A
gricultural waste represents one
of the largest anthropogenic
sources of methane present in
the atmosphere. Anaerobic digesters
can turn these wastes into biogas
as renewable energy, containing
at least 50% of methane, and the
solid residues into fertilizers rich in
nutrients. Anaerobic digestion has
a long history and many different
digesters are implemented all around
the world in farms.
There is no standard designed digester
for different reasons: in one hand, the
situations are very diverse in operating
conditions and in the other one, there
remain many research issues still
incomplete concerning microbiology,
microbial ecology, metabolic pathways,
modelling, technology.
14 |November - December 2018
Biogas industry in South Africa
The South African biogas industry
is in its infancy. One of the factors
hampering the development of the
industry are general poor impressions
in the Food and Agro-industries,
including the notion that Biogas does
not work. This is either as an organic
waste management technology, or as
a source of renewable energy. Another
would be the belief that biogas is
prohibitively expensive and that Solar
Energy is a more reliable and more
cost-effective technology in its stead. South African renewable energy scene,
biogas as a technology has been
highly successful in both Europe and
the developing world. The Anaerobic
Digestion process, wherein organic
compounds are broken down through
the inter-action of colonies of anaerobic
bacteria to produce biogas (a mixture
of approximately 65% Methane, and
35% Carbon Dioxide), is naturally
occurring. A modern biogas plant
simply contains and controls this
naturally occurring process, to regulate
and optimise the production of biogas.
Global Energy is determined to
debunk these myths and present an
alternative, fact-based, perspective. In Germany alone, there are over
10 000 biogas plants in operation,
and in countries such as China and
India, the number of biogas digesters
runs to tens of millions. So clearly
there is little doubt that the process
Biogas does not work
While a relative new-comer on the