Operation and Use
The day-to day operation of a biogas unit requires a high level of discipline and routine to
maintain a high gas production and to ensure a long life-span of the biogas unit. Many
problems in the performance of biogas plants occur due to user mistakes or operational
neglect. Often, these problems can be reduced,
• by less complicated designs that are adapted to the substrate, the climatic conditions
and the technical competence of the user,
• by high-quality and user-friendly appliances,
• by design and lay-out of the biogas for convenient work routine,
• by proper training and easy access to advice on operation problems.
During design selection, planning, construction, handing over and follow-up, the biogas
extension program should emphasize further on a reduction of the users’ workload for
operating the biogas unit and using the gas and the slurry. In particular during work peaks for
farm work, it is important that the biogas unit relieves the user from work rather than adding
to the workload. As a general rule, the farming family should have less work with a biogas
unit than without it, while enjoying the additional benefits in terms of a clean fuel and high
quality fertilizer.
Daily operation
Feeding of the digester
In larger biogas units, the dung, urine and other substrate usually enter the plant by pipes,
channels, belts or pumps. The available substrate has to enter the digester as soon as it is
available to avoid pre-digestion outside the digester. The functioning of the feeding
mechanisms has to be checked daily. Separators for unsuitable material have to be checked
and emptied. The amounts of substrate fed into the digester may be recorded to monitor the
performance of the biogas plant.
Smaller plants in developing countries are fed by hand. The substrates, often dung and
urine, should be thoroughly mixed, plant residues should be chopped, if necessary.
Obstructive materials like stones and sand should be removed from the mixing chamber.
Simple tools like a rubber squegee, a dipper, forks to fish out fibrous material, proper buckets
and shovels greatly facilitate this work. Filling work is further made easier by smooth
concrete stable-floors and a minimized distance between the stable and the plant.
Agitation
In industrialized countries and for large plants in developing countries, engine driven stirring
devices are the norm. Usually, but not always, they are operated automatically. The user,
however, should check the operation of the stirring device daily.
Small size biogas plants have manual stirring devices that have to be turned by hand as
recommended. If there is no stirring device, poking with sticks through the inlet and outlet is
recommended. The stick should be strong, long enough but not too heavy. It should have a
plate fixed at the end (small enough to fit in the inlet-/outlet pipes) to produce a movement of
the slurry. Regular poking also ensures that the inlet/outlet pipes do not clog up. The drums
of floating drum plants should be turned several times a day.
Experience shows that stirring and poking is hardly ever done as frequently as it should be.
Farmers should be encouraged to run a trial on gas production with and without stirring. The
higher gas production will convince the user more than any advice.
Controlling the overflow
A special problem of small scale fixed dome plants is the clogging up of the overflow point.
This can lead to over-pressure (the hydraulic pressure increases with the slurry level in the
expansion chamber) and to clogging of the gas outlet if too much slurry flows back into the
digester. The overflow point should, therefore, be checked and cleaned daily.
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