biogas plant can also play an important role and are described seperatly: Heating systems,
pumps, weak ring.
Construction details
The section on construction of biogas plants provides more information on:
• Agitation
• Heating
• Piping systems
• Plasters and Coats
• Pumps
• Slurry equipement
• Underground water
Starting the plant
Initial filling
The initial filling of a new biogas plant should, if possible, consist of either digested slurry
from another plant or cattle dung. The age and quantity of the inoculant (starter sludge) have
a decisive effect on the course of fermentation. It is advisable to start collecting cattle dung
during the construction phase in order to have enough by the time the plant is finished. When
the plant is being filled for the first time, the substrate can be diluted with more water than
usual to allow a complete filling of the digester.
Type of substrate
Depending on the type of substrate in use, the plant may need from several days to several
weeks to achieve a stable digesting process. Cattle dung can usually be expected to yield
good gas production within one or two days. The breaking-in period is characterized by:
• low quality biogas containing more than 60% CO2
• very odorous biogas
• sinking pH and
• erratic gas production
Stabilization of the process
The digesting process will stabilize more quickly if the slurry is agitated frequently and
intensively. Only if the process shows extreme resistance to stabilization should lime or more
cattle dung be added in order to balance the pH value. No additional biomass should be put
into the biogas plant during the remainder of the starting phase. Once the process has
stabilized, the large volume of unfermented biomass will result in a high rate of gas
production. Regular loading can commence after gas production has dropped off to the
expected level.
Gas quality
As soon as the biogas becomes reliably combustible, it can be used for the intended
purposes. Less-than-optimum performance of the appliances due to inferior gas quality
should be regarded as acceptable at first. However, the first two gasholder fillings should be
vented unused for reasons of safety, since residual oxygen poses an explosion hazard.
Managing input- and output-material
Substrate input
For a simple, small-scale biogas system, only a minimum amount of time and effort must be
spent on procuring the feedstock and preparing it for fermentation. The technical equipment
is relatively inexpensive. Theoretically any organic material can be digested. Substrate pre-
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