Filling the plant
Filling means: mixing the substrate with water, removing bouyant materials, allowing the fill material
to warm up, flushing it into the digester, and removing sand and stones. The simple mixing pit
shown in figure 5.16 can handle a daily fill quantity of up to 500 1.
Digested-slurry storage/utilization
The further processing of digested slurry is a critical point in that it can be quite toilsome (cf. chapter
3.4).
In designing the plant, care must be taken to ensure that the slurry store will be large enough.
Fixed-dome plants in particular should be equipped with an overflow, so that the digested slurry
does not have to be hauled away every day.
Daily activities:
- fill the plant
- clean the mixing pit
- agitate the digester contents
- check the gas pressure
- check the gasholder contents
- check the appearance and odor of the digested slurry
Weekly/monthly activities:
- remove/use the digested slurry
- clean and inspect the gas appliances
- check the gas valves, fittings and appliances for leaks
- inspect the water trap
Annual activities:
- inspect the digester for scum formation and remove as necessary by opening the plant
- inspect the plant for water tightness and gas tightness
- pressure-test the gas valves, fittings and pipes
- check the gasholder for rust and repaint as necessary
Monitoring the process
If the plant is properly started before being handed over to the user, it may be assumed to be in
proper working order. The user will have become familiar with what optimum plant operation
involves. This is very important, because from then on he himself will have to watch for any
appreciable changes in how the plant functions; the main indication of a beginning malfunction is a
change in the daily gas output.
7.3 Plant maintenance
The maintenance scope for a biogas plant includes all work and inspections needed to ensure
smooth functioning and long service life. To the extent possible, all maintenance work should be
done by the user.
Biogas plants can develop a number of operational malfunctions. The most frequent problem,
"insufficient gas production", has various causes. Often enough, it takes the work of a "detective" to
locate and remedy the trouble. It may be necessary to experiment with and monitor the plant for
months on end in cooperation with the user.
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