- cook 2-3 meals or
- operate one refrigerator all day and two lamps for 3 hours or
- operate a 3 kW motor generator for 1 hour.
Of the many alternative forms of agricultural biogas systems, two basic types have gained
widespread acceptance by reason of their time-tested reliability and propagability:
- floating-drum plants with a floating metal gasholder,
- fixed-dome plants with gas storage according to the displacement principle.
The main difference between the two is that the biogas generated in a fixed-dome plant collects in
the domed roof of the digester, while that produced in a floating-drum plant collects in a metal
gasholder. The gasholder, the purpose of which is to cover peak demand, is directly hooked up to
the consumers (kitchen, living quarters, refrigerator, motor generator, . . .) by way of pipes.
Plant construction is effected with as much local material as possible, i.e.:
- bricks, rocks, sand, cement for the digester,
- metal or plastic tubes for the gas pipes,
- metal for the gasholder,
- gas valves, fittings and appliances.
Target groups and applications
The prime field of application for biogas plants is family farms, particularly those engaging in animal
husbandry. Also, biogas plants are a proven successful means of disposal for wastewater and
organic waste. Differentiation is made between the following groups of users:
- Small and medium-sized farms equipped with family-size plants (6-25 m³ digester) use
biogas for cooking and lighting. The installation of a biogas plant usually goes hand in hand
with a transition to either overnight stabling or zero grazing. The modified stabling, coupled
with the more intensive care given to the animals, improves the quality of animal husbandry
as an inherent advantage of biogas technology.
- Specialized stock-farming operations involving the medium to large-scale production of
cattle, pigs and/or poultry can use medium-to-large biogas systems with digester volumes
ranging from 50 m³ upward. The resultant safe disposal of fresh manure is a real
contribution toward environmental protection, particularly with regard to the prevention of
water pollution. Moreover, that contribution is rewarding for the farmer, too, since the biogas
constitutes an autonomous source of energy for production processes.
- For agroindustrial estates and slaughterhouses, the pro-biogas arguments are similar to
those mentioned above in connection with stock farms: safe disposal of potentially
hazardous solid and liquid waste materials, coupled with a private, independent source of
energy for generating electricity, powering coolers, etc.
- Biogas plants in schools, hospitals and other public institutions provide a hygienic means of
toilet/kitchen-waste disposal and a low-cost alternative source of energy. Schools in
particular can serve as multipliers for the dissemination of information on biogas.
5