Digester loading:
Ld = TS/VS-input: Vd
Ld = 18: 18 = 1.0 kgTS/m³ Vd
Ld = 12: 18 = 0.7 kg VS/m³ Vd
Gasholder volume:
Vg = 1.6 m³, as calculated on the basis of:
consumption volume:
Vg1 = 0.175 m³/h x 2 flames x 3 h = 1.05 m3
Storage volume:
Vg2 = 10 h x 0.15 m³ gas/h = 1.5 m³
Vd:Vg=18: 1.6=11 :1
5. Biogas technique
The design aspects dealt with below concentrate solely on the principles of construction and
examples of simple biogas plants, i.e. plants:
- for small family farms requiring digester volumes of between 5 m³ and 30 m³,
- with no heating or temperature control,
- with no motor-driven agitators or slurry handling equipment,
- with simple process control,
- built with (at least mostly) local materials,
- built by local craftsmen.
Fig. 5.1: Three-stage anaerobic
fermentation (Source: Baader et.
al 1978)
5.1 Fundamental principles, parameters, terms
Biochemical principles
The generation of biogas by organic conversion (anaerobic fermentation) is a natural biological
process that occurs in swamps, in fermenting biomass and in intestinal tracts, particularly those of
ruminants.
The symbiotic relationships existing between a wide variety of microorganisms leads, under air
exclusion, to the degradation and mineralization of complex biomass in a sequence of intermeshing
stages. The resultant biogas, consisting primarily of methane (CH4) and carbon dioxide (CO2) and
the mineralized slurry constitute the ultimate catabolites of the participating bacteria and residual
substances.
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