Summary of AFBI digester performance
Following intensive monitoring of the on-farm anaerobic slurry digester at AFBI, Hillsborough during of operation with dairy cow slurry as the input, AFBI has observed that, on average:-
Anaerobic digester at AFBI showing from left to right: feedstock tank; feeder for solids such as grass silage; digester tank; and digestate tank
- 1 tonne of dairy cow slurry at 69g/kg dry matter produced 15.2 cubic meters of biogas containing 85 kWh of energy
- 1 tonne of organic matter in slurry produced 280 cubic meters of biogas (0.28 m3/kg organic matter)
- 32 kWh energy (as heat) per tonne of input slurry was required to maintain mean digester temperature at 37.10C (39% of gross energy produced )
- The available nitrogen concentration in digestate was 19% greater than in raw slurry
- Digestate did not require mixing before land spreading and did not crust
- The average H2S concentration of the biogas was 1,670 ppm.
- The dry matter concentration of digestate was 20% lower than the raw slurry
- The COD of digestate was 28% less than that of raw slurry
- Digester operation required an average of approximately 1.3 person hours per day
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