Performance, operation and benefits of an anaerobic digestion system on a closed piggery farm

Abstract In February, 1981, a closed piggery farm with forty-five productive sows and 300 fattening pigs started to use biogas produced in an anaerobic digester treating pig manure. The biogas plant was installed by the farmer himself under the supervision of the Faculty of Agricultural Sciences, State University of Gent. Raw pig manure (5–6% dry matter) is pumped from the holding pits to a cylindrical reactor (73 m 3 working volume) which operates in the mesophilic temperature range with hydraulic residence times of about 40–50 days and low loading rates. Completely automated plant operation ensures a continuous biogas production. The steady-state production corresponds to 18–20 m 3 biogas (65–70% CH 4 ) per cubic metre pig slurry. The biogas replaces fuel oil for heating farrowing units. During the first year of operation, the 8600 m 3 of biogas produced replaced half of the fuel oil consumption. After the expansion of the piggery houses to 600 fattening pigs, the farm will be self-supporting in its fuel supply. This will produce a saving of 140 000 BF a year. The investment costs of the digestion system were low (400 000 BF or ca . 8000 US dollars) because the farmer constructed the plant by himself.