ABSTRACT
The running of five full scale plants in breeding farms is analized here in relation to their yield. The digesters were operated at HRT between 10 and 40 days with pig, pig and cattle and cattle waste. The digesters fed by pig waste gave a biogas yield between 0.28 and 0.50 m3. kg−1 VSo.d−1 at HRT of 10 – 15 days, at an average organic loading rate of 0.84 – 2.55 kg VS.m−3. d−1, and at a temperature of digestion of 28 – 40°C. One of the plants fed by mixed waste and operated at an organic loading rate of 0.65 – 1.95 kg VS.m−3.d−1 gave a biogas yield of 0.39 – 0.48 m3.kg− VSo.d−1, at a HRT of 20 – 35 days and at a digestion temperature of 30° – 34°C. Plug flow plant operating on cattle waste gave a biogas yield of 0.25 – 0.40 m.kg−1 VSo.d−1, at a HRT of 24 – 40 days, at an organic loading rate of 2.7 – 4.6 kg VS.m−3.d−1 and at a digestion temperature above 35°C. The organic loading rate and the biogas production were lower than expected due to problems of the settling of solids in the piggeries, to a difficult flow in the sewage and to an animal live weight lower than that of design data.
