Anaerobic co-digestion of meat-processing by-products and sewage sludge – Effect of hygienization and organic loading rate

Anaerobic co-digestion of a mixture of animal by-products (ABP) from meat-processing industry and of sewage sludge was studied at 35 °C for co-digesting such by-products in digesters at wastewater treatment plants. The three reactors were fed with ABP mixture and sewage sludge (1) in a ratio of 1:7 (v/v), (2) in the same ratio but with hygienization (70 °C, 60 min) and (3) in a ratio of 1:3 (v/v). Hydraulic retention time (HRT) was decreased from 25 to 20 days and finally to 14 days, while organic loading rates (OLR) ranged from 1.8 to 4.0 kg VS/m3 day. The highest specific methane yields were achieved with 20-days-HRT (1) 400 ± 30, (2) 430 ± 40, (3) 410 ± 30 m3 CH4/t VS. Hygienization improved methane production to a level above the highest OLR applied (feed ratio 1:3 (3)), while the quality of the digestate remained similar to the other reactors.