Investigation on large and medium scale biogas plants and biological properties of digestate in Jiangsu province

Biogas plant construction has rapid development in recent years. However, studies on its operation and management were few, especially for large and medium-sized ones. To explore the problems existing in operation and management, a field investigation on 21 plants of large and medium-sized biogas was carried out in intensive pig and dairy farms in Jiangsu province. The investigation included the operation status of the plants and the raw materials and digestion slurry was sampled to analyze the content of COD, residual biogas production and the count of fecal coliform. Results showed that the design and construction of all the biogas plants was performed by professional company with well-appointed facilities, whereas the biogas volume produced and the utilization of biogas and digestion slurry were low. The main raw materials for anaerobic digestion were waste water from pig and dairy farms, with low content of total solid (i.e., TS < 3%). Most raw materials could not be digested completely. COD contents from 62% digestion slurry samples were more than 5 000 mg/L, which caused appreciable quantities of methane produced from digestion slurry. Twelve digestion slurry samples could produce methane more than100 mL/L at 35℃. Anaerobic digestion could significantly reduce the survival of fecal coliform, reaching 92.9% on average. However, the digestion slurry still contained high concentrations of fecal coliform, which could not reach the requirement of sanitary. These results could provide a theoretical reference for the stable and healthy operation and management of large and medium-sized biogas plants.