Performance evaluation of a Chinese medium‐sized agricultural biogas plant at ambient temperature

Abstract

Many Chinese biogas plants run at the lower range of mesophilic conditions. In this study, the performance of a representative agricultural biogas plant operating at ambient temperature was evaluated by mass balance and routine chemical analysis. Fluxes into and out of the biogas plant (organic dry matter [ODM], biogas production, CH4, and CO2 concentration) were analyzed for seven weeks. The biogas plant was operated with mixed substrate at an extremely low organic loading rate (0.4–0.8 kg ODM m−3 d−1), with a hydraulic retention time (HRT) of 35 days. Between 68% and 73% of ODM fed to the plant was converted to biogas. The measured methane production on‐site was higher than the estimated methane production derived from ODM input/output data for the plant and methane production data from batch tests on the individual substrates at 37°C and 20°C. Suggested reasons were: (i) difficulties in precise determination of mass fluxes, (ii) sediment in the biogas plant contributing to biogas production, (iii) stimulation of biogas production by mixed substrate, and (iv) potential gas production of activated organic matters from the time before the monitoring program. A heating system and power unit are suggested to improve the overall performance of the digester.