Effects of Temperature and Carbon-Nitrogen (C/N) Ratio on the Performance of Anaerobic Co-Digestion of Dairy Manure, Chicken Manure and Rice Straw: Focusing on Ammonia Inhibition

TLDR

Anaerobic digestion is a promising alternative for disposing organic waste, and co‑digestion of mixed wastes has recently gained interest. The study examined how temperature and C/N ratio affect anaerobic co‑digestion of dairy manure, chicken manure, and rice straw. Higher temperatures increased methane potential, yet the rate dropped from mesophilic to thermophilic conditions because of ammonia inhibition; significant inhibition occurred at C/N 15 (35 °C) and C/N 20 (55 °C), but raising the C/N ratio to 25–30 mitigated this effect and maximized methane production, indicating an interactive temperature‑C/N relationship that requires higher C/N at elevated temperatures to avoid inhibition.

Abstract

Anaerobic digestion is a promising alternative to disposal organic waste and co-digestion of mixed organic wastes has recently attracted more interest. This study investigated the effects of temperature and carbon-nitrogen (C/N) ratio on the performance of anaerobic co-digestion of dairy manure (DM), chicken manure (CM) and rice straw (RS). We found that increased temperature improved the methane potential, but the rate was reduced from mesophilic (30∼40°C) to thermophilic conditions (50∼60°C), due to the accumulation of ammonium nitrogen and free ammonia and the occurrence of ammonia inhibition. Significant ammonia inhibition was observed with a C/N ratio of 15 at 35°C and at a C/N ratio of 20 at 55°C. The increase of C/N ratios reduced the negative effects of ammonia and maximum methane potentials were achieved with C/N ratios of 25 and 30 at 35°C and 55°C, respectively. When temperature increased, an increase was required in the feed C/N ratio, in order to reduce the risk of ammonia inhibition. Our results revealed an interactive effect between temperature and C/N on digestion performance.