Effects of organic loading rate on anaerobic digestion of chicken manure under mesophilic and thermophilic conditions

Abstract

This study compared the mesophilic and thermophilic anaerobic digestion of chicken manure under two organic loading rates (OLR) i.e. 1.6 and 2.5 kg volatile solids (VS) m−3 d−1. A 180-day continuous study was carried out to analyze the effects of OLR on biogas production, specific methanogenic activities (SMA) and process mass balances. The results demonstrated that the mesophilic reactor yield methane at 252 and 245 mL CH4 g−1 Total Solid at the two OLRs. However, in the thermophilic reactor, the methane yield was lower, i.e.220 mL CH4 g−1 TS for OLR of 1.6 kg VS m−3d−1 and 94 mL CH4 g−1 TS for OLR of 2.5 kg VS m−3d−1. High free ammonia nitrogen (FAN) concentration, particularly at a high OLR, led to a high concentration of VFAs which negatively affected SMA, while under mesophilic condition the VFAs was lower and SMA was not affected. Principal component analysis indicated that OLR, TAN, and FAN have an effect on biogas production. It was concluded that mesophilic and thermophilic reactors could work comparatively well at a low OLR, but that the thermophilic condition had significantly deleterious effects on the efficiency of anaerobic digestion above all at the higher OLR.