Anaerobic Mesophilic Codigestion of Rice Straw and Chicken Manure: Effects of Organic Loading Rate on Process Stability and Performance

To investigate the effects of organic loading rate (OLR) on performance and stability of mesophilic co-digestion of rice straw (RS) and chicken manure (CM), benchtop experiments (40 L) were carried out at OLRs of 3.0, 3.6, 4.2, 4.8, 6.0, 8.0, and 12.0 kg volatile solid (VS)/(m3·day) with volatile solid (VS) ratio of 1:1 (RS/CM) which was based on batch tests. Anaerobic co-digestion was slightly and severely inhibited by the accumulation of ammonia when the digester was overloaded at an OLR of 6 and 12 kg VS/(m3·day), respectively. The recommended OLR for co-digestion is 4.8 kg VS/(m3·day), which corresponds to average specific biogas production (SBP) of 380 L/kg VS and volumetric biogas production rate (VBPR) of 1.8 m3/(m3·day). An OLR of 6–8 kg VS/(m3·d) with SBP of 360–440 L/kg VS and VBPR of 2.1–3.5 m3/(m3·day) could be considered, if an Anaerobic digestion (AD) system assisted by in situ removal of ammonia was adopted.