Effect of temperature and organic loading rates on anaerobic digestion of pig manure

Many of the biogas plants in China run at the lower range of mesophilic conditions and low organic loading rates. The objective of this study was to evaluate the performance (methane yield, production of volatile fatty acid (VFA) and total inorganic carbon (TIC)) of completely stirred tank reactor which was fed with pig manure semi-continuously at different temperature (20, 28, 38℃) and organic loading rates (0.3-4.3?kg/(m3·d)). The results showed that the start-up phase last for a long time at 20℃ with low methane yield at organic loading rate (OLR) of 0.3 kg/(m3·d) and pH was kept stable with additional NaHCO3 at OLR of 1.3 kg/(m3·d). There was no significant difference on methane yield between 28℃ and 38℃ at each phase of this experiment. However, at 28℃, VFA accumulation was observed at OLR of 3.3 and 4.3 kg/(m3·d) and the VFA/TIC ratio was 0.4 and 0.6, respectively. For a biogas plant running with low organic loading rate, it seemed to be an energy input saving way if the operation temperature was kept at 28℃. The results of this study are valuable for the management of agricultural biogas plants.