Kinetics evaluation of a semi-continuously fed anaerobic digester treating pig manure at two mesophilic temperatures.

Anaerobic digestion of animal waste at a low range of mesophilic conditions has not been well described to date. In this study, laboratory-scale semi-continuously fed anaerobic digesters treating pig manure were operated at 28 and 38 °C with organic loading rates ranging from 1.3 to 4.3 g ODM L(-1) d(-1). The estimated biomass yield was higher at 28 °C (0.065 g VSS g(-1) COD(removed)) than at 38 °C (0.016 g VSS g(-1) COD(removed)). The resulting calculated biomass concentration range at 28 and 38 °C was 1.2-2.4 and 0.3-0.6g VSS L(-1), respectively, which fitted well with a Michaelis-Menten type function. These VSS results are one or two orders of magnitude lower than previously reported for manure-fed digesters. Although maximum specific substrate utilisation rate at 38 °C is five-fold that at 28 °C, higher biomass yield in the digester at 28 °C seemed to compensate for the adverse effects of lower temperature on digester performance.