Kinetic evaluation of palm oil mill effluent digestion in a high rate up-flow anaerobic sludge fixed film bioreactor

A kinetic study of the anaerobic digestion process of palm oil mill effluent (POME) was carried out in a laboratory-scale up-flow anaerobic sludge fixed film (UASFF) bioreactor at mesophilic temperature (38 °C). Influent COD concentrations in the range of 5260–34725 mg/l were applied at steady state conditions. Chen and Hashimoto kinetic equation and a simplified Monod's model was employed to describe kinetics of POME anaerobic digestion at organic loading rates in the range of 0.88–34.73 g COD/l day. The hydraulic retention times (HRT) ranged between 1 and 6 days. Throughout the experiment, the removal efficiency of COD was between 80.6 and 98.6%. The methane production rate was between 0.287 and 0.348 l CH4/g CODremoved day. Biokinetic coefficients; apparent half-velocity constant, A, half-velocity constant, Ks, maximum specific microbial growth rate, μm, methane yield constant, YM, and growth yield constant, Yx, were evaluated. The apparent rate constants, K, calculated by simplified Monod model were in the range of 2.9–7.4 l CH4/g COD day. At different influent COD concentrations, K values showed a linear relationship with variations of VSS content of the reactor.