A kinetic study of a mesophilic aerobic moving bed biofilm reactor (MBBR) treating paper and pulp mill effluents: The impact of phenols on biodegradation rates

This study investigated the impact that phenols have on the biodegradation rate of paper and pulp mill effluents in a bench-scale aerobic moving bed biofilm reactor (MBBR). Paper and pulp mill effluents were collected from recycle and neutral sulfite semi-chemical mills. The phenol concentrations of the four individual paper and pulp mill effluents were 4.61, 29.1, 42.65 and 60.6 mg/L. The removal of chemical oxygen demand (COD) was continuously monitored for individual effluents during the experiments. The hydraulic residence time (HRT) and organic loading rates (OLR) in the experiment were varied between 5 and 45 h and 2-6 kg COD/m3.day, respectively. The biodegradable chemical oxygen demand (COD) removal efficiency at a hydraulic residence time (HRT) of 16 h was 86, 65, 60 and 46% for individual mill effluents. The Kincannon-Stover, first order and Grau second order kinetic models were evaluated to describe the removal of organics in a mesophilic aerobic MBBR. The highest correlation coefficients (r2) were found for the Kincannon-Stover model. According to the Kincannon-Stover model, the maximum substrate removal rates were 11.14, 10.46, 5.31 and 4.63 gCOD/L.day for mill effluents containing 4.61, 29.1, 42.65 and 60.6 mg/L phenols, respectively. The trend indicated that phenols inhibited the biodegradation rates of paper and pulp mill effluents in a mesophilic aerobic MBBR. Additional intermediate or pre-treatment may be required to remove excessive phenols to ultimately increase the performance of MBBRs in the paper and pulp industry.