Optimization of biological treatment of paper mill effluent in a sequencing batch reactor

Laboratory scale research on the effects of operating parameters, including mixed liquor suspended solid (MLSS) concentration, volumetric exchange rate (VER), aeration time, temperature and daily operation cycle on biological treatment of the pulp and paper mill effluent was studied using four 4 l sequencing batch reactors (SBR). The results revealed that chemical oxygen demand (COD) removal efficiency was up to 93.1 ± 0.3% and the volumetric loading reached 1.9 kg BOD m−3 day−1 under optimal operating conditions. The treatment performance of organic removal by the SBR system remained stable during the operation. The effluent quality was satisfied with the discharge standard set by the local authority and the filamentous bulking problem was solved. At the same time, the sludge settleability, in terms of sludge volume index (SVI), was improved to the healthy level (SVI = 52.7 ± 1.3 ml g−1).