Combining activated sludge process with membrane separation to obtain recyclable quality water from paper mill effluent

Abstract

The present study was carried out for the treatment of paper mill effluent using combination of activated sludge process and membrane separation. An integrated paper mill employing OCEOPHH sequence (oxidation, chlorination, alkali extraction re-enforced by oxygen and peroxide, hypo-1, and hypo-2) for the bleaching of hardwood pulp was selected for the study. The purpose of this work was to examine the water quality and membrane performance when combining activated sludge process with different membrane separation processes in series. Pollutant removal including adsorbable organic halides (AOX) was compared among different treatment combinations; (i) ASP + microfiltration (MF), (ii) ASP +MF + ultrafiltration (UF), (iii) ASP +MF + UF + nanofiltration (NF), and (iv) ASP +MF + UF + NF + reverse osmosis (RO) to select the optimal treatment scheme for water recycling in the paper mill. Different initial inlet pressures were used for the UF and NF (6.8, 10.3, and 13.7 bar) and for RO (10.3, 13.7, and 17.2) The retentate from each membrane was recycled back to the feed and retreated until the inlet pressure increased to the maximum cut-off pressure for each membrane. After separation, 100 % total suspended solids, total dissolved solids, color removal and 94.2 % chemical oxygen demand, and 86 % AOX removal was observed. This study suggests the potential application of the combination of membrane separation with activated sludge process for recycling water in the paper industry.