The treatment of wastewater of paper mill with integrated membrane process

Abstract

The wastewater of the Chinese Paper Mill is currently treated with the conventional A–O–O method, which consists of a balance tank, a first sedimentation tank, an anoxic tank, an aerobic tank and a secondary sedimentation tank. The conventional treatment cannot meet the requirements of water quality for the paper making process. The integrated membrane process in pilot scale which consists of the membrane bioreactor (MBR), the continuous membrane filtration (CMF) and the reverse osmosis (RO) is used to treat the wastewater of this paper mill. The discharged water from the first sedimentation tank was treated with the anoxic/aerobic/MBR membrane system to eliminate NH 3–N and organic compound dissolved or undissolved. Although the permeate met the quality standards of feed for RO system, the CMF unit before RO system is still used in this integrated system in order to keep RO system operation safely, in case the bad water input the RO unit when the MBR system have some trouble. In this system a low-pressure RO unit with the form of anti-fouling spiral-wound membrane was accepted to purify the influent from CMF unit. The recovery of water for RO system was over 65%. The result showed that the RO permeate with the high quality could meet the whole standards of process water of paper mill. The conductivity of RO permeate was less than 200 μS/cm, COD less than 15 mg/L, the turbidity less than 0.1 NTU, and the chroma of RO permeate was less than 15 PCU. As the result, the treated water by the integrated membrane process could be reused in paper manufacturing process perfectly.