Biological treatment of pulp mill wastewater using sequencing batch reactors

Lab-scale sequencing batch reactors were used to treat chemithermomechanical pulping wastewater that had chemical oxygen demand (COD) and biochemical oxygen demand (BOD) in the range of 5,980-8,990 mg/L, and 2,240-3,190 mg/L, respectively. A cycle time of 24 hour, with a hydraulic retention time of 34.3 hours was used. With 1 hour of settling, COD and BOD reductions of 30-41% and 67-78% were observed. However, with a 4-hour settling, COD and BOD reductions of 53-62% and 88-94% were achieved, respectively. Most of the oxygen demand reductions occurred within the first 16 hours of aeration. Adjustment of pH did not result in significant improvement in COD removal. Resin acids and fatty acids concentrations in the CTMP wastewater were reduced in the SBR process; however, they were still not fully detoxified in the effluent.