Evaluation of the potential use of powdered activated carbon in the treatment of effluents from bleached kraft pulp mills

Abstract

Pulp mill effluents contain organic compounds derived from wood processing that resist conventional biological treatment. Studies suggest that powdered activated carbon (PAC) can enhance the quality of these effluents. Two types of PAC, chemically activated (PAC1) and physically activated (PAC2), were characterized and applied in dosages of 1, 2, and 3 g/L to reduce chemical oxigen demand (COD) and color in kraft pulp mill effluent. In Phase 1, physicochemical tests identified the optimal PAC type, dosage, and maximum cycles for effective COD and color reduction. In Phase 2, biological aerobic sequencing batch reactors (SBR) were tested with the optimal PAC from Phase 1. Results indicated PAC1 could be reused for COD reduction for up to 8 cycles and PAC2 for up to 6 cycles. For color reduction, PAC1 was effective for up to 4 cycles, while PAC2 failed to reduce color. The type of activation used by PAC1 proved to be more effective in reducing both COD and color than PAC2. Adding PAC1 (3 g/L) to the SBR increased COD removal from 70.5 % to 75.5 % and color removal from 26.6 % to 43.8 %, also improving sludge settling.