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UBC Theses and Dissertations

Effect of coagulation and flocculation technology on bleached kraft mill effluent quality Hodgson, Andrew Trevor


Since January 1995 the tertiary colour removal clarifier at Crestbrook Forest Industries' Pulp Division in Skookumchuck, B.C. has removed 60±4% of the biologically treated effluent colour. Over the same period, BOD5 was reduced by 26% and TSS was increased by 19 mg/L across tertiary treatment. This study revealed that the colour removal system removed 24%, 23%, 80%, and 18% of the COD, AOX, 2,3,7,8-TCDF, and mixed function oxygenase induction, respectively. A study of the effect that basic effluent parameters had on system performance revealed that the dual polymer system used at Crestbrook Forest Industries operated well over a wide range of temperature, pH, and BOD₅. Colour removal improved when pH was decreased to pH 3; below this pH the system performance declined. The increased colour removal at lower pH values could not be achieved by an increase in coagulant dose. Decreasing the temperature improved colour removal slightly, and different levels of BOD5 had no effect on the percentage of colour removed. Bench scale tests with segregated effluent streams (bleach plant filtrates and pulping area sewers), indicated that there are no possible reductions in polymer usage when these streams are treated separately from the rest of the mill effluent. Polymers used in the full scale system were well suited to treat chlorination stage effluent, achieving acceptable floe formation at relatively low polymer applications. The extraction stage effluent did not produce quality floes when treated, and required high polymer doses to achieve moderate floe quality.

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