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Pulp mill condensate treatment in an automated sequencing batch reactor Woo, Norman


In an effort to both meet more stringent air quality guidelines and to be able to recycle a potential waste water stream, kraft mill evaporator condensate has been identified as a waste water stream that can be reused in other pulp and paper mill operations. This study involves the treatment of kraft mill combined condensate in a sequencing batch reactor (SBR). It is proposed that an inline SBR can be used to effectively treat a combined condensate waste stream such that all methanol in the stream is rapidly and economically removed by the system. This research was conducted in cooperation with Crestbrook Forest Industries Ltd. Pulp Division, Skookumchuck pulp mill. Previous work by Milet and Duff (1998) showed that an automated sequencing batch reactor was capable of reducing methanol and chemical oxygen demand (COD) concentrations by 100% and >70%, respectively. However, the reactor operated at or near zero dissolved oxygen (D.O.) concentration through much of the cycle time and had no means to control sludge age. In order to address some of the deficiencies of the previous work, feedback D.O. control was implemented, such that the reactor could run above zero D.O. concentrations. As well, a solids probe was installed on the SBR such that the mixed liquor suspended solids (MLSS) and sludge age could be monitored and controlled. One hundred percent methanol removal was achieved, while 77% of the COD was removed from the combined condensate in the SBR. The proportional only PID controller for D.O. control consistently controlled the D.O. to a desired level of 2 mg/L. The MLSS concentration in the reactor was also effectively controlled to within ±100mg/L of the desired setpoints during a 30 day run. Oxygen limitations were discovered to occur for the treatment of methanol, as degradation rate was better by 1,3x to 2x during non-oxygen limited conditions. Sludge age in the SBR ranged from 2 to 8 days during controlled biomass concentrations, while sludge age was 10 to 20 days when the system was allowed to grow.

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