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Aerobic treatment of CTMP wastewater in sequencing batch reactors Dubeski, Cara V.


This research evaluated the application of a bench-scale aerobic SBR system to the treatment of CTMP/TMP wastewater. The wastewater treated was from Quesnel River Pulp, and had a COD of approximately 7200 mg/I and BOD₅ of roughly 2700 mg/I. SBR cycle times used were 24 and 48 hours, with hydraulic retention times of 34.3 and 68.6 hours respectively. The 24-hour cycle consisted of 22 hours aeration, one hour settling and one hour decant. Sludge retention times were 20 days for most runs. By the end of the study, the sludge in the system had been run on effluent from the same source from the same mill for 1 and 1/2 years. For the runs without pH adjustment, COD removals of 32-41% and BOD₅ reductions of 70-75% were achieved by the end of each 24-hour cycle (after one hour in-situ settling). When the decanted wastewater was settled for an additional three hours, COD reductions of 53-59% and BOD₅ reductions of 90-94% were obtained. From intermediate time point samples, it was found that most of the oxygen demand reduction occurred within the first 16 hours of the cycle. Little improvement was found in effluent from 48-hour cycles compared to 24-hour cycles. The rate of COD removal was greatly decreased in the 48-hour cycles, even during the early hours of aeration. Comparison of columns with unregulated pH to pH-controlled columns at 6.5 and 7.5 pH showed little difference in COD removals. COD and BOD₅ percentage removals in samples after the longer settling, were almost as high as in other aerobic systems treating similar wastewaters, though the SBR system had a higher loading. MLVSS concentrations were 3900 to 4600 mg/I at the end of 24-hour cycles, and Sludge Volume Indices ranged from 54 to 78 ml/g (for reactors without pH adjustment). Sludge yields in the 24-hour cycle runs were about 0.12 kg MLVSS per kg COD removed, and 0.15-0.18 kg MLVSS per kg BOD₅ removed. This is only about one quarter the sludge yields typical in AS systems, both on a COD and BOD₅ basis. Some recommendations for the design of an SBR pilot system for a pulp mill are made.

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