| Summary: | Effluents from high-yield TMP and CTMP mills contain biochemical oxygen demand and toxicity levels that are much higher than the effluents from low-yield kraft mills and if not properly treated before disposal can impose environmental threats to water bodies. Therefore, this study was undertaken to demonstrate the ability of a rotating biological contactor to remove organic matter from such a CTMP wastewater when operated at different flowrates and temperatures.
An apparatus was constructed to allow for temperature control of the wastewater and the flexibility to change flowrates and disc rotational speed. Parameters studied included BOD₅, COD, suspended solids, dissolved oxygen, sulfur compounds, acetic acid and nutrient uptake. Because the lab device exposes a thin film of liquid to the air over an extensive surface, evaporation from the RBC as high as 87% at temperatures of ~ 30°C were experienced during the experiment.
Results of this study showed that for hydraulic residence times (HRT) of 1 to 2 days the BOD₅ removal ranged from 77 to 86% with a corresponding COD removal of 63 to 72%. Increases in flowrate (decreases in HRT) resulted in a slight decrease in percent BOD (COD) removed and an increase in loading rate and BOD (COD) removal rate. An increase in temperature from 20 to 30°C increased BOD removal from 70.1 to 85% and COD removal from 45.8 to 71.4% at HRT=1.5 days. Dissolved oxygen, pH and MLVSS had no distinct effects on the removal of BOD₅ and COD. Losses due to evaporation of major volatile compounds tested were minimal at the pH of operation. Start-up time of the RBC was of the order of 1 day during the experiment.
An attempt to do a run without microorganism activity by adding 50 mg/1 HgCl₂ failed to eliminate all the organisms present in the wastewater and RBC.
Tracer studies revealed that the RBC was close to being perfectly mixed. === Applied Science, Faculty of === Chemical and Biological Engineering, Department of === Graduate
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