CTMP wastewater treatment using a rotating biological contactor

Studies on the treatment of CTMP mill wastewater were done using a laboratory-scale rotating biological contactor (RBC). Analysis of the wastewater is given. The effects of organic loading rates in the range 0.007 to 0.033 kg BOD m-2 day-1 (0.012 to 0.055 kg COD m-2 day-1) and temperature (20 and 31 °C) on the percent removal of BOD and COD are presented. Average BOD (COD) removals ranged from 70% (46%) at 20 °C to 86% (72%) at 31 °C. The acetic acid content of the wastewater was almost completely biologically oxidized in the RBC and very little acetic acid volatilization was observed. Sulfite and sulfide compounds tended to be oxidized to sulfate compounds during the RBC treatment. Over the range of dissolved oxygen (DO) concentrations (0.3 to 2.0 mg/L) measured in the RBC trough, DO appeared to have no effect on BOD removal, even though some of these DO levels were very low. The discs carried wet microbial biofilms of the order of 0.5 kg m-2. Biomass sloughed off the discs at a rate that was approximately 0.04 kg m-2 day-1.