Treatability Evaluation of Municipal Wastewater and Anaerobically-Treated Industrial Effluent in a Rotating Biological Contactor

Abstract

Performance of a rotating biological contactor (RBC) in treating municipal wastewater from primary sedimentation basin and anaerobically treated industrial effluent from an upflow anaerobic sludge blanket (UASB) reactor was investigated. The 280-L six-stage RBC pilot was operated at different organic loading rates and biodisc speeds. The overall removal efficiencies of soluble BOD decreased with increasing organic loading rates. Disk rotational speed did not have significant effect on performance in the range studied. The results showed that satisfactory treatment of UASB effluent to meet regulatory requirement for agricultural purposes (effluent BOD of 100 mg L-1) can be achieved with sufficient margin of safety at organic loading rate of up to 4.9±0.4 g SBOD m-2 d-1 with SBOD removal efficiency of 59±9%. For municipal wastewater, it was possible to achieve SBOD effluent values of below 20 mg L-1all the time. Most of the organics were removed in the first three stages with minimal contribution from the remaining stages of the RBC reactor. There was a decrease in SBOD removal efficiency to 74 ± 3% at OLR value of 17.8 ± 2.1 g SBOD m-2 d-1 and 66 ± 6% at OLR value of 4.7 ± 1.9 g SBOD m-2 d-1 for UASB effluent and municipal wastewater, respectively. The results for elimination capacity (EC) values indicated a linear relationship with first stage organic loading rates without any signs of limitation in the range of OLR values investigated in this study. However, average first-stage elimination capacity rates of 3.2 and 2 at OLR values of 17.8 and 11 gSBOD m-2 d-1 for UASB effluent and 1.3 and 2 at OLR values of 4.7 and 5.3 gSBOD m-2 d-1 for municipal wastewater were relatively lower than previous studies of RBC performance using domestic or industrial wastewater without anaerobic pretreatment. It was suggested that the lower EC values were due to the fact that a smaller fraction of UASB effluent was biodegradable as reflected in SBOD/SCOD ratios of 0.47± 0.04. For municipal wastewater, even though SBOD/SCOD ratios were 0.49± 0.03, the low EC values were suggested to be contributed to lower influent concentration potential considering first-order kinetics governing biochemical reactions.