Posttreatment of upflow anaerobic sludge blanket-treated industrial wastewater by a rotating biological contactor.

The performance of a rotating biological contactor (RBC) for posttreatment of the slaughterhouse effluent from an upflow anaerobic sludge blanket (UASB) reactor was investigated in this study. The 280-L, six-stage RBC pilot plant was operated at different organic loading rates (OLRs) and biodisk speeds. The overall removal efficiencies for soluble biochemical oxygen demand (SBOD), total biochemical oxygen demand (TBOD), and total chemical oxygen demand (TCOD) decreased with increasing OLRs. Disk rotational speed did not have a significant effect on performance in the range studied. The results showed that satisfactory posttreatment to meet regulatory requirements for agricultural purposes (effluent biochemical oxygen demand of 100 mg/L) can be achieved at an OLR of 5.3 +/- 2.9 g SBOD x m(-2) x d(-1), with an SBOD removal efficiency of 85 +/- 3%. 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 an OLR value of 17.8 +/- 2.1 g SBOD x m(-2) x d(-1). The results for elimination capacity indicated a linear relationship with first-stage OLRs without any signs of limitation at the range of loading rates investigated in this study. However, average first-stage elimination capacity rates of 4.8 and 3.8 g x m(-2) x d(-1) at OLR values of 17.8 and 11 g SBOD x m(-2) x d(-1) were relatively lower than previous studies of RBC performance using domestic or industrial wastewater without anaerobic pretreatment. It was suggested that the lower elimination capacity rates were due to the fact that a smaller fraction of UASB effluent was biodegradable as reflected in TBOD/TCOD ratios of 0.47 +/- 0.04.