Effect of sludge recycle on performance of a rotating biodisc contactor treating saline wastewater

Abstract

A rotating biodisc contactor (RBC) was used for biological treatment of synthetic saline wastewater with and without sludge (cell) recycle. Synthetic wastewater composed of diluted molasses, urea, KH_zPO₄, MgSO₄ and 3% salt (NaCl) was fed to the RBC unit with different flow rates. Underflow from a sedimentation tank placed at the end of RBC unit was recycled to the RBC unit with a constant flow rate. COD removal rates and efficiencies were determined for the cases of with and without sludge recycle and compared.

COD removal efficiencies and rates obtained with sludge recycle were higher than those obtained without sludge recycle at low A/Q ratios (high flow rate) because of extra residence time provided by sedimentation tank. However, no significant difference was observed in the performance of RBC with and without sludge recycle at high A/Q ratios (low flow rates).

Because of poor sedimentation characteristics of the culture no significant increase in biomass concentration in the RBC was observed when the system was operated with sludge recycle.