Different bioreactors for treating secondary effluent from recycled paper mill.

Secondary effluent from paper mill was characterized by poor biodegradability and containing recalcitrant compounds. In this study, four bioreactors, including a sequencing batch biofilm reactor (SBBR), a stirred-tank reactor (STR) and two submerged aeration reactors (SAR) were used to treat secondary effluent from a recycled paper mill respectively. The results indicated that chemical oxygen demand (COD) was increased by SAR2 treatment and COD removal efficiency for SBBR, SAR1 and STR was 39.7%, 15.7% and 30.9% respectively. It is suggested that recalcitrant compounds were removed by SBBR, SAR1 and STR respectively. Total nitrogen (TN) and total phosphorus (TP) of wastewater were increased by treatments of each bioreactor, which suggested that endogenous respiration of biomass occurred during the treatment. Microbial analysis of sludge from different bioreactors suggested that the removal of recalcitrant compounds in SBBR and STR might be related to the presence of unique microorganisms in each reactor.