A Study Of Application Of Sequencing Batch Biofilm Reactor(SBBR)for Removing Recalcitrant Organic Matter And Nitrogen In Wastewater

The removal of recalcitrant compounds and nitrogen has always been a serious issue for the treatment of industrial wastewater such as paper mill wastewater.Biofilm reactor owes a good application prospect in the treatment of these industrial wastewater due to its ability of removing recalcitrant compounds and realizing autotrophic nitrogen removal process.Therefore,the paper studied the application of sequencing batch biofilm reactor(SBBR)in wastewater treatment for removing recalcitrant compounds and realizing autotrophic nitrogen removal process.Secondary effluent from paper mill was characterized by poor biodegradability and containing recalcitrant compounds.In this study,four bioreactors,including a 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.The long initiation period of the single stage nitrogen removal over nitrite and anammox(SNAP)process is a major hindrance to its practical application.In this study,the SNAP process was initiated in a SBBR inoculated with conventional activated sludge within 46 days when the ammonium removal efficiency(ARE)and total nitrogen removal efficiency(TNRE)reached 86.9% and 76.8%,respectively.After the 46 days,ARE of 93.7 ± 2.8% and TNRE77.5 ± 2.3% were achieved.The rapid initiation of the SNAP process could be attributed to biomass retention provided by biofilm and regulation of parameters including dissolved oxygen(DO),p H,temperature,organic matter,inorganic carbon(IC),free ammonium(FA),and free nitrite acid(FNA).The microbial analysis suggested that microbial richness of biomass increased while the microbial diversity reduced during the initiation of the SNAP process.Nitrosomonas and Candidatus Brocadia were the main ammonium oxidizing bacteria(AOB)and anammox bacteria(An AOB),respectively,and were found to be enriched.Nitrospira was the main nitrite oxidizing bacteria(NOB)and relative abundance of it was decreased.The heterotrophic denitrification established rapidly and then gradually declined during the start-up of the SNAP process.Considering that organic matter can significantly affect the nitrogen removal performance of SNAP process,effect of organic carbon on nitrogen removal was detected.TNRE at COD/N ratios of 0,0.5,1.0,2.0 and 4.0 were 81.3±1.3%,69.7±5.6%,68.6±3.7%,45.8±4.4%and 33.0±5.1% respectively,suggesting that the feasible COD/N ratio for implementation of SNAP process in SBBR is below 1.0.Microbial communities analysis indicated that at COD/N ratios of 0.5 and 1.0,the An AOB activities were decreased by the proliferation of NOB and denitrifying bacteria respectively;at COD/N ratios of 2.0 and 4.0,the traditional nitrification/denitrification process became predominant with An AOB activities being dramatically decreased;and An AOB in flocculent biomass were supposed to be more vulnerable to organic compounds than in biofilm.