Study On The Performance Of Simultaneous Nitrification Denitrification And Phosphorus Removal In SBBR

With the rapid development of economy and society,the discharge of domestic sewage in rural areas has increased year by year,resulting in the phenomenon of "dirty,messy and poor" in rural areas.Rural domestic wastewater has the characteristics of scattered sources,difficult collection,complex composition,fluctuating water quantity,unstable water quality and low carbon to nitrogen ratio.Simultaneous nitrification denitrification phosphorus removal(SNDPR)process is a combination of biological phosphorus removal process and simultaneous nitrification denitrification process(SND),which can achieve the removal of carbon,nitrogen and phosphorus simultaneously in a single reactor,and is gaining attention in biological wastewater treatment.In this study,a sequencing batch biofilm reactor(SBBR)operating in anaerobic/aerobic(A/O)mode was used to treat simulated rural domestic wastewater.The effects of operating cycle,influent carbon to nitrogen ratio,magnesium ions and other conditions on the performance of SNDPR were investigated to obtain optimal operating parameters to ensure efficient and stable operation of the system;the mechanisms of fermentative phosphorus-polymerizing bacteria and denitrifying phosphorus-polymerizing bacteria in the simultaneous nitrification denitrification SBBR were explored.The effect of simultaneous nitrification denitrification and phosphorus removal was enhanced by adopting the strategy of discharging phosphorusrich liquid in the anaerobic stage.This study was conducted to provide a reference for rural domestic wastewater treatment.The research contents and conclusions of this study are as follows:(1)Shortening the operating cycle of A/O-SBBR process from 12 h to 8 h and increasing the aeration intensity had no significant effect on the effluent ammonia nitrogen,while the average effluent phosphorus concentration decreased from 2.65mg/L to 0.87 mg/L.Under the conditions of influent C/N of 7,3 and 5,SBBR could achieve good denitrification effect with an average removal rate of 99.6% of ammonia nitrogen,but the phosphorus removal effect was unstable,corresponding average concentration of phosphorus in the effluent was 0.87 mg/L,1.7 mg/L and 2.46 mg/L respectively.There was no significant effect on ammonia removal when the feed water magnesium ion was 2.5,10,20,25,and 30 mg/L,and the removal rate of ammonia nitrogen was more than 98%,but only when the magnesium ion was 25 mg/L,the phosphorus in the effluent met the first grade A standard of Pollutant Discharge Standards for Urban Sewage Treatment Plants.(2)The SBBR was conducive to the enrichment of fermentative polyphosphoric bacteria,denitrifying polyphosphoric bacteria and denitrifying polysaccharide bacteria in the whole low oxygen environment.The biochemical reaction was speculated be completed by fermentative polyphosphoric bacteria and denitrifying polysaccharide bacteria in cooperation.The mass transfer rate bad a great influence on the performance of the biofilm reactor for nitrogen removal and phosphorus removal.(3)Enhanced biological phosphorus removal by SBBR through anaerobic phase discharge of phosphorus-rich liquid.Method 1,the normal influent was fed,and after the phosphorus-rich liquid was discharged at the end of the anaerobic phase,the normal influent was fed again in equal amount.This method was effective for phosphorus removal by A/O-SBBR process,and the effluent phosphorus concentration and removal rate were 0.64 mg/L and 87.16%,but it would cause ammonia nitrogen accumulation.Method 2,to reduce the influence on ammonia nitrogen load,the influent contained500mg/L COD without N,P,and after discharging phosphorus-rich liquid,the SBBR was fed with the same amount of normal influent.This method was effective for phosphorus removal in A/O-SBBR process,and the phosphorus concentration of the effluent was 0.31mg/L after the first time strengthening,but the phosphorus removal effect of the system became deteriorate after meeting the effluent phosphorus standard for 5 days.Method 3,side-stream discharge of phosphorus-rich liquid.the normal influent was fed,and after in the anaerobic stage,a certain amount of phosphorus-rich liquid is discharged into the side-stream tank,and phosphorus remover is added to the side-stream tank,and then the treated phosphorus-rich liquid is added to the reactor.The phosphorus removal effect of this method depended on the drainage ratio.When the drainage ratio is 15%,the average phosphorus effluent concentration was 0.04mg/L,which met first grade A standard of Pollutant Discharge Standards for Urban Sewage Treatment.