Effect Of Side-Stream Condition On Performance And Microorganism Of Side-Stream Enhanced Biological Phosphorus Removal Reactor

The low C/P ratio of influent water in municipal wastewater treatment plants is an important bottleneck affecting the performance and stability of enhanced biological phosphorus removal(EBPR)process.In order to solve this problem,a side-stream enhanced biological phosphorus removal(S2EBPR)process has been inn ovated and received extensive attention.However,the effect of side-stream conditions on the performance and stability of this process is still insufficient.In this study,a side-stream reflux sludge fermentation(SSR)type S2EBPR wastewater treatment system was constructed in the laboratory.Combined with the sequential batch experiment of activated sludge anaerobic fermentation,the release rules of organic matter and nutrients during side-stream sludge anaerobic fermentation,the pollutant removal performance of S2EBPR process,and the changes of functional microbial activity and community structure under different side-stream conditions were studied.The operation mechanism and regulation mechanism of the process are preliminarily revealed.Key findings were as follows:(1)The sequential batch experiment of anaerobic fermentation of activated sludge showed that the release rate of organic matter,nitrogen and phosphorus nutrients in activated sludge gradually decreased and tended to be flat with the increase of anaerobic fermentation time.The release efficiency of C,N and P was better when the sludge was fermented for 36-120 h.During this period,the release of COD,total nitrogen(TN)and normal phosphate(PO43--P)accounted for 74%,69%and 64%of the total,respectively.An appropriate duration of anaerobic fermentation can promote the biological phosphorus uptake and phosphorus release activities of phosphate-accumulating bacteria(PAOs)and make it superior to glycans bacteria(GAOs)in the competition,accompanied by significant sludge reduction,with a 6%reduction in TSS and a 10%reduction in VSS within 120h.(2)The experimental results of S2EBPR reactor under different side-stream conditions under low carbon and phosphorus ratio(C/P=24)showed that the changes of diversion ratio and side-stream sludge retention time(SRTss)had little effect on COD removal,and the reactor had stable and efficient treatment ability for the easily degraded organic matter in the influent-water under all side-stream conditions.The effluent COD concentration was 31.37±10.29 mg/L,and the removal rate was 89.3±3.3%.The S2EBPR reactor had good PO43--P removal performance and stability at 10%-20%diversion ratio(SRTss=72-144 h),and the average PO43--P removal efficiency was higher than 90%.However,under the condition of 30%and 5%lateral flow ratio(SRTSS～48 and 288 h),the average PO43--P removal rate was less than 70%.The average TN and NH4+-N concentrations in the effluent were 12.52 mg/L and 0.63 mg/L,respectively.The average TN and NH4+-N removal rates were 60.6%and 97.4%,respectively.When SRTss ≥144 h,the NH4+-N removal efficiency of the system was slightly reduced.(3)The results of microbial activity experiment showed that the phosphorus removal activity of PAOs was greatly affected by lateral flow conditions.When SRTss=72 to 144 h,PAOs showed higher phosphorus removal activity.When SRTSS≥288 h,PAOs activity was greatly inhibited.The results of typical cycle experiments and mass balance showed that the diversion condition not only affected the activity of functional microorganisms,but also regulated the nutrient load of the main and side-stream reactors,which was a key factor affecting the performance and stability of the system.Acid production by activated sludge fermentation in side-stream reactor not only solved the problem of insufficient carbon source for PAOs,but also provided additional carbon source for the main stream,increasing the C/P ratio of the main stream by 16%-26%and the C/N ratio of the main stream by 14%-19%.However,over-long SRTss(≥144 h)would produce a large amount of NH4+-N,which would increase the pressure on mainstream nitrogen removal.(4)High-throughput sequencing results showed that the richness and diversity of microorganisms in the reactor decreased with the increase of SRTss,indicating that the extension of anaerobic conditions in the side-stream reactor had a screening effect on microorganisms.The dominant genera were Candidatus Competibacter,Saccharimonadales,Tetrasphaera,Dechloromonas and so on.Among the PAOs,Tetrasphaera and Dechloromonas(relative abundance of the total known PAOs and GAOs)increased significantly from 7.9%and 8.4%at the start-up to 22.9%and 19.0%,respectively.However,Accumulibacter abundance increased when SRTss=48 to 144 h and decreased when SRTss>144 h,indicating that too long SRTss may be detrimental to Accumulibacter growth enrichment.The abundance of Dechloromonas and Zoogloea(relative abundance of microorganisms accounting for the total known nitrogen removal)significantly increased from 7.7%and 7.5%at the start to 36.3%and 21.5%,respectively.Changes in the composition and relative abundance of functional microorganisms related to nitrogen and phosphorus removal greatly affect the effluent quality of the reactor.