Effect Of Anaerobic Side-stream Phosphorus Recovery On Phosphorus Removal Performance And Microbial Population Structure Of Mainstream Ebpr Subjected To Low-consumption

Anaerobic side-stream phosphorus recovery is to extract the phosphate-rich supernatant of the mainstream EBPR system at the end of anaerobic phase with a certain proportion to the side-stream precipitation tank for phosphorus recovery.After the side-stream reaction,the supernatant of the precipitation tank was returned to the mainstream EBPR system to participate in the subsequent aerobic reaction to complete the biological phosphorus removal process.In addition,aeration is the largest energy consumption unit in the biological treatment system,and over-aeration is easy to cause system failure and the effluent phosphorus does not meet the standards.In this study,the dissolved oxygen real-time control strategy was adopted,and a low-consumption EBPR system based on anaerobic side-stream phosphorus recovery technology was established.The system can not only meet the requirements of biological phosphorus removal,but also make the maximum recovery of phosphorus from sewage.Therefore,phosphorus recovery and biological phosphorus removal can be carried out simultaneously,which has certain economic and environmental benefits.In the first phase,SBR reactor was empolyed to investigate the optimal reaction conditions for side-stream phosphorus recovery under the condition of low dissolved oxygen(DO=1.0 mg·L^-1)and the effect of side-stream phosphorus recovery on the performance of mainstream EBPR system.The results showed the optimal magnesium source,temperature,stirring speed and equilibrium time for side-stream phosphorus recovery were: Mg Cl2·6H2O,25?,150 rpm and 60 min,respectively.Through XRD characterization and SEM-EDS analysis,the phosphorus recovery product is magnesium ammonium phosphate,but contains certain impurities.Besides,side-stream reaction was found to have an impact on the performance of the mainstream EBPR owing to aerobic phase shortened,p H and inorganic ions increased as well as the decrease of poly-P in PAOs in the experiment phase of adding side-stream extraction.And the sludge sedimentation performance deteriorated,so it was no longer suitable for side-stream phosphorus extraction.Therefore,the phosphorus recovery operation was stopped at this time,and the system was operated under anaerobic/aerobic conditions.It was found that the phosphorus removal performance and sludge sedimentation performance of the system rapidly recovered.In the phosphorus recovery stage,although the phosphorus removal performance of the mainstream system decreased slightly,the mean phosphorus removal rate was still stable more than 90%,and a certain phosphorus recovery efficiency was achieved.Therefore,it is feasible to extract the anaerobic phosphate-rich supernatant from the mainstream EBPR under the condition of low DO for phosphorus recovery.This process can solve the contradiction between phosphorus resource shortage and water eutrophication.Therefore,it can bring certain social and environmental benefits and is also environmentally friendly.The second phase of the experiment studied the effect of phosphorus recovery on the mainstream EBPR system under low temperature?14±1??and low consumption(DO=1.0 mg·L^-1).The results showed the low-consumption mainstream EBPR system was successfully started under low temperature.When the system was running steadily,the side-stream extraction operation was added.It was found that the phosphorous removal performance was poor and phosphorus concentration in the effluent was high in the mainstream system.After the system was operated for a period of time,the concentration of phosphorus in the effluent in the mainstream system was always high and did not show a decreasing trend.The sludge sedimentation performance at this stage was also poor,sludge bulking was observed,which may lead to sludge loss in severe cases.In this case,the operation of side-stream phosphorus extraction was stopped.The phosphorus removal performance of the system was recovered after 6 days of alternating operation under anaerobic/aerobic conditions,and the sludge sedimentation performance showed a better trend.However,the anaerobic phosphorus release capacity of the mainstream system is low at low temperature,and sludge bulking caused by low temperature cannot be avoided,so low temperature is not conducive to side-stream phosphorus recovery operation.In addition,the anaerobic phosphorus release rate and the aerobic phosphorus uptake rate of PAOs under different temperature conditions were fitted,and it was found that temperature had certain influence on both anaerobic phosphorus release process and aerobic phosphorus uptake process.According to Arrhenius formula,the temperature coefficients of the anaerobic stage and the aerobic stage were 1.105 and 1.092 respectively,indicating that the temperature has more significant influence on the process of anaerobic phosphorus release.In the third stage,the effects of phosphorus recovery on phosphorus removal,nitrogen removal and sludge performance of mainstream EBPR system under fluctuation of influent quality were investigated.The results showed that,with the change of influent COD concentration,the amount of phosphorus released at the end of anaerobic phase of the mainstream system decreases with the decrease of influent COD concentration,and the phosphorus removal efficiency decreased from 96.7% to 87.7%,while NH₄⁺-N removal performance was always good.When influent COD was 400 mg L-1,the phosphorus recovery efficiency was the highest?61.5%?.Under the fluctuation of influent phosphate concentration,the amount of phosphorus released at the end of anaerobic phase of the mainstream system decreased with the decrease of influent phosphate concentration,but the phosphorus removal performance was always good.The mean phosphorus removal efficiency in the three phases was 97.5%.Similarly,NH₄⁺-N removal performance was also good.The phosphorus recovery efficiency was the highest?61.5%?when the influent phosphate concentration was 12 mg·L^-1.Under the condition of fluctuation of influent ammonia nitrogen concentration,with the increase of influent ammonia nitrogen,the phosphorus release rate of the mainstream system at the end of anaerobic phase firstly increased and then decreased.When influent ammonia nitrogen was 50 mg·L^-1,the effluent phosphorus concentration of the system was low and the phosphorus removal performance was stable,the NH₄⁺-N concentration of the effluent of the system at this stage was close to 0,and the phosphorus recovery efficiency was 75.7%.With the side-stream extraction,the intracellular poly-P content of sludge in the three stages showed a slow decreasing trend,while the sludge sedimentation performance was always better.Considering the system's phosphorus removal performance,nitrogen removal performance,phosphorus recovery efficiency and the stable operation of side-stream phosphorus extraction,it was comprehensively found that the influent COD concentration was 400 mg·L^-1,phosphate concentration was 12 mg·L^-1,and ammonia nitrogen concentration was 50 mg·L^-1 as the optimal influent concentration.In the fourth stage,the effects of long-term side-stream phosphorus recovery on phosphorus removal performance and microbial population structure of low-consumption mainstream EBPR system were investigated under the optimal influent conditions(COD=400 mg·L^-1,PO₄^3--P=12 mg·L^-1 and NH₄⁺-N=50 mg·L^-1).The results showed that the concentration of phosphate in the end of anaerobic phase tended to decrease and a certain amount of residual phosphate was in the effluent when the system was carried out long-term side-stream phosphorus recovery operation.In the early stage of the side-stream experiment for a long time,NH₄⁺-N of the system was completely oxidized,and in the later experiment,at the end of the aerobic system,there is a certain concentration of NH₄⁺-N,and the NO₃^--N concentrations in the effluent of long-term side-stream was reduced,this may be due to the long side-stream process causes other bacteria proliferation,so the activity of nitrifying bacteria reduce or decline.High-throughput sequencing of microorganisms in EBPR system before and after long-term side-stream phosphorus recovery showed that Chao1 index before and after long-term side-stream were 581.68 and 581.26 respectively,indicating that the microflora did not change significantly before and after long-term side-stream extraction.And Shannon index decreased from 7.04 before lateral flow to 5.48 after side-stream,indicating that long-term side-stream phosphorus recovery has a certain impact on microbial diversity.A comparison of bacteria at the microbial phylum level showed that Proteobacteria,Bacteroidetes and Chloroflexi were the main bacteria in low-consumption EBPR before long-term side-stream extraction.In the later stage of long-term side-stream extraction,Proteobacteria increased in EBPR,the proportion of Nitrospirae and Planctomycetes decreased.A comparison of bacteria at the microbial genus level showed that the proportions of Candidatus Accumulibacter?PAOs dominant bacteria?and Nitrospira decreased before and after side-stream extraction.Candidatus Accumulibacter decreased from 15.8% to 6.4%,Nitrospira decreased from 5.34% to 0.75%.However,the proportion of Candidatus Competibacte?GAOs dominant bacteria?increased from 18.2% to 38.1%.The results of high-throughput sequencing proved the reason of the degradation of phosphorus removal performance after long-term extraction.