| Enhanced biological phosphorus removal(EBPR)is the most widely used and economical phosphorus removal process in the world,which can effectively control eutrophication of water bodies.Studies on polyphosphate accumulating organisms(PAOs),the main functional bacteria in the system,have also been extensively conducted.Traditionally,PAOs are mostly metabolized by volatile fattyacids(VFAs)as carbon sources,such as Candidatus Accumulibacter Phosphatis.With further research,another kind of PAOs with fermentation function was also found,such as Tetraspharea,whose fermentation product VFAs could also be used for metabolism by other bacteria.Part of COD in municipal sewage belongs to organic matter that is difficult to be utilized by traditional PAOs,while fermentative PAOs can absorb it and generate more VFAs by its own fermentation function,so as to carry out collaborative nitrogen and phosphorus removal with other bacteria,which has a broad application prospect.In this study,different types of organic carbon sources were taken as research objects to explore the preference of fermentative PAOs to various organic compounds and the effects of anaerobic duration on their fermentation performance,in order to provide a new idea for collaborative nitrogen and phosphorus removal in wastewater treatment plants with low influent VFAs concentration.sequencing batch reactor(SBR)through 3 sequencing batch reactor(SBR),labeled as SBR1,SBR2,SBR3,artificial simulated wastewater,long-term operation of each reactor in anaerobic/aerobic alternating mode,monitoring reactor performance at each stage.The results are as follows:(1)When glucose was used as the sole carbon source for SBR1 acclimation,the system had poor phosphorus removal efficiency,and the average phosphorus removal rate was lower than 40%.When the carbon source type was gradually changed to the mixed amino acid composed of glutamic acid,aspartic acid,glycine and proline,the phosphorus removal efficiency of the system was gradually improved,and the phosphorus removal rate could be stabilized at more than 85%.However,due to the hydrolysis of amino acids,the concentration of ammonia nitrogen in the system was greatly increased,and the denitrification performance continued to deteriorate,with the removal rate of ammonia nitrogen only below 20%.In the middle stage of operation,sludge swelling occurred,and after adjusting aeration rate,the swelling phenomenon was inhibited,and SVI was reduced to less than 200mg·L-1.High throughput sequencing revealed that Thiothrix,Terrimonas,Flavobacterium,Accumulibacter and Tetrasphaera were present in the system,and a cooperative phosphorus removal model had been established.Long-term operation results showed that compared with glucose,fermentative PAOs preferred amino acid fermentation as carbon source,and preferred glutamic acid and aspartic acid as carbon source among the four mixed amino acids.(2)When SBR2 was acclimated with casein hydrolysate as the only carbon source,the average phosphorus removal rate was about 45%.When the carbon source type gradually changed to the mixed amino acid composed of glutamic acid,aspartic acid,glycine and proline,the phosphorus removal efficiency of the system was significantly improved,and the phosphorus removal rate could be stabilized at more than 90%.Due to the high concentration of ammonia nitrogen in the amino acid hydrolysis system,the removal rate of ammonia nitrogen was poor at the initial stage.In the later stage of operation,the removal rate of ammonia nitrogen increased to more than 95% with the gradual enrichment of bacteria with the ability of nitrogen removal.In the middle stage of operation,sludge expansion also occurred,but compared with SBR1,the expansion phenomenon was lighter,the recovery of sludge settling performance was accelerated,and SVI could be stabilized below 150mg·L-1.After high-throughput sequencing,there are Nitrospira,Nitrosomonas,Thiothrix,Thauera,Accumulibacter,Tetrasphaera and other bacteria genera in the system,and a cooperative nitrogen and phosphorus removal model has been established.The long-term operation results showed that fermentative PAOs still had strong fermentation effect when fewer kinds of mixed amino acids were used as carbon sources,and its risk resistance ability was significantly stronger than that of glucose-acclimated systems.(3)Half of the sludge acclimated with casein hydrolysate as the sole carbon source in SBR2 was removed and transferred to SBR3 for continued operation.The carbon source type gradually changed to the mixed amino acid composed of glutamic acid,aspartic acid,glycine and proline,and the anaerobic duration was shortened by 2 hours.After the change of carbon source type,the phosphorus removal efficiency of the system is greatly improved,and the phosphorus removal rate can be stabilized above 95%.Due to the high concentration of ammonia nitrogen in the amino acid hydrolysis system,the removal rate of ammonia nitrogen was poor in the early stage.In the later stage of operation,with the accumulation of bacteria with the ability to remove nitrogen,the denitrification performance gradually recovered.However,compared with the low removal rate of ammonia nitrogen in SBR2,the denitrification performance could only be improved to about 85%.Sludge settling performance decreased slightly,but no expansion occurred,and SVI could be stabilized below 80mg·L-1.By high throughput sequencing,Thiothrix,Terrimonas,Flavobacterium,Accumulibacter and Tetrasphaera are present in the system,and a cooperative nitrogen and phosphorus removal model has been established.Long-term operation results showed that fermentation-type PAOs still had good fermentation effect in a short anaerobic duration,which could guarantee better nitrogen and phosphorus removal efficiency and improve sewage treatment efficiency. |
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