The Effects Of AHLs And Fulvic Acids On Nitrogen Removal Performance And Microbial Structure Analysis Of Anammox Process Under Low Temperatures

It is essential to improve the nitrogen removal performance and stability of anammox process under low temperatures for improving the effectiveness and environmental protection of biological nitrogen removal technology.Acyl-homoserine lactones(AHLs)as signal molecules could regulate the performance of biological nitrogen removal system through quorum sensing,and fulvic acid has the potential to promote electron transport in anammox systems.In this test,anammox biofilm reactors were built and run continuously for 242 d,with the temperature decreased from 15 ℃to 5 ℃ and then increased to 10 ℃.Signal molecules and fulvic acid were chose as accelerators,and control reactors without accelerators were set up to investigate the influence of accelerators on anammox system under low temperatures,so as to find an effective method for the application of anammox process at low temperature.Compared with the control reactor,both accelerators significantly improved the denitrification capacity and specific anammox activity(SAA)of the system when the temperature between 10 ℃ and 15 ℃,and the signal molecules had better promoting effects.Adding signal molecules made the average total nitrogen removal rate achieve70%,which was only 7% in the control reactor.The average total nitrogen removal rate reached 47% when fulvic acid was added,while it was 8% in the control reactor.At5 ℃,the total nitrogen removal rated of all reactors decreased to below 20 mg TN/(L·d),and the SAA(about 1.9 g TN/(g VSS·d))was lowest at that time,but the decline was still less than 20%,signal molecules lose advantages at 5 ℃.Both signal molecules and fulvic acid could increase the EPS secretion and PN/PS value in the system,and fulvic acid did better in stimulating secretions of EPS.The highest EPS concentration appeared at 5 ℃,while the highest PN/PS was observed at the end of the test,indicating the promotion of biofilm stability in the system.Signal molecules and fulvic acid additions promoted the production of some signal molecules in the reactor and enhanced the quorum sensing of the system.High-throughput sequencing analysis showed that exogenous signal molecules and fulvic acid changed the bacterial community structures of anammox systems in different ways.The relative abundance of An AOB was improved by 81% and 39%,respectively,and the rise of Candidatus Kuenenia was higher.The proportion of Candidatus Kuenenia in the total anammox bacteria in the signal molecular reactor and control reactor was 84% and 27%,respectively,and the proportion of Candidatus Brocadia in the total anammox bacteria was 14% and 68%,respectively.In addition,compared with the control reactor,the two accelerators also effectively inhibited the growth of nonfunctional bacteria.Compared with the signal molecules,the relative abundance of nitrifying bacteria(AOB)and denitrifying bacteria(DNB)in the fulvic acid reactor was higher.At the end of the test,the contents of these two kinds of bacteria in the fulvic acid reactor were 45% and 49% higher than that in the signal molecule reactor,respectively.