Denitrification Of Mature Landfill Leachate By Integrated Continuous Flow Deammonification Process

Anaerobic ammonia oxidation（ANAMMOX）process has the advantages of low energy consumption,no need to add organic carbon source and low sludge output.It has been widely used in the denitrification of high ammonia nitrogen wastewater.The ANAMMOX process can be divided into two types:multiple-steps and one-step.The one-step process realizes all reactions in one reactor,which can greatly reduce the cost of capital construction.It has a wide application prospect in the denitrification treatment of mature landfill leachate.In this study,two sets of new one-step autotrophic nitrogen removal reactors were constructed using integrated reactors:Integrated Semi-fixed Activated Sludge reactor（ISFAS）and Multiple Continuous Fixed Bio-film Reactor（MCFBR）.The feasibility of two reactors applied to the denitrification treatment of mature landfill leachate was explored,which provided theoretical basis for its engineering application and promotion.The two sets of reactors were started by artificial water distribution.Through the adjustment of working conditions,both sets of reactors finally achieved good autotrophic nitrogen removal effect,and the total nitrogen removal rate of ISFAS（80%）was lower than that of MCFBR（90%）.In the stage of treating mature landfill leachate,MCFBR finally achieved a total nitrogen removal rate of 95%and a total nitrogen removal load of0.18kg N/m³·d.However,the accumulation of nitrate and nitrogen in ISFAS from the start-up stage resulted in a total nitrogen removal rate of only 70%and a total nitrogen removal load of0.1kg N/m³·d.The data of nitrogen remove showed that MCFBR realized the coupling of autotrophic denitrification and denitrification improved the removal rate of total nitrogen and avoided the accumulation of nitrate nitrogen.The reasons for the operation failure of ISFAS reactor were DO control,sludge activity collocation,reactor structure,which showed that MCFBR was more suitable for the operation of one-step process.The analysis of EPS content and composition of ISFAS sludge in different stages of operation shows that when microorganisms are faced with harmful components in mature landfill leachate,they will produce more EPS to resist adverse environment,so as to maintain the stable operation of the reactor.By adjusting measures such as adding inhibitor hydrazine and high concentration of free FA,the accumulation of nitrate and nitrogen in ISFAS effluent can be alleviated to a certain extent,and△NO₃^-N/△NH₄⁺-N decreases from 0.2 to 0.15.In MCFBR working condition adjustment,effluent reflux and prolonged HRT are effective measures to alleviate the inhibition of toxic components in mature landfill leachate on microbial activity.Finally,the microbial community structure in the MCFBR was analyzed.Bacteroidete,Chloroflexi,Proteobacteria and Actinobacteriota were the most abundant bacteria.The main anammox bacteria are Candidatus Jettenia,Candidatus Brocadia.The abundance of AOB bacteria Nitrosomonas in MCFBR aerobic chamber is higher than that of NOB bacteria Nitrospiraceae,which ensures the stable process of partial nitrification.Moreover,denitrifying bacteria Truepera is found in the pre-anaerobic zone,which can degrade toxic components in landfill leachate.A natural buffer zone is formed at the front of the reactor.The species richness in the middle room of MCFBR was the highest,and there was no significant difference in species richness between the modified and unmodified fillers,while a large number of OTU in ISFAS was common to all samples.