Hydroxylamine Promotes Nitrogen Removal And Microbial Mechanism During In-situ Aerobic Remediation Of Landfill

Large amounts of landfill leachate and landfill gas discharged in Municiple Solid Waste landfills are key factors restricting the sustainable development of domestic waste landfills,especially the high concentration of ammonia nitrogen in the landfills which seriously pollutes the soil and groundwater.And a large amount of CH₄ emission increase the greenhouse effect.Therefore,there is an urgent need to develop a cost-effective landfill leachate denitrification technology.The in-situ remediation technology's resource-based characteristics make it the technology of choice.Therefore,there is an urgent need to develop a cost-effective landfill leachate denitrification technology.The in-situ remediation technology's resource-based characteristics make it the technology of choice.To this end,we have constructed an in-situ aerobic-anaerobic leachate recycling landfill?AARLs?remediation system,using native microorganisms in the landfill to conduct denitrification studies on aged landfill leachate;In order to further solve the problem of NO₃^--N accumulation caused by insufficient carbon source in AARLs,the feasibility of nitrogen removal by methane oxidation coupled denitrification?AME-D?was explored,and the mechanism of nitrogen removal was analyzed by different microbial molecular methods;Using the methane oxidation characteristics of ammonia oxidizing bacteria?AOB?,the effects of hydroxylamine and AOB on the nitrogen removal effect of AME-D in landfills and microbial mechanisms were studied.Primary results were listed as follows:?1?Aerobic-anaerobic leachate recycling landfills?AARLs?had a good removal effect on ammonia nitrogen and COD in aged landfill leachate.The final removal rates were above 90%and 75%,respectively.The physical and chemical indicators of the section effluent were gradually stabilized.Adding hydroxylamine to AARLs would contribute to the improvement of simultaneous nitrification and denitrification?SND?efficiency and total nitrogen?TN?removal rate in AARLs,mainly reflected in the improvement of ammonia oxidation capacity in the early aerobic stage and the promotion of nitrate reduction in the middle and late anaerobic stages.According to high-throughput sequencing,norank?f?anaerolineaceae,Truepera,and norank?JG30-KF-CM45,as the main denitrifying microorganisms in AARLs,had achieved the decomposition of refractory organic matter in old landfill leachate.At the same time,the abundance of methane oxidizing bacteria Methylocaldum and Nitrosomonas in the hydroxylamine treatment group had been significantly improved,which would help accelerate the carbon and nitrogen cycle in the landfill.?2?Using the aged refuse enriched in methane oxidizing bacteria to study the effect of methane oxidation coupled denitrification and denitrification in landfills and changes in microbial community structure.Simultaneous reduction of CH₄ and NO₃^--N concentrations during the laboratory experiment showed the feasibility of AME-D deep nitrogen removal in AARLs landfill.When the O₂ content was 20%,the methane oxidation rate could reach a maximum of 4.94 mmol/d,and the nitrogen removal rate conld reach a maximum of 0.21 mmol NO₃^--N/d.The methane oxidation process significantly improved the methane oxidation function gene pmo A and denitrification function gene nir S in aged refuse,up to 1.39E+09 copies/g and 1.22E+10 copies/g.The denitrification microorganisms were transformed from traditional denitrification microorganisms norank?f?JG30-KF-CM45,Truepera to Methylobacterium,UBA6140and the substantial enrichment of methylophilic denitrification bacteria was likely the main improvement of the AME-D denitrification efficiency in landfill the reason.From the results of PICRUSt analysis,it could be observed that during the methane oxidation process of mineralized waste,the overall microbial metabolic function showed a downward trend,while the cellular process and signal transmission,information storage,and processing functions were improved.?3?A laboratory experiments of the contribution rate of methane oxidation proved that the important role of ammonia oxidizing bacteria?AOB?in the methane oxidation process was 45.16-54.27%.Among them,artificial activation of AOB combined with hydroxylamine treatment could significantly increase the methane oxidation and nitrogen removal efficiency.Through the dynamic study of the concentration of key enzymes?AMO/HAO?in AOB,it could be seen that the increasing in AMO enzyme activity promoted the methane oxidation process.The HAO enzyme continuously released electrons in the presence of hydroxylamine to supplement the reduction equivalent of the methane oxidation process,and only when AOB remained active and hydroxylamine was present,AOB-mediated methane oxidation efficiency could be achieved.At the same time,the significant increasing in the relative abundance of AOB during the methane oxidation indicated that the AOB-mediated methane oxidation in the landfill could not be ignored.