Study On Advanced Nitrogen Removal From Landfill Leachate By Coupling Biological Deep Denitrification Process

The high ammonia nitrogen characteristics of landfill leachate make it difficult for traditional biological treatment process to achieve high efficiency and low nitrogen consumption.In the case of serious nitrogen pollution and increasingly strict total nitrogen（TN）emission standards,it is imperative to find efficient and low consumption biological nitrogen removal technology.Based on the process transformation of a leachate treatment plant,the pilot test of landfill leachate treatment with A/O-SBR+EGSB-A/O-MBR+NF combined process was carried out to verify the feasibility of A/O-SBR+EGSB process for short cut nitrification and denitrification coupled with other processes.Because the pilot process needs additional carbon source to achieve deep nitrogen removal,it is not economical.In order to further improve the nitrogen removal performance of the process,a two-stage autotrophic deep nitrogen removal pilot system based on partial nitrification and denitrification coupled with anaerobic ammonium oxidation（ANAMMOX）+sulfur autotrophic denitrification（S⁰dAD）was constructed.In the pilot test,the pH of SBR tank was adjusted to be 6.8～7.8,DO was controlled to be1～1.5 mg/L,NH₄⁺-N concentration of influent was stabilized,and the nitrosation rate was more than 98%.Analysis of the characteristics of FNA and FA during start-up showed that the start-up and stable operation of SBR was the result of high FA in the early stage and the alternate inhibition of FNA on nob in the late stage.The results showed that MLSS and MLSS/MLVSS were about 5000mg/L and 0.4,SV₃₀was 45～50%and SVI was 88～100ml/g,respectively,in the stable operation of shortcut nitrification sludge.The sludge settling performance was good,which ensured the stable nitrogen removal effect of the system.The results of 150 day pilot run showed that the concentration of TN in the influent leachate was（2091±325）mg/L,and the concentration of NH₄⁺-N was（1857±340）mg/L,80%TN and 33%COD can be removed by A/O-SBR+EGSB process by adding methanol;18%TN and 26%COD can be removed by A/O-MBR process,and nanofiltration（NF）system is used as advanced treatment guarantee effluent.The average removal rates of COD,NH₄⁺-N and TN in the whole process system are 96%,99.8%and 98.7%respectively,and the final effluent concentrations are（63.7±18）、（2.7±18）and（26±9）mg/L respectively,which meet the emission standard of nanotube.Nitrogen balance analysis showed that 63.9%of nitrogen was removed by partial nitrification and denitrification.Under the condition of fluctuating water quality,the combined process has a certain ability to resist impact load,and the nitrogen removal effect is good.In order to verify the feasibility,stability and economy of the combined process of partial nitrification and denitrification anaerobic ammonium oxidation（ANAMMOX）-sulfur autotrophic denitrification（S⁰dAD）in the long-term operation of landfill leachate,a small-scale experiment was conducted.Partial nitrification was achieved by controlling the aeration time and observing the end-point pH.the nitrification rate was about 81%and the effluent NO₂^--N/NH₄⁺-N ratio was1:1-1.4:1,which met the influent requirements of anammox reactor.The anammox reactor was operated for 240 days by shortening HRT.When the average volume load（NLR）of TN was up to 5.7 kg/（L·d）,the TN removal rate was still above 68%,and the nitrogen removal effect of the reactor was stable and good.It was found that Anammox reaction was the main reaction in the reactor,and some heterotrophic denitrification improved the nitrogen removal ability of the reactor.By adjusting the parameters,it was found that the removal efficiency of NO_x^--N was the best when HRT was 4h.When the influent NO₃^--N concentration was（70.9±4.8）mg/L,the average volume load of TN was 0.69kg/（L·d）,the removal efficiency of NO_x^--N was 97.5%,and the effluent TN concentration was 19.7mg/l,which was far less than the national standard nitrogen emission requirements（TN≤40 mg/L）,indicating that the coupling s0dad process could achieve stable deep nitrogen removal.In addition,the acute toxicity of leachate treated by each coupling process was improved,from severe toxicity to poisoning,which reduced the impact on the water body of the tube,indicating that microorganisms in each reactor had a certain tolerance in the process of landfill leachate treatment.Through the analysis and calculation of the internal nitrogen removal pathway of the coupled process system,it is concluded that compared with the whole nitrification process,the partial nitrification process can save 22.5%of the oxygen supply and reduce the aeration power consumption of the system;compared with the partial nitrification and denitrification process,the anammox denitrification process can save nearly 65%of the oxygen consumption and 100%of the additional carbon source;compared with the traditional heterotrophic denitrification process,the S⁰dAD process uses methanol as the electricity source In theory,the electron donor cost can be reduced by 62%.Therefore,the coupled process has considerable economy for nitrogen removal of wastewater with low C/N ratio and high NH₄⁺-N.