Optimization And Nitrogen Removal Mechanism Of Alcaligenes Faecalis TF-1 Screened From Landfill Leachate

Landfill leachate pollution has received increasing attention from the society,and it is also a major problem of environmental area that the country needs to focus on.However,the composition of landfill leachate is complex(high ammonia nitrogen,high organic matter and high salt)and difficult to treat.It has serious harm to the ecological environment and human health without treatment.Traditional biological process are difficult to treat landfill leachate due to its poor tolerance of strains to high ammonia nitrogen and slow growth.Some existing novel biotechnologies can respectively solve the problems of poor tolerance to high ammonia nitrogen and slow growth.However,in the face of the comprehensive extreme environment of high ammonia nitrogen,high organic matter and high salt,the existing strains are still unable to efficiently remove nitrogen.In this study,through the biological technology,the microorganisms screened in the landfill leachate was enriched,a heterotrophic nitrifying strain with excellent tolerance of high ammonia nitrogen and high salt was obtained.By optimizing the influencing factors of the strain's nitrogen removal performance,the best conditions of the strain cultured were obtained.The high-throughput sequencing technology was used to explore the mechanism and way of strain nitrogen removal.Finally,the performance of the strain in the treatment of real landfill leachate was verified,this can provide a theoretical basis and practical guidance for the development of a new type of landfill leachate treatment process.The main conclusions are as following:1.The microorganisms screened from the landfill leachate are enriched and domesticated,and the obtained mixed microorganisms can grow rapidly in an environment with an ammonia nitrogen concentration of 1400mg/L.After 48 hours,the OD value can reach 1.76,and the ammonia nitrogen removal rate is 45.93%,which proves that the mixed flora can tolerate high ammonia nitrogen.After the mixed microorganisms were separated and purified,a single pure colony was obtained,and named TF-1.The shape of the TF-1 colony was round in morphological observation,and the surface was smooth and moist,and opaque.Scanning electron microscopy results showed that the TF-1 was short rod-shaped with a size of(1?m?2?m)×(0.5?m?0.8?m).The nucleic acid sequence in Gen Ban K was used for homology comparison,and the strain TF-1 was determined to be Alcaligenes faecalis.2.Under the condition of 200 mg/L of ammonia nitrogen,the cumulative amount of NO₂^--N of strain TF-1 is as high as 22.60 mg/L,and there is no accumulation of nitrate.Under the condition that the nitrate nitrogen and nitrite nitrogen concentrations are both 200 mg/L,the OD₆₀₀ of strain TF-1 is reduced,and these two nitrogen sources cannot be used to convert part of the ammonia nitrogen into intracellular nitrogen,but still some ammonia nitrogen is converted to nitrogen by other means.Therefore,it is speculated that the nitrogen removal pathway of the strain is:NH₄⁺?NH₂OH?N₂O?N₂.In the mixed system of three nitrogen sources,the strain can only use NH₄⁺-N,and the NO₃^--N and NO₂^--N do not affect the nitrification reaction of strain TF-1.3.The strain TF-1 under the conditions of sodium citrate as carbon source,C/N=16,p H=7,and NH₄⁺-N concentration of 808.21 mg/L,the removal rate of NH₄⁺-N can reach 99.98%.The optimum p H range of strain TF-1 for nitrogen removal is 6?10,further lowering the p H will affect its growth and denitrification,and the lower p H has certain limitations on the performance in acid wastewater.Strain TF-1 has a NH₄⁺-N removal rate of 52.87%under the conditions of salinity 70 g·L-1 and NH₄⁺-N concentration of 919.2 mg/L,which proves that the strain has a certain application prospect in the treatment of high salt and high ammonia nitrogen leachate.4.The experimental conditions of strain TF-1 were analyzed by four-factor four-level orthogonal experiment,and the optimal parameters were NH₄⁺-N concentration of 500 mg/L,sodium acetate as carbon source,and COD concentration of 10000 mg/L.The speed is 120 r·min-1.The experimental results show that,under the optimal conditions,the degradation rate of NH₄⁺-N and COD by TF-1 is 100%,and the degradation rate of TN is 94.45%,an increase of 1.53%.5.The real landfill leachate was treated with strain TF-1.Using the strain TF-1 to treat the landfill leachate of a landfill in Rongchang,the removal rates of ammonia nitrogen and total nitrogen were 94.21%and 92.48%.The maximum removal rates of ammonia nitrogen and total nitrogen were 13.34 and 13.30 mg.L^-1.h^-1,and the average removal rates were 6.29 and 6.25 mg.L^-1.h^-1.In addition,the strain TF-1 has strong activity and stability in the leachate,which is conducive to its application in practical engineering.