Experimental Study On Biological Denitrification And Remediation Of Groundwater Polluted By High Ammonia Nitrogen In Landfill Leachate

Due to the lack of an anti-seepage system in informal landfills,the leakage of landfill leachate causes high-concentration ammonia nitrogen（NH₄⁺-N）pollution in groundwater.Ammonia nitrogen has strong mobility in groundwater and spreads in a wide range,which may cause serious harm to the environment and human health.The existed physical and chemical technologies for removing high ammonia nitrogen have many disadvantages such as highly economic costs and easily secondary pollution.However,Biological denitrification technologies provide a green,environmental friendly,cost-effective and efficient in-situ remediation method to treat the nitrogen-polluted groundwater.Among them,heterotrophic nitrification-aerobic denitrification（HN-AD）bacteria can grow well in aerobic and anaerobic environments,and can simultaneously perform nitrification and denitrification,which is a hot research topic.The research is based on the groundwater polluted by a certain landfill leachate with high ammonia nitrogen as the research object.In the study,three indigenous and facultative HN-AD strains were screened and token a series research on denitrification effect and environmental influence factors.At the same time,different equal ratio combination modes that contain two or more species of bacteria for producing the composite bacteria was investigated on the denitrification performance in different ammonia nitrogen concentrations.Finally,simulated composite bacteria repair the groundwater polluted by high ammonia nitrogen in the landfill leachate for preliminary exploration through the sand column experiment.The research provides three new functional strains and data supporting for biological denitrification and repair of groundwater polluted by high ammonia nitrogen.The main findings are as follows:（1）Nine strains of indigenous and facultative HN-AD were isolated by enrichment,primary screening and re-screening.Through the 16S r DNA,electron microscopy scanning,bacterial morphology,physiological and biochemical identification,the three HN-AD strains with better denitrification effects were determined to be Pseudomonas stutzeri H-6,Pseudomonas chlororaphis H-8,and Pseudomonas frederiksbergensis H-9.（2）A series of single-factor experiments were token to investigate single bacteria growth and the removal effiency of ammonia nitrogen and total nitrogen under different carbon source conditions,it was found that the best carbon source for nitrogen removal of the three bacteria was sodium succinate.The Box-Behnken response surface method was used to design experiments for C/N,p H value,temperature and shaking table speed.Under the best conditions,the ammonia nitrogen removal rate of strains H-6,H-8 and H-9 were 93.42%,92.35%and 89.25%,respectively,and the total nitrogen removal were 93.42%,92.35%and 89.25%,respectively.Through investigating the growth in different concentration gradients ammonia nitrogen solution,it showed that all the three strains have good tolerance for high ammonia nitrogen concentration,but high initial ammonia nitrogen concentration inhibites the growth and denitrification of the strains.Through the concentration determinations of the intermediate products（NO₃^-,NO₂^-）,it was further verified that the three bacteria could perform denitrification simultaneously when performing heterotrophic nitrification.When the initial ammonia nitrogen concentration of the three bacteria were under 200 mg/L,the denitrification effect is better,and the removal rates of ammonia nitrogen and total nitrogen are all above 87%and 77%,respectively.When the initial ammonia nitrogen concentrations are exceeded400 mg/L,the denitrification effect is unsatisfactory,and the removal rates of ammonia nitrogen and total nitrogen are both lower than 50%and 42%respectively.（3）Through the antagonism experiment,it was found that the three single bacteria exist no antagonistic reaction between each other.Then the three single bacteria were compounded in equal ratio.And the obtained composite bacteria were used for denitrification experiments in different ammonia nitrogen concentration.It was found that under the same conditions,the composite bacteria D（H-6+H-8+H-9）has the best denitrification efficiency,especially when the initial ammonia nitrogen concentrations are 400mg/L and 800mg/L,the removal rate of ammonia nitrogen are80.12%and 67.96%,which are 31.03%and 42.56%higher than the single bacteria with the best ammonia nitrogen removal effect,and the total nitrogen removal rates are 73.64%and 60.71%,better than the single bacteria with the best total nitrogen removal effect increased by 26.73%and 48.07%respectively.（4）Simulation of groundwater polluted by a certain landfill leachate with high ammonia nitrogen through sand column experiment.Then the research on the denitrification effect of composite bacteria D under different temperature and hydraulic retention time（HRT）conditions were investigated.The results showed that the ammonia nitrogen removal rate of composite bacteria D at a 0.03 m L/min flow rate was25℃（60%）>35℃（53%）>15℃（33%）,and the total nitrogen removal rate was 25℃（53%）>35℃（48%）>15℃（43%）;at a temperature of 15℃,the ammonia nitrogen removal rate was 72 h（40%）>48 h（29%）>24 h（18%）,and the total nitrogen removal rate was 72 h（35%）>48 h（22.5%）>24 h（12.5%）.