Effect Of Indigenous Denitrifying Bacteria On Nitrogen Removal By Permeable Reactive Barrier

A large number of researches have shown that there are different degrees of nitrate pollution in groundwater around the world.Groundwater as a source of drinking water,is of indispensable significance to human production and life.The high concentration of NO₃^--N in drinking water is extremely unfavorable to human health.Therefore,the problem of nitrate pollution in groundwater needs to be solved urgently.The in-situ repair technology of PRB has been developed more mature.However,most of the materials used as fillers are synthetic materials that are not native to nature,and the environmental compatibility is poor.In this research,from the perspective of environmental ecological engineering,soil and sawdust,which are two kinds of substances widely existing in nature,were selected as the fillers of simulated osmotic reaction column,and bioaugmentation technology was used in parallel to explore the effect of inoculation of indigenous denitrifying bacteria on the denitrification effect of simulated osmotic reaction column and to explore the internal causes of the change of microbial community structure.The research results provide more theoretical basis and practical guidance for the ecological management of nitrate pollution,which is of great significance to the ecological restoration of nitrate pollution.The main results of this study are as follows.（1）Indigenous denitrifying bacteria with good denitrification performance were screened from the soil of the experimental reaction column.The indigenous denitrifying bacteria were cultured at 37°C for 72 h,and the removal rate of NO₃^--N in the denitrifying liquid medium reached 90.77%.It was identified as a new strain of Pseudomonas and named Pseudomonas sp.P10.（2）Explore the effect of indigenous denitrifying bacteria on the denitrification effect of the reaction column.Inoculating indigenous denitrifying bacteria Pseudomonas sp.P10into the reaction column can shorten the start-up time of NO₃^--N removal.The dominant bacteria in the treatment group inoculated with indigenous denitrifying bacteria were Pseudomonas,and the relative abundance reached 18.23%.It shows that indigenous denitrifying bacteria can adapt to the environment well.Under the condition of 10 mg/L NO₃^--N concentration simulated wastewater,the treatment group inoculated with indigenous denitrifying bacteria had better NO₃^--N removal effect than other treatment groups.When the concentration of NO₃^--N in simulated wastewater was 30 mg/L and 50mg/L,the removal effect of NO₃^--N in the treatment group with the mixture of soil and sawdust was better than that in other treatment groups.When the hydraulic retention time reached 48 h,the removal rate of NO₃^--N reached 94.18%and 96.05%respectively,which was higher than that of other treatment groups,indicating that the soil itself had good denitrification performance.The original soil could achieve strong denitrification effect in the presence of solid carbon source.The treatment group inoculated with indigenous denitrifying bacteria showed NH₄⁺-N accumulation,and other treatment groups had different degrees of removal effect on NH₄⁺-N.There was no accumulation of NO₂^--N in the effluent of all treatment groups.The TOC concentration of the effluent met the water quality standard,and the p H value of the effluent was between 7.0 and 8.0.Under the condition of 10 mg/L NO₃^--N concentration simulated wastewater influent,the effluent TN concentration was higher than the TN concentration in the simulated wastewater.In the condition of 30 mg/L and 50 mg/L NO₃^--N concentration simulated wastewater influent,the TN removal rate of each reaction column was between 50%and 70%.（3）To explore the effect of indigenous denitrifying bacteria on the denitrification effect of non-homologous soil filling reaction column.The soil in the filler layer of the reaction column was changed to the heterogeneous soil of the denitrifying bacteria Pseudomonas sp.P10.Under the influent NO₃^--N concentration of 10 mg/L,30 mg/L and 50 mg/L,the removal rates of NO₃^--N in the treatment group inoculated with Pseudomonas sp.P10reached 40.53%,22.10%and 37.68%respectively when the hydraulic retention time was 6h.The removal rates of NO₃^--N in the treatment group with soil and sawdust mixture were35.47%,13.17%and 25.14%respectively under the condition of 6 h hydraulic retention time.The results showed that the inoculation of Pseudomonas sp.P10 could accelerate the start-up time of NO₃^--N removal.However,when the hydraulic retention time reached 48h,under the condition of 30 mg/L and 50 mg/L NO₃^--N concentration,the removal rates of NO₃^--N in the treatment group with soil and sawdust mixture were 90.05%and 82.27%respectively,which were higher than those in the other treatment groups,indicating that the dominant bacteria in the sustainable denitrification process of the reaction column were still indigenous denitrifying bacteria in the soil,which further indicated that the soil itself had better denitrification potential.Soil and wood chips as fillers have good environmental compatibility while being economical.There was no accumulation of NH₄⁺-N and NO₂^--N in each reaction column.Under the influent concentration of 30 mg/L nitrate nitrogen,the removal rate of TN in each reaction column was between 20%and 30%.The p H value of effluent was similar to that of groundwater,and the effluent TOC met the water quality standard.How to effectively reduce the TN concentration in the effluent of the constructed reaction column still needs a holistic and systematic research.