Study On The Enrichment,immobilization And Application Of High-efficiency Denitrifying Bacteria

In recent years,the total nitrogen concentration of water has increased due to the massive combustion of ore fuel,the excessive discharge of industrial wastewater and domestic sewage,which have aggravated the nitrogen pollution of water.The high concentration of total nitrogen in surface water,which was mainly nitrate,not only has adverse effects on the safety of the ecosystem,but also threats the human health.Physical and chemical technology can not effectively reduce nitrate of surface water,but biological treatment method of nitrate in surface water not only operated easily and effectively,but also simplified the process and reduced the investment cost.Firstly,influences of different carbon sources to enrich the high-efficiency denitrifying bacteria were explored in this study.Secondly,the removal efficiency of high-efficiency denitrifying bacteria immobilized by different carriers was investigated,and the best carrier for the high-efficiency denitrifying bacteria was selected.Finally,the high-efficiency denitrifying bacteria immobilized by selected carrier were applied to the nitrate treatment of surface water,the efficiency and stability were observed during the operation time.The main results of the study were as follows.(1)Glucose and sodium acetate were used as carbon source,and added into continuous-flowing denitrification reactors to enrich the high-efficiency denitrifying bacteria.Results showed that different carbon sources had a significant effect on the enrichment of high-efficiency denitrifying bacteria(P<0.05).After enriching,the denitrification rates in glucose and sodium acetate systems were 8.56 mg N/(g VSS·h)and 11.26 mg N/(g VSS·h),respectively,which were 2.09 times and 2.75 times than that of the initial sample.The accumulation of nitrite and ammonia nitrogen in glucose system was significantly higher than that of sodium acetate system(P<0.05).The microbial diversity decreased after enriching,and the types of carbon source affected the composition of microorganism community and the relative abundance.The high abundance of Pseudomonas and Thauera verified that sodium acetate is the optimal carbon source to enrich the high-efficiency denitrifying bacteria.In addition,glucose as a carbon source was contributed to the expression of the nirS gene,and sodium acetate as a carbon source was contributed to the expression of the nirK gene.(2)The cultivated high-efficiency denitrifying bacteria were further immobilized with the carriers of polystyrene,polyvinyl alcohol pellets and mycelial pellets.Results showed that biomass of high-efficiency denitrifying bacteria immobilized by polystyrene,polyvinyl alcohol pellets and mycelial pellets carriers were increased by 0.12 g/L,0.21 g/L and 0.41 g/L,and cell mortality were decreased by 5.00%,7.70% and 13.65%.The nitrate removal efficiency of high-efficiency denitrifying bacteria immobilized by polystyrene,polyvinyl alcohol pellets and mycelial pellets were enhanced by 2.44%,5.05%,and 19.72%,the accumulation of nitrite and ammonia nitrogen concentrations were effectively alleviated by carriers,and the total nitrogen removal efficiency were increased by 2.75%,11.87%,and 24.78%,respectively.The dense structure of polyvinyl alcohol pellets was beneficial to resist low temperature,but it was also easily broken under high rotation speed and alkaline conditions.Mycelial pellets with stable network structure could maintain high stability under the interference of external factors and multiple cycles,and the network structure of mycelial pellets was beneficial to multiple cycles,which is the most suitable carrier for the immobilization of high-efficiency denitrifying bacteria.(3)High-efficiency denitrifying bacteria immobilized by mycelial pellets can effectively treat nitrate of surface water.The mycelial pellets can effectively intercept biomass and maintain the microbial activity,the nitrate removal efficiency of high-efficiency denitrifying bacteria immobilized by mycelial pellets were increased by 31.82%,36.02% and 37.30% at 30?,15? and 4?,and the total nitrogen removal efficiency were enhanced by 48.25%,21.90% and 23.63%,respectively,compared to free high-efficiency denitrifying bacteria.In addition,the biomass and cell activity for high-efficiency denitrifying bacteria immobilized by mycelial pellets were significantly improved and was less affected with temperature changes.The microbial diversity increased with the decreasing temperature at first,then decreased with the further decrease of the temperature,and the system exerted the maximum microbial diversity at temperature of 15°C.The nitrate removal efficiency of systems was related to the changes of relative abundance of Unclassified_f_Enterobacteriaceae,Raoultella and Thermomonas,and the nitrite accumulation was related to Chryseobacterium and Rhizobium in the system.The changes of relative abundance of Zoogloeas,Simplicispira,Flavobacterium,Dechloromonas and Acidaminobacter were the adaptive adjustment of temperature change in the system.