Isolation Of Aerobic Deuitrifying Strain Achromobacter Xylosoxidans GR7397 And Its Application In The Biological Nitrogen Removal System

Excessive nitrate in water bodies can pose a serious safety hazard to aquaculture,public health,and ecosystem function,and the use of biotechnology to achieve efficient nitrate removal has become a research priority for wastewater treatment plants.This study isolated and purified a novel strain of aerobic denitrifying bacteria with high nitrate removal capacity from the aeration basin activated sludge of a domestic wastewater treatment plant,which was identified as Achromobacter xylosoxidans based on its phylogenetic characteristics and named as GR7397.Five denitrification reductases were detected in strain GR7397 by electrophoretic analysis of PCR amplification products,containing periplasmic nitrate reductase(NAP),membranous nitrate reductase(NAR),nitrite reductase(NIR),nitrite oxide reductase(NOS)and nitric oxide reductase(NOR),demonstrating that the strain has a complete denitrification metabolic pathway.Further studies showed that strain GR7397 could reduce nitrate-nitrogen concentration from 93.90 mg/L to 4.73 mg/L in 6 h with sodium acetate as electron donor,COD/TN ratio of 4,pH of 8,and temperature of 30℃,with the best nitrate-nitrogen removal rate of 14.86 mg·L-1·h-1 and removal efficiency of 94.97%,and no nitrite There was no accumulation of nitrite nitrogen.The nitratenitrogen removal rate in the SBR inoculated with 30%strain GR7397 concentrate reached removal rates in the range of 15.48-28.55 mg·L-1·h-1,much higher than the blank control group,indicating that the aerobic denitrification performance of this strain has great potential for application in activated sludge systems.The strain GR7397 was immobilized with hydrophilic polyurethane filler in denitrification medium,and then the anoxic-aerobic(AO)reactor simulating municipal wastewater was treated with bioaugmentation,and the microbial community structure of activated sludge and packed biofilm in the system was analyzed by high-throughput sequencing.The dominant genera of activated sludge operation stabilization include Achromobacter，Terrimonas,Hydrogenophaga,Thauera,and Dechloromonas.The relative abundance of the genus Achromobacter in the initial activated sludge was very low at 0.0094%,however,the abundance of Achromobacter in the activated sludge after 40 days of operation was 0.059%compared to the initial sludge,indicating that the immobilization of strain GR7397 by hydrophilic polyurethane foam and its injection into the reactor would affect the microbial community in the activated sludge system to some extent.The structure of the activated sludge system was affected and changed to some extent.The relative abundance of Achromobacter in activated sludge tended to increase with the extension of reactor operation time and the load shock of ammonia nitrogen,and the relative abundance of Achromobacter on biofilm was 0.27%after stable operation,which was 0.056%higher than that in sludge.The results showed that the hydrophilic polyurethane filler domesticated by strain GR7397 could not only increase the relative abundance of this genus in the activated sludge system,but also provide an environment for the growth and reproduction of other aerobic denitrifying bacteria.This study provides a new way for the immobilization of aerobic denitrification strain GR7397 and its denitrification in practical engineering.