Screening And Identification Of Multi-function Arsenic Oxidizing Bacteria

With the development of industries and agriculture, more and more pollutants enter into the environment and coexist. The complexicity of the enviroment and ecosystems worsens the adverse effect of pollutants which makes environmental management more difficult. Wastewater generated by agricultural or pesticide industry, vitriol plants and tungsten smelting process, often contains high concentrations of both arsenic and nitrate. In addition, natural migrating process of arsenic also produces wastewater with high arsenic and nitrogen content. Due to the coexistence of pollutants, traditional treatment technologies to remove single pollutant are unable to meet the requirements in applications. It is therefore necessary to develop new technologies to remove a variety of coexisting pollutants.To our best knowledge, there has been little research worldwide on the treatment of wastewater-borne arsenic and nitrogen, in particular the involvement of biological process. In the present study, arsenic oxidizing bacterial strains with denitrifying function were isolated from an arsenic polluted area, and their abilities of arsenite oxidation and denitrification were investigated. This pioneering work is significant to advance our understanding of the roles of microorganisms in simultaneously removing arsenic and nitrogen.In this study, a total of 43 aresnic-resisting bacterial strains were isolated from water and sediment samples taken from Hechi, Guangxi Province. Among them,27 strains were classified as arsenite oxidizers,7 of which were also aerobic denitrifiers. A total of 19 isolates were identified as Paracoccus sp., Rhizobium sp., Thauera sp., Hydrogenophaga sp., and Agrobacterium sp..A new arsenic speciation method was developed in this tudy. Arsenite was first oxidized to arsenate by KMnO4, and arsenate was then determined with HPLC-UV. The effect of culture medium on the accuracy and reproductivity of arsenic determination was evaluated and it was found that minimal medium was the best culture medium with the minimal interference with the arsenic signals on HPLC-UV.The effect of coexistence of arsenic and nitrogen on the performance of arsenite oxidation and denitrification was investigated with Strain c11-35 as a model bacterium. Both denitrification and arsenic oxidation were found improved in the coexistence of nitrate and arsenic.The removal of nitrate was 53.65% when only nitrate was present, while it increased to 75.27% when both arsenite and nitrate were present. The conversion of arsenite was over 99% which was enhanced at the presence of nitrate. This phenomenon may be related to the electron transmission process of aerobic denitrification and the dynamic balance during arsenite oxidation.