Applicability Of Biogenic Mn Oxides Remediation For As Contaminated Agricultural Soil In A Typical Mine-based Oasis

The concentrations of heavy metal(loid)s in farmland soil exceeded the allowable limits in the agricultural soil due to nearly 40 years of sewage irrigation history,which had seriously threatened crops quality and soil ecological environment in Dongdagou stream in Baiyin City,Gansu Province.Therefore,it was urgent to adopt appropriate technology to remediate contaminated soil,and reduced the mobility and bioavailability of heavy metal(loid)s.In many technologies,this study focused on biogenic Mn oxides remediation technology,and took As contaminated agricultural soil as the research object in typical mine-based oasis,to research the applicability of technology in As pollution degree,degree of salinization,As remediation efficiency,crops safety-soil exchangeable As fraction concentration,and economic costs.On the field investigation basis,study on the remediation efficiency of Pseudomonas taiwanensis(P4 bacteria)and Pseudomonas plecoglossicida(G1 bacteria)to immobilization of heavy metal(loid)s contaminated agricultural soil.The XPS,FTIR characterization and the Tessier sequential extraction analysis were used to study the characteristics of biogenic Mn oxides,and the morphological changes and remediation mechanisms of As in the soil after immobilization.The biogenic Mn oxides remediation technology had the advantages of simple operation,low treatment cost and no secondary contamination.The main results were as follows:(1)After microbial remediation of contaminated soil,the soil exchangeable As fraction concentrations decreased,the mobility and bioavailability of As reduced.When P4 or G1 bacteria were used to remediate As alone,the mean value was 80.82% and 78.74%,respectively.But the mean efficiency was only 66.4% when the two bacteria were combined;(2)Soil organic matter content and total nitrogen content were positively correlated with As efficiency of microbial remediation,respectively;(3)Adding organic fertilizer to the soil could improve the efficiency of microbial remediation of As;(4)The applicability of biogenic Mn oxides remediation technology was reflected in the following aspects: suitable for remediation of As slightly polluted to heavily polluted soil;suitable for remediation of non-salinized to moderate salinized soil;the remediation efficiency of this technology for As was higher than phytoremediation technology;after remediation,the exchangeable As concentration of soil was within the allowable safe concentration range of As in soil under the condition that the crops did not exceed the standard;economic costs were low;(5)The exchangeable As fraction in soil was adsorbed on the surface of the biogenic Mn oxides minerals or fixed in the mineral crystal lattice to reduce the mobility and environmental risk of As.