Study On The Patterns And Controlling Factors Of Arsenic Release From Aquifer Matrix

High arsenic(As)groundwater is a common groundwater environmental problem in the world.The reductive dissolution of iron and manganese oxides mediated by microorganisms is considered to be the key process for the formation of high As groundwater.Organic matter can be used as the energy substance of microbial activity and the important electron donor in redox reaction to participate in the As release directly.Due to the complexity of biogeochemical properties of organic matter in nature,the understanding of As release and subsequent enrichment process under the joint action of organic matter,ferromanganese mineral and microorganism in aquifer remains unclear.To study the release process of As from arsenic bearing ferromanganese oxides mediated by microorganisms under the action of organic matter alone is helpful to understand the factors affecting As release and the mechanism of As migration and transformation in groundwater.The sediments in the high arsenic aquifer were selected to carry out batch experiments and column experiments to simulate the influence of the change of pH and redox conditions of the system on As migration and transformation under the condition of infiltration of small molecular organic matter.The main process of As,Fe,Mn and other trace elements release caused by different kinds and contents of organic matter was analyzed,and the mechanism of iron and manganese minerals on As release under the action of microorganism was explored.The small molecular organics(glucose,sodium lactate)used in this study can only be used as carbon source for microbial activities,without complex competitive adsorption and complexation,which can directly reflect the effect of microbial dissimilation reduction on the biogeochemical process of As release.The results showed that the release of As,Fe and Mn in the aquifer sediment was mainly determined by the activity and concentration of organic matter and the microorganism which plays a leading role.Glucose and sodium lactate can promote the formation of reduction environment and the release of As.The main source of As in aqueous solution may be the release of iron/manganese oxides combined with As.The presence of humic acid can significantly accelerate this process.The release degree of Fe/Mn in the sediment determined the release amount of As.Organic matter promotes the reductive dissolution of iron-bearing minerals and the release of As(Ⅲ)in the system by affecting the abundance and activity of Fe and As reducing bacteria and the promotion effect of glucose is more significant.High As concentration corresponds to high Bix,FI value and low Hix value.Combined with fluorescence indexes such as SUVA254,SR and S275-295,it is indicated that low molecular weight and high activity of organic matter compounds related to microbial activity have significant indicative effect on As release.Under the action of microorganism and organic matter,the release of As,Fe and Mn decreased significantly in the later stage,and the formation of secondary minerals of FeS and its coprecipitation to As may contribute significantly to this.Under the action of acid producing bacteria,Fe-reducing bacteria,As-reducing bacteria,S-reducing bacteria and other reducing bacteria,the organic matter first promoted the release of Fe and As,but in the later stage,the production of sulfide/oxidation secondary minerals inhibited the increase of Fe and As concentration.