Conceptual Model of Redox Zonation in High Arsenic Groundwater System Under the Effect of Microorganisms

Microbial activities have important effects on chemical composition and redox condition of groundwater,and also migration and transformation of arsenic.Researches on redox zonation in high arsenic groundwater system can help people to further understand the migration and transformation of arsenic in groundwater under the effect of microorganisms,and provide the theoretical basis for in-situ remediation of high arsenic groundwater.By reviewing the results of previous studies,this paper elucidates the adsorption,release and readsorption of arsenic in different biogeochemical stages,and depicts the conceptual model of redox zonation in high arsenic groundwater system.Along the groundwater flow paths,the electron acceptors are consumed sequentially in the order as dissolved oxygen>nitrate>Fe(III)>sulfate>CO₂.In dissolved oxygen and nitrate reduction stage,groundwater is in partial oxidation environment,and the arsenic will not be released into the groundwater as the Fe(III) reduction is inhibited.In Fe(III) reduction stage,groundwater is in reduction environment and the reductive dissolution of Fe(III) is the main process,so the arsenic will be released into the groundwater.When SO^2-₄reduction starts,groundwater is in strong reducing environment,and the sulfide that generated by combination of HS^- and Fe²⁺will adsorb or coprecipitate the arsenic,thus decreasing arsenic concentration in the groundwater.