Research On The Coupled Kinetics Model For The Reactions In Arsenic-microbe-iron Oxide System

Soil heavy metal pollution is a hot issue in the current environmental field.Various biotic and abiotic components affect the morphological distribution and migration of heavy metals in the soil.Exploring the effects of multiple soil components on the environmental behavior of heavy metals is important to understand the dynamics of heavy metals.Arsenic(As)is a common toxic heavy metal in soil with various valence states.The dynamic behavior of As in soil is affected by both iron oxides and microbes,and is controlled by a series of coupled dynamic processes.The objective of this study is to develop a quantitative model for describing the coupling reactions of As in the presence of microbes and iron oxides.In this study,we first built microbe-As-single iron oxide kinetic model for describing the reduction of As(V)by microbes and the adsorption/desorption of As(III)and As(V)on ferrihydrite or goethite in this system.The kinetic process focused on the competition of microbes with As for the adsorption sites on iron oxides.The kinetic model was based on a large number of experimental data from 11 published literatures,and then the data were fitted by the kinetic model.These experiments involve different reaction conditions,types of microbial strains,biomass and iron oxide types and concentrations.Results indicate that the kinetic model can well reproduce the data of 11 literatures,quantitatively describe the dynamic distribution of As and the characteristics of reduction,adsorption/desorption reaction rates in this system.Based on this model,we further built microbe-As-various iron oxide kinetic model,which can describe the reduction of As(V)by microbes and the adsorption/desorption,incorporation and dissolution of As(III)and As(V)on ferrihydrite and magnetite during the phase transformation of iron oxides.The model focused on the relationship between the reduction rate of microorganisms and transcription of As(V)reducing genes.The kinetic model which was based on experimental data can quantitatively describe the kinetic process and morphological distribution of As in different As/Fe ratio systems(0.1,0.08,0.04,and 0.008).The kinetic model of As coupling reaction developed in this study can quantitatively describe the dynamic behavior of As in the microbe-As-iron oxide system,and can explain the dynamic coupling of various reaction processes of As(reduction,adsorption,desorption,incorporation and dissolution processes).The model reflected the influence of biological components in soil on the environmental behavior of As,highlighted the competition of microbes with As for adsorption sites on iron oxides,and demonstrated the importance of the existence of microorganisms to promote As desorption.Furthermore,the model emphasized the delay of the reduction rate of microbes,and quantitatively analyzed the reduction rate of microbes at the genetic scale,which built the foundation for a more comprehensive explanation of the microbial reduction rate coefficients in the model.The model also took into account the dissolution and transformation of iron oxides in the presence of microbes,and described the adsorption/desorption and incorporation of As(III)and As(V)on the surface of iron oxides during kinetic reactions,which systematically improve the kinetic model of microbe-As-iron oxide system.The kinetic model established in this study has wide applicability,and can be used in multiple systems involving multi-component and multi-reaction processes.It provides a new model framework for studying the environmental behavior of As in the complex soil environment and developing comprehensive models involving more coupling reactions.Results in this study will benefit us a lot for predicting the cycling and speciation changes of As in biogeochemical processes.