Transport model for sequential release of Mn, Fe and As under anaerobic soil water environment

Groundwater contamination has been rising as a critical issue to be solved. Prediction of distribution and fate of different contaminants need to be obtained prior to designing an appropriate monitoring and remediation scheme. To model bacteria mediated redox processes a one-dimensional, multi-component reactive transport model that accounts for the reaction coupling the major redox elements was presented. Mass transport equation was used to simulate transport processes of different pollutants. For the numerical modelling of mass transport in the mobile phase, the method of characteristics was used considering fundamental geochemical processes. Then, solute transport was coupled to microbially mediated organic carbon degradation. To model a complete redox sequence (aerobic or denitrifiers, Mn(IV)-reduction, Fe(III)-reduction, respiration bacteria of iron and arsenic compounds, and As(V) reduction) five functional bacterial groups (X₁, X₂, X₃, X ₄ and X₅) were defined. Microbial growth was assumed to follow Monod type kinetics. The exchange between the different phases (mobile, bio, and matrix) was also considered in this approach. Results from a soil column experiment were used to verify the simulation results of the model. It was concluded that the transport model provides a useful framework for predicting the transport of arsenic in the groundwater aquifer.