A Numerical Approach to Simulate the Biogeochemical Involvement in a Coastal Reduced Groundwater Environment

Bacteria-mediated reduction processes play a decisive role in the water quality alterations in the subsurface environment of coastal aquifers. Availability of organic carbon as the electron donor with other electron acceptors such as NO₃ ^?, MnO₂, Fe(OH)₃ and SO₄ ^2? induces different bacteria to activate under aerobic and anaerobic conditions. A two-dimensional reactive transport model has been developed to simulate the bacteria-mediated reduction reactions in a coastal aquifer. The model explains the utilisation of O₂, NO₃ ^?, MnO₂, Fe(OH)₃ and SO₄ ^2? as electron acceptors for the oxidation of organic carbon in the aquifer under aerobic and anaerobic conditions. The conceptual model consists of three different phases named as bio phase, mobile phase and matrix phase. Model parameters are adopted from literature on bacteria-mediated multi-component modelling and bioremediation processes. Monod kinetic equation is assumed to formulate the bacterial growth. The model explains the behaviours of aerobic and anaerobic bacteria under the availability of organic carbon. Two scenarios are tested and numerical results are discussed. The present numerical study highlights the possibility of the simulation of the formation of reduced environments in coastal aquifers which has not received much attention of groundwater modelling community yet.