Interplay of biofilm growth, NAPL biodegradation and micro-scale heterogeneity in natural attenuation of aquifers delineated by pore-network modelling

Abstract

The biofilm plays an important role in NAPL bioremediation, natural attenuation and the flow behaviour of contaminant in porous media. Therefore, NAPL biodegradation in the presence of any bacteria in the porous media needs to be considered for more accurate prediction of contaminant remediation from the soil and groundwater. The complex interaction between the NAPL biodegradation/dissolution and physiochemical bacteria (biofilm) growth which depends on both time and space results in difficulties in simulation of NAPL bioremediation in the porous media. In this work, the natural attenuation process is simulated using three-dimensional pore network models to investigate natural bioremediation and dissolution of NAPL in presence of different heterogeneities arising from uncorrelated and correlated pore radii distribution. The impact of an additional phase (biofilm) on transport and NAPL dissolution is dynamically incorporated in the pore network model with simplifying assumptions such as fully available NAPL for biodegradation and dissolution. Under such assumptions, the results indicate that as pore scale heterogeneity (in the form of correlation length of pore radii of pore networks) increases, the biofilm growth decreases resulting in a reduction of NAPL bioremediation and dissolution. As such it is critical to consider pore scale heterogeneity in predicting bioremediation efficiency. Additionally, we found that Kozeny-Carman equation fail to predict the permeability changes due to biofilm growth/extinction.