Simulating the biodegradation of toluene at the macroscopic and pore-level scale for aerobic and nitrate reducing conditions

Mathematical formulations that can explain mechanistically the simultaneous utilization of more than one electron acceptor were explored, and an experiment that can eventually be used to verify such a formulation was developed. Based on the nature of Pseudomonas putida F1 and Thauera aromatica T1, a numerical model was formulated which considers advection, diffusion, and chemical/biological transformations for toluene, oxygen, and nitrate. The simulation results for the location near the column inlet showed that sufficient oxygen is present throughout the whole domain of biofilm to maintain the whole biofilm aerobic. At the column location where the measured concentration of oxygen in the column pore water was 1 mg/L, simulations showed that the inner portion of biofilm is depleted of dissolved oxygen. Aerobic bacteria dominated the outer portion of biofilm, where oxygen was present, while denitrifying bacteria dominated the inner part of the biofilm where oxygen was absent. In the column location where no oxygen was detected, the whole biofilm consisted of denitrifying bacteria.