A steady-state biofilm model for simultaneous reduction of nitrate and perchlorate, part 1: Model development and numerical solution

A multispecies biofilm model is developed for simultaneous reduction of nitrate and perchlorate in the H ₂-based membrane biofilm reactor. The one-dimension model includes dual-substrate Monod kinetics for a steady-state biofilm with five solid and five dissolved components. The solid components are autotrophic denitrifying bacteria, autotrophic perchlorate-reducing bacteria, heterotrophic bacteria, inert biomass, and extracellular polymeric substances (EPS). The dissolved components are nitrate, perchlorate, hydrogen (H ₂), substrate-utilization-associated products, and biomass-associated products (BAP). The model explicitly considers four mechanisms involved in how three important operating conditions (H ₂ pressure, nitrate loading, and perchlorate loading) affect nitrate and perchlorate removals: (1) competition for H ₂, (2) promotion of PRB growth due to having two electron acceptors (nitrate and perchlorate), (3) competition between nitrate and perchlorate reduction for the same resources in the PRB: electrons and possibly reductase enzymes, and (4) competition for space in the biofilm. Two other special features are having H ₂ delivered from the membrane substratum and solving directly for steady state using a novel three-step approach: finite-difference for approximating partial differential and/or integral equations, Newton-Raphson for solving nonlinear equations, and an iterative scheme to obtain the steady-state biofilm thickness. An example result illustrates the model's features.