A steady-state biofilm model for simultaneous reduction of nitrate and perchlorate, part 2: Parameter optimization and results and discussion

Part 1 of this work developed a steady-state, multispecies biofilm model for simultaneous reduction of nitrate and perchlorate in the H ₂-based membrane biofilm reactor (MBfR) and presented a novel method to solve it. In Part 2, the half-maximum-rate concentrations and inhibition coefficients of nitrate and perchlorate are optimized by fitting data from experiments with different combinations of influent nitrate and perchlorate concentrations. The model with optimized parameters is used to quantitatively and systematically explain how three important operating conditions (nitrate loading, perchlorate loading, and H ₂ pressure) affect nitrate and perchlorate reduction and biomass distribution in these reducing biofilms. Perchlorate reduction and accumulation of perchlorate-reducing bacteria (PRB) in the biofilm are affected by four promotion or inhibition mechanisms: simultaneous use of nitrate and perchlorate by PRB and competition for H ₂, the same resources in PRB, and space in a biofilm. For the hydrogen pressure evaluated experimentally, a low nitrate loading (<0.1 g N/m ²-d) slightly promotes perchlorate removal, because of the beneficial effect from PRB using both acceptors. However, a nitrate loading of >0.6 g N/m ²-d begins to inhibit perchlorate removal, as the competition effects become dominant.