Modeling Competition of Denitrification, Sulfate-Reduction, and Methanogenesis in a Hydrogen-Based Membrane Biofilm Reactor (MBfR)

The hollow-fiber membrane biofilm reactor (MBfR) for drinking and wastewater treatment is based on membranes that deliver a gaseous substrate to biofilm formed on the membrane exterior. The MBfR is able to safely deliver hydrogen gas, a non-toxic electron donor, to support autotrophic denitrification. Naturally-occurring sulfate and carbon dioxide support sulfate-reducing bacteria and methanogens that can compete with denitrifying bacteria for hydrogen and space within the biofilm. We used one-dimensional (1-d) and two-dimensional (2-d) multispecies models to explore microbial competition under varying conditions. Results suggested sulfate and carbon concentrations have minimal impact on rates of denitrification when excess nitrate was available, though increasing biofilm thickness hinders denitrification and increased sulfate-reduction. Using 2-d modeling, frequent sloughing events are shown to favor faster-growing denitrifying bacteria. The study also highlights important the advantages and disadvantages of 1-d and 2-d models for multispecies biofilm simulation.