Microbial Ecology of Nitrate-, Selenate-, Selenite-, and Sulfate-Reducing Bacteria in a H2-Driven Bioprocess

A hydrogen (H2)-based membrane biofilm reactor (H2-MBfR) can reduce electron acceptors nitrate (NO3−), selenate (SeO42−), selenite (HSeO3−), and sulfate (SO42−), which are in wastewaters from coal mining and combustion. This work presents a model to describe a H2-driven microbial community comprised of hydrogenotrophic and heterotrophic bacteria that respire NO3−, SeO42−, HSeO3−, and SO42−. The model provides mechanistic insights into the interactions between autotrophic and heterotrophic bacteria in a microbial community that is founded on H2-based autotrophy. Simulations were carried out for a range of relevant solids retention times (0.1 to 20 days) and with adequate H2-delivery capacity to reduce all electron acceptors. Bacterial activity began at an ∼0.6-day SRT, when hydrogenotrophic denitrifiers began to accumulate. Selenate-reducing and selenite-reducing hydrogenotrophs became established next, at SRTs of ∼1.2 and 2 days, respectively. Full nitrate, selenate, and selenite reductions were complete by an SRT of ∼5 days. Sulfate reduction began at an SRT of ∼10 days and was complete by ∼15 days. The desired goal of reducing nitrate, selenate, and selenite, but not sulfate, was achievable within an SRT window of 5 to 10 days. Autotrophic hydrogenotrophs dominated the active biomass, but non-active solids were a major portion of the solids, especially for an SRT ≥ 5 days.