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 (SRT; 0.1-20 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 NO3-, SeO42-, and HSeO3- reductions were complete by an SRT of ∼5 days. SO42- reduction began at an SRT of ∼10 days and was complete by ∼15 days. The desired goal of reducing NO3-, SeO42-, and HSeO3-, but not SO42-, was achievable within an SRT window of 5-10 days. Autotrophic hydrogenotrophs dominated the active biomass, but nonactive solids were a major portion of the solids, especially for an SRT ≥ 5 days.