Microbial ecology of nitrate-, selenate-, selenite-, and sulfate-reducing bacteria in a H2-driven bioprocess

A hydrogen (H-2)-based membrane biofilm reactor (H-2-MBfR) can reduce electron acceptors nitrate (NO3 -), selenate (SeO4 2-), selenite (HSeO3 -), and sulfate (SO4 (2)-), which are in wastewaters from coal mining and combustion. This work presents a model to describe a H-2-driven microbial community comprised of hydrogenotrophic and heterotrophic bacteria that respire NO3 -, SeO4 (2)-, HSeO3 -, and SO4 (2)-. The model provides mechanistic insights into the interactions between autotrophic and heterotrophic bacteria in a microbial community that is founded on H(2-)based autotrophy. Simulations were carried out for a range of relevant solids retention times (SRT; 0.1-20 days) and with adequate H-2-delivery capacity to reduce all electron acceptors. Bacterial activity began at an similar to 0.6-day SRT, when hydrogenotrophic denitrifiers began to accumulate. Selenate-reducing and selenite-reducing hydrogenotrophs became established next, at SRTs of similar to 1.2 and 2 days, respectively. Full NO3 -, SeO4 2-, and HSeO3 - reductions were complete by an SRT of similar to 5 days. SO4 (2)- reduction began at an SRT of similar to 10 days and was complete by similar to 15 days. The desired goal of reducing NO3 -, SeO4 (2)-, 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