To explore the relationships between denitrifying bacteria (DB) and sulfate-reducing bacteria (SRB) in H2-fed biofilms, we used two H2-based membrane biofilm reactors (MBfRs) with or without restrictions on H2 availability. DB and SRB compete for H2 and space in the biofilm, and sulfate (SO42-) reduction should be out-competed when H2 is limiting inside the biofilm. With H2 availability restricted, nitrate (NO3-) reduction was proportional to the H2 pressure and was complete at a H2 pressure of 3 atm; SO42- reduction began at H2 ≥ 3.4 atm. Without restriction on H2 availability, NO3- was the preferred electron acceptor, and SO 42- was reduced only when the NO3- surface loading was ≤0.13 g N/m2-day. We assayed DB and SRB by quantitative polymerase chain reaction targeting the nitrite reductases and dissimilatory sulfite reductase, respectively. Whereas DB and SRB increased with higher H2 pressures when H2 availability was limiting, SRB did not decline with higher NO3- removal flux when H2 availability was not limiting, even when SO4 2- reduction was absent. The SRB trend reflects that the SRB's metabolic diversity allowed them to remain in the biofilm whether or not they were reducing SO42-. In all scenarios tested, the SRB were able to initiate strong SO42- reduction only when competition for H2 inside the biofilm was relieved by nearly complete removal of NO3-.
ASJC Scopus subject areas
- Environmental Chemistry