Interactions between Nitrate-Reducing and Sulfate-Reducing Bacteria Coexisting in a Hydrogen-Fed Biofilm

Abstract

To explore the relationships between denitrifying bacteria (DB) and sulfate-reducing bacteria (SRB) in H(2)-fed biofilms, we used two H(2)-based membrane biofilm reactors (MBfRs) with or without restrictions on H(2) availability. DB and SRB compete for H(2) and space in the biofilm, and sulfate (SO(4)(2-)) reduction should be out-competed when H(2) is limiting inside the biofilm. With H(2) availability restricted, nitrate (NO(3)(-)) reduction was proportional to the H(2) pressure and was complete at a H(2) pressure of 3 atm; SO(4)(2-) reduction began at H(2) ≥ 3.4 atm. Without restriction on H(2) availability, NO(3)(-) was the preferred electron acceptor, and SO(4)(2-) was reduced only when the NO(3)(-) surface loading was ≤ 0.13 g N/m(2)-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 H(2) pressures when H(2) availability was limiting, SRB did not decline with higher NO(3)(-) removal flux when H(2) availability was not limiting, even when SO(4)(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 SO(4)(2-). In all scenarios tested, the SRB were able to initiate strong SO(4)(2-) reduction only when competition for H(2) inside the biofilm was relieved by nearly complete removal of NO(3)(-).

Assessing microbial competition in a hydrogen‐based membrane biofilm reactor (MBfR) using multidimensional modeling

“…In accordance with the literature, the 1‐d modeling results showed DNB to effectively outcompete SRB and MET (Ontiveros‐Valencia et al, ; Tang et al, ; Ziv‐El and Rittmann, ). Nitrate flux went unaffected by bulk sulfate concentrations between 10 and 150 g · m −3 (Fig.…”

“…By increasing the H 2 pressure, a point will be reached where the onset of sulfate reduction occurs. Raising the H 2 pressure past this onset point results in a large gain in sulfate reduction, but little change in the rate of denitrification (Ontiveros‐Valencia et al, , ; Tang et al, ). We explored the effect of intramembrane pressure (Section S3) and the results agreed with the aforementioned studies, as excess H 2 led to unwanted growth of SRB and MET.…”

“…However, SRB and MET can be difficult to remove once established at the inner regions of the biofilm. SRB have been demonstrated to persist in an experimental MBfR biofilm, even during periods of low sulfate‐reducing activity (Ontiveros‐Valencia et al, ). Sloughing events can remove the SRB and MET, though reduced fluxes and/or H 2 export to the bulk liquid may lead to undesirable consequences.…”

Pyrosequencing Analysis Yields Comprehensive Assessment of Microbial Communities in Pilot-Scale Two-Stage Membrane Biofilm Reactors

“…21,23 In the lead MBfRs, the NO3 -+ O2 flux was greater than ~ 0.34 g H2/m 2 -212 day 23 (Table 2), which completely suppressed SO4 2-reduction and is consistent with the 213 bench-scale results of Ontiveros-Valencia et al 45 and modeling work by Tang et al 46 …”

“…reduction. 33,45 . Likewise, the relative abundance of "unclassified" bacteria and minor 307 phylotypes (microbial groups at <1% abundance) (not shown in Figure 3) went from an (Table S1).…”