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Cited by 10Wastewater Treatment and Nitrogen RemovalMicrobial Fuel Cells and BioremediationAnaerobic Digestion and Biogas Production

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

Open access
Boltz, Joshua P, Rittmann, Bruce E·2024·FEMS Microbiology Ecology
DOI 10.1093/femsec/fiae125PMC PMC11523051
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Abstract

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.

AI snapshot

Written from the paper’s full text.

TL;DR

A thermodynamic and process model of an H2-fed CFSTR shows that solids retention time (SRT) controls a microbial community reducing NO3−, SeO42−, HSeO3−, and SO42−, with full NO3−/SeO42−/HSeO3− reduction by ~5 days and SO42− reduction beginning ~10 days. Autotrophic hydrogenotrophs dominate active biomass, while nonactive solids become a large fraction at longer SRTs.

Key findings

  • SRT thresholds: denitrification began at ~0.6 days and was nearly 100% by ~2 days; selenate reducers appeared at ~1.2 days with full SeO42− reduction by ~2 days; selenite reduction initiated at ~2 days and was complete by ~5 days; SO42− reduction began at ~10 days and was complete by ~15 days. The desired NO3−, SeO42−, and HSeO3− reduction without SO42− reduction was achievable in an SRT window of 5–10 days.
  • Kinetic hierarchy based on specific growth rate: nitrate-reducing heterotrophs > selenate-reducing heterotrophs > selenite-reducing heterotrophs > nitrate-reducing hydrogenotrophs > fermenting bacteria > selenate-reducing hydrogenotrophs > selenite-reducing hydrogenotrophs > sulfate-reducing heterotrophs > sulfate-reducing hydrogenotrophs.
  • Autotrophic hydrogenotrophs dominated active biomass; nonactive solids (EPS, endogenous decay products, and Se0) were ~46% of total solids at 5 days, ~56% at 15 days, and ~52% at 20 days. Denitrifying heterotrophs were at most 4% of solids at SRT = 10 days.
  • Protein-based BAP was the dominant organic product, peaking at 20 g COD/m3 at a 15-day SRT, only ~1.6% of the COD of delivered H2; all other organic components were <~2 g COD/m3.

Methods

  • Thermodynamic electron-equivalent and process modeling applied to a continuous-flow stirred tank reactor (CFSTR), including H2-oxidizing autotrophs respiring NO3−, SeO42−, HSeO3−, or SO42− and heterotrophs oxidizing soluble endogenous decay products or acetate; the model also included fermentation, EPS, soluble microbial products, hydrolytic enzymes, and endogenous decay.
  • Simulations were run for SRTs of 0.1–20 days with nonlimiting H2 delivery, using influent concentrations relevant to coal-fired power plant flue-gas-desulfurization wastewater: NO3− = 50 g N/m3, SeO42− = 1 g Se/m3, SeO32− = 0 mg Se/L, SO42− = 500 g S/m3, Se0 = 0 g/m3, and COD = 0 g/m3.
  • Biomass yields, maximum specific growth rates, and minimum SRTs were calculated from energetics (Table 1), and model outputs were analyzed as concentrations and biomass distributions versus SRT.

Limitations

  • Stated in the paper: the model does not directly represent the biofilm of an H2-MBfR; it provides mechanistic insight as specific growth rate is systematically decreased. It assumes no influent organic carbon, pH 7, nonrate-limiting alkalinity, and nonlimiting H2 delivery.
  • Evident from the text: no experimental validation or direct microbial community measurements are reported; the simulations rely on literature-derived parameters and assumed partitioning fractions (e.g., EPS fraction 0.18, EPS protein/carbohydrate 0.40/0.60, endogenous decay distribution 80% XEDP, 10% XEDP,U, 9% XEPS,P, 1% XEPS,C).

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1093/femsec/fiae125

Cites

16 of 16 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

0 of 14 cited sources checked · 0 supported · 0 flagged

Verify all 3 references — free account
  • Findingown data

    Autotrophic hydrogenotrophs dominated the active biomass.

    “Autotrophic hydrogenotrophs dominated the active biomass, but nonactive solids were a major portion of the solids, especially for an SRT ≥ 5 days.”
    Quote in the paperSubstantial claim
    • The authors state this as an assumption: The influent wastewater does not contain organic carbon and has a pH of 7.
    • The authors state this as an assumption: Nitrate-, selenate-, and selenite-reducing heterotrophic bacteria can use soluble endogenous decay products as an electron donor.
    • The authors state this as an assumption: Selenium-reducing heterotrophic bacteria can utilize soluble endogenous decay products and acetate as electron donors.
    • The authors state this as an assumption: Hydrogenotrophic bacteria obtain carbon from inorganic carbon (e.g. HCO3−).
    • The authors state this as an assumption: Heterotrophic bacteria obtain carbon from soluble endogenous-decay products or acetate.
    • The authors state this as an assumption: Ammonium is the nitrogen source for hydrogenotrophic and heterotrophic bacteria.
    • The authors state this as an assumption: Sulfate-reducing heterotrophic bacteria can utilize only acetate as an electron donor.
    • The authors state this as an assumption: Fermentation of soluble endogenous decay products converts them into acetate.
    • Rests on an assumption: H2 is the common electron donor for all electron acceptors transformed by nitrate-, selenate-, selenite-, and sulfate-reducing hydrogenotrophic bacteria.
  • Findingown data

    The steady demand for H2 for SO42− reduction is obvious from SRT ∼10 days to ∼15 days.

    “However, the steady demand for H2 for SO42− reduction is obvious from SRT ∼10 days to ∼15 days.”
    Quote in the paperNot a substantial claim
  • Findingown data

    The consumption of H2 paralleled the onsets of electron acceptor reductions.

    “Figure 6 documents that the consumption of H2 paralleled the onsets of electron acceptor reductions.”
    Quote in the paperNot a substantial claim
  • Findingown data

    Organic products accumulated and became more important with longer SRT.

    “Figure 7 shows that organic products accumulated and became more important with longer SRT.”
    Quote in the paperNot a substantial claim
  • Findingown data

    A large shift takes place for SRT ≥ 15 days, when the sulfate-reducing hydrogenotrophs become the large component of active biomass due to the onset of complete SO42− reduction.

    “A large shift takes place for SRT ≥ 15 days, when the sulfate-reducing hydrogenotrophs become a the large component of active biomass due to the onset of complete SO42− reduction.”
    Quote in the paperSubstantial claim
  • May combine two claims. 23
  • Classified as probably not a substantial claim. 10
  • The quote only partly states this claim. 1

  • May combine two claims.

    Findingown data

    Selenate-reducers began to appear at an SRT of ∼1.2 day and had full SeO42− reduction by an SRT of ∼2 day.

    “The next bacteria to accumulate were the selenate-reducers, and Fig. 4 shows that they began to appear at an SRT of ∼1.2 day and had full SeO42− reduction by an SRT of ∼2 day.”
    • Also stated in: § Conclusion · plain
      “Selenate-reducing and selenite-reducing hydrogenotrophs became established at SRTs of ∼1.2 and 2 days, respectively.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingnone given

    Selenite-reducing hydrogenotrophs cannot be visualized, but they are present for SRT ≥ 2 days.

    “While selenite-reducing hydrogenotrophs cannot be visualized, they are present for SRT ≥ 2 days”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    The H2 concentration began to decline at an SRT ∼0.6 day, the onset of denitrification, and its major decline was in place at ∼1 day, when denitrification was more than 95% complete.

    “The H2 concentration began to decline at an SRT ∼0.6 day, the onset of denitrification, and its major decline was in place at ∼1 day, when denitrification was more than 95% complete (Fig. 3).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    The only type of heterotrophic biomass that can be visualized in Fig. 8 is the denitrifying heterotrophs, and they are at most 4% of the solids (at SRT = 10 days).

    “The only type of heterotrophic biomass that can be visualized in Fig. 8 is the denitrifying heterotrophs, and they are at most 4% of the solids (at SRT = 10 days).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    HSeO3− reducers initiated HSeO3− reduction at an SRT ∼2 days and had full HSeO3− reduction by an SRT of ∼5 days.

    “Next to appear were the HSeO3− reducers (Fig. 4), which initiated HSeO3− reduction at an SRT ∼2 days and had full HSeO3− reduction by an SRT of ∼5 days.”
    • Also stated in: § Conclusion · plain
      “Selenate-reducing and selenite-reducing hydrogenotrophs became established at SRTs of ∼1.2 and 2 days, respectively.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    The advent of SO42− reduction increased the active fraction, but the nonactive solids still were ∼52% for an SRT of 20 days.

    “The advent of SO42− reduction increased the active fraction, but the nonactive solids still were ∼52% for an SRT of 20 days.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    The dominant organic component was protein-based BAP, which has slow biodegradation kinetics.

    “By far the dominant organic component was protein-based BAP, which has slow biodegradation kinetics.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    The peak concentration of protein-based BAP was only 20 g COD/m3 (at a 15-day SRT), a concentration only ∼1.6% of the COD of the delivered H2.

    “However, its peak concentration was only 20 g COD/m3 (at a 15-day SRT), a concentration only ∼1.6% of the COD of the delivered H2.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    The H2-oxidizing denitrifiers have a μmax of 1.8/d, which corresponds to a minimum SRT of ∼0.6 day.

    “This corresponds to the H2-oxidizing denitrifiers, which are the autotrophic foundation of the process, having 1.8/d µmax, which corresponds to a minimum SRT of ∼0.6 day.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingnone given

    Selenate-reducing hydrogenotrophs were present, but cannot be seen due to their small biomass.

    “Selenate-reducing hydrogenotrophs were present, but cannot be seen due to their small biomass.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingreasoning

    All bacterial types can be suppressed with μ > 1.8 days, corresponding to a minimum SRT of ∼0.6 day for the H2-oxidizing denitrifiers.

    “In contrast, all bacterial types can be suppressed with µ > 1.8 days, which corresponds to a minimum SRT of ∼0.6 day for the H2-oxidizing denitrifiers.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Findingreasoning

    The onsets and build ups of SeO42− and HSeO3− reductions (from 1.2 to 5 days) are not perceptible in Fig. 6 because of the small influent concentration of SeO42−.

    “The onsets and build ups of SeO42− and HSeO3− reductions (from 1.2 to 5 days, Fig. 4) are not perceptible in Fig. 6 because of the small influent concentration of SeO42−.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingnone given

    Bacterial activity began at an approximately 0.6-day SRT, when hydrogenotrophic denitrifiers began to accumulate.

    “Bacterial activity began at an ∼0.6-day SRT, when hydrogenotrophic denitrifiers began to accumulate.”
    Quote in the paperSubstantial claim
    • The authors state this as an assumption: The influent wastewater does not contain organic carbon and has a pH of 7.
    • The authors state this as an assumption: Nitrate-, selenate-, and selenite-reducing heterotrophic bacteria can use soluble endogenous decay products as an electron donor.
    • The authors state this as an assumption: Selenium-reducing heterotrophic bacteria can utilize soluble endogenous decay products and acetate as electron donors.
    • The authors state this as an assumption: Hydrogenotrophic bacteria obtain carbon from inorganic carbon (e.g. HCO3−).
    • The authors state this as an assumption: Heterotrophic bacteria obtain carbon from soluble endogenous-decay products or acetate.
    • The authors state this as an assumption: Ammonium is the nitrogen source for hydrogenotrophic and heterotrophic bacteria.
    • The authors state this as an assumption: Sulfate-reducing heterotrophic bacteria can utilize only acetate as an electron donor.
    • The authors state this as an assumption: Fermentation of soluble endogenous decay products converts them into acetate.
    • Rests on an assumption: H2 is the common electron donor for all electron acceptors transformed by nitrate-, selenate-, selenite-, and sulfate-reducing hydrogenotrophic bacteria.

  • May combine two claims.

    Findingown data

    By 15 days, nonactive fractions comprised ∼56% of the total solids mass, and they were about 46% at 5 days.

    “By 15 days, they comprised ∼56% of the total solids mass, and they were about 46% at 5 days.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    Denitrification began at an SRT of ∼0.6 day and rapidly increased to almost 100% removal by SRT ∼2 day.

    “Figure 3 shows that denitrification began at an SRT of ∼0.6 day and rapidly increased to have almost 100% removal by SRT ∼2 day.”
    • Also stated in: § Conclusion · plain
      “Bacterial activity began at an ∼0.6-day SRT, when hydrogenotrophic denitrifiers were able to accumulate.”
    Quote in the paperSubstantial claim
    • The authors state this as an assumption: H2 is the only supplied electron donor in the modeled bioreactor.
    • The authors state this as an assumption: Hydrogenotrophic bacteria compete for the common electron donor H2.

  • Classified as probably not a substantial claim.

    Findingown data

    Table 1 shows significant differences in Ym and μmax,m values.

    “Striking about Table 1 are the significant differences in Ym and µmax,m values.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    The average specific growth rate in a biofilm process can be manipulated by changes to shear stress or turbulence induced by the normal liquid flow regime or by intentional biofilm-management strategies to periodically remove some of the biofilm.

    “which can be manipulated by changes to shear stress or turbulence induced by the normal liquid flow regime (Rittmann 1982, Laspidou and Rittmann 2004a,b, Wanner et al. 2006) or by intentional biofilm-management strategies to periodically remove some of the biofilm.”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites Rittmann 1982 source
    • cites Laspidou and Rittmann 2004a,b

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites Wanner et al. 2006

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductnone given

    The model does not directly represent the biofilm of an H2-MBfR.

    “While the model does not directly represent the biofilm of an H2-MBfR”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Interpretationreasoning

    The model provides mechanistic insight into the interactions between autotrophic and heterotrophic bacteria as their specific growth rate is systematically decreased.

    “it provides mechanistic insight into the interactions between autotrophic and heterotrophic bacteria as their specific growth rate is systematically decreased.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    The SO42− concentration is substantial and will lead to a large production of sulfide if SO42− reduction is not suppressed by lack of electron-donor supply, a low SRT, or a combination.

    “Second, the SO42− concentration is substantial and will lead to a large production of sulfide if SO42− reduction is not suppressed by lack of electron-donor supply, a low SRT, or a combination.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    SRT control readily applies to suspended-growth processes, which use controlled solids wasting to establish the SRT.

    “In practice, SRT control readily applied to suspended-growth processes, which use controlled solids wasting to establish the SRT (Rittmann and McCarty 2020).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites Rittmann and McCarty 2020

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • May combine two claims.

    Study design and conductnone given

    The maximum H2-delivery capacity used in the modeling simulations was sufficient for complete reductions of NO3−, SeO42−, and SO42−; thus, the available control parameter was the SRT.

    “The maximum H2-delivery capacity used in the modeling simulations was sufficient for complete reductions of NO3−, SeO42−, and SO42−; thus, the available control parameter was the SRT.”
    Quote in the paperSubstantial claim
    • The authors state this as an assumption: H2 is the only supplied electron donor in the modeled bioreactor.

  • The quote only partly states this claim.

    Interpretationreasoning

    The advantages indicated by both parameters suggest a kinetic hierarchy based on specific growth rate: nitrate-reducing heterotrophic bacteria > selenate-reducing heterotrophic bacteria > selenite-reducing heterotrophic bacteria > nitrate-reducing hydrogenotrophic bacteria > fermenting bacteria > selenate-reducing hydrogenotrophic bacteria > selenite-reducing hydrogenotrophic bacteria > sulfate-re

    “The advantages indicated by both parameters suggest a kinetic hierarchy based on the specific growth rate: nitrate-reducing heterotrophic bacteria > selenate-reducing heterotrophic bacteria > selenite-reducing heterotrophic bacteria > nitrate-reducing hydrogenotrophic bacteria > fermenting bacteria > selenate-reducing hydrogenotrophic bacteria > selenite-reducing hydrogenotrophic bacteria >”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Microbial communities that develop in an H2-MBfR commonly have distinct hydrogenotrophic and heterotrophic bacteria populations, despite treating wastewater that does not contain organic carbon.

    “The microbial communities that develop in an H2-MBfR commonly have distinct hydrogenotrophic and heterotrophic bacteria populations, despite treating waste-water that does not contain organic carbon (Ontiveros-Valencia et al. 2018).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites Ontiveros-Valencia et al. 2018 source

  • Probably not a substantial claim: may not pass S4 (based).

    Interpretationnone given

    Hydrogenotrophs have significantly larger energy demands of synthesis than heterotrophs.

    “That advantage is important to the hydrogenotrophs, because they have significantly larger energy demands of synthesis as shown in the next section.”
    Quote in the paperNot a substantial claim
    • The authors state this as an assumption: Hydrogenotrophic bacteria obtain carbon from inorganic carbon (e.g. HCO3−).
    • The authors state this as an assumption: Heterotrophic bacteria obtain carbon from soluble endogenous-decay products or acetate.
    • The authors state this as an assumption: Ammonium is the nitrogen source for hydrogenotrophic and heterotrophic bacteria.

  • May combine two claims.

    Interpretationreasoning

    The onset of HSeO3− reduction depended on having substantial SeO42− reduction to HSeO3−, which was in place with an SRT of ∼2 days.

    “The onset of HSeO3− reduction depended on having substantial SeO42− reduction to HSeO3−, which was in place with an SRT of ∼2 days.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    The H2-driven biomass was dominated by H2-oxidizing autotrophs, although some heterotrophs were present due to their ability to oxidize organic components generated by the autotrophs.

    “Thus, the H2-driven biomass was dominated by H2-oxidizing autotrophs, although some heterotrophs were present due to their ability to oxidize organic components generated by the autotrophs.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    Based on the kinetic parameters in Table 1, the SRT range of 0.1-20 days should span from washout of all bacteria at the lowest SRTs (greater than ∼0.6 day) to accumulation of all bacteria at the higher SRTs (greater than ∼7 day).

    “Based on the kinetic parameters in Table 1, this range should span from washout of all bacteria at the lowest SRTs (i.e., a value greater than ∼0.6 day) to accumulation of all bacteria at the higher SRTs (i.e. greater than ∼7 day).”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    All bacteria carry out oxidation-reduction reactions to obtain energy for synthesis and cell maintenance, and they undergo endogenous processes.

    “All bacteria carry out oxidation–reduction reactions to obtain energy for synthesis and cell maintenance, and they undergo endogenous processes (Rittmann and McCarty 2020).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites Rittmann and McCarty 2020

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • May combine two claims.

    Interpretationown data

    The desired reductions of NO3−, SeO42−, and HSeO3− could be achieved with an SRT > ∼5 days, but suppression of SO42− reduction meant keeping the SRT < ∼10 days.

    “The results in Figs 3–5 mean that the desired reductions of NO3−, SeO42−, and HSeO3− could be achieved with an SRT > ∼5 days, but suppression of SO42− reduction meant keeping the SRT < ∼10 days.”
    • Also stated in: § Conclusion · hedged
      “Thus, the desired goal of full reductions of NO3−, SeO42−, and HSeO3−, but no SO42− reduction, was possible in an SRT window of 5–10 days when the H2 supply was not limiting.”
    Quote in the paperSubstantial claim
    • The authors state this as an assumption: H2 is the only supplied electron donor in the modeled bioreactor.

  • May combine two claims.

    Interpretationreasoning

    Selenate- and selenite-reducing bacteria can be only a very small fraction of the total biomass and can oxidize only a small fraction of the electron donors.

    “This means that selenate- and selenite-reducing bacteria can be only a very small fraction of the total biomass and can oxidize only a small fraction of the electron donors.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    Applying a safety factor of 3 means that suppression of all bacterial types may occur for SRT < ∼1.8 day, while all H2-oxidizing bacterial types may accumulate for an SRT > ∼10 days.

    “Applying this safety factor means that the suppression of all bacterial types may occur for SRT < ∼1.8 day, while all H2-oxidizing bacterial types may accumulate for an SRT > ∼10 days.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    In a biofilm process, the average specific growth rate of the bacteria is equal to the first-order detachment rate.

    “In a biofilm process, the average specific growth rate of the bacteria is equal to the first-order detachment rate (Rittmann and McCarty 2020)”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites Rittmann and McCarty 2020

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

33 of 33

  • The authors state this as an assumption.

    The influent wastewater does not contain organic carbon and has a pH of 7.

    “We assume that the influent wastewater does not contain organic carbon and has a pH of 7.”

  • The authors state this as an assumption.

    Nitrate-, selenate-, and selenite-reducing heterotrophic bacteria can use soluble endogenous decay products as an electron donor.

    “We assume that nitrate-, selenate-, and selenite-reducing heterotrophic bacteria can use soluble endogenous decay products as an electron donor.”

  • The authors state this as an assumption.

    Selenium-reducing heterotrophic bacteria can utilize soluble endogenous decay products and acetate as electron donors.

    “Nitrate-reducing heterotrophic bacteria and, we assume, selenium-reducing heterotrophic bacteria can utilize soluble endogenous decay products (i.e. C10H19O3N) and acetate (CH3COO−) as electron donors.”

  • The authors state this as an assumption.

    Hydrogenotrophic bacteria obtain carbon from inorganic carbon (e.g. HCO3−).

    “We assume hydrogenotrophic bacteria obtain carbon from inorganic carbon (e.g. HCO3−), and the energy associated with synthesis (i.e. the energy required to convert a carbon source to activated acetate, or ΔGp) is 109.6 kJ/e− eq.”

  • The authors state this as an assumption.

    Heterotrophic bacteria obtain carbon from soluble endogenous-decay products or acetate.

    “We assume heterotrophic bacteria obtain carbon from soluble endogenous-decay products or acetate, and they have the same synthesis-associated energies (ΔGp): 3.5 kJ/e− eq (Rittmann and McCarty 2020).”

  • The authors state this as an assumption.

    Ammonium is the nitrogen source for hydrogenotrophic and heterotrophic bacteria.

    “We assume ammonium is the nitrogen source for hydrogenotrophic and heterotrophic bacteria.”

  • The authors state this as an assumption.

    Sulfate-reducing heterotrophic bacteria can utilize only acetate as an electron donor.

    “We model sulfate-reducing heterotrophic bacteria as able to utilize only acetate as an electron donor (Noguera et al. 1998).”

  • The authors state this as an assumption.

    Fermentation of soluble endogenous decay products converts them into acetate.

    “We model fermentation of soluble endogenous decay products (C10N19O3N) as a conversion into acetate (CH3COO−).”

  • The paper relies on this without support.

    H2 is the common electron donor for all electron acceptors transformed by nitrate-, selenate-, selenite-, and sulfate-reducing hydrogenotrophic bacteria.

    “H2 is the common electron donor for all electron acceptors transformed by nitrate-, selenate-, selenite-, and sulfate-reducing hydrogenotrophic bacteria.”

  • The authors state this as an assumption.

    Alkalinity is nonrate limiting and pH is neutral in the model.

    “Alkalinity is considered nonrate limiting, and the pH is neutral in this model.”

  • The authors state this as an assumption.

    H2 is the only supplied electron donor in the modeled bioreactor.

    “The unique feature of the model is that it simulated a bioreactor in which the only supplied electron donor was H2”

  • The authors state this as an assumption.

    Hydrogenotrophic bacteria compete for the common electron donor H2.

    “Hydrogenotrophic bacteria compete for the common electron donor H2.”

  • The authors state this as an assumption.

    Heterotrophic bacteria compete for the common electron donors soluble endogenous decay products, acetate, UAP, and BAP.

    “Heterotrophic bacteria compete for the common electron donors soluble endogenous decay products (denoted SEDP), acetate (denoted SA), utilization associated products (UAP; denoted SUAP), protein-biomass associated products (denoted SBAP, P), and carbohydrate-biomass associated products (denoted SBAP, C).”

  • The authors state this as an assumption.

    All bacteria compete for essential nutrients N, P, S, and Se.

    “All bacteria compete for essential nutrients that include N (as ammonium), P (as orthophosphate), S (as hydrogen sulfide), and Se (as hydrogen selenide).”
14 of 14

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • EPS hydrolysis rate ratio is 120-fold, not 32-fold

    Minor

    The stated carbohydrate-EPS and protein-EPS hydrolysis rate coefficients are 6.00 and 0.05 per day. Their ratio is 120, not 32.

    Reported 32 · recomputed 120

  • Specific growth rate is expressed in days rather than per day

    Minor

    The stated threshold for μ has units of days, whereas the paper elsewhere expresses this specific growth rate as 1.8 per day.

  • Washout is assigned to SRTs above the onset of activity

    Minor

    The text identifies SRTs greater than approximately 0.6 day as the washout range, but also reports active denitrifying hydrogenotrophs at 0.75 and 1.0 day.

  • Maximum H2 concentration is given in incompatible units

    Minor

    The methodology gives the maximum H2 concentration as 1,220 mg COD/m3, while the Figure 6 caption gives it as 1220 mg COD/l. These differ by a factor of 1,000 and affect the stated H2-delivery calculation.

4 of 4

Cites

Flagged first, then by citations

Research works printed but not linked: 3

  1. McCarty, 1971, Energetics and bacterial growth
  2. Olin, 2020, Chemical Thermodynamics of Selenium
  3. Rittmann, 2020, Environmental Biotechnology: Principles and Applications

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Authors
Boltz, J. P., & Rittmann, B. E.
Affiliations
  • Woodard & Curran, Inc. , 12 Mountfort Street , Portland, ME 04101,
  • Arizona State University (US)
Corresponding author
Rittmann, Bruce E
ORCID
Rittmann, Bruce E
Venue
FEMS Microbiology Ecology
Publisher
Oxford University Press (OUP)
Published
2024-09-14
Volume
100
Issue
11
ISSN
  • 0168-6496 (ISSN-L)
  • 1574-6941
DOI
10.1093/femsec/fiae125
PMC
PMC11523051
OpenAlex
W4402548346
Semantic Scholar
677216cfa291ada97703bf2f1310c25a3b8ff74f
Cited by
10
References
16
Citations by year
2026: 4 · 2025: 6
FWCI
0.97
Type
journal article
Language
en
Open access
Licence
Locations
  • FEMS Microbiology Ecology (publishedVersion, cc-by-nc-nd)
  • PubMed Central (publishedVersion, cc-by-nc-nd)
  • PubMed (publishedVersion)
Topics
  • Physical Sciences › Environmental Science › Pollution › Wastewater Treatment and Nitrogen Removal
  • Physical Sciences › Environmental Science › Environmental Engineering › Microbial Fuel Cells and Bioremediation
  • Physical Sciences › Engineering › Building and Construction › Anaerobic Digestion and Biogas Production
Keywords
hydrogenotrophic bacteria, membrane biofilm reactor, nitrate reduction, selenate reduction, selenite reduction, sulfate reduction, coal mine wastewater, sludge retention time, microbial community modeling
MeSH terms
Bacteria, Hydrogen, Nitrates, Oxidation-Reduction, Sulfates, Selenium Compounds, Biofilms, Bioreactors, Selenious Acid, Autotrophic Processes, Wastewater, Selenic Acid

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Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.

Claims read by deepseek-v4.1-flash under definition version 3 (extract-v3) on 2026-11-06.

Classified by jev-1.13-20260917 (gold-guideline-v0.2) on 2026-11-06.

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