Membrane Fouling Potentials of an Exoelectrogenic Fouling-Causing Bacterium Cultured With Different External Electron Acceptors

Specific gaps in this paper, with an experiment that would close each.

• High No systematic variation of anode potential between +0.2 V and lower/higher values to identify optimal redox window for fouling suppression.

  Paper applies only +0.2 V vs. Ag/AgCl; cites Kim et al. (2017) showing +0.5 V enhanced product yield in K. pneumoniae, suggesting potential is tunable. No dose–response curve provided.

  Try. Anode potential sweep (−0.1 to +0.5 V vs. Ag/AgCl) with measurement of current, SMP protein/biopolymer, and membrane resistance to identify fouling-minimizing potential.

• High No measurement of intracellular redox state (NADH/NAD⁺ ratio) or gene expression to mechanistically link electron acceptor type to SMP composition.

  Discussion hypothesizes that 'extracellular redox states (i.e., the availability and type of external electron acceptors) has considerable influences on intracellular redox balance (i.e., the ratio of NADH/NAD⁺)' but provides no direct evidence. Authors state 'Further study is required to verify this hypothesis.'

  Try. Measure NADH/NAD⁺ ratio and transcriptome (genes for EPS synthesis, protein secretion, fermentation) under each electron acceptor condition.

• Medium No testing of mixed-population biofilms or co-cultures with other common MBR bacteria to assess whether S05 fouling behavior generalizes.

  Authors acknowledge: 'only one isolated strain was investigated as a model microorganism in this study. Thus, identification and characterization of other exoelectrogenic FCB are necessary to understand whether these findings are S05 strain specific or more general characteristic of exoelectrogenic FCB.'

  Try. Repeat key conditions (anode +0.2 V, oxygen sufficient, fermentation) with S32, S33, and mixed activated sludge; measure fouling potential and SMP composition.

• Medium No variation of hydraulic retention time (HRT), current density, or glucose concentration to map operating windows for fouling suppression.

  Batch culture only; no continuous-flow or varying substrate/current conditions tested. Real MBR operates at fixed HRT and variable influent composition.

  Try. Continuous-flow reactor at HRTs 4–24 h, controlled current density 0.2–1.0 A/m², varying glucose (10–50 mM) with daily SMP and fouling monitoring.

• Medium No quantification of biomass-associated products (BAP) vs. utilization-associated products (UAP) to distinguish decay-driven fouling from metabolism-driven fouling.

  Authors note: 'BAP and UAP could not be quantified separately in the present study, which needs to be addressed in the future.' This distinction is critical for predicting fouling under transient conditions.

  Try. Fractionate SMP using size-exclusion chromatography or enzymatic degradation to separate BAP (>10 kDa, refractory) from UAP (<1 kDa, labile) and correlate each to fouling.

• Medium No measurement of N-species (NO₃⁻, NO₂⁻, N₂O, NH₄⁺) during nitrate respiration to assess denitrification efficiency and N₂O accumulation risk.

  Nitrate consumption measured (8.82±2.22 mmol) but no product speciation. Paper title and focus include nitrogen cycling but no N-balance or N₂O data provided.

  Try. Gas chromatography and ion chromatography to quantify NO₃⁻ → NO₂⁻ → NO → N₂O → N₂ pathway; measure N₂O in headspace and dissolved phase under nitrate-sufficient and nitrate-limited conditions.