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Algae-assisted bioelectrochemical system with ammonium, sulfide removal and parallel biomethanation
Angelov, Bratkova, Ivanov, Velichkova
KI-Zusammenfassung
72 % KonfidenzThis paper demonstrates an algae-assisted bioelectrochemical system (BES) integrated with anaerobic digestion of ethanol stillage, achieving 76.5% ammonium removal (NH4+-N: 141–180 mg/L → 25–28 mg/L) and 89.5% COD reduction at 0.9 V MEC mode with 0.34 A/m² current density. Algae in the cathode zone generate oxygen via photosynthesis, enhancing cathodic potential and enabling complete H2S removal from biogas. The system improves methane content from 59–61% (standalone AD) to 72–75% (MEC 0.9 V) while maintaining stable biogas yield (~0.9 dm³/24h) over 80 days at 10-day HRT.
Zentrale Erkenntnisse
Zielkonflikt Ammonium removal scales with applied voltage: MEC 0.9 V achieved 76.5% removal (25 mg/L final) versus MFC 41.7% (105 mg/L final), driven by higher current density (0.34 vs 0.05 A/m²).
Was heißt das. Operators targeting >70% ammonia removal must apply ≥0.9 V external voltage; MFC mode alone is insufficient for high-nitrogen substrates.
Mechanismus Dissolved oxygen in cathode zone increased from 7.5 to 8.5 mg/L during algal log-phase (days 4–12), directly raising cathodic potential and OCV from ~400 mV to 540 mV.
Was heißt das. Synchronize BES operation with algal exponential growth phase (days 4–12 in this setup) to maximize oxygen-driven cathode performance; stationary phase (day 15+) yields lower OCV.
Schwellenwert H2S removal from biogas is complete (100%) in both MEC modes but only 78–84% in MFC mode, despite similar H2S liquid-phase removal patterns.
Was heißt das. If H2S-free biogas is critical, use MEC mode (≥0.6 V); MFC mode leaves residual H2S gas that may require downstream scrubbing.
Zielkonflikt COD reduction correlates strongly with current density: 89.5% at 0.34 A/m² (MEC 0.9 V), 80.4% at 0.13 A/m² (MEC 0.6 V), 71.2% at 0.05 A/m² (MFC).
Was heißt das. Design for current density ≥0.3 A/m² if targeting >85% COD removal; lower densities plateau below 75%.
Leistung Algal photosynthesis phase (light vs dark) modulates power density by 28% (29.0 W/m² light vs 22.6 W/m² dark) and current density marginally (115 vs 112 mA/m²), both at day 10 log-phase.
Was heißt das. Expect 20–30% power fluctuation in algae-assisted BES on a 12:12 light:dark cycle; design load resistance and external voltage to tolerate this variation.
Ansatzpunkte6
Konkrete Lücken in dieser Publikation, jeweils mit einem Experiment, das sie schließen würde.
Hoch No measurement of nitrite (NO2-) or N2O accumulation in anode or cathode zones despite ammonium removal and nitrification claims.
Paper states 'parallel process of nitrification' in cathode zone (Table 2 caption) but provides no NO2- or N2O data; ammonium removal mechanism (electrochemical vs biological nitrification) remains uncharacterized.
Versuch. Measure NO2-, NO3-, and N2O in both anode and cathode liquids and gas phases across all four operating modes; use isotope tracing (15N) to distinguish electrochemical oxidation from microbial nitrification.
Mittel No investigation of cathode pH effect on ammonium speciation and removal efficiency.
Anode pH increased from 7.4–7.8 to 7.8–8.2 across modes (Table 2), but cathode pH not reported; ammonia/ammonium equilibrium (pKa ~9.25) and electrochemical oxidation kinetics are pH-sensitive.
Versuch. Vary cathode pH from 6.5 to 9.0 while holding other parameters constant; measure NH4+ removal rate and final concentration; correlate with cathodic potential and dissolved oxygen.
Mittel Lack of C/N ratio optimization; only one substrate composition tested (TKN 310–325 mg/L, COD 9.45–11.90 g/L).
Paper does not vary C/N ratio or test whether ammonium removal is limited by carbon availability or electrochemical capacity; ethanol stillage C/N ratio ~30:1 is not compared to other ratios.
Versuch. Test C/N ratios from 10:1 to 50:1 by adjusting substrate dilution or supplementing with glucose; measure ammonium removal rate and COD consumption to identify optimal ratio.
Mittel No direct measurement of electrode potential (anode and cathode) during MEC operation; only OCV and external voltage reported.
Anode and cathode potentials are shown only for open-circuit conditions (Fig. 2b); actual potentials under 0.6 V and 0.9 V applied voltage are not provided, limiting mechanistic understanding of ammonium oxidation pathway.
Versuch. Use potentiostat to measure anode and cathode potentials independently during MEC 0.6 V and 0.9 V operation; correlate with ammonium removal rate and current density.
Mittel Biofilm composition on anode not characterized; SEM shows only morphology (coccoid bacteria 1–1.5 μm) without taxonomic or functional identification.
Paper claims 'methanogenic bacteria' on anode (Fig. 5a caption) but does not identify whether these are methanogens, exoelectrogens, or sulfate-reducers; functional role in ammonium removal unclear.
Versuch. Perform 16S rRNA gene sequencing and metatranscriptomics on anode biofilm; correlate microbial community composition with ammonium removal rate and current density across operating modes.
Niedrig No investigation of ammonium migration mechanism (electrochemical vs diffusion) or cation exchange membrane (CEM) selectivity.
Paper uses CMI-7000S cation exchange membrane but does not measure ion flux, membrane potential, or selectivity; ammonium removal could be driven by electromigration, diffusion, or algal uptake.
Versuch. Measure ion concentrations (NH4+, Na+, K+, Ca2+) in anode, cathode, and membrane pore water; calculate Faraday efficiency for ammonium removal; test alternative membranes (AEM, bipolar) to isolate electrochemical contribution.
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Was gemacht wurde
- Systemtyp
- MEC
Was funktioniert hat
Zusammenfassung
In a two-section bioelectrochemical system (BES), the processes of biomethanation of ethanol stillage in the anode zone and oxygenic photosynthesis in the cathodic zone are combined.There is a reduction of ammonium ions and removal of H2S in the anode zone, and at the same time, there is a positive impact on the process of biomethanation from ethanol stillage in parallel to the anode anaerobic bioreactor.Chemical oxygen demand (COD) reductions ranging from 71.2% to 89.5% were achieved in the 3 BES operating modes studied.The dynamics of the main technological parameters in the bioanode and biocathode area of the BES during continuous operation of the anaerobic bioreactor and photobioreactor (PBR) at a contact time of 10 days is established.Depending on the selected variant of operation of BES -microbial fuel cell (MFC), microbial electrolysis cell (MEC) with 0.6V and 0.9V, a decrease in the ammonium concentration is found to varying degrees, as in the MEC mode with an external electrical voltage of 0.9V the highest degree of 76.5% is reached.At the same time, complete removal of H2S is found, in the liquid and gas phases in MEC -mode and partially (78 -84 %) in MFC -mode.The influence of the photosynthetic phases on the electrochemical parameters of MFC was also investigated, with maximum values for power and current densities of 29 W/m 2 and 115 mA/m 2 , respectively.
Schlagwörter
Kennungen
- Zeitschrift
- Bulgarian Chemical Communications
- Jahr
- 2023
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