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Treatment of Mineral Oil Refinery Wastewater in Microbial Fuel Cells Using Ionic Liquid Based Separators
Hasna Addi, Francisco Mateo-Ramírez, Víctor Ortiz-Martínez, María Salar-García +6
KI-Zusammenfassung
72 % KonfidenzThis paper demonstrates treatment of mineral oil refinery wastewater in single-chamber air-cathode MFCs using an ionic liquid-based polymer inclusion membrane ([MTOA+][Cl−]) as separator. Over 9 days at 25 °C with 1 kΩ external load, the system achieved 81% COD removal (1760 to 334 mg/L), 50% Kjeldahl nitrogen reduction (11.2 to 5.6 mg/L), and 51% sulphate removal (263.5 to 128.5 mg/L), generating 45 mW/m³ power density and 105 mV voltage. The ionic liquid membrane remained stable despite some leaching of chloride (3.28% loss) and nitrogen (8.85% loss) into the medium.
Zentrale Erkenntnisse
Leistung Kjeldahl nitrogen decreased 50% (11.2 to 5.6 mg/L) in MFCs versus only 25% in baseline and 37.5% in control, showing electrochemical conditions accelerate nitrogen removal beyond passive anaerobic digestion.
Was heißt das. Operators should expect enhanced nitrogen removal in MFC mode compared to conventional anaerobic treatment, but the mechanism (denitrification vs. assimilation) is not identified and should be confirmed.
Leistung Nitrite concentration remained nearly unchanged across all conditions (0.48 to 0.38–0.42 mg/L), showing no accumulation or preferential reduction despite active electrochemical conditions.
Was heißt das. Nitrite does not appear to be a bottleneck or product in this system, but the absence of N2O measurement leaves the fate of reduced nitrogen species unknown.
Mechanismus Coulombic efficiency was only 1.5% despite 81% COD removal, indicating most substrate carbon was consumed by heterotrophic growth rather than electrochemical oxidation.
Was heißt das. For nitrogen cycling studies, recognize that in unacclimated, mixed-culture MFCs on complex wastewater, most nitrogen removal is likely via assimilation or heterotrophic pathways, not electrochemical denitrification.
Leistung Ammonium decreased from 2.67 to 1.40 mg/L in MFCs (48% removal), more than in baseline (45%) and control (18%), suggesting electrochemical conditions favor ammonium uptake or oxidation.
Was heißt das. Ammonia recovery or nitrification pathways may be active but were not measured; operators should monitor dissolved oxygen at cathode and pH gradients to infer nitrification potential.
Schwellenwert Ionic liquid membrane lost 3.28% chloride and 8.85% nitrogen (from the [MTOA+][Cl−] cation) to the bulk solution during 217 h operation, yet maintained structural integrity and proton conductivity.
Was heißt das. Leaching of ionic liquid components may affect long-term membrane performance and introduce organic contaminants; test membrane lifetime and chloride/nitrogen leaching kinetics over weeks to months.
Ansatzpunkte6
Konkrete Lücken in dieser Publikation, jeweils mit einem Experiment, das sie schließen würde.
Hoch No measurement of N2O, NO, or N2 gas production despite active nitrogen cycling; cannot distinguish denitrification from assimilation or nitrification.
Paper reports 50% Kjeldahl nitrogen removal and 48% ammonium removal but provides no gas chromatography, isotope tracing, or N-balance to identify pathways. Section 3.1 states 'several mechanisms are involved for each ion species' but does not resolve them.
Versuch. Measure headspace N2O, NO, and N2 via GC-ECD or membrane inlet mass spectrometry; perform 15N-labeling on NO3− and NH4+ to quantify denitrification vs. assimilation rates under MFC vs. baseline conditions.
Hoch No variation of cathode potential, anode potential, or applied voltage to map the operating window for nitrogen removal vs. power generation trade-offs.
Paper operates at fixed 1 kΩ external load (105 mV output) but does not explore how cathode potential (which controls dissolved oxygen and pH) or anode potential (which controls electron availability) affect nitrogen species fate. Polarization curve (Figure 5) shows voltage-current relationship but not potential-dependent nitrogen removal.
Versuch. Vary external load from 10 Ω to 100 kΩ (or use potentiostat to set anode/cathode potentials independently); measure Kjeldahl N, NO3−, NO2−, NH4+, and N2O at each potential; identify threshold potentials for nitrification vs. denitrification.
Hoch No measurement of dissolved oxygen, pH, or redox potential in anode and cathode compartments; cannot infer nitrification or denitrification conditions.
Paper reports pH shift from 8.19 to 6.78 in MFC but does not measure spatial or temporal DO/pH gradients. Section 3.1 states 'protons produced are not accumulated' and 'transferred through the ionic liquid membrane' but does not measure cathode pH or DO, which control nitrification kinetics.
Versuch. Install DO and pH probes in anode and cathode; measure profiles over 9 days; correlate cathode DO and pH with ammonium and nitrite trends.
Mittel No characterization of microbial community composition or enrichment; cannot identify which organisms drive nitrogen removal.
Paper uses 'natural occurring bacteria' from refinery wastewater (Section 3.3) but provides no 16S rRNA sequencing, culture isolation, or functional gene analysis (nxrA, nirS, nosZ). Baseline and control reactors show similar nitrogen removal, suggesting abiotic or non-electroactive pathways may dominate.
Versuch. Perform 16S rRNA gene sequencing on anode biofilm and bulk liquid at days 0, 3, 6, 9; identify nitrifiers (Nitrosomonas, Nitrobacter) and denitrifiers (Paracoccus, Pseudomonas); correlate abundance with nitrogen species dynamics.
Mittel No variation of C/N ratio, HRT, or initial substrate concentration to map nitrogen removal kinetics and saturation.
Paper uses single wastewater composition (initial Kjeldahl N = 11.2 mg/L, COD = 1760 mg/L, C/N ≈ 157 by mass) and fixed 9-day batch operation. No exploration of how C/N ratio or residence time affect nitrogen removal efficiency or N2O accumulation.
Versuch. Test C/N ratios of 10, 50, 100, 200 by diluting or spiking wastewater; vary HRT from 3 to 15 days; measure Kjeldahl N removal rate (mg N/L/day) and final NO2−, NO3−, NH4+ concentrations.
Mittel Ionic liquid membrane leaching (3.28% Cl, 8.85% N loss) not quantified over longer timescales; long-term stability and impact on nitrogen cycling unknown.
EDX analysis (Table 2) shows leaching after 217 h but paper does not measure leaching kinetics, cumulative loss over weeks, or whether leached ionic liquid affects microbial metabolism or nitrogen removal pathways.
Versuch. Operate MFC for 30–60 days; measure chloride and nitrogen concentration in bulk liquid weekly; perform mass balance on ionic liquid; test whether leached [MTOA+][Cl−] inhibits or promotes nitrification/denitrification in batch cultures.
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Was gemacht wurde
- Systemtyp
- MFC
- Substrat
- real wastewater
- Inokulum
- mixed culture from wastewater
Was funktioniert hat
Zusammenfassung
Microbial fuel cells (MFCs) are an environmentally friendly technology that can recover electricity directly from several wastes at ambient temperatures. This work explores the use of mineral oil refinery wastewater as feedstock in single-chamber air-cathode MFC devices. A polymer inclusion membrane based on the ionic liquid methyltrioctylammonium chloride, [MTOA+][Cl−], at a concentration of 70% w/w, was used as separator, showing a good efficiency in power production and chemical oxygen demand (COD) removal. The power and the chemical oxygen demand removal reached values of 45 mW/m³ and over 80%, respectively. The evolution of other parameters of the wastewater including nitrites, phosphates and sulphates were also studied. Kjeldahl nitrogen and sulphates were significantly reduced during MFC operation. The results show that mineral oil refinery wastewater can be used as feedstock in air breathing cathode-microbial fuel cells based on polymer ionic liquid inclusion membranes. This configuration could represent a good alternative for wastewater depuration while producing energy during the process.
Schlagwörter
Kennungen
- Zeitschrift
- Applied Sciences
- Jahr
- 2018
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