Forschungsdaten – Titel und Zusammenfassungen von Publikationen, extrahierte Daten und Katalogeinträge – erscheinen in ihrer Originalsprache Englisch.
Ammonium Recovery and Biogas Upgrading in a Tubular Micro-Pilot Microbial Electrolysis Cell (MEC)
Lorenzo Cristiani, Marco Zeppilli, Cristina Porcu, Mauro Majone
KI-Zusammenfassung
78 % KonfidenzA 12-liter tubular MEC with cation exchange membrane was operated as a post-treatment unit for anaerobic digestate, coupling biogas upgrading (CO₂ removal via bioelectromethanogenesis) with ammonium recovery. Three nitrogen loading rates (73–2229 mg N/Ld) were tested at fixed anode potential (+0.2 V vs. SHE) and organic load (2.55 g COD/Ld). Ammonium migration through the membrane increased dramatically with N load, from 1% to 100% of ionic current, enabling recovery of up to 2.5 g N/day. CO₂ removal remained stable (~450 mmol/day, 65% removal). Energy consumption for N recovery was 2.3 kWh/kg N, competitive with benchmark technologies.
Zentrale Erkenntnisse
Schwellenwert Ammonium contribution to ionic current increased non-linearly with influent concentration: 5-fold increase in N load (73→365 mg N/Ld) caused 22-fold increase in transported charge (1%→22%), while 30-fold increase (73→2229 mg N/Ld) caused only 100% increase (1%→100%).
Was heißt das. Operators should expect saturation of ammonium-driven ionic transport at high N loads; design catholyte spill rates accordingly to avoid exceeding electroneutrality capacity.
Zielkonflikt Coulombic efficiency (CE) dropped from 77% at low N load to 18% at high N load (73→2229 mg N/Ld), while COD removal efficiency increased from 29% to 70%, indicating non-electroactive COD removal pathways (sorption, biofilm entrapment) became dominant.
Was heißt das. At high ammonium loads, do not assume all COD removal is electrochemical; account for biomass growth and physical sorption when calculating electron balance and energy efficiency.
Zielkonflikt Cathodic capture efficiency (CCE) peaked at 98% during the middle N-load period (365 mg N/Ld) but dropped to 81% at the highest load (2229 mg N/Ld), despite stable methane production rate (14±2 mmol/day).
Was heißt das. High ammonium loads may reduce cathodic current utilization efficiency; monitor CCE as an early indicator of cathode performance degradation or competing reactions.
Mechanismus Cell voltage decreased from −2.66 V at low N load to −1.48 V at high N load, a 44% reduction, while current remained relatively stable (190→157 mA), indicating improved ionic conductivity from ammonium migration.
Was heißt das. Increasing ammonium concentration reduces ohmic losses; design power supplies for lower voltage requirements when treating high-N digestates, improving energy efficiency.
Schwellenwert No inhibition of methanogens or electroactive biofilm was observed even at 1341 mg N/L influent ammonium (2229 mg N/Ld load), and no ammonia was detected in outlet gas, indicating complete retention and recovery.
Was heißt das. Ammonium concentrations up to ~1000 mg N/L are tolerable in MEC anodes; design recovery systems to capture all migrated ammonium in catholyte spill to prevent ammonia volatilization.
Widersprüche1
Nur Konflikte, die die Publikation selbst zeigt, jeweils am Text geprüft.
Innerhalb der Publikation COD removal efficiency increased sharply while coulombic efficiency decreased sharply at the highest N load, suggesting a decoupling of electrochemical and total COD removal.
Eine SeiteCOD removal efficiency increased to 89±20% at 2229 mg N/Ld
“The increase of the COD removal efficiency up to 70% probably indicated an underestimation of the biomass growth in the anodic chamber or the presence of non-electroactive COD removal pathways like COD sorption or entrapment in the biofilm mat”
Andere SeiteCoulombic efficiency dropped to 18±2% at the same condition
“the CE of the process, which was only 18 ± 2%”
Einordnung der Autoren. Authors attribute the discrepancy to biomass growth and non-electroactive sorption/entrapment, implying that total COD removal includes both electrochemical oxidation (low CE) and physical/biological processes (high removal efficiency). This is mechanistically plausible but not quantitatively resolved in the paper.
Ansatzpunkte6
Konkrete Lücken in dieser Publikation, jeweils mit einem Experiment, das sie schließen würde.
Hoch No measurement of nitrite (NO₂⁻) or nitrate (NO₃⁻) accumulation in anode or cathode across any N-load condition; denitrification or nitrification pathways not characterized.
Paper focuses on ammonium recovery but does not report whether any N oxidation or reduction occurs. At anode potential +0.2 V vs. SHE, nitrification is thermodynamically possible; at cathode, denitrification could compete with methanogenesis.
Versuch. Measure NO₃⁻, NO₂⁻, N₂O, and N₂ in anode and cathode effluent and gas phases across all three N-load periods; use ¹⁵N tracing if needed.
Hoch No systematic variation of anode potential; only +0.2 V vs. SHE tested. Operating window for ammonium recovery vs. nitrification not explored.
Paper states anode was 'maintained' at +0.2 V but does not justify this choice or test alternatives. Higher potentials might suppress ammonium migration or promote nitrification; lower potentials might reduce current.
Versuch. Test anode potentials from −0.1 to +0.4 V vs. SHE at fixed N load (e.g., 365 mg N/Ld); measure ammonium migration rate, current, and any N-oxide formation.
Mittel Catholyte pH not actively controlled; ranged 7.5±1 across periods. Effect of pH on ammonium speciation (NH₄⁺ vs. NH₃) and migration not isolated.
At pH 7.5, ~99% of total ammonia is NH₄⁺, but pH drift could shift this. Paper does not report pH control strategy or sensitivity analysis.
Versuch. Operate at fixed pH (6.5, 7.0, 7.5, 8.0) in cathode; measure ammonium migration rate and N₂O/NH₃ emissions.
Mittel Hydraulic retention time (HRT) fixed at 0.52 days; no variation tested. Effect of HRT on ammonium removal efficiency and N-species selectivity unknown.
Paper states HRT was 0.52 d but does not explore shorter or longer residence times. Shorter HRT might reduce ammonium removal; longer HRT might enable denitrification.
Versuch. Test HRT 0.25, 0.52, 1.0, 2.0 days at fixed N load and anode potential; measure N removal efficiency and N-species balance.
Hoch No N₂O measurement or quantification; only CO₂, CH₄, and H₂ reported in gas phase. N₂O emissions from cathode (denitrification) or anode (nitrification) not ruled out.
Bioelectrochemical systems can produce N₂O as a byproduct of denitrification or nitrification. Paper does not report whether N₂O was measured or below detection limit.
Versuch. Analyze cathode and anode gas outlets for N₂O using GC-ECD or IRMS; quantify N₂O production rate as function of N load and potential.
Mittel Biomass composition and electroactive biofilm characterization not reported; only VSS measured. Microbial community structure and electron transfer mechanisms not identified.
Paper reports VSS in anode effluent (84–106 mg/L) but does not characterize biofilm on electrodes or identify key electroactive taxa. Mechanism of ammonium tolerance unclear.
Versuch. Perform 16S rRNA gene sequencing and FISH on anode and cathode biofilms at each N-load period; measure extracellular electron transfer rates via cyclic voltammetry.
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Literatur-Priors
Was gemacht wurde
- Systemtyp
- MEC
Was funktioniert hat
Zusammenfassung
Here, a 12-liter tubular microbial electrolysis cell (MEC) was developed as a post treatment unit for simultaneous biogas upgrading and ammonium recovery from the liquid effluent of an anaerobic digestion process. The MEC configuration adopted a cation exchange membrane to separate the inner anodic chamber and the external cathodic chamber, which were filled with graphite granules. The cathodic chamber performed the CO2 removal through the bioelectromethanogenesis reaction and alkalinity generation while the anodic oxidation of a synthetic fermentate partially sustained the energy demand of the process. Three different nitrogen load rates (73, 365, and 2229 mg N/Ld) were applied to the inner anodic chamber to test the performances of the whole process in terms of COD (Chemical Oxygen Demand) removal, CO2 removal, and nitrogen recovery. By maintaining the organic load rate at 2.55 g COD/Ld and the anodic chamber polarization at +0.2 V vs. SHE (Standard Hydrogen Electrode), the increase of the nitrogen load rate promoted the ammonium migration and recovery, i.e., the percentage of current counterbalanced by the ammonium migration increased from 1% to 100% by increasing the nitrogen load rate by 30-fold. The CO2 removal slightly increased during the three periods, and permitted the removal of 65% of the influent CO2, which corresponded to an average removal of 2.2 g CO2/Ld. During the operation with the higher nitrogen load rate, the MEC energy consumption, which was simultaneously used for the different operations, was lower than the selected benchmark technologies, i.e., 0.47 kW/N·m³ for CO2 removal and 0.88 kW·h/kg COD for COD oxidation were consumed by the MEC while the ammonium nitrogen recovery consumed 2.3 kW·h/kg N.
Schlagwörter
Kennungen
- Zeitschrift
- Molecules
- Jahr
- 2020
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