Forschungsdaten – Titel und Zusammenfassungen von Publikationen, extrahierte Daten und Katalogeinträge – erscheinen in ihrer Originalsprache Englisch.
The concept of load ratio applied to bioelectrochemical systems for ammonia recovery
Mariana Rodríguez Arredondo, Philipp Kuntke, Annemiek ter Heijne, Cees JN Buisman
KI-Zusammenfassung
82 % KonfidenzThis study validates the load ratio concept—the ratio of current density to TAN loading rate—as a predictor of ammonia recovery efficiency in bioelectrochemical systems (BES) treating urine. Operating three microbial electrolysis cells coupled to gas-permeable membrane modules, the authors achieved maximum TAN removal of 60.9% at a load ratio of 0.7 (119 gN m⁻² day⁻¹, 1.9 kWh kgN⁻¹). The load ratio framework successfully predicts BES performance across varying dilutions and feed compositions, but ionic competition and low TAN mole fractions limit achievable load ratios (<1.5) and energy efficiency in practice.
Zentrale Erkenntnisse
Schwellenwert TAN removal efficiency increases monotonically with load ratio up to 0.7, reaching 60.9% maximum, but load ratios >0.8 were never achieved in BES due to current limitations.
Was heißt das. Operators should target load ratios of 0.6–0.7 for optimal energy-to-recovery trade-off; higher current densities are needed to exceed this window, but the paper did not identify a limiting load ratio where energy cost becomes prohibitive.
Mechanismus Transport efficiency >100% occurs at low current densities (0.5–0.7 A m⁻²) due to diffusion contribution, allowing high TAN removal (>50%) despite low load ratios (<0.2).
Was heißt das. Do not rely on load ratio alone at very low currents; diffusion-driven transport can supplement electromigration, but this effect diminishes as current increases.
Zielkonflikt Ionic composition (TAN mole fraction relative to competing cations Na⁺, K⁺) critically modulates the load ratio needed for high removal: urine with 70% less TAN (mole fraction 0.23) required much higher current to achieve equivalent removal compared to standard urine (mole fraction 0.69).
Was heißt das. Pre-characterize feed ionic composition; if TAN mole fraction is <0.3, expect to need 2–3× higher current density and energy input to reach 60% removal.
Mechanismus TMCS effectiveness is essential: when the TMCS unit failed or was absent, negative TAN removal occurred due to back-diffusion of ammonia from cathode to anode, negating electromigration gains.
Was heißt das. Ensure catholyte ammonia stripping is robust; a non-functional TMCS will cause system failure even at high load ratios.
Mechanismus BES achieved lower maximum load ratios (<1.5) than electrochemical systems (ES) because current density depends on microbial oxidation of organic matter, which cannot be independently controlled from TAN loading rate.
Was heißt das. If targeting load ratios >1.5 for >70% removal, use ES with applied voltage control rather than BES; BES is limited by bioanode kinetics.
Widersprüche1
Nur Konflikte, die die Publikation selbst zeigt, jeweils am Text geprüft.
Innerhalb der Publikation Load ratio predicts BES performance, yet BES cannot achieve the load ratios needed for high removal that ES can.
Eine Seite'BES and ES show the same general relationship between TAN removal efficiency and load ratio' (Abstract and Figure 4A).
“BES and ES show the same general relationship between TAN removal efficiency and load ratio.”
Andere Seite'Higher TAN removal efficiencies were achieved with an ES compared to the BESs, due to the higher load ratios obtained' (Results section).
“Higher TAN removal efficiencies were achieved with an ES compared to the BESs, due to the higher load ratios obtained.”
Einordnung der Autoren. The relationship is the same (both follow the trend), but BES is constrained to lower load ratios by microbial kinetics, so it cannot reach the same absolute removal efficiencies as ES. The model is valid but the operating window is narrower for BES.
Ansatzpunkte6
Konkrete Lücken in dieser Publikation, jeweils mit einem Experiment, das sie schließen würde.
Hoch No experiments tested anode potentials more negative than −0.3 V (or more positive than −0.4 V) to determine if higher current density and load ratio are achievable by tuning anode potential.
Anode potential was held constant at −0.3 V for most experiments (with one exception at −0.4 V for 34 days). The paper states 'Higher current densities, and insights into the factors limiting current, are needed' but does not systematically vary anode potential to find the optimum.
Versuch. Vary anode potential from −0.5 to −0.1 V vs Ag/AgCl; measure current density, TAN removal, and energy input; identify potential window that maximizes load ratio without excessive overpotential loss.
Mittel No experiments tested cathode potential or cathode material optimization to increase hydrogen evolution rate and thus current density.
Cathode materials (platinized flow field and RuMMO-coated titanium mesh) are mentioned but not compared. Current density is limited by anode (microbial oxidation), but cathode kinetics may also constrain the system.
Versuch. Compare cathode materials (Pt, RuMMO, IrO₂, carbon) at fixed anode potential; measure current density and cathode overpotential; identify cathode that enables highest current without excessive voltage penalty.
Mittel No systematic study of HRT (hydraulic retention time) or residence time in the anode chamber on current density and TAN removal.
Anolyte inflow rates varied from 0.2 to 6.3 mL min⁻¹ (Table 1), implying HRTs from ~2 to ~60 min in the 200 mL anode chamber, but HRT is not reported or analyzed as a variable.
Versuch. Fix all other parameters; vary HRT from 10 to 120 min; measure current density, COD removal, and TAN removal efficiency; determine if longer residence time increases current by allowing more complete substrate oxidation.
Mittel No experiments tested the effect of competing cations (Na⁺, K⁺) concentration on load ratio and TAN removal at fixed TAN loading rate.
Ionic composition (TAN mole fraction) is shown to be critical (Figure 2, 'Transport efficiencies <30%' section), but the paper only observes this as a consequence of TAN pre-treatment, not as a controlled variable.
Versuch. Prepare synthetic urine with fixed TAN (e.g., 500 mg L⁻¹) but vary Na⁺ + K⁺ from 0 to 2000 mg L⁻¹; measure current density, TAN transport efficiency, and removal efficiency; quantify the Na⁺/K⁺ threshold above which TAN recovery becomes impractical.
Hoch No measurement of N2O, NO₃⁻, NO₂⁻, or other nitrogen species in the anode or cathode effluent; nitrogen balance is incomplete.
The paper focuses on TAN recovery but does not report whether any TAN is oxidized to NO₃⁻, NO₂⁻, or N2O at the anode, or whether any reduction to N2 or N2O occurs at the cathode. Nitrogen balance is not closed.
Versuch. Measure NO₃⁻, NO₂⁻, N2O, and N2 in anode and cathode effluent by ion chromatography and gas chromatography; calculate nitrogen balance; determine if any TAN is lost to oxidation or if any undesired reduction products form.
Niedrig No experiments tested the effect of dissolved oxygen (DO) in the anode chamber on current density and TAN removal.
The paper mentions gas vents and anaerobic conditions but does not report DO measurements or test the effect of DO on performance. Oxygen could compete with TAN as an electron acceptor at the cathode or inhibit the bioanode.
Versuch. Operate the anode chamber at controlled DO levels (0, 2, 5, 10 mg L⁻¹); measure current density, TAN removal, and anode potential; determine if DO improves or inhibits performance.
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Zusammenfassung
Abstract BACKGROUND The load ratio is a crucial parameter to optimize the current driven recovery of total ammonia nitrogen (TAN) from urine. The load ratio is the ratio between the current density and the TAN loading rate. It is currently not known if the load ratio concept applies to a bioelectrochemical system (BES) because the current density and TAN loading rate cannot be controlled independently. RESULTS We found a clear increasing trend in TAN removal efficiency with respect to load ratio in the BES for both human and synthetic urine. The maximum TAN removal efficiency was 60.9% at a load ratio of 0.7, corresponding to a TAN transport rate of 119 gN m −2 day −1 at an electrical energy input of 1.9 kWh kgN −1 (synthetic urine). Low load ratios (<1) were obtained, indicating that the current was not enough to transport all the TAN across the membrane. CONCLUSIONS BES and ES show the same general relationship between TAN removal efficiency and load ratio. Therefore, given a stable current density, the concept of load ratio can also predict the TAN removal efficiency in BES. Higher current densities, and insights into the factors limiting current, are needed to increase the load ratio and therefore the TAN removal efficiency. © 2019 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.
Schlagwörter
Kennungen
- Zeitschrift
- Journal of Chemical Technology & Biotechnology
- Jahr
- 2019
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