Catholyte pH Research Articles

Critical Roles of pH and Activated Carbon on the Speciation and Performance of an Archetypal Organometallic Complex for Aqueous Redox Flow Batteries

A lack of suitable high-potential catholytes (posolytes) hinders the development of aqueous redox flow batteries (RFBs) for large-scale energy storage. Hydrolysis of the charged (oxidized) catholyte typically occurs when its redox potential approaches that of water, with a negative impact on battery performance. Here we elucidate and address such behavior for a representative iron-based organometallic complex, showing that the associated voltage and capacity losses can be curtailed by several simple means.1 We discovered that addition of activated carbon cloth (ACC) to the reservoir of low-cost, high-potential [Fe(bpy)3]2+/3+ catholyte-limited aqueous redox flow batteries (Fig. 1) extends their lifetime and boosts discharge voltage – two typically orthogonal performance metrics. Similar effects are observed when the catholyte’s graphite felt electrode is electrochemically oxidized (overcharged) and by modifying the catholyte solution’s pH, which was monitored in situ for all flow batteries. Modulation of solution pH alters hydrolytic speciation of the charged catholyte from the typical dimeric species, µ-O-[FeIII(bpy)2(H2O)]2 4+, converting it to a higher-potential µ-dihydroxo form, µ-[FeIII(bpy)2(H2O)(OH)]2 4+, at lower pH. The existence of free bpyH2 2+ at low pH is found to strongly correlate with battery degradation. Near-neutral-pH RFBs employing a viologen anolyte, (SPr)2V, in excess with the [Fe(bpy)3]2+/3+ catholyte containing ACC exhibited high-voltage discharge for up to 600 cycles (41 days) with no discernible capacity fade. Correlating pH and voltage data offers powerful fundamental insight into organometallic (electro)chemistry with potential utility beyond battery applications. The findings, with implications toward a host of other “near-neutral” active species, illuminate the critical and underappreciated role of electrolyte pH on intracycle and long-term aqueous flow battery performance.(1) Burghoff, A.; Holubowitch, N. E. Critical Roles of pH and Activated Carbon on the Speciation and Performance of an Archetypal Organometallic Complex for Aqueous Redox Flow Batteries. J. Am. Chem. Soc. 2024, 146 (14), 9728-9740. DOI: 10.1021/jacs.3c13828.Figure 1. pH monitored in situ during long-term green catholyte experiment with ACC additions. (a) Schematic of pH probe experimental setup; (b) raw data for voltage and catholyte pH vs. time; (c) voltage and pH around the first ACC addition (80 mg at t = 37 h); (d) voltage and pH around the second ACC addition (80 mg at t = 64 h). Figure 1

Pilot microbial electrolysis cell closes the hydrogen loop for hydrothermal wet waste conversion to jet fuel

The global shift toward net-zero emissions necessitates resource recovery from wet waste. In this study, we demonstrate the first feasibility of combining pilot-scale microbial electrolytic cells (MECs) with hydrothermal liquefaction (HTL) for simultaneous post-hydrothermal liquefaction wastewater (PHW) treatment and efficient hydrogen (H₂) production to meet biocrude upgrading requirements. Long-term single reactor operation revealed that fixed anode potential enabled rapid startup, and low catholyte pH and high salinity were effective in suppression of cathodic methanogenesis and acetogenesis – resulting in high current density of 16.6 A m−2 and 9.3 A m−2 when feeding synthetic wastewater and PHW respectively. Additionally, the anode biofilm exhibited spatial variations in response to local environmental conditions. Onsite parallel or serial operations of multiple MECs showed good performance using actual PHW with a record-high H2 production rate of 0.5 L LR day−1 for MEC over 10 liters scale, and the optimal chemical oxygen demand (COD)-to-H2 yield reached 0.127 kg-H2 per kg-COD, supporting a self-sufficient, closed-loop upgrade to jet fuel.

PH Variation in the Acidic Electrochemical CO2 Reduction Process.

To address the carbonate problem in the alkaline electrochemical CO2 reduction reaction (CO2RR), more attention has been paid to the CO2RR conducted in acidic electrolytes. The pH stability of such an acidic electrolyte is vital to make sure that the conclusion made in the so-called acidic CO2RR is reliable. Herein, based on reported model electrocatalysts for acidic CO2RR, by monitoring the varying of pH and alkali cation (K+) concentration along with the CO2RR performance in initially acidic electrolyte solution (K2SO4 with pH = 3.5), we unveil their remarkable CO2RR performance along with the rapid pH increase up to 9.5 in the cathode chamber and decrease down to 2.4 in the anode chamber due to the diffusion of K+ along with protons through the proton exchange membrane from the anode to the cathode chamber. We further reveal the rapid collapse of their CO2RR performance in a constant acid solution. This means that some previously reported "remarkable acidic CO2RR performances" actually originate from the alkaline rather than acidic electrolyte, and the conclusions made in such work need to be reconsidered. We also summarize the actual relationship between the CO2RR performance and catholyte pH in widely used Bi- and Sn-based catalysts. This work provides deeper insights into the stability of acidity and the pH effect on electrocatalysts for the CO2RR.

Boosting the Electroreduction of CO2 to CO by Ligand Engineering of Gold Nanoclusters

AbstractThe electrochemical CO2 reduction reaction (CO2RR) has been widely studied as a promising means to convert anthropogenic CO2 into valuable chemicals and fuels. In this process, the alkali metal ions present in the electrolyte are known to significantly influence the CO2RR activity and selectivity. In this study, we report a strategy for preparing efficient electrocatalysts by introducing a cation‐relaying ligand, namely 6‐mercaptohexanoic acid (MHA), into atom‐precise Au25 nanoclusters (NCs). The CO2RR activity of the synthesized Au25(MHA)18 NCs was compared with that of Au25(HT)18 NCs (HT=1‐hexanethiolate). While both NCs selectively produced CO over H2, the CO2‐to‐CO conversion activity of the Au25(MHA)18 NCs was significantly higher than that of the Au25(HT)18 NCs when the catholyte pH was higher than the pKa of MHA, demonstrating the cation‐relaying effect of the anionic terminal group. Mechanistic investigations into the CO2RR occurring on the Au25 NCs in the presence of different catholyte cations and concentrations revealed that the CO2‐to‐CO conversion activities of these Au25 NCs increased in the order Li+<Na+<K+<Cs+, and are gated by the cation‐coupled electron transfer step. These results were confirmed by the Nernstian shifts of the polarization curves at different cation concentrations.

Boosting the Electroreduction of CO2 to CO by Ligand Engineering of Gold Nanoclusters.

The electrochemical CO2 reduction reaction (CO2RR) has been widely studied as a promising means to convert anthropogenic CO2 into valuable chemicals and fuels. In this process, the alkali metal ions present in the electrolyte are known to significantly influence the CO2RR activity and selectivity. In this study, we report a strategy for preparing efficient electrocatalysts by introducing a cation-relaying ligand, namely 6-mercaptohexanoic acid (MHA), into atom-precise Au25 nanoclusters (NCs). The CO2RR activity of the synthesized Au25(MHA)18 NCs was compared with that of Au25(HT)18 NCs (HT=1-hexanethiolate). While both NCs selectively produced CO over H2, the CO2-to-CO conversion activity of the Au25(MHA)18 NCs was significantly higher than that of the Au25(HT)18 NCs when the catholyte pH was higher than the pKa of MHA, demonstrating the cation-relaying effect of the anionic terminal group. Mechanistic investigations into the CO2RR occurring on the Au25 NCs in the presence of different catholyte cations and concentrations revealed that the CO2-to-CO conversion activities of these Au25 NCs increased in the order Li+<Na+<K+<Cs+, and are gated by the cation-coupled electron transfer step. These results were confirmed by the Nernstian shifts of the polarization curves at different cation concentrations.

Enhancing proton conduction by regulating proton carrier position in polyamide layer of forward osmosis membrane in osmotic microbial fuel cell

Osmotic microbial fuel cell (OsMFC) encounters the problem of slow transport of proton, which results in a pH imbalance between the anode and cathode, and then a decreased cell performance. Forward osmosis (FO) membrane plays a critical role in proton transport in OsMFC, but the proton transmembrane migration is greatly hindered by the absence of particular proton transfer unit in FO membrane. In this study, high proton conductive carrier sulfo (−SO3H) was imported in the polyamide (PA) layer of FO membrane. The results demonstrated that the position of sulfo on benzene ring in PA polymer chain had a significant effect on proton migration and further the OsMFC property. As sulfo is in the ortho and para of the amino group on benzene ring, the optimal FO-1 membrane was acquired. It indicated that the OsMFC loaded with FO-1 membrane completed 88.31 % increase of water extraction, 50.72 % promotion of maximum power density and 6.02 % enhancement of chemical oxygen demand (COD) removal compared to those of the OsMFC with commercial FO membrane. The molecular dynamics simulation elucidated that the hydrogen bond and electrostatic interaction between atoms both played crucial roles in the proton-transfer process. This method of introducing proton carrier at molecular level aiming to alleviate the rising catholyte pH is economical and convenient for the potential scale-up applications of the OsMFC.

A novel electrochemical method for the removal of aluminum from ionic rare earth leachate

The separation of aluminum (Al) from ionic rare earth (RE) leachate is a complex challenge due to their similar chemical properties. Conventional industrial separation process required the use of chemical precipitant leads to considerable loss of RE. Herein, a novel cleaner approach of anionic membrane electrolysis (AME) combined with cyclone electrolysis for removal Al from ionic rare earth leachate was developed. The diffusion of RE3+ and neutralization of H+and OH– were inhibited efficiently by the anionic membrane. Cyclone mixing reduced the loss of rare earth and improved Al removal compared with mechanical mixing. Working parameters including electrode speed, temperature, pH and Al concentration of catholyte, magnesium sulfate concentration and initial pH of anolyte were investigated to explore ways for more efficient Al removal and reduction of rare earth loss. Under the optimal conditions, the removal efficiency of Al and the loss ratio of RE were 93.3 % and 1.84 % respectively. The Al removal data was fitted to the pseudo-zero order model under optimal conditions, k was 0.409 mg·L−1·min−1. Loss of RE was attributed to the direct deposition on the electrode surface due to the high local pH of cathode. This work provides a new insight into the clean removal of Al impurity from actual RE leachate in magnesium sulfate system.

Employing the Cost-effective Composite Cathodes for Bio-Fenton facilitated degradation of Acid Red 114 integrated into Hydrogen Peroxide Synthesizing Microbial Fuel Cell

The foremost obstacle in scale up application of Bioelectro-Fenton dye wastewater treatment process is high cost of cathode material. The study proposes a low-cost activated carbon/stainless steel (AC/SS) and Graphite powder/stainless steel (GP/SS) composite cathodes, where SS allocates the current, while AC/GP concurrently supports Hydrogen peroxide (H2O2) production. Composite AC/SS and GP/SS cathode enabled Acid Red 114 (AR 114) oxidative removal by means of bio-electro-Fenton in microbial fuel cell (MFC) is also investigated. Characterized by different microscopic, spectroscopic, and electrochemical techniques, it is observed that the composite AC/SS and GP/SS cathodes may well be fabricated and involve in H2O2 and power generation of 1420 µM /2680 µM and 4000 mWm−3/4050 mWm−3 respectively. The results also disclose that the MFC system efficiency is crucially associated to operating conditions involving initial AR 114 concentration (20 mg/L), catholyte pH (3), different catholytes, their concentration (75 mM), and Fe2+ dosage (0.5 mM). All investigated conditions are observed to impact the degradation efficiency and apparent first order rate constant for AR 114. The corresponding rate constants and efficiency for the degradation for both cathodes are 0.13 h−1/ 0.08 h−1 and 96%/90%, respectively. The outcomes validate these fabricated cathodes as sustainable substitute of expensive and complex material.

A comprehensive analysis of key factors influencing methane production from CO2 using microbial methanogenesis cells

With increasing attention on carbon capture and utilization (CCU) technologies for the conversion of CO2 into chemical products, microbial methanogenesis cells (MMCs) have been extensively studied over the past few decades for biomethane production. Using rapidly accumulating data for MMCs with varying configurations and operating conditions, a comprehensive analysis was conducted here to investigate the critical factors that influence methane production rates (MPR) in these systems. A comparison of MPR and set potentials or current densities showed weak linear relationships (R2 < 0.6, p < 0.05), indicating the significant contributions of other important factors impacting methane production. A non-quantitative analysis of these additional parameters indicated the potential importance of using metal catalysts for anode materials where oxygen evolution reaction occurs, while most previous MMC research focused more on cathode materials where the biocatalytic reaction occurs. The use of undefined mixed anaerobic cultures as inocula was found to be sufficient for producing high MPRs, as the electrochemical environment at the cathode provides a strong selective pressure to converge on desirable methanogenic cultures. Other operational parameters, such as catholyte pH control and CO2 supply methods, were also important factors impacting MPR in MMCs, indicating the cumulative impact of these various factors will require careful consideration in future research.

Nickel–iron-driven heterogenous bio-electro-fenton process for the degradation of methylparaben

Discharge of emerging contaminants such as parabens in natural water bodies is a grievous concern. Among parabens, methylparaben (MP) is most prevalent due to its extensive usage in personal care and food products and has been purported to trigger hormonal-related diseases. In this regard, the bio-electro-Fenton (BEF) process garners attention for remediating refractory compounds because of its ability to generate in situ hydroxyl radicals (•OH) utilising the energy harvested from electroactive microorganisms. In the present investigation, a Ni–Fe-driven heterogenous BEF system (BEF-MFC) was used to degrade MP from different matrices. At neutral catholyte pH, 99.54 ± 0.22% of MP was removed from an initial concentration of 10 mg/L in 240 min of retention time with an estimated treatment cost of about 1.01 $/m3. The removal rate ameliorated when the catholyte pH was dropped to 3.0 and by imposing an external voltage of 0.5 V, requiring just 120 min to achieve comparable MP removal efficiencies. However, catalyst leaching was higher at acidic pH (leaching of Fe ions = 0.44 mg/L and Ni ions = 0.06 mg/L) and applying external voltage increased the treatment cost slightly to 1.08 $/m3. Further, treatment of 10 mg/L MP-spiked real wastewater at pH of 7.0 with the BEF-MFC attained 85.70 ± 3.30% and 56.50 ± 1.70% reduction in MP and total organic carbon, respectively, in 240 min. In addition, a maximum power density of 205.90 ± 2.27 mW/cm2 was harvested in the BEF-MFC; thus, portraying the dual benefit of Ni–Fe heterogeneous catalyst. Even though, Ni–Fe performed reasonably well as Fenton-cum-cathode catalyst, future endeavours should be poised to fine-tune catalysts to accelerate H2O2 and •OH generation, which will reinforce the scalability of this system.

Optimization of a self-powered chemical photosynthesis desalination cell operation

BackgroundChemical photosynthetic desalination cells (CPDCs) are among the last generations of desalination cells which use microalgae in their structure. In the cathode chambers of previous desalination cells, expensive catalysts and toxic chemicals were employed for electricity generation, similar to other bio-electrochemical systems. Many parameters affect the CPDC performance, which are still unknown. MethodsIn this study, the optimization of CPDC operating parameters was investigated utilizing response surface methodology (RSM). The investigated parameters were catholyte flow rate, catholyte pH, inlet salinity concentration, saltwater flow rate, anolyte pH, anolyte concentration, and anolyte flow rate. Three different anolyte types were investigated which were an acidic anolyte (10 mM HCl), neutral anolyte (12 g/L NaCl solution) and alkaline anolyte (10 mM NaOH solution). Significant FindingsUsing the optimum values for these parameters, the predicted (from RSM) and experimental salinity removal percentage values were found to be 77.76% and 75.33%, respectively. The alkaline anolyte showed higher salinity removal percentage, and power generation values (71% and 36.8 W/m2), respectively.

Technology for increasing the precious metals content in copper concentrate obtained by flotation

In the established technologies, the use of classic depressants of pyrite, such as lime represents one of the main problems in the flotation of gold-bearing copper (Cu) ores. Lime addition leads to the depression of the noble metals - gold (Au) and silver (Ag) that end up in tailings. Thus, the operator incurs economic losses. The current paper presents research aimed at replacing in flotation of copper pyrite ore, bearing gold and silver, the classical depressor lime with catholyte, i. e. with solution obtained during the electrolysis of water (pure or aqueous solutions) using a diaphragm electrolyser. Data from the conducted research show an increase in the content of precious metals in the obtained copper concentrate - from 148. 04 g/Mg Au and 112. 8 g/Mg Ag achieved by classical process to 216.45 g/Mg Au and 174.03 g/Mg Ag obtained by the proposed treatment. At the same time the Cu recovery increased by 3 % and the grade of Cu concentrate was 27.5 % Cu (compared to 16.2 % in the classical process). It seems that the main parameter influencing the selection separation process is the catholyte pH value.

Phosphorus recovery directly from sewage sludge as vivianite and simultaneous electricity production in a dual chamber microbial fuel cell

Phosphorus (P) recovery from waste streams is a crucial option for the looming global P crisis, and P recovery from sewage sludge, as the final effluent of P from wastewater treatment plant (WWTP), is even more significant. In this study, a dual chamber microbial fuel cell (MFC) was constructed in order to directly recover P from sewage sludge utilizing cathodic Fe reduction to produce a more valuable product of vivianite for the first time, avoiding the pre-treatment of sludge and simultaneously producing energy. The results showed that a recovery efficiency of 99.08% for dissolved P from sludge was reached, while the production of newly formed vivianite was approximately 2.33 mg/g calculated by P fractionation and demonstrated using X-ray diffraction and X-ray photoelectron spectroscopy. The best P recovery efficiency was obtained at an initial catholyte pH of 7 and Fe/P molar ratio of 1, while the concentration of anolyte initial dissolved chemical oxygen demand (COD) affected the rate of electricity production. The electrical energy output of MFC had a highly positive relationship with the anolyte total COD degradation efficiency (R2 = 0.9716). This research opens up a new possibility for MFC systems to directly recover phosphorus from sewage sludge.

Electromigration separation of lithium isotopes: The effect of electrolytes

The high-abundance lithium isotopes are key materials for the development of the nuclear industry. Lithium amalgamation is currently the only industrial method used to produce lithium isotopes, but it involves serious environmental pollution. Electromigration separation is one of the green and promising alternatives. Here, a “lithium salt aqueous solution │ organic solution │ aqueous solution” electromigration system was fabricated for lithium isotope separation. At a higher or lower voltage, the effects of species and initial pH of catholyte on the separation effects of lithium isotopes during electromigration were studied with different migrate time, and the origin of isotope separation was discussed. It was found that the initial pH values of the catholyte had an effect on the pH values of the anolyte. While the dramatic variation of pH in the electrolyte during electromigration was averse to the migration of Li+ and isotope separation. Furthermore, an extremely high isotope separation coefficient (1.6) was obtained at a very low Li+ migration ratio that is based on the dynamic separation. While the separation coefficient decreases with the increase of Li+ migration ratio rapidly and finally levels off, that is based on the equilibrium separation. This work provides important guidance for understanding the electromigration process and the origin of isotope separation in this system.

Electrochemical Reduction of Flue Gas CO2 in a Dual Methanol/Water Electrolysis System for the Synthesis of Methyl Formate

The conversion of waste CO2 to value-added chemicals through electrochemical reduction is a promising technology for mitigating climate change while simultaneously providing economic opportunities. The use of the nonaqueous solvent methanol allows for higher CO2 solubility and novel products through the incorporation of methanol as an intermediate. In this work, the electrochemistry of CO2 reduction in acidic methanol catholyte at a Pb working electrode was investigated while using a separate aqueous anolyte to promote a sustainable water oxidation half-reaction. The selectivity among methyl formate (a product unique to reduction of CO2 in methanol), formic acid, and formate was critically dependent on the catholyte pH, with a faradaic efficiency for methyl formate as high as 75% measured in pH < 2. Furthermore, strategies to limit the concentration of formic acid and maintain the surface oxide of the catalyst have been shown to be effective at improving the steady-state durability of the CO2-to-methyl formate process. Tests with simulated flue gas as the feedstock have shown a high level of tolerance for the Pb-catalyzed electrolysis to SO2, NO, and dilute O2 contaminants. Finally, a comparative technoeconomic analysis will be discussed to highlight target performance metrics and the viability of alternate pathways for electrochemical conversion of CO2 to methyl formate.

Facilitating proton transport by endowing forward osmosis membrane with proton conductive sites in osmotic microbial fuel cell

A major challenge of the osmotic microbial fuel cell (OsMFC) application is the sluggish proton transport from anode to cathode. As a result, an extra overpotential is caused by the remarkable catholyte alkalinization and anolyte acidification. Thus, the efficiency of water extraction and biodegradation of organic pollutants are adversely affected simultaneously. To address this issue, proton conductive sites were introduced into the forward osmosis (FO) membrane by importing sulfonic acid radical groups. The results demonstrated that the proton transport flux improved after FO membrane modification. The OsMFC system with an optimal FO membrane achieved a 58.86 % reduction in artificial seawater salinity, enhanced the volume of water extraction by 61.90 %, increased the chemical oxygen demand removal efficiency by 6.39 %, and improved the current density by 16.56 %. In particular, the maximum power density of the optimized OsMFC (7.08 ± 0.42 W·m−3) was enhanced by 108.85 % and 60.18 % compared with those with Nafion and pristine FO membrane, respectively. Meanwhile, the mechanism of proton transport in the OsMFC system has been elucidated. The proton migration was reinforced under the synergistic effect of improved water flux and electromigration derived from internal electric field. This method to mitigate the catholyte pH through self-buffering in situ is green and economical. This will further open a novel avenue for OsMFC application in large-scale actual wastewater treatment.

Electrochemical Reduction of Flue Gas CO2 in a Dual Methanol/Water Electrolysis System for the Synthesis of Methyl Formate

The conversion of waste CO2 to value-added chemicals through electrochemical reduction is a promising technology for mitigating climate change while simultaneously providing economic opportunities. The use of the nonaqueous solvent methanol allows for higher CO2 solubility and novel products through the incorporation of methanol as an intermediate. In this work, the electrochemistry of CO2 reduction in acidic methanol catholyte at a Pb working electrode was investigated while using a separate aqueous anolyte to promote a sustainable water oxidation half-reaction. The selectivity among methyl formate (a product unique to reduction of CO2 in methanol), formic acid, and formate was critically dependent on the catholyte pH, with a faradaic efficiency for methyl formate as high as 75% measured in pH < 2. Tests with simulated flue gas as the feedstock have shown a high level of tolerance for the Pb-catalyzed electrolysis to SO2, NO, and dilute O2 contaminants.

Boron Removal from Reverse Osmosis Permeate Using an Electrosorption Process: Feasibility, Kinetics, and Mechanism.

Boron is present in the form of boric acid (B(OH)3 or H3BO3) in seawater, geothermal waters, and some industrial wastewaters but is toxic at elevated concentrations to both plants and humans. Effective removal of boron from solutions at circumneutral pH by existing technologies such as reverse osmosis is constrained by high energy consumption and low removal efficiency. In this work, we present an asymmetric, membrane-containing flow-by electrosorption system for boron removal. Upon charging, the catholyte pH rapidly increases to above ∼10.7 as a result of water electrolysis and other Faradaic reactions with resultant deprotonation of boric acid to form B(OH)4- and subsequent removal from solution by electrosorption to the anode. Results also show that the asymmetric flow-by electrosorption system is capable of treating feed streams with high concentrations of boron and RO permeate containing multiple competing ionic species. On the basis of the experimental results obtained, a mathematical model has been developed that adequately describes the kinetics and mechanism of boron removal by the asymmetric electrosorption system. Overall, this study not only provides new insights into boron removal mechanisms by electrosorption but also opens up a new pathway to eliminate amphoteric pollutants from contaminated source waters.

High-rate microbial electrosynthesis using a zero-gap flow cell and vapor-fed anode design

Microbial electrosynthesis (MES) cells use renewable energy to convert carbon dioxide into valuable chemical products such as methane and acetate, but chemical production rates are low and pH changes can adversely impact biocathodes. To overcome these limitations, an MES reactor was designed with a zero-gap electrode configuration with a cation exchange membrane (CEM) to achieve a low internal resistance, and a vapor-fed electrode to minimize pH changes. Liquid catholyte was pumped through a carbon felt cathode inoculated with anaerobic digester sludge, with humidified N2 gas flowing over the abiotic anode (Ti or C with a Pt catalyst) to drive water splitting. The ohmic resistance was 2.4 ± 0.5 mΩ m2, substantially lower than previous bioelectrochemical systems (20–25 mΩ m2), and the catholyte pH remained near-neutral (6.6–7.2). The MES produced a high methane production rate of 2.9 ± 1.2 L/L-d (748 mmol/m2-d, 17.4 A/m2; Ti/Pt anode) at a relatively low applied voltage of 3.1 V. In addition, acetate was produced at a rate of 940 ± 250 mmol/m2-d with 180 ± 30 mmol/m2-d for propionate. The biocathode microbial community was dominated by the methanogens of the genus Methanobrevibacter, and the acetogen of the genus Clostridium sensu stricto 1. These results demonstrate the utility of this zero-gap cell and vapor-fed anode design for increasing rates of methane and chemical production in MES.

Elimination of recalcitrant micropollutants by medium pressure UV-catalyzed bioelectrochemical advanced oxidation process: Influencing factors, transformation pathway and toxicity assessment

Bio-electro-Fenton (BEF) processes have been widely studied in recent years to remove recalcitrant micropollutants from wastewater. Though promising, it still faces the critical challenge of residual iron and iron sludge in the treated effluent. Thus, an innovative medium-pressure ultraviolet-catalyzed bio-electrochemical system (MUBEC), in which medium-pressure ultraviolet was employed as an alternative to iron for in-situ H2O2 activation, was developed for the removal of recalcitrant micropollutants. The influence of operating parameters, including initial catholyte pH, cathodic aeration rate, and input voltage, on the system performance, was explored. Results indicated that complete reduction of 10 mg L−1 of model micro-pollutants ibuprofen (IBU) and carbamazepine (CBZ) was achieved at pH 3, with an aeration rate of 1 mL min−1 and a voltage of 0.3 V, following pseudo-first-order kinetics. Moreover, potential transformation pathways and the associated intermediates during the degradation were deduced and detected, respectively. Thus, the MUBEC system shows the potential for the efficient and cost-effective degradation of recalcitrant micropollutants from wastewater.