Rational Designing Microenvironment of Gas-Diffusion Electrodes via Microgel-Augmented CO2 Availability for High-Rate and Selective CO2 Electroreduction to Ethylene.

Efficient electrochemical CO2 reduction reaction (CO2RR) requires advanced gas-diffusion electrodes (GDEs) with tunned microenvironment to overcome low CO2 availability in the vicinity of catalyst layer. Herein, for the first time, pyridine-containing microgels-augmented CO2 availability is presented in Cu2O-based GDE for high-rate CO2 reduction to ethylene, owing to the presence of CO2-phil microgels with amine moieties. Microgels as three-dimensional polymer networks act as CO2 micro-reservoirs to engineer the GDE microenvironment and boost local CO2 availability. The superior ethylene production performance of the GDE modified by 4-vinyl pyridine microgels, as compared with the GDE with diethylaminoethyl methacrylate microgels, indicates the bifunctional effect of pyridine-based microgels to enhance CO2 availability, and electrocatalytic CO2 reduction. While the Faradaic efficiency (FE) of ethylene without microgels was capped at 43% at 300 mA cm-2, GDE with the pyridine microgels showed 56% FE of ethylene at 700 mA cm-2. A similar trend was observed in zero-gap design, and GDEs showed 58% FE of ethylene at -4.0 cell voltage (>350 mA cm-2 current density), resulting in over 2-fold improvement in ethylene production. This study showcases the use of CO2-phil microgels for a higher rate of CO2RR-to-C2+, opening an avenue for several other microgels for more selective and efficient CO2 electrolysis.

Biological bromate reduction coupled with in situ gas fermentation in H2/CO2-based membrane biofilm reactor.

Bromate, a carcinogenic contaminant generated in water disinfection, presents a pressing environmental concern. While biological bromate reduction is an effective remediation approach, its implementation often necessitates the addition of organics, incurring high operational costs. This study demonstrated the efficient biological bromate reduction using H2/CO2 mixture as the feedstock. A membrane biofilm reactor (MBfR) was used for the efficient delivery of gases. Long-term reactor operation showed a high-level bromate removal efficiency of above 95 %, yielding harmless bromide as the final product. Corresponding to the short hydraulic retention time of 0.25 d, a high bromate removal rate of 4 mg Br/L/d was achieved. During the long-term operation, in situ production of volatile fatty acids (VFAs) by gas fermentation was observed, which can be regulated by controlling the gas flow. Three sets of in situ batch tests and two groups of ex situ batch tests jointly unravelled the mechanisms underpinning the efficient bromate removal, showing that the microbial bromate reduction was primarily driven by the VFAs produced from in situ gas fermentation. Microbial community analysis showed an increased abundance of Bacteroidota group from 4.0 % to 18.5 %, which is capable of performing syngas fermentation, and the presence of heterotrophic denitrifiers (e.g., Thauera and Brachymonas), which are known to perform bromate reduction. Together these results for the first time demonstrated the feasibility of using H2/CO2 mixture for bromate removal coupled with in situ VFAs production. The findings can facilitate the development of cost-effective strategies for groundwater and drinking water remediation.

Pyrogenic Carbon Promotes Anaerobic Oxidation of Methane Coupled with Iron Reduction via the Redox-Cycling Mechanism.

Pyrogenic carbon (PC) can mediate electron transfer and thus catalyze biogeochemical processes to impact greenhouse gas (GHG) emissions. Here, we demonstrate that PC can contribute to mitigating GHG emissions by promoting the Fe(III)-dependent anaerobic oxidation of methane (AOM). It was found that the amendment PCs in microcosms dominated by Methanoperedenaceae performing Fe(III)-dependent AOM simultaneously promoted the rate of AOM and Fe(III) reduction with a consistent ratio close to the theoretical stoichiometry of 1:8. Further correlation analysis showed that the AOM rate was linearly correlated with the electron exchange capacity, but not the conductivity, of added PC materials, indicating the redox-cycling electron transfer mechanism to promote the Fe(III)-dependent AOM. The mass content of the C═O moiety from differentially treated PCs was well correlated with the AOM rate, suggesting that surface redox-active quinone groups on PCs contribute to facilitating Fe(III)-dependent AOM. Further microbial analyses indicate that PC likely shuttles direct electron transfer from Methanoperedenaceae to Fe(III) reduction. This study provides new insight into the climate-cooling impact of PCs, and our evaluation indicates that the PC-facilitated Fe(III)-dependent AOM could have a significant contribution to suppressing methane emissions from the world's reservoirs.

Integrated urban water management by coupling iron salt production and application with biogas upgrading.

Integrated urban water management is a well-accepted concept for managing urban water. It requires efficient and integrated technological solutions that enable system-wide gains via a whole-of-system approach. Here, we create a solid link between the manufacturing of an iron salt, its application in an urban water system, and high-quality bioenergy recovery from wastewater. An iron-oxidising electrochemical cell is used to remove CO2 (also H2S and NH3) from biogas, thus achieving biogas upgrading, and simultaneously producing FeCO3. The subsequent dose of the electrochemically produced FeCO3 to wastewater and sludge removes sulfide and phosphate, and enhances sludge settleability and dewaterability, with comparable or superior performance compared to the imported and hazardous iron salts it substitutes (FeCl2, and FeCl3). The process enables water utilities to establish a self-reliant and more secure supply chain to meet its demand for iron salts, at lower economic and environmental costs, and simultaneously achieve recovery of high-quality bioenergy.

Impact of electrochemically generated iron on the performance of an anaerobic wastewater treatment process.

Anaerobic treatment of domestic wastewater has the advantages of lower biomass yield, lower energy demand and higher energy recover over the conventional aerobic treatment process. However, the anaerobic process has the inherent issues of excessive phosphate and sulfide in effluent and superfluous H2S and CO2 in biogas. An electrochemical method allowing for in-situ generation of Fe2+ in the anode and hydroxide ion (OH-) and H2 in the cathode was proposed to overcome the challenges simultaneously. The effect of electrochemically generated iron (e­iron) on the performance of anaerobic wastewater treatment process was explored with four different dosages in this work. The results showed that compared to control, the experimental system displayed an increase of 13.4-28.4 % in COD removal efficiency, 12.0-21.3 % in CH4 production rate, 79.8-98.5 % in dissolved sulfide reduction, 26.0-96.0 % in phosphate removal efficiency, depending on the e­iron dosage between 40 and 200 mg Fe/L. Dosing of the e­iron significantly upgraded the quality of produced biogas, showing a much lower CO2 and H2S contents in biogas in experimental reactor than that in control reactor. The results thus demonstrated that e­iron can significantly improve the performance of anaerobic wastewater treatment process, bringing multiple benefits with the increase of its dosage regarding effluent and biogas quality.

Electrochemical iron production to enhance anaerobic membrane treatment of wastewater.

Although iron salts such as iron(III) chloride (FeCl3) have widespread application in wastewater treatment, safety concerns limit their use, due to the corrosive nature of concentrated solutions. This study demonstrates that local, electrochemical generation of iron is a viable alternative to the use of iron salts. Three laboratory systems with anaerobic membrane processes were set up to treat real wastewater; two systems used the production of either in-situ or ex-situ electrochemical iron (as Fe2+ and Fe2+(Fe3+)2O4, respectively), while the other system served as a control. These systems were operated for over one year to assess the impact of electrochemically produced iron on system performance. The results showed that dosing of electrochemical iron significantly reduced sulfide concentration in effluent and hydrogen sulfide content in biogas, and mitigated organics-based membrane fouling, all of which are critical issues inherently related to sustainability of anaerobic wastewater treatment. The electrochemical iron strategy can generate multiple benefits for wastewater management including increased removal efficiencies for total and volatile suspended solids, chemical oxygen demand and phosphorus. The rate of methane production also increased with electrochemically produced iron. Economic analysis revealed the viability of electrochemical iron with total cost reduced by one quarter to a third compared with using FeCl3. These benefits indicate that electrochemical iron dosing can greatly enhance the overall operation and performance of anaerobic membrane processes, and this particularly facilitates wastewater management in a decentralized scenario.

Mycolicibacter acidiphilus sp. nov., an extremely acid-tolerant member of the genus Mycolicibacter.

A nonmotile, facultatively anaerobic and rod-shaped bacterial strain, designated M1T was isolated from a bioreactor being operated at pH ~2 at Brisbane, Australia. Colonies appeared to be convex and white. Phylogenetic analysis of its genome revealed an affiliation with the genus Mycolicibacter and its closest species based on 16S rRNA gene analysis were Mycolicibacter algericus DSM 45454T (98.8 % similarity) and Mycolicibacter terrae CIP 104321T (98.8 %) with which strain M1T shared average nucleotide identity of 81.2 % and digital DNA-DNA hybridization similarity of 23.8 %. Strain M1T grew optimally at 0 % NaCl, at pH 6 and at between 30-33 °C. The polar lipid profile of strain M1T consisted of diphosphatidylglycerol, aminophosphoglycolipid, phosphatidylcholine, phospholipid, aminolipid, phosphoglyolipid, phosphatidylglycerol, two unidentified glycolipids and four unidentified lipids. The dominant cellular fatty acids (>10 %) were C16 : 0 and C18 : 1 ω9c and summed feature 7 (C19 : 1 ω7c and/or C19 : 1 ω6c). The DNA G+C content of strain M1T was 69.1 mol%. Based on in silico phylogenomic analysis coupled with physiological and chemotaxonomic characterizations, we classify strain M1T as representing a novel species within the genus Mycolicibacter, for which the name Mycolicibacter acidiphilus nov. is proposed. The type strain is M1T (=MCCC 1H00416T=KCTC 49392T).

Centralized iron-dosing into returned sludge brings multifaceted benefits to wastewater management.

Iron salts (i.e. FeCl3) are the most used chemicals in the urban wastewater system. Iron is commonly dosed into sewage or the mainstream system, which provides multiple benefits such as enhanced phosphorus removal and improved sludge settleability/dewaterability. This study reported and demonstrated a new approach that dosed FeCl3 into returned sludge in order to bring two more benefits to wastewater management: short-cut nitrogen removal via the nitrite pathway and less biomass production. This approach is achieved based on our findings that with similar amount of FeCl3, centralized iron dosing into a sidestream sludge unit generated iron concentration two orders of magnitude higher than the common mainstream dosing (e.g. 10-40 mg Fe/L-wastewater), leading to sludge acidification (pH = 2.1) with Fe (III) hydrolysis. Together with accumulated nitrite in the supernatant of the sludge, ppm-level of free nitrous acid was generated and thus enabled sludge disintegration, cell lysis, and selective elimination of nitrite-oxidizing bacteria (NOB). Long-term effects on nitrifying bacteria and overall reactor performance were evaluated using two laboratory reactor experiments for over one year. The experimental reactor showed stable nitrite accumulation with an average NO2-/(NO2- + NO3-) ratio above 80% and ∼30% observed biomass yield reduction compared to those in control reactors. In addition, the centralized sludge dosing strategy still provided benefits such as improved settleability and dewaterability of sludge and enhanced phosphorus removal.

Strategies to improve viability of a circular carbon bioeconomy-A techno-economic review of microbial electrosynthesis and gas fermentation.

A circular carbon bioeconomy has potential to halt atmospheric accumulation of greenhouse gases causing climate change and sustainably produce chemical, agricultural and fuel products. Here, we report application of a simplified technoeconomic assessment to critically review two approaches in this space - microbial electrosynthesis and gas fermentation. For microbial electrosynthesis, decoupling of surface-dependant abiotic process for electron delivery from volume-dependant biotic carbon fixation, is shown as the only economically viable strategy to scale-up due to comparatively low biofilm electron consumption rate. This is effectively an electrolyser-assisted gas fermentation system. Targeting high-value products, such as protein for human food consumption is one of the few pathways forward for electrolyser-assisted gas fermentation. Alternatively, gas fermentation of reformed biogas presents an interesting and potentially more sustainable implementation pathway to improve economic viability of chemicals. This critical review suggests linking water treatment resource recovery with gas fermentation is attractive for bioplastics and butanol in terms of competitiveness and market demand.

Development of radio-frequency identification (RFID) sensors suitable for smart-monitoring applications in sewer systems.

Sanitary and stormwater sewers are buried assets that play important roles in the prevention of diseases and the reduction of health risks for our societies. Due to their hidden nature, these assets are not frequently assessed and maintained to optimal conditions. The lack of maintenance can cause sewer blockages and overflows that result in the release of pathogens into the environment. For cities, monitoring sewer conditions on a large-scale can be costly, time-consuming, and labor-intensive if using current low-throughput technologies, such as dye testing or closed-circuit television. Alternatively, smart sensor systems can provide low-cost, high-throughput, and automatic data-driven features for real-time monitoring applications. In this study, we developed ultrahigh-frequency radio-frequency identification (UHF RFID)-based sensors that are flushable and suitable for sanitary and stormwater pipes quick surveys. 3D printed RFID sensors were designed to float at the water-air interface and minimize the water interference to RF signal communications. The optimal detection range was also determined to support the design and installation of the reader in various utility holes. Field trials demonstrated that the UHF RFID system is a low-cost, high-throughput, and robust solution for monitoring blockage, illicit-connection, and water flow in sewer networks.

Tuning the Product Selectivity of the Cu Hollow Fiber Gas Diffusion Electrode for Efficient CO2 Reduction to Formate by Controlled Surface Sn Electrodeposition.

The efficient CO2 electrochemical reduction reaction (CO2RR) relies not only on the development of selective/active catalysts but also on the advanced electrode configuration to solve the critical issue of poor CO2 mass transport and derived sluggish cathodic reaction kinetics. In this work, to achieve a favorable reaction rate and product selectivity, we designed and synthesized an asymmetric porous Cu hollow fiber gas diffusion electrode (HFGDE) with controlled Sn surface electrodeposition. The HFGDE derived from the optimal Sn electrodeposition condition exhibited a formate Faradaic efficiency (FE) of 78% and a current density of 88 mA cm-2 at -1.2 V versus reversible hydrogen electrode, which are more than 2 times higher than those from the pristine Cu HFGDE. The achieved performance outperformed most of the other Sn-based GDEs, indicating the creation of sufficient contact among CO2, electrolyte, and electrode catalyst through the design of the hollow fiber pore structure and catalytic active sites. The enhancement of formate production selectivity and the suppression of the hydrogen by-product were attributed to the optimized ratio of SnOx species on the electrode surface. The best performance was seen in the HFGDE with the highest Sn2+/Sn4+ (120 s deposition), likely due to the modulating effect of the Cu substrate via electron donation with Sn species. The selectivity control strategy developed in the asymmetric HFGDE provides an efficient and facile method to stimulate selective electrochemical reactions in which the gas-phase reactant with low solubility is involved.