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•Current status of MECs for CO2 electromethanogenesis was summarized.•The working principles of CO2 electromethanogenesis were summarized.•Several test methods was proposed to analyze ...the properties.•The critical factors effecting CH4 production have been discussed.
Given the aggravated greenhouse effect caused by CO2 and the current energy shortage, CO2 capture and reuse has been gaining ever-increasing concerns. Microbial Electrolysis Cells (MECs) has been considered to be a promising alternative to recycle CO2 bioelectrochemically to low-carbon electrofuels such as CH4 by combining electroactive microorganisms with electrochemical stimulation, enabling both CO2 fixation and energy recovery. In spite of the numerous efforts dedicated in this field in recent years, there are still many problems that hinder CO2 bioelectroconversion technique from the scaling-up and potential industrialization. This review comprehensively summarized the working principles, extracellular electron transfers behaviors, and the critical factors limiting the wide-spread utilization of CO2 electromethanogenesis. Various characterization and electrochemical testing methods for helping to uncover the underlying mechanisms in CO2 electromethanogenesis have been introduced. In addition, future research needs for pushing forward the development of MECs technology in real-world CO2 fixation and recycling were elaborated.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•A two-chamber microbial electrolysis cells was developed for the reduction of CO2.•Biocathode as electron donor was the vital driving force for electromethanogenesis.•FISH analysis confirmed the ...mechanisms of direct electron transfer.•Multiple pathways of electron transfer between cell-electrode were proposed.
To better understand the underlying mechanisms for methane bioelectrosynthesis, a two-chamber MECs containing a carbon biocathode was developed and studied. Methane production substantially increased with increasing cathode potential. Considerable methane yield was achieved at a poised potential of −0.9V (vs. Ag/AgCl), reaching 2.30±0.34mL after 5h of operation with a faradaic efficiency of 24.2±4.7%. Confirmatory tests done at 0.9V by switching the type of flushed substrates (CO2/N2) or the electrical exposure modes (ON/OFF) demonstrated that cathode serving as an electron donor was the vital driving force for methanogenesis occurring at microbe–electrode surface. Fluorescence in situ hybridization reveled Methanobacteriaceae (particularly Methanobacterium) was the predominant methanogens, supporting the mechanisms of direct electron transfer between cell-electrode. Additionally, the analysis of scanning electron microscope confirmed that the multiple pathways of electron transfer, including direct cathode-to-cell, interspecies exchange and semi-conductive conduits all together ensured the successful electromethanogenesis process.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•A concept of AnMBR-PN/A process was proposed for mainstream treatment.•In-situ FA/FNA exposure eliminated Nitrospira while retained Nitosonomas community.••DO limitation prevented switch of the NOB ...community in the mainstream conditions.•The effluent TN of the mainstream PN/A system was lower than 10 mg-N/L.•Enhanced hydrodynamic shear force resulted in sludge settleability deterioration.
In this pilot-scale study, an innovative mainstream treatment process that couples the anaerobic membrane reactor (AnMBR) with a one-stage PN/A system was proposed for advancing the concept of carbon neutrality in the municipal wastewater treatment plant. This work demonstrates the start-up procedure of a pilot-scale one-stage PN/A system for mainstream treatment. The 255-day start-up of the one-stage PN/A system involved the cultivation of ammonium-oxidizing bacteria (AOB) from the activated sludge, suppression of nitrite-oxidizing bacteria (NOB), investigation of in-situ growth kinetics of anammox bacteria (AnAOB), and the 50-day operation of the pilot-scale AnMBR-PN/A process for natural mainstream treatment. It is verified in the pilot-scale system for the first time that the in-situ free ammonia (FA) and free nitrous acid (FNA) exposure could effectively eliminate the Nitrospira (the NOB genus) while retaining the Nitosonomas (the AOB genus) community in the suspended sludge. NOB community rebounding was not detected even at the mainstream conditions with low nitrogen concentrations (Influent ammonium concentration=38±6 mg-NH4+-N/L) by intermittent aeration to control the system dissolved oxygen (DO) below 0.5 mg/L. The results of the mainstream treatment showed that the average effluent total nitrogen (TN) in the coupled process was generally lower than 10 mg-N/L, which meets the discharge limits of most prefectures in Japan. The investigated results of the in-situ anammox bacteria (AnAOB) growth kinetics suggested that the promoted start-up strategy of taking advantage of the warm months with higher mainstream temperature to achieve the rapid in-situ growth of the AnAOB is applicable in the investigated regions. From the perspective of the removal performance of the TN and organic substance, the AnMBR-PN/A process has great potential as the layouts of the carbon-neutral mainstream wastewater treatment plants.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•Performance of anaerobic co-digestion of microalgae with food waste was examined.•Kinetic modeling and synergistic impact evaluation were performed.•Co-digestion achieved 4.99-fold ...methane increase than that of microalgae alone.•Cone model had the highest reliability to describe the co-digestion kinetics.•The synergy improved methanogenesis rate and subsequent methane output.
Continuous primary energy consumption has motivated the scientists of the world to search for renewable energy sources that could substitute fossil fuels. Microalgae can be an alternative substrate for renewable energy recovery. In this study, biochemical methane potential (BMP) assays were used as a tool to examine the technical potential of methane production from microalgae (MA) through co-digesting with food waste (FW) at different MA: FW ratios on volatile solids (VS). Three mathematical models (i.e. first-order kinetic, modified Gompertz, and Cone models) were also utilized to fit the experimental data, with the purpose of elucidating the biological degradation and principle kinetics of the co-digestion. The results showed that supplementing food waste significantly improved microalgae digestion performance, with the highest methane yield of 639.8±1.3mL/g VSadded obtained at a MA:FW ratio of 0.2:0.8, which was 4.99-fold increase with respect to that (106.9±3.2mL/g VSadded) of the microalgae alone. Cone model had the best fitness and reliability to the experimental results and could describe the co-digestion kinetics more reasonably. Parameter analysis and synergistic impact evaluation together revealed that the improvement in methanogenesis potential (fd) caused by the synergy of co-digestion might be the fundamental cause for the upgraded methane production. These results validated the superiority of co-digestion as a step towards maximizing methane production from microalgae, aiding the development of multi-biomass co-disposal and ultimately bioenergy recovery techniques.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
We propose that the chiral anomaly of Weyl superconductors gives rise to negative thermal magnetoresistivity induced by emergent magnetic fields, which are generated by vortex textures of order ...parameters or lattice strain. We establish this scenario by combining the argument based on Berry curvatures and the quasiclassical theory of the Eilenberger equation with quantum corrections arising from inhomogeneous structures. It is found that the chiral anomaly contribution of the thermal conductivity exhibits characteristic temperature dependence, which can be a smoking-gun signature of this effect.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UL, UM
Anaerobic membrane bioreactor (AnMBR) holds great promise to treat a broad range of waste streams for concurrent pollutants transformation and biofuels harvest while producing less digestate ...residuals. In this review, recent research advances, new discoveries and commercial application status of AnMBR technique were summarized and reported. A comprehensive comparison analysis designed herein demonstrated its fascinating superiorities over the conventional activated sludge-based processes with regards to good permeate quality, less digestate residuals, low operational costs, net profit/energy output, and outstanding economic and environmental benefits. Despite the great progress achieved previously, there are still numerous challenges head for AnMBR platform applications to be tackled, particularly for severe membrane fouling, low methane content in biogas, highly dissolved methane, poor ammonia removal and phosphorus recovery, etc. To address the above problems, a new-generation process, i.e. so-called “Integrated Multistage Bio-Process (IMBP)” constituted of solar-driven bioelectrochemical system (BES)-AnMBR, partial nitritation/anammox (PN/A), nitrate reduction via anaerobic oxidation of methane (AOM) and biological/chemical phosphorus precipitation units, was proposed in this article, with versatile capabilities in simultaneous biowastes valorization, CO2 electromethanogenesis and simultaneous biogas upgrading, in-situ fouling control, ammonia removal, dissolved methane reutilization, and phosphorus recover as hydroxyapatite-rich nutrients. Despite the uncertainties about whether this approach possesses the powerful potential to dominate the future, but most surely, this hybrid concept will enhance the deployment and industrial competitiveness of AnMBR-based technologies in real-world scenarios, facilitating the establishment of the energy-sustainable and low-carbon society. Of course, more efforts are still required to demonstrate the feasibility of this integrated biorefinery approach. Nonetheless, this review opens up new research opportunities to integrate with other newly emerging processes to develop robust, multifunctional and sustainable AnMBR-based technologies towards biowaste biorefinery, chemical energy harvest and green, carbon-neutral society.
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•Advances in anaerobic membrane bioreactor for biowaste valorization were reviewed.•Technical issues limiting the commercial applications of AnMBR were discussed.•A comprehensive comparison for five different treatment processes was conducted.•A multifunctional process for biowaste treatment and bioenergy recovery was proposed.•Future perspectives of AnMBR in real-world applications were elucidated.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•Five different carbon-based cathode materials were physically prepared and examined.•Carbon stick + graphite felt assembly (CS-GF) had the highest methane production.•Material ...properties affected microbe growth, contact behaviors and electron exchange.•CS-GF facilitated the enrichment of microorganisms to catalyze CO2 via direct electron transfer.•Carbon stick + carbon cloth (CS-CC) biocathode was H2-concnetration dependent.
Each carbon-based material, due to the discrepancy in critical properties, has distinct capability to enrich electroactive microbes able to electrosynthesize methane from CO2. To optimize electromethanogenesis process, this study physically prepared and examined several carbon-based cathode materials: carbon stick (CS), CS twined by Ti wire (CS-Ti) or covered with carbon fiber (CS-CF), graphite felt (CS-GF) and carbon cloth (CS-CC). CS-GF electrode had constantly stable methane production (75.8 mL/L/d at −0.9 V vs. Ag/AgCl) while CS-CC showed a suppressed performance over time caused by the desposition of inorganic shell. Electrode material properties affected biofilms growth, cell-electrode contact behaviors and electron exchange. Methane formation with CS-CC biocathode was H2-concnetration dependent; CS-GF cathode possessed high antifouling properties and extensive space, enriching the microorganisms capable of catalyzing electromethanogenesis through more efficient non-H2 route. This study re-interpreted the application potentials of carbon-based materials in CO2 electroreduction and electrofuel recovery, providing valuable guidance for materials’ selection.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
This research investigated the effects of various dilute acid (HCl, H2SO4, HNO3, H3PO4) pretreatment on the solubilization of marine macroalgal biomass Gelidium amansii and subsequent hydrogen ...fermentation in a batch vials. The dry grounded biomass was hydrolyzed at temperature of 121 °C, solid/liquid (S/L) ratio of 5% (w/v), dilute acid concentration (1%) of various reagents, and reaction time of 30 min. The hydrolyzates obtained at these conditions were then fed to batch hydrogen fermentation. Results revealed that only H2SO4 pretreatment method had a significant effect on improvement of biohydrogen production from Gelidium amansii, whereas the other pretreatment conditions were even worse than the control experiment. Dilute sulfuric acid (1%) provided a maximum hydrogen production of 52 mL-H2/g-dry biomass, whereas control experiment provided a hydrogen efficiency of 27 mL-H2/g-dry biomass. The results showed that selection of appropriate pretreatment method is essential for enhanced hydrogen production from macroalgal biomass.
•Effects of various pretreatment methods have been assessed.•Dilute 1% sulfuric acid pretreatment yielded the peak sugar release of 57%.•Peak hydrogen yield of 52 mL H2/g TS was achieved.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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•Two UASB processes were investigated by continuously feeding with starch wastewater.•The predominant methanogenic pathways in the two processes were different.•Different surface ...attachments were observed on the granules in the two processes.•The microbial function of the one-stage UASB shifted to hydrogen fermentation.
Poor processing stability has been cited as the fatal shortcoming of the up-flow anaerobic sludge blanket (UASB) reactor treating starch wastewater (SW). In this study, the SW treatment performance in a one-stage UASB reactor and a pre-acidification equipped UASB process were evaluated together with the microbial dynamics. The results revealed that the pre-acidification provided improvements in terms of the substrate utilization diversity and the stability of the microbial community structure on the UASB reactor. Anaerolineaceae/Methanosaeta was the core functional microbiota in the pre-acidification equipped UASB reactor, indicated the superior abilities on the acetogenic methanogenesis of granules. The genus of Methanobacterium, a hydrogenotrophic methanogen was dominant in the archaeal community in the one-stage UASB reactor. The granules performed very strong hydrogen affinity in methane production, a small amount of propionate was detected in the effluent. These were abnormal, which suggested the high hydrogen turn-over rate in the one-stage UASB reactor.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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