Performance of a continuous flow microbial reverse-electrodialysis electrolysis cell using a non-buffered substrate and catholyte effluent addition

Feasibility of Producing Electricity, Hydrogen, and Chlorine via Reverse Electrodialysis

Reverse electrodialysis (RED) is a technology to generate electricity from two streams with different salinities. While RED systems have been conventionally used for electricity generation, recent works explored combining RED for production of valuable gases. This work investigates the feasibility of producing hydrogen and chlorine in addition to electricity in an RED stack and identifies potential levers for improvement. A simplified one-dimensional model is adopted to assess the technical and economic feasibility of the process. We notice a strong disparity in typical current densities of RED fed with seawater and river water and that in typical water (or chlor-alkali) electrolysis. This can be partly mitigated by using brine and seawater as RED feeds. Considering such an RED system, we estimate a hydrogen production of 1.37 mol/(m² h) and an electrical power density of 1.19 W/m². Although this exceeds previously reported hydrogen production rates in combination with RED, the levelized costs of products are 1-2 orders of magnitude higher than the current market prices at the current state. The levelized costs of products are very sensitive to the membrane price and performance. Hence, going forward, manufacturing thinner and highly selective membranes is required to make the system competitive against the consolidated technologies.

Recent progress in treatment of dyes wastewater using microbial-electro-Fenton technology

Globally, textile dyeing and manufacturing are one of the largest industrial units releasing huge amount of wastewater (WW) with refractory compounds such as dyes and pigments. Currently, wastewater treatment has been viewed as an industrial opportunity for rejuvenating fresh water resources and it is highly required in water stressed countries. This comprehensive review highlights an overall concept and in-depth knowledge on integrated, cost-effective cross-disciplinary solutions for domestic and industrial (textile dyes) WW and for harnessing renewable energy. This basic concept entails parallel or sequential modes of treating two chemically different WW i.e., domestic and industrial in the same system. In this case, contemporary advancement in MFC/MEC (METs) based systems towards Microbial-Electro-Fenton Technology (MEFT) revealed a substantial emerging scope and opportunity. Principally the said technology is based upon previously established anaerobic digestion and electro-chemical (photo/UV/Fenton) processes in the disciplines of microbial biotechnology and electro-chemistry. It holds an added advantage to all previously establish technologies in terms of treatment and energy efficiency, minimal toxicity and sludge waste, and environmental sustainable. This review typically described different dyes and their ultimate fate in environment and recently developed hierarchy of MEFS. It revealed detail mechanisms and degradation rate of dyes typically in cathodic Fenton system under batch and continuous modes of different MEF reactors. Moreover, it described cost-effectiveness of the said technology in terms of energy budget (production and consumption), and the limitations related to reactor fabrication cost and design for future upgradation to large scale application.

Benefits of Age-Improved Resistance of Mature Electroactive Biofilm Anodes in Anaerobic Digestion

Anaerobic digestion (AD) and microbial electrochemical technologies (MET) can be combined in manifold ways. Recent studies show negative influences of AD effluents on the performance of pre-grown Geobacter spp.-dominated biofilm anodes. In this study, it was investigated how such biofilm anodes are affected by AD effluents. Therefore, experiments using AD effluents in different concentrations (0-100%) in combination with biofilms of different ages were performed. Furthermore, the activity of methanogens was inhibited and minimized by application of 2-bromoethanesulfonate (2-BES) and microfiltration, respectively. Biofilms pre-grown for 5 weeks show higher resistance against AD effluents compared to biofilms pre-grown for only 3 weeks. Nevertheless, adaptation of biofilms to AD effluents was not successful. Biofilm activity in terms of coulombic efficiency and maximum current density (j_max) dropped by factor 32.2 ± 3.2 and 38.9 ± 8.4, respectively. The application of 2-BES and microfiltration had positive effects on the biofilm activity. The results support the assumption that methanogens or further compounds not studied here, for example, protozoans, which may have been inhibited or removed by 2-BES application or microfiltration, have an immediate influence on the stability of Geobacter spp.-dominated biofilms and may limit their practical application in AD environments.

A review on self-sustainable microbial electrolysis cells for electro-biohydrogen production via coupling with carbon-neutral renewable energy technologies

Microbial electrolysis cell (MEC) technology is a promising bioelectrochemical hydrogen production technology that utilizes anodic bio-catalytic oxidation and cathodic reduction processes. MECs require a lower external energy input than water electrolysis; however, as they also require the application of external power sources, this inevitably renders MEC systems a less sustainable option. This issue is the main obstacle hindering the practical application of MECs. Therefore, this review aims to introduce a self-sustainable MEC technology by combining conventional MECs with advanced carbon-neutral technologies, such as solar-, microbial-, osmotic-, and thermoelectric-powers (and their combinations). Moreover, new approaches to overcome the thermodynamic barriers and attain self-sustaining MECs are discussed in detail, thereby providing a working principle, current challenges, and future perspective in the field. This review provides comprehensive insights into reliable hydrogen production as well as the latest trends towards self-sustainable MECs for practical application.

State of the art and challenges of biohydrogen from microalgae

Biohydrogen from microalgae has attracted extensive attention owing to its promising features of abundance, renewable and self sustainability. Unlike other well-established biofuels like biodiesel and bioethanol, biohydrogen from microalgae is still in the preliminary stage of development. Criticisms in microalgal biohydrogen centered on its practicality and sustainability. Various laboratory- and pilot-scale microalgal systems have been developed, and some research initiatives have exhibited potential for commercial application. This work provides a review of the state of the art of biohydrogen from microalgae. Discussions include metabolic pathways of light-driven transformation and dark fermentation, reactor schemes and system designs encompassing reactor configurations and light manipulation. Challenges, knowledge gaps and the future directions in metabolic limitations, economic and energy assessments, and molecular engineering are also delineated. Current scientific and engineering challenges of microalgal biohydrogen need to be addressed for technology leapfrog or breakthrough.

Salinity-gradient energy driven microbial electrosynthesis of value-added chemicals from CO2 reduction

Biological conversion of CO₂ to value-added chemicals and biofuels has emerged as an attractive strategy to address the energy and environmental concerns caused by the over-reliance on fossil fuels. In this study, an innovative microbial reverse-electrodialysis electrolysis cell (MREC), which combines the strengths of reverse electrodialysis (RED) and microbial electrosynthesis technology platforms, was developed to achieve efficient CO₂-to-value chemicals bioconversion by using the salinity gradient energy as driven energy sources. In the MREC, maximum acetate and ethanol concentrations of 477.5 ± 33.2 and 46.2 ± 8.2 mg L^-1 were obtained at the cathode, catalyzed by Sporomusa ovata with production rates of 165.79 ± 11.52 and 25.11 ± 4.46 mmol m^-2 d^-1, respectively. Electron balance analysis indicates that 94.4 ± 3.9% of the electrons derived from wastewater and salinity gradient were recovered in acetate and ethanol. This work for the first time proved the potential of innovative MREC configuration has the potential as an efficient technology platform for simultaneous CO₂ capture and electrosynthesis of valuable chemicals.