Scalability of microbial electrochemical technologies: Applications and challenges

Comparing the performance of microbial electrochemical assisted and aerated treatment wetlands in pilot-scale: Removal of major pollutants and organic micropollutants

The combination of treatment wetlands (TWs) with microbial electrochemical technologies (MET) is often studied in the lab to improve the performance and decrease the footprint of TWs. In this article we evaluated the long-term performance of four pilot-scale vertical sub-surface flow TWs for major pollutants' and organic micropollutants' removal from domestic wastewater. Three of them were filled with electroconductive material and operated under saturated (MET SAT), unsaturated (MET UNSAT) and unsaturated-saturated (MET HYBRID) conditions while the fourth one was a saturated intensified aerated system (AEW) filled with gravel. The MET-TWs achieved significant removals of COD (>78 %) with no clogging issues at the maximum applied OLR (249 g COD m-3 d-1) while under these loading conditions TSS removal exceeded 84 %. Among all electroactive TWs, UNSAT could remove 25 g NH4-N m-3 d-1 through nitrification when peak ammonium loading rate was applied; however this removal was significantly lower than AEW (35 g NH4-N m-3d-1). No important removal of P was observed in all systems with the exception of MET-SAT were precipitation reactions of P with iron occurred when anaerobic pretreated wastewater was used. The removal of the sum of studied organic micropollutants ranged between 70 ± 18 % (MET UNSAT) to 91 ± 4 % (AEW) and improved with feeding pulses increase. Moderate to high removal of specific microcontaminants was observed depending on the target compound, the studied system and the operational conditions. AEW and MET HYBRID systems complied with the limits set by EU for wastewater discharge to non-sensitive water bodies and for Class B water reuse. Scale-up calculations for a settlement of 500 PE showed that these systems require much less area per PE (0.51 m2 PE-1) comparing to conventional TWs while the operational cost was calculated to 0.07 € m-3 for the AEW and 0.02 € m-3 for the MET HYBRID.

Performance and mechanism of antibiotic resistance removal by biochar-enhanced sediment microbial fuel cell

This study is the first to explore the performance and mechanism of biochar-impacted sediment microbial fuel cell for removing antibiotic resistance genes (ARGs), and examines the effects of different biochar contents. The addition of 5% biochar produced the highest output voltage and power density, which increased by 100% and 219%, respectively, while simultaneously reducing the abundance and risk of ARGs. Comparatively, the addition of moderate amount of biochar (1-5%) promoted the removal of ARGs, while the opposite was true for excessive (10%) biochar. Biochar affected ARGs through prophages, insertion sequence, and transposons. Biological factors and voltage jointly influenced ARGs variation, with the former accounting for 56%. Further analysis of functional genes indicated that biochar controlled ARGs by regulating the synthesis of genetic material and amino acids to influence metabolism. Overall, findings of this study shed light on the potential removal of ARGs in microbial electrochemical systems.

Synthetic greywater treatment using a scalable granular activated carbon bioelectrochemical reactor

Greywater reuse has emerged as a promising solution for addressing water shortages. However, greywater needs treatment before reuse to meet the required water quality standards. Conventional wastewater treatment technologies are unsuitable for recreating highly decentralized domestic greywater. This study evaluated bioelectrochemical reactors (BERs) with granular activated carbon (GAC) as a sustainable alternative for developing decentralized and low-cost biological treatment systems. BERs using GAC as the anode material and conventional GAC biofilters (BFs) for synthetic greywater treatment were operated in batch mode for 110 days in two stages: (i) with polarized anodes at -150 mV vs. Ag/AgCl and (ii) as a microbial fuel cell with an external resistance of 1 kΩ. Anode polarization produced an electrosorption effect, increasing the ion removal of the BERs. Power production during the operation and cyclic voltammetry tests of the extracted granules revealed electrochemically active biofilm development on the BERs. Although low power density (0.193 ± 0.052 µW m-3) was observed in BERs, they showed a similar performance in sCOD removal (BER = 91.6-89.6 %; BF = 96.2-93.2 %) and turbidity removal (BER = 81-82 %; BF = 30-62 %) to BFs that used 50 % aeration. Additionally, scanning electron microscopy of sampled granules showed higher biomass formation in BER granules than in BF granules, suggesting a higher contribution of sessile (vs. planktonic) cells to the treatment. Thus, the results highlight the synergistic removal effect of the GAC-based BER. The scalable design presented in this study represents a proof-of-concept for developing BERs to use in decentralized greywater treatment systems.

Biohydrogen upgradation and wastewater treatment in 3-chambered bioelectrochemical system assisted with H2/O2-based redox reactions

The current need for the upgradation of biohydrogen generation and contaminant removal in two-chambered microbial electrolysis cells (MECs) compels the design of alternatives i.e. bioelectrochemical systems (BESs) to conventional reactors. In this study, a novel three-chambered design of MEC (BES-1) was developed with a common anodic chamber and a two-cathodic chambers at both ends of the anodic chamber, separated by a membrane (MEC-MEC). To facilitate electricity recovery, a microbial fuel cell (MFC) was integrated with an MEC in BES-2. Cathodic hydrogen recovery of 8.89 and 4.81 mL/L.day, and organic matter removal of 82% and 76% were obtained in BES-1 and BES-2, respectively, demonstrating their capabilities for bioremediation. Electrochemical analyses also revealed that cathodic reduction reactions improved with the effective utilization of protons during integration. Our design regulates H2/O2-associated electrochemical reactions and is beneficial for maintaining pH equilibrium. From cost and energy perspectives, the integrated BES provides a platform for two different reactions simultaneously and is capable of boosting overall hydrogen recovery and organic matter removal. Moreover, the compactness and competitiveness of such an integrated BES increase its scope for real-world applications.

Optimizing electrochemically active microorganisms as a key player in the bioelectrochemical system: Identification methods and pathways to large-scale implementation

The rapid global economic growth driven by industrialization and population expansion has resulted in significant issues, including reliance on fossil fuels, energy scarcity, water crises, and environmental emissions. To address these issues, bioelectrochemical systems (BES) have emerged as a dual-purpose solution, harnessing electrochemical processes and the capabilities of electrochemically active microorganisms (EAM) to simultaneously recover energy and treat wastewater. This review examines critical performance factors in BES, including inoculum selection, pretreatment methods, electrodes, and operational conditions. Further, authors explore innovative approaches to suppress methanogens and simultaneously enhance the EAM in mixed cultures. Additionally, advanced techniques for detecting EAM are discussed. The rapid detection of EAM facilitates the selection of suitable inoculum sources and optimization of enrichment strategies in BESs. This optimization is essential for facilitating the successful scaling up of BES applications, contributing substantially to the realization of clean energy and sustainable wastewater treatment. This analysis introduces a novel viewpoint by amalgamating contemporary research on the selective enrichment of EAM in mixed cultures. It encompasses identification and detection techniques, along with methodologies tailored for the selective enrichment of EAM, geared explicitly toward upscaling applications in BES.

Paradigm shift in Nutrient-Energy-Water centered sustainable wastewater treatment system through synergy of bioelectrochemical system and anaerobic digestion

With advancements in research and the necessity of improving the performance of bioelectrochemical system (BES), coupling anaerobic digestion (AD) with BES is crucial for energy gain from wastewater and bioremediation. Hybridization of BES-AD concept opens new avenues for pollutant degradation, carbon capture and nutrient-resource recovery from wastewater. The strength of merging BES-AD lies in synergy, and this approach was employed to differentiate fads from strategies with the potential for full-scale implementation and making it an energy-positive system. The integration of BES and AD system increases the overall performance and complexity of combined system and the cost of operation. From a technical standpoint, the primary determinants of BES-AD feasibility for field applications are the scalability and economic viability. High potential market for such integrated system attract industrial partners for more industrial trials and investment before commercialization. However, BES-AD with high energy efficacy and negative economics demands performance boost.

Bioremediation of hydrocarbon by co-culturing of biosurfactant-producing bacteria in microbial fuel cell with Fe2O3-modified anode

The most common type of environmental contamination is petroleum hydrocarbons. Sustainable and environmentally friendly treatment strategies must be explored in light of the increasing challenges of toxic and critical wastewater contamination. This paper deals with the bacteria-producing biosurfactant and their employment in the bioremediation of hydrocarbon-containing waste through a microbial fuel cell (MFC) with Pseudomonas aeruginosa (exoelectrogen) as co-culture for simultaneous power generation. Staphylococcus aureus is isolated from hydrocarbon-contaminated soil and is effective in hydrocarbon degradation by utilizing hydrocarbon (engine oil) as the only carbon source. The biosurfactant was purified using silica-gel column chromatography and characterised through FTIR and GCMS, which showed its glycolipid nature. The isolated strains are later employed in the MFCs for the degradation of the hydrocarbon and power production simultaneously which has shown a power density of 6.4 W/m3 with a 93% engine oil degradation rate. A biogenic Fe2O3 nanoparticle (NP) was synthesized using Bambusa arundinacea shoot extract for anode modification. It increased the power output by 37% and gave the power density of 10.2 W/m3. Thus, simultaneous hydrocarbon bioremediation from oil-contamination and energy recovery can be achieved effectively in MFC with modified anode.

A review on recent environmental electrochemistry approaches for the consolidation of a circular economy model

Availability of raw materials in the chemical industry is related to the selection of the chemical processes in which they are used as well as to the efficiency, cost, and eventual evolution to more competitive dynamics of transformation technologies. In general terms however, any chemically transforming technology starts with the extraction, purification, design, manufacture, use, and disposal of materials. It is important to create a new paradigm towards green chemistry, sustainability, and circular economy in the chemical sciences that help to better employ, reuse, and recycle the materials used in every aspect of modern life. Electrochemistry is a growing field of knowledge that can help with these issues to reduce solid waste and the impact of chemical processes on the environment. Several electrochemical studies in the last decades have benefited the recovery of important chemical compounds and elements through electrodeposition, electrowinning, electrocoagulation, electrodialysis, and other processes. The use of living organisms and microorganisms using an electrochemical perspective (known as bioelectrochemistry), is also calling attention to "mining", through plants and microorganisms, essential chemical elements. New process design or the optimization of the current technologies is a major necessity to enhance production and minimize the use of raw materials along with less generation of wastes and secondary by-products. In this context, this contribution aims to show an up-to-date scenario of both environmental electrochemical and bioelectrochemical processes for the extraction, use, recovery and recycling of materials in a circular economy model.

Engineered nanomaterials for carbon capture and bioenergy production in microbial electrochemical technologies: A review

The mounting threat of global warming, fuelled by industrialization and anthropogenic activities, is undeniable. In 2017, atmospheric carbon dioxide (CO2), the primary greenhouse gas, exceeded 410 ppm for the first time. Shockingly, on April 28, 2023, this figure surged even higher, reaching an alarming 425 ppm. Even though extensive research has been conducted on developing efficient carbon capture and storage technologies, most suffer from high costs, short lifespans, and significant environmental impacts. Recently, the use of engineered nanomaterials (ENM), particularly in microbial electrochemical technologies (METs), has gained momentum owing to their appropriate physicochemical properties and catalytic activity. By implementing ENM, the MET variants like microbial electrosynthesis (MES) and photosynthetic microbial fuel cells (pMFC) can enhance carbon capture efficiency with simultaneous bioenergy production and wastewater treatment. This review provides an overview of ENMs' role in carbon capture within MES and pMFC, highlighting advancements and charting future research directions.

Scale-up and techno-economic analysis of microbial electrolysis cells for hydrogen production from wastewater

Microbial electrolysis cells (MECs) have demonstrated high-rate H₂ production while concurrently treating wastewater, but the transition in scale from laboratory research to systems that can be practically applied has encountered challenges. It has been more than a decade since the first pilot-scale MEC was reported, and in recent years, many attempts have been made to overcome the barriers and move the technology to the market. This study provided a detailed analysis of MEC scale-up efforts and summarized the key factors that should be considered to further develop the technology. We compared the major scale-up configurations and systematically evaluated their performance from both technical and economic perspectives. We characterized how system scale-up impacts the key performance metrics such as volumetric current density and H₂ production rate, and we proposed methods to evaluate and optimize system design and fabrication. In addition, preliminary techno-economic analysis indicates that MECs can be profitable in many different market scenarios with or without subsidies. We also provide perspectives on future development needed to transition MEC technology to the marketplace.

Industrial bioelectrochemistry for waste valorization: State of the art and challenges

Bioelectrochemistry has gained importance in recent years for some of its applications on waste valorization, such as wastewater treatment and carbon dioxide conversion, among others. The aim of this review is to provide an updated overview of the applications of bioelectrochemical systems (BESs) for waste valorization in the industry, identifying current limitations and future perspectives of this technology. BESs are classified according to biorefinery concepts into three different categories: (i) waste to power, (ii) waste to fuel and (iii) waste to chemicals. The main issues related to the scalability of bioelectrochemical systems are discussed, such as electrode construction, the addition of redox mediators and the design parameters of the cells. Among the existing BESs, microbial fuel cells (MFCs) and microbial electrolysis cells (MECs) stand out as the more advanced technologies in terms of implementation and R&D investment. However, there has been little transfer of such achievements to enzymatic electrochemical systems. It is necessary that enzymatic systems learn from the knowledge reached with MFC and MEC to accelerate their development to achieve competitiveness in the short term.

A Review of Biohydrogen Production from Saccharina japonica

Saccharina japonica (known as Laminaria japonica or Phaeophyta japonica), one of the largest macroalgae, has been recognized as food and medicine for a long time in some Asian countries, such as China, South Korea, Japan, etc. In recent years, S. japonica has also been considered the most promising third-generation biofuel feedstock to replace fossil fuels, contributing to solving the challenges people face regarding energy and the environment. In particular, S. japonica-derived biohydrogen (H2) is expected to be a major fuel source in the future because of its clean, high-yield, and sustainable properties. Therefore, this review focuses on recent advances in bio-H2 production from S. japonica. The cutting-edge biological technologies with suitable operating parameters to enhance S. japonica’s bio-H2 production efficiency are reviewed based on the Scopus database. In addition, guidelines for future developments in this field are discussed.

Critical review of biochemical pathways to transformation of waste and biomass into bioenergy

In recent years, biofuel or biogas have become the primary source of bio-energy, providing an alternative to conventionally used energy that can meet the growing energy demand for people all over the world while reducing greenhouse gas emissions. Enzyme hydrolysis in bioethanol production is a critical step in obtaining sugars fermented during the final fermentation process. More efficient enzymes are being researched to provide a more cost-effective technique during enzymatic hydrolysis. The exploitation of microbial catabolic biochemical reactions to produce electric energy can be used for complex renewable biomasses and organic wastes in microbial fuel cells. In hydrolysis methods, a variety of diverse enzyme strategies are used to promote efficient bioethanol production from various lignocellulosic biomasses like agricultural wastes, wood feedstocks, and sea algae. This paper investigates the most recent enzyme hydrolysis pathways, microbial fermentation, microbial fuel cells, and anaerobic digestion in the manufacture of bioethanol/bioenergy from lignocellulose biomass.

Microbial electrosynthesis: carbonaceous electrode materials for CO2 conversion

Microbial electrosynthesis (MES) is a sustainable approach to address greenhouse gas (GHG) emissions using anthropogenic carbon dioxide (CO₂) as a building block to create clean fuels and highly valuable chemicals. The efficiency of MES-based CO₂ conversion is closely related to the performance of electrode material and, in particular, the cathode for which carbonaceous materials are frequently used. Compared to expensive metal electrodes, carbonaceous materials are biocompatible with a high specific surface area, wide range of possible morphologies, and excellent chemical stability, and their use can maximize the growth of bacteria and enhance electron transfer rates. Examples include MES cathodes based on carbon nanotubes, graphene, graphene oxide, graphite, graphite felt, graphitic carbon nitride (g-C₃N₄), activated carbon, carbon felt, carbon dots, carbon fibers, carbon brushes, carbon cloth, reticulated vitreous carbon foam, MXenes, and biochar. Herein, we review the state-of-the-art MES, including thermodynamic and kinetic processes that underpin MES-based CO₂ conversion, as well as the impact of reactor type and configuration, selection of biocompatible electrolytes, product selectivity, and the use of novel methods for stimulating biomass accumulation. Specific emphasis is placed on carbonaceous electrode materials, their 3D bioprinting and surface features, and the use of waste-derived carbon or biochar as an outstanding material for further improving the environmental conditions of CO₂ conversion using carbon-hungry microbes and as a step toward the circular economy. MES would be an outstanding technique to develop rocket fuels and bioderived products using CO₂ in the atmosphere for the Mars mission.

Recent Advances in Bioelectrochemical Systems for Nitrogen and Phosphorus Recovery Using Membranes

Bioelectrochemical systems (BESs) have emerged as a technology that is able to recover resources from different kinds of substrates, especially wastewater. Nutrient recovery, mostly based on membrane reactor configuration, is a clear niche for BES application. The recovery of nitrogen or phosphorus allows for treatment of wastewater while simultaneously collecting a concentrated stream with nutrients that can be reintroduced into the system, becoming a circular economy solution. The aim of this study is to review recent advances in membrane-based BESs for nitrogen and phosphorus recovery and compare the recovery efficiencies and energy requirements of each system. Finally, there is a discussion of the main issues that arise from using membrane-based BESs. The results presented in this review show that it would be beneficial to intensify research on BESs to improve recovery efficiencies at the lowest construction cost in order to take the final step towards scaling up and commercialising this technology.

Integration of two-stage anaerobic digestion process with in situ biogas upgrading

High impurity concentration of biogas limits its wide commercial utilization. Therefore, the integration of two-stage anaerobic digestion process with in situ biogas upgrading technologies is reviewed, with emphasis on their principles, main influencing factors, research success, and technical challenges. The crucial factors that influence these technologies are pH, alkalinity, and hydrogenotrophic methanogenesis. Hence, pH fluctuation and low gas-liquid mass transfer of H₂ are some major technical challenges limiting the full-scale application of in situ upgrading techniques. Two-stage anaerobic digestion integration with various in situ upgrading techniques to form a hybrid system is proposed to overcome the constraints and systematically guide future research design and advance the development and commercialization of these techniques. This review intends to provide the current state of in situ biogas upgrading technologies and identify knowledge gaps that warrant further investigation to advance their development and practical implementation.

Pretreatment of cyanobacterial biomass for the production of biofuel in microbial fuel cells

The present study delves into phototrophic cyanobacterial biomass production by concomitant CO₂ sequestration, selecting an effective pretreatment condition followed by using this as feedstock for green fuel or bioelectricity production by Microbial Fuel Cells (MFC). The performance of the various photobioreactors were put up against Anabaena sp. PCC 7120 biomass production. Maximum microalgal biomass of 1.15 gL^-1 was attained in an airlift bioreactor for 9 days under a light intensity of 100 µEm^-2s^-1. Pretreatment methods like sonication, HCl acid, and H₂O₂ treatment (2 % vv^-1) were applied to digest harvested biomass. Higher power output (6.76 Wm^-3) was attained, and 73.5 % COD was eliminated using 2 % (vv^-1) acid pre-treated biomass. Better results were obtained using acid pre-treated biomass because the conductivity of the anolyte increased with the neutralization of acid-pre-treated biomass. The results demonstrate that cyanobacterial biomass could be employed successfully as a renewable resource for green fuel generation in MFCs.

Tailoring a highly conductive and super-hydrophilic electrode for biocatalytic performance of microbial electrolysis cells

Bioelectrochemical hydrogen production via microbial electrolysis cells (MECs) has attracted attention as the next generation of technology for the hydrogen economy. MECs work by electrochemically active bacteria reducing organic compounds at the anode. However, the hydrophobic nature of carbon-based anodes suppresses the release of the produced gas and water penetration, which significantly reduces the possibility of microbial attachment. Consequently, a limited surface area of the anode is used, which decreases hydrogen production efficiency. In this study, the bifunctional material poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) was applied to the surface of a three-dimensional carbon felt anode to enhance the hydrogen production efficiency of an MEC owing to the high conductivity of PEDOT and super-hydrophilicity of PSS. In experiments, the PEDOT:PSS-modified anode almost doubled the hydrogen production efficiency of the MEC compared with the control anode owing to the increased capacitance current (239.3 %) and biofilm formation (220.7 %). The modified anode reduced the time required for the MEC to reach a steady state of hydrogen production by 14 days compared to the control anode. Microbial community profiles demonstrated that the modified anode had a greater abundance of electrochemically active bacteria than the control anode. This simple method could be widely applied to various bioelectrochemical systems (e.g., microbial fuel cells and solar cells) and to scaling up MECs.

Application of Low-Cost Plant-Derived Carbon Dots as a Sustainable Anode Catalyst in Microbial Fuel Cells for Improved Wastewater Treatment and Power Output

Microbial fuel cells (MFC) can generate electric energy from wastewater which can be enhanced further by anode catalysts. The recovery of electrons produced by oxidation of organics catalyzed by bacteria in the anode was enhanced when carbon dots(CDs) were added into the MFC. In this present study, a novel strategy for designing anode material and the fabrication of a high-efficient and environmentally friendly anode for energy generation from wastewater was reported. The CDs were synthesized by the pyrolysis of a peanut shell at the temperature of 250 °C for 2 h with a heating rate of 10 °C min−1. Thus synthesized CDs were characterized by transmission electron microscopy (TEM), UV/Vis spectroscopy, and fluorescence spectroscopy. The TEM analysis showed morphology with an average size of 1.62 nm. The UV/Vis absorbance of the CDs shows a wide absorption band without a characteristic peak. The excitation spectrum of CDs recorded at the emission wavelength of 440 nm exhibits a peak around 320 nm. CDs were investigated as an anode material in a MFC utilizing acetate as the organic substrate. The average chemical oxygen demand (COD) removal in closed circuit operation mode was 89%. The maximum power density production (7.2 W/m3) was observed in MFC containing 1 mg/cm2 CD-impregnated anode (CDsIA). The CDsIA provides the ability to promote efficient biofilm formation. These results emphasize the application of CD-based electrodes in MFCs for the simultaneous treatment of wastewater and electricity generation while also providing additional benefits.

Scale-up of the bioelectrochemical system: Strategic perspectives and normalization of performance indices

Electrochemists and ecological engineers find environmental bioelectrochemistry appealing; however, there is a big gap between expectations and actual progress in bioelectrochemical system (BES). Implementing such technology opens new opportunities for novel electrochemical reactions for resource recovery and effective wastewater treatment. Loopholes of BES exist in its scaling-up applications, and numerous attempts toward practical applications (200, 1000, and 1500 L) are key successive indicators toward its commercialization. This review emphasized the critical rethinking of standardization of performance indices i.e. current generation (A/m²), net energy recovery (kWh/kg·COD), product/resource yield (mM), and economic feasibility ($/kWh) to make fair comparison with the existing treatment system. Therefore, directional perspectives, including modularity, energy-cost balance, energy and resource recovery, have been proposed for the sustainable market of BES. The current state of the art and up-gradation in resource recovery and contaminant removal warrants a systematic rethinking of functional worth and niches of BES for practical applications.

Degradation of β-lactam antibiotic ampicillin using sustainable microbial peroxide producing cell system

The enormous use of synthetic antibiotic and personal care products has impacted the natural microbiome and ecosystem. Overtime, treatment technologies developed suffered due to incomplete removal hence, a pilot dual-chambered microbial peroxide-producing cell that degrades ampicillin catalyzed by homogenous Fenton-reaction was designed. The system reported maximum current at 16.714 ± 0.048 µAcm^-2, power output of 1.956 ± 0.015 mW m^-2; 88 ± 2.90 mM of H₂O₂ generation with Na₂SO₄ that degraded 95.9 ± 3.00 to 97.8 ± 3.20% of 10 mg L^-1ampicillin within 72 hrs with electro-active Shewanella putrefaciens. An E. coli bioactivity assay with ampicillin exhibited no sensitivity zone due to the loss of activity. Analytical spectroscopic studies reveal β-Lactam ring deformation; Liquid Chromatography-Mass Spectroscopy clearly shows the presence of degradation metabolites. A sustainable wastewater treatment with 72 ± 4.5% reduction in anodic chemical oxygen demand was achieved. Present results designate the technology, as promising for effective antibiotics removal for wastewater treatment concomitant with electricity generation.

Microbial Electrosynthesis Inoculated with Anaerobic Granular Sludge and Carbon Cloth Electrodes Functionalized with Copper Nanoparticles for Conversion of CO2 to CH4

Microbial electrosynthesis (MES) can sustainably convert CO₂ to products and significant research is currently being conducted towards this end, mainly in laboratory-scale studies. The high-cost ion exchange membrane, however, is one of the main reasons hindering the industrialization of MES. This study investigates the conversion of CO₂ (as a sole external carbon source) to CH₄ using membraneless MES inoculated with anaerobic granular sludge. Three types of electrodes were tested: carbon cloth (CC) and CC functionalized with Cu NPs, where Cu NPs were deposited for 15 and 45 min, respectively. During the MES experiment, which lasted for 144 days (six cycles), methane was consistently higher in the serum bottles with CC electrodes and applied voltage. The highest CH₄ (around 46%) was found in the second cycle after 16 days. The system’s performance declined during the following cycles; nevertheless, the CH₄ composition was twice as high compared to the serum bottles without voltage. The MES with Cu NPs functionalized CC electrodes had a higher performance than the MES with plain CC electrodes. Microbial profile analysis showed that the Methanobacterium was the most dominant genus in all samples and it was found in higher abundance on the cathodes, followed by the anodes, and then in the suspended biomass. The genus Geobacter was identified only on the anodes regarding relative bacterial abundance at around 6–10%. Desulfovibrio was the most dominant genus in the cathodes; however, its relative abundance was significantly higher for the cathodes with Cu NPs.

Recovery of Nutrients from Residual Streams Using Ion-Exchange Membranes: Current State, Bottlenecks, Fundamentals and Innovations

The review describes the place of membrane methods in solving the problem of the recovery and re-use of biogenic elements (nutrients), primarily trivalent nitrogen N^III and pentavalent phosphorus P^V, to provide the sustainable development of mankind. Methods for the recovery of NH₄⁺ − NH₃ and phosphates from natural sources and waste products of humans and animals, as well as industrial streams, are classified. Particular attention is paid to the possibilities of using membrane processes for the transition to a circular economy in the field of nutrients. The possibilities of different methods, already developed or under development, are evaluated, primarily those that use ion-exchange membranes. Electromembrane methods take a special place including capacitive deionization and electrodialysis applied for recovery, separation, concentration, and reagent-free pH shift of solutions. This review is distinguished by the fact that it summarizes not only the successes, but also the “bottlenecks” of ion-exchange membrane-based processes. Modern views on the mechanisms of NH₄⁺ − NH₃ and phosphate transport in ion-exchange membranes in the presence and in the absence of an electric field are discussed. The innovations to enhance the performance of electromembrane separation processes for phosphate and ammonium recovery are considered.

Recent Application of Nanomaterials to Overcome Technological Challenges of Microbial Electrolysis Cells

Microbial electrolysis cells (MECs) have attracted significant interest as sustainable green hydrogen production devices because they utilize the environmentally friendly biocatalytic oxidation of organic wastes and electrochemical proton reduction with the support of relatively lower external power compared to that used by water electrolysis. However, the commercialization of MEC technology has stagnated owing to several critical technological challenges. Recently, many attempts have been made to utilize nanomaterials in MECs owing to the unique physicochemical properties of nanomaterials originating from their extremely small size (at least <100 nm in one dimension). The extraordinary properties of nanomaterials have provided great clues to overcome the technological hurdles in MECs. Nanomaterials are believed to play a crucial role in the commercialization of MECs. Thus, understanding the technological challenges of MECs, the characteristics of nanomaterials, and the employment of nanomaterials in MECs could be helpful in realizing commercial MEC technologies. Herein, the critical challenges that need to be addressed for MECs are highlighted, and then previous studies that used nanomaterials to overcome the technological difficulties of MECs are reviewed.

Electro-fermentation: Sustainable bioproductions steered by electricity

The market of biobased products obtainable via fermentation processes is steadily increasing over the past few years, driven by the need to create a decarbonized economy. To date, industrial fermentation (IF) employs either pure or mixed microbial cultures (MMC) whereby the type of the microbial catalysts and the used feedstock affect metabolic pathways and, in turn, the type of product(s) generated. In many cases, especially when dealing with MMC, the economic viability of IF is hindered by factors such as the low attained product titer and selectivity, which ultimately challenge the downstream recovery and purification steps. In this context, electro-fermentation (EF) represents an innovative approach, based on the use of a polarized electrode interface to trigger changes in the rate, yield, titer or product distribution deriving from traditional fermentation processes. In principle, the electrode in EF can act as an electron acceptor (i.e., anodic electro-fermentation, AEF) or donor (i.e., cathodic electro-fermentation, CEF), or simply as a mean to control the oxidation-reduction potential of the fermentation broth. However, the molecular and biochemical basis underlying the EF process are still largely unknown. This review paper provides a comprehensive overview of recent literature studies including both AEF and CEF examples with either pure or mixed microbial cultures. A critical analysis of biochemical, microbiological, and engineering aspects which presently hamper the transition of the EF technology from the laboratory to the market is also presented.