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Building on the Frontiers in Science lead article by Schröder et al. (1), this Viewpoint highlights selected engineering and systems-level challenges and opportunities that will determine whether microbial electrochemical technologies (METs) can transition from promising concepts to scalable, real-world wastewater treatment solutions. While the merits of METs are well established, materials-and product-related techno-economic barriers continue to limit full-scale deployment. These challenges can be overcome by enhancing energy and product recovery through innovative system design for optimized electron flow, by developing circular economy-driven integrated configurations, and by expanding the role of METs through a nexus-based approach to environmental sustainability (2).MET operation relies on the synergy between electrodes, membranes, and, most critically, microbial biofilms. Advances in electrode materials have shifted preference from metal-based to carbon-based electrodes because of their biocompatibility and cost-effectiveness, albeit often at the expense of electrical conductivity. Likewise, membrane separators, such as ionexchange membranes, are used to separate anode and cathode compartments but can induce localized pH imbalances, pore clogging, and increased internal resistance. Together, these components and biofilm dynamics strongly influence MET performance. Addressing electrode or membrane limitation in isolation is insufficient; a conducive environment for microbial enrichment and efficient electron transfer kinetics is essential.To reduce oxygen intrusion and substrate diffusion barriers while enhancing electron transfer kinetics and cathodic reaction potential, the electrode-membrane-biofilm interface must be optimized (3). Dynamic membrane separators have shown promise in addressing interface limitations in METs. Conductive dynamic membranes that combine permeability enhancement, oxygen suppression, and electron transfer functions offer improved oxygen reduction kinetics, enhanced mass transport, and potential-driven microbial enrichment (4). Synthetic biology combined with materials engineering may further enhance electron transfer (5). For example, incorporating conductive materials on electrodes or within biofilms can significantly increase current density. Introducing conductive materials into individual microbes via in situ nanoparticle synthesis may further improve microbe-electrode electron transfer, although the feasibility of such approaches in practical applications requires further investigation.System design directly affects power density and the production of value-added outputs.Internal resistance is the major bottleneck, while electrode selection and sizing also influence performance. Increasing electrode surface in large-scale reactors has led to increased internal resistance and decreased power outputs in microbial fuel cells (MFCs). Electrode spacing similarly affects electron transfer efficiency. Optimizing electrode packing density per reactor volume may help address limitations associated with electrode size and spacing (6). Larger reactors are frequently configured as stacked cells, leading to challenges related to flow distribution, electrode pairing, mass transport, and substrate utilization. Anode-cathode interconnections and material combinations further complicate system performance, and trade-offs persist between electricity generation and economic feasibility as reactor size increases.Air cathodes are commonly used in MFCs to enable passive oxygen transport, with oxygen serving as the preferred terminal electron acceptor. Aerated biocathodes may facilitate faster and more effective cathodic reduction reactions. The energy required for aeration can be minimized through intermittent aeration cycles that improve oxygen utilization efficiency.Biocathodes can also mitigate the trade-off between electricity generation and chemical oxygen demand (COD) removal by enabling additional COD reduction and nutrient (nitrogen and phosphorus) recovery, supporting more efficient treatment pathways for water reuse. In aerated biocathode MFCs, oxygen supply and utilization become key process variables that must be systematically evaluated at scale. Biocathodes can also mitigate the trade-off of METs operating at low COD removal rates for higher electricity generation by providing a comprehensive approach for further COD removal and or recovery of nutrients (nitrogen and phosphorous) from wastewater leading to more efficient treatment alternatives for water reuse. There are many biological cathodes that could be considered for this purpose. In aerated biocathode MFCs, oxygen supply and utilization efficiencies become additional process variables impacting energy performance which must be studied systematically for large-scale reactors.Pilot-scale demonstrations remain limited despite extensive laboratory research. Recent studies have begun to address unanswered questions regarding energy recovery and treatment feasibility at larger scales, yet cost-performance uncertainty persists due to variable results.Reported power densities and treatment efficiencies span a wide range across wastewater types, including artificial wastewaters. Cathode material and reaction mechanisms play a significant role, with air cathodes generally yielding lower power densities in reactors exceeding 100 L. Experience with biocathodes is sparse, although one study reported promising performance for a 1500L reactor (7). More long-term, in situ pilot-scale studies using real wastewaters are needed to generate reliable performance benchmarks. System design and optimization may also benefit from artificial intelligence, including machine learning and deep learning approaches, to develop predictive models that improve efficiency and reduce costs, provided data quality and consistency are adequately addressed.METs are not yet viable as standalone wastewater treatment systems but can perform effectively within integrated settings that meet regulatory requirements. Advanced treatment coupled with resource recovery represents a practical pathway toward circular economydriven MET deployment. Integrated configurations such as MFC-microbial electrolysis cell (MEC) systems can provide synergistic benefits, with MFCs serving as pre-treatment steps and MECs functioning as secondary treatment processes that capitalize on shared inputs and outputs. In such systems, MFCs treat wastewater while generating electricity and CO2, which can support hydrogen production in MECs. Additional integrated configurations, including combinations with constructed wetlands, hydroponics, electrochemical systems, and membrane bioreactors, have demonstrated encouraging technology readiness levels (8), with some showing feasibility in under-resourced settings (1). These systems require further evaluation to establish circular economy-based treatment strategies that enhance overall process resilience. Integrating METs with anaerobic digestion (AD) to enhance carbon and energy recovery is a particularly promising approach. AD generates biogas and nutrient-rich digestate suitable for agricultural reuse, while thermochemical conversion of sludge to (9). At present, AD is typically operated as a standalone unit in linear economy designs and this paradigm must evolve. Ultimately, MET circularity will depend on the ability to deliver diverse, value-added products cost-effectively. Cooperative multispecies biofilms or granule-based processes may enable breakdown of recalcitrant molecules into simpler molecules which could be further converted into useful products through synergistic microbial interactions.The application of METs extends beyond wastewater treatment and Sustainable Development Goal 6. METs are well suited to complex environmental nexus scenarios, including foodenergy-water, water-carbon-energy, water-energy-materials, and water-energy-land nexus.Their application can be expanded to groundwater and soil remediation and to the conversion of atmospheric CO2 into valuable products. An underexplored opportunity lies in mitigating gaseous emissions from industrial, hazardous, and municipal waste management processes, where METs could capture and convert pollutants into useful products. At scale, MET deployment could contribute to multiple Sustainable Development Goals (SDG2,3,7,9,12,13, and 15) at the global level.Within the food-energy-water nexus, integrated MET systems have been used to treat concentrated agricultural and food-processing wastewaters, offering insights transferable to municipal wastewater treatment. AD-MET configurations with biochar amendments showcase the water-carbon-energy nexus. The water-energy-materials nexus is particularly relevant given the growing importance of recovering critical raw materials such as nitrogen, phosphorous, and precious metals. These elements can be selectively recovered from wastewater via cathodic reduction, with cathode potential enabling targeted metal recovery (10).Future MET development must adopt a holistic perspective that supports scale-up of critical components while preserving microbial biofilm efficiency and system resilience. Recent advances have transformed miniature laboratory scale METs into pilot-scale operations, strengthening links between the microbial electrochemistry and environmental sustainability.