Scaling-up up-flow microbial electrolysis cells with a compact electrode configuration for continuous hydrogen production

Biochemical production with microbial bioelectrochemical systems

Microbial bioelectrochemical systems (BES) represent a promising platform for sustainable biochemical production by leveraging microbial electrocatalysis. These systems utilize electrical energy to drive microbial metabolic processes, enabling the recovery of CO₂ into valuable organic molecules such as methane, acetate, ethanol, and other biochemicals. This approach aligns with global efforts to mitigate greenhouse gas emissions and create circular carbon economies. The advancement of BES technology requires both scale-down and scale-up strategies to ensure feasibility and scalability. Scale-down approaches focus on optimizing operational parameters, enhancing electron transfer efficiencies, and understanding microbial community dynamics under controlled conditions. Scale-up efforts address the challenges of maintaining system stability, energy efficiency, and economic viability in larger, industrial-scale operations. Together, these strategies bridge the gap between fundamental laboratory research and real-world applications, positioning microbial BES as a key technology for sustainable biochemical production and captured carbon utilization.

Recent Advances in Scaling up Bioelectrochemical Systems: A Review

Bioelectrochemical systems (BESs) are devices capable of converting chemical energy into electrical energy using microorganisms as catalysts. These systems have been extensively studied at the laboratory level, but, due to multiple difficulties, their large-scale implementation has been explored only sparingly. This study presents the most recent technological advances for scaling up BESs. In the same way, the main technical and economic challenges that hinder the correct implementation of these systems at a large scale are mentioned. The study concludes with a review of successful case studies in scaling up BESs and discusses future directions and emerging trends.

Biohydrogen generation from distillery effluent using baffled up-flow microbial electrolysis cell

Microbial electrolysis cell (MEC) is gaining importance not only for effectively treating wastewater but also for producing hydrogen. The up-flow microbial electrolysis cell (UPMEC) is an innovative approach to enhance the efficiency, and substrate degradation. In this study, a baffled UPMEC with an anode divided into three regions by inserting the baffle (sieve) plates at varying distances from the cathode was designed. The effect of process parameters, such as flow rate (10, 15, and 20 mL/min), electrode area (50, 100, and 150 cm2), and catholyte buffer concentration (50, 100, and 150 mM) were investigated using distillery wastewater as substrate. The experimental results showed a maximum of 0.6837 ± 0.02 mmol/L biohydrogen at 150 mM buffer, with 49 ± 1.0% COD reduction using an electrode of area 150 cm2. The maximum current density was 1335.94 mA/m2 for the flow rate of 15 mL/min and surface area of 150 cm2. The results showed that at optimized flow rate and buffer concentration, maximum hydrogen production and effective treatment of wastewater were achieved in the baffled UPMEC. PRACTITIONER POINTS: Biohydrogen production from distillery wastewater was investigated in a baffled UPMEC. Flowrate, concentration and electrode areas significantly influenced the hydrogen production. Maximum hydrogen (0.6837±0.02mmol/L.day) production and COD reduction (49±1.0%) was achieved at 15 mL/min. Highest CHR of 95.37±1.9 % and OHR of 4.6±0.09 % was observed at 150 mM buffer concentration.

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.

Enhanced wettability improves catalytic activity of nickel-functionalized activated carbon cathode for hydrogen production in microbial electrolysis cells

A nickel-functionalized activated carbon (AC/Ni) was recently developed for microbial electrolysis cells (MECs) and showed a great potential for large-scale applications. In this study, the electroactivity of the AC/Ni cathode was significantly improved by increasing the oxygen (16.9%) and nitrogen (124%) containing species on the AC using nitric acid oxidation. The acid-treated AC (t-AC) showed 21% enhanced wettability that consequently reduced the ohmic resistance (6.7%) and the charge transfer resistance (33.3%). As a result, t-AC/Ni achieved peak values of hydrogen production rate (0.35 ± 0.02 L-H₂/L-d), energy yield (129 ± 8%), and cathodic hydrogen recovery (93 ± 6%) in MECs. The hydrogen production rate was 84% higher using t-AC/Ni cathode than the control, likely due to the enhanced wettability and a higher fraction of N on the t-AC. Also, the increases in polyvinylidene fluoride (PVDF) binder loadings (from 4.6 mg-PVDF/cm² to 7.3 mg-PVDF/cm²) demonstrated 47% higher hydrogen productions rates in MECs.

A scalable model of fluid flow, substrate removal and current production in microbial fuel cells

Mathematical modelling can reduce the cost and time required to design complex systems, and is being increasingly used in microbial electrochemical technologies (METs). To be of value such models must be complex enough to reproduce important behaviour of MET, yet simple enough to provide insight into underlying causes of this behaviour. Ideally, models must also be scalable to future industrial applications, rather than limited to describing existing laboratory experiments. We present a scalable model for simulating both fluid flow and bioelectrochemical processes in microbial fuel cells (MFCs), benchmarking against an experimental pilot-scale bioreactor. The model describes substrate transport through a two-dimensional fluid domain, and biofilm growth on anode surfaces. Electron transfer is achieved by an intracellular redox mediator. We find significant spatial variations in both substrate concentration and current density. Simple changes to the reactor layout can greatly improve the overall efficiency, measured in terms of substrate removal and total current generated.

Scalability of microbial electrochemical technologies: Applications and challenges

During wastewater treatment, microbial electrochemical technologies (METs) are a promising means for in situ energy harvesting and resource recovery. The primary constraint for such systems is scaling them up from the laboratory to practical applications. Currently, most research (∼90%) has been limited to benchtop models because of bioelectrochemical, economic, and engineering design limitations. Field trials, i.e., 1.5 m³ bioelectric toilet, 1000 L microbial electrolysis cell and industrial applications of METs have been conducted, and their results serve as positive indicators of their readiness for practical applications. Multiple startup companies have invested in the pilot-scale demonstrations of METs for industrial effluent treatment. Recently, advances in membrane/electrode modification, understanding of microbe-electrode interaction, and feasibility of electrochemical redox reactions have provided new directions for realizing the practical application. This study reviews the scaling-up challenges, success stories for onsite use, and readiness level of METs for commercialization that is inexpensive and sustainable.

Anaerobic digestion beyond biogas

Anaerobic digestion (AD) is a matured technology for waste (water) remediation/stabilization and bioenergy generation in the form of biogas. AD technology has several inherent benefits ranging from generating renewable energy, remediating waste (water), and reducing greenhouse gas emission to improving health/hygiene and the overall socio-economic status of rural communities in developing nations. In recent years, there has been a paradigm shift in applications of AD technology beyond biogas. This special issue (SI) entitled, "Anaerobic Digestion Beyond Biogas (ADBB-2021)," was conceptualized to incorporate some of the recent advances in AD in which the emphasis is beyond biogas, such as anaerobic biorefinery, chain elongation, treatment of micropollutants, toxicity and system stability, digestate as biofertilizer, bio-electrochemical systems, innovative bioreactors, carbon sequestration, biogas upgrading, microbiomes, waste (water) remediation, residues/waste pre-treatment, promoter addition, and modeling, process control, and automation, among others. This VSI: ADBB-2021 contains 53 manuscripts (14 critical reviews and 39 research). The key findings of each manuscript are briefly summarized here, which can serve as a valuable resource for AD researchers to learn of major advances in AD technology and identify future research directions.