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BACKGROUND: The increase in energy and water demand due to industrialization and urbanization requires prioritized solutions for a sustainable future. Microbial electrolysis cells (MECs) have shown huge potential for biohydrogen production along with wastewater treatment. This study examined the effectiveness of employing nickel foam as an anode material for biohydrogen production from the widely available potato industry effluent. RESULTS: Hydrogen production rate increases exponentially with the increase in applied voltage. A maximum hydrogen production rate of 0.69 ± 0.02 m3 H2 m−3 reactor volume d−1 was achieved at 0.9 V with a maximum chemical oxygen demand removal efficiency of 97% at 0.8 V. The effluent of the 0.8 V cycle had the least salinity, low total dissolved solids, 84% reduced total hardness, highest effluent clarity (4.30 NTU, and negligible quantity of heavy metals. CONCLUSION: This study successfully produced biohydrogen from potato wastewater within 5 days of operation along with wastewater treatment of the substrate. The improved performance of the system can be attributed to the unique characteristics of nickel foam, such as high porosity, large surface area and excellent conductivity. The findings of this study have implications for the sustainable treatment of domestic and agro‐industrial wastewater and the development of efficient and low‐cost bio‐electrochemical systems for renewable energy production. © 2023 Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

The focus on renewable energy is increasing globally to lessen reliance on conventional sources and fossil fuels. For renewable energy systems to work at their best and produce the desired results, precise feedback control is required. Microbial electrochemical cells (MEC) are a relatively new technology for renewable energy. In this study, we design and implement a model-based robust controller for a continuous MEC reactor. We compare its performance with those of traditional methods involving a proportional integral derivative (PID), H-infinity (H ∞ ) controller and PID controller tuned by intelligent genetic algorithms. Recently, a dynamic model of a MEC continuous reactor was proposed, which describes the complex dynamics of MEC through a set of nonlinear differential equations. Until now, no model-based control approaches for MEC have been proposed. For optimal and robust output control of a continuous-reactor MEC system, we linearize the model to state a linear time-invariant (LTI) state-space representation at the nominal operating point. The LTI model is used to design four different types of controllers. The designed controllers and systems are simulated, and their performances are evaluated and compared for various operating conditions. Our findings show that a structured linear fractional transformation (LFT)-based H ∞ control approach is much better than the other approaches against various performance parameters. The study provides numerous possibilities for control applications of continuous MEC reactor processes. [ABSTRACT FROM AUTHOR]

Summary: Microbial electrolysis cells (MECs) are one of the most promising innovation amongst bio‐electrochemical systems for biohydrogen production. A wide variety of wastewaters and organic wastes that is, sodium acetate, glucose, glycerol, domestic wastewater, sugar industries effluent, food processing wastewater, industrial wastewater, etc. can be utilized as substrates in MEC. The objective of this comprehensive review is to study the effects of reactor configuration, electrode materials, and substrates on the maximum hydrogen production rate (HPR) and columbic efficiency (CE) of the MEC system. The obtained results were summarized based on reactor configuration, substrate concentration, electrodes, applied voltage, HPR, and CE. Despite this significant progress, MEC technology still requires substantial developments to be recognized as a commercially viable technology. At the end of this review, the most promising future perspectives were also discussed which could be the appealing solutions for various problems associated with MEC technology. This review supports energy engineers and researchers to analyze the performance of various MECs for future assistance in research. [ABSTRACT FROM AUTHOR]

Summary: The microbial electrolysis cell (MEC) is an emerging technology for bioenergy production using organic wastewater. Normally, a preassimilated bio‐anode is utilized by the MEC to break down the organic content, but the formation and assimilation of microbial community at the anode surface is a time‐consuming process. This study utilized a novel unassimilated Ni‐foam anode for the first time in solar‐powered MEC for bioenergy production. Synthetic dairy manure wastewater (SDMW) was used both as substrate and an inoculum in the solar‐powered tubular MEC. The impacts of the exposed surface area of the bio‐anode on bioenergy production were evaluated by utilizing two different separation techniques (rate‐limited bio‐anode – MEC and fully exposed bio‐anode ‐ MEC). The former technique achieves a maximum methane production rate of 30.35 ± 0.03 mL/L, 14.2% more than that achieved by the later mentioned technique (26.4 ± 0.05 mL/L). Hydrogen production was approximately 800 ± 5 mm3 in both experimentations. The maximum generated current in the rate limited bio‐anode – MEC was 35.5 mA. Scanning electron microscope images confirmed the formation of rod‐shaped along with round‐shaped microbial communities on the anode surface, and, interestingly, round‐shaped bacteria were also grown on the cathode surface. The bioenergy (H2 and CH4) produced using SDMW within first 13 days of operation, along with the formation of a microbial community, was a significant success in this area and has opened up many research opportunities for producing instant bioenergy from organic waste. [ABSTRACT FROM AUTHOR]

Microbial electrolysis cell (MEC) is a fundamental type of bio-electrochemical system. MEC is a novel and emerging renewable energy technology that is based on biomass. The behavior of the MEC system is highly nonlinear due to the complexity of its dynamics. For the desired optimal production of hydrogen, feedback control of MEC processes is necessary. Due to the novelty of MEC, limited research is available on its control. Studies on linear model-based robust control of MEC processes are missing. In this article, we develop a nonlinear dynamic model for MEC, linearize this model, and calculate a linear time-invariant transfer function. Based on this linearization, a fixed-structure, optimal and robust controller is proposed to achieve a fast-settling time exhibiting no overshoot and having zero steady-state error. The robustness of the developed controller is evaluated for parameter uncertainty, measurement noise, and disturbance rejection. Batch biomass processes are fed only at the start of each process cycle. The output does not follow the desired response when the substrate or biomass is consumed. Then, the error accumulates, and it causes the control effort to increase unboundedly. The existing literature on control of fed-batch MEC processes does not consider this integral windup phenomenon. In this article, we also develop an anti-windup control strategy to eliminate the integral windup error and to avoid any possible instability or destruction. The overall conclusion of our study is that the developed robust controller achieves a faster and more robust response than the existing controllers. We provide an anti-integral windup solution to eliminate windup errors in feedback control of fed-batch MEC processes. [Display omitted] • We design an optimal robust controller for a dynamic model of microbial electrolysis cells. • We linearize the non-linear model and calculate a time-invariant transfer function. • We evaluate uncertainty, noise, and disturbance of the controller. • We develop a strategy to eliminate windup error and avoid instability. • Our controller achieves a more fast and robust response than the existing controllers. [ABSTRACT FROM AUTHOR]

• Metabolic pathways for algal biohydrogen production are discussed. • Hydrogen-producing hydrogenases and nitrogenases in microorganisms are reported. • Current innovations towards genetic modification to increase biohydrogen are reviewed. • Scaling of biohydrogen production using innovative integrated strategies is presented. • Commercial biohydrogen production projects are cited. Clean fuels play a crucial role in the industrialized world's efforts to combat greenhouse gas emissions. Among the cleanest fuels available, hydrogen stands out as it produces water as a byproduct during combustion. To ensure the sustainable generation of clean fuels, it is imperative to produce hydrogen from environmentally friendly and renewable sources. Biological processes present a promising avenue for the production of hydrogen from affordable and sustainable bio-resources, including biomass and solar energy, using diverse techniques such as direct/indirect photolysis, photo-fermentation, dark-fermentation, and Microbial electrolysis cell. This comprehensive study delves into various aspects of biological hydrogen production, encompassing discussions on microorganisms, different types of substrates and their concentrations, the role of chemical additives, and key operational parameters like temperature, pH, agitation, and insights into hydrogenase and nitrogenase properties. For light-dependent processes, the study also explores the influence of illumination systems. Furthermore, the research examines different configurations of biological processes, integrating light, dark, and photo-fermentation in two- and three-component systems. By investigating these critical factors, the study aims to shed light on optimizing biological hydrogen production. The findings offer valuable insights for advancing the sustainable and efficient utilization of clean fuels in the global effort to mitigate greenhouse gas emissions. [ABSTRACT FROM AUTHOR]