Hydrogen production from macroalgae by simultaneous dark fermentation and microbial electrolysis cell

Potential mechanisms of propionate degradation and methanogenesis in anaerobic digestion coupled with microbial electrolysis cell system: Importance of biocathode

Microbial electrolysis cells (MEC) have the potential for enhancing the efficiency of anaerobic digestion (AD). In this study, microbiological and metabolic pathways in the biocathode of anaerobic digestion coupled with microbial electrolysis cells system (AD-MEC) were revealed to separate bioanode. The biocathode efficiently degraded 90 % propionate within 48 h, leading to a methane production rate of 3222 mL·m-2·d-1. The protein and heme-rich cathodic biofilm enhanced redox capacity and facilitated interspecies electron transfer. Key acid-degrading bacteria, including Dechloromonas agitata, Ignavibacteriales bacterium UTCHB2, and Syntrophobacter fumaroxidans, along with functional proteins such as cytochrome c and e-pili, established mutualistic relationships with Methanothrix soehngenii. This synergy facilitated a multi-pathway metabolic process that converted acetate and CO2 into methane. The study sheds light on the intricate microbial dynamics within the biocathode, suggesting promising prospects for the scalable integration of AD-MEC and its potential in sustainable energy production.

Sustainable hydrogen production via microalgae: Technological advancements, economic indicators, environmental aspects, challenges, and policy implications

Hydrogen has emerged as an alternative energy source to meet the increasing global energy demand, depleting fossil fuels and environmental issues resulting from fossil fuel consumption. Microalgae-based biomass is gaining attention as a potential source of hydrogen production due to its green energy carrier properties, high energy content, and carbon-free combustion. This review examines the hydrogen production process from microalgae, including the microalgae cultivation technological process for biomass production, and the three main routes of biomass-to-hydrogen production: thermochemical conversion, photo biological conversion, and electrochemical conversion. The current progress of technological options in the three main routes is presented, with the various strains of microalgae and operating conditions of the processes. Furthermore, the economic and environmental perspectives of biomass-to-hydrogen from microalgae are evaluated, and critical operational parameters are used to assess the feasibility of scaling up biohydrogen production for commercial industrial-scale applications. The key finding is the thermochemical conversion process is the most feasible process for biohydrogen production, compared to the pyrolysis process. In the photobiological and electrochemical process, pure hydrogen can be achieved, but further process development is required to enhance the production yield. In addition, the high production cost is the main challenge in biohydrogen production. The cost of biohydrogen production for direct bio photolysis it cost around $7.24 kg-1; for indirect bio photolysis it costs around $7.54 kg-1 and for fermentation, it costs around $7.61 kg-1. Therefore, comprehensive studies and efforts are required to make biohydrogen production from microalgae applications more economical in the future.

An Overview of Microbial Fuel Cell Technology for Sustainable Electricity Production

The over-exploitation of fossil fuels and their negative environmental impacts have attracted the attention of researchers worldwide, and efforts have been made to propose alternatives for the production of sustainable and clean energy. One proposed alternative is the implementation of bioelectrochemical systems (BESs), such as microbial fuel cells (MFCs), which are sustainable and environmentally friendly. MFCs are devices that use bacterial activity to break down organic matter while generating sustainable electricity. Furthermore, MFCs can produce bioelectricity from various substrates, including domestic wastewater (DWW), municipal wastewater (MWW), and potato and fruit wastes, reducing environmental contamination and decreasing energy consumption and treatment costs. This review focuses on recent advancements regarding the design, configuration, and operation mode of MFCs, as well as their capacity to produce bioelectricity (e.g., 2203 mW/m2) and fuels (i.e., H2: 438.7 mg/L and CH4: 358.7 mg/L). Furthermore, this review highlights practical applications, challenges, and the life-cycle assessment (LCA) of MFCs. Despite the promising biotechnological development of MFCs, great efforts should be made to implement them in a real-time and commercially viable manner.

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.

Boosting hydrogen production from fermentation effluent of biomass wastes in cylindrical single-chamber microbial electrolysis cell

Microbial electrolysis cells (MECs) are considered as green technologies for H₂ production with simultaneously wastewater treatment. Low H₂ recovery and production rate are two key bottlenecks of MECs fed with real H₂ fermentation effluent of biomass wastes. This work established a 1 L cylindrical single chamber MEC and enriched electroactive anodic biofilms from cow dung compost to overcome the bottlenecks. These MEC components (platinum-coated cylindrical titanium mesh cathode and cylindrical graphite felt anode) were arranged in a concentric configuration. A high H₂ production rate of 6.26 ± 0.23 L L^-1 day^-1 with H₂ yield of 5.75 ± 0.16 L H₂ L^-1 fermentation effluent was achieved at 0.8 V. The degradation of acetate and butyrate (main components of H₂ fermentation effluent) could reach to 95.3 ± 2.1% and 78.4 ± 3.6%, respectively. The microbial community analysis for anode showed the abundance of Geobacter (22.6%), Syntrophomonas (8.7%), and Dysgonomonas (6.3%) which are responsible to complex substrate oxidation, electrical current generation, and H₂ production. These results prove the feasibility of cylindrical single-chamber MEC for high H₂ production rate and high acetate and butyrate removal from H₂ fermentation effluent.

Suppressing Methane Production to Boost High-Purity Hydrogen Production in Microbial Electrolysis Cells

Hydrogen gas (H₂) is an attractive fuel carrier due to its high specific enthalpy; moreover, it is a clean source of energy because in the combustion reaction with oxygen (O₂) it produces water as the only byproduct. The microbial electrolysis cell (MEC) is a promising technology for producing H₂ from simple or complex organics present in wastewater and solid wastes. Methanogens and non-archaeal methane (CH₄)-producing microorganisms (NAMPMs) often grow in the MECs and lead to rapid conversion of produced H₂ to CH₄. Moreover, non-archaeal methane production (NAMP) catalyzed by nitrogenase of photosynthetic bacteria was always overlooked. Thus, suppression of CH₄ production is required to enhance H₂ yield and production rate. This review comprehensively addresses the principles and current state-of-the-art technologies for suppressing methanogenesis and NAMP in MECs. Noteworthy, specific strategies aimed at the inhibition of methanogenic enzymes and nitrogenase could be a more direct approach than physical and chemical strategies for repressing the growth of methanogenic archaea. In-depth studies on the multiomics of CH₄ metabolism can possibly provide insights into sustainable and efficient approaches for suppressing metabolic pathways of methanogenesis and NAMP. The main objective of this review is to highlight key concepts, directions, and challenges related to boosting H₂ generation by suppressing CH₄ production in MECs. Finally, perspectives are briefly outlined to guide and advance the future direction of MECs for production of high-purity H₂ based on genetic and metabolic engineering and on the interspecific interactions.

Biohydrogen production using algae: Potentiality, economics and challenges

The biohydrogen production from algal biomass could ensure hydrogen's sustainability as a fuel option at the industrial level. However, some bottlenecks still need to be overcome to achieve the process's economic feasibility. This review article highlights the potential of algal biomasses for producing hydrogen with a detailed explanation of various mechanisms and enzymes involved in the production processes. Further, it discusses the impact of various experimental parameters on biohydrogen production. This article also analyses the significant challenges confronted during the overall biohydrogen production process and comprehends the recent strategies adopted to enhance hydrogen productivity. Furthermore, it gives a perception of the economic sustenance of the process. Moreover, this review elucidates the future scope of this technology and delineates the approaches to ensure the viability of hydrogen production.

Enhanced hydrogen production from water hyacinth by a combination of ultrasonic-assisted alkaline pretreatment, dark fermentation, and microbial electrolysis cell

In this study, hydrogen (H₂) production from water hyacinth (WH) was enhanced by the integration of the ultrasonic-assisted alkaline (UAA) pretreatment, dark fermentation (DF), and microbial electrolysis cell (MEC). The results showed that UAA pretreatment improved around 350% in H₂ production in the DF stage and nearly 400% in the whole process compared to un-pretreated. The H₂ yield in the DF stage reached the maximum value of 110.4 mL/g-VS at a WH concentration of 20 g-TS/L. However, high concentrations of co-produced soluble metabolite products (SMPs) and suspended solid in DF effluent adversely affected the efficiency of the MEC stage. Consequently, a WH concentration of 5 g-TS/L was optimal for the UAA-DF-MEC process that achieved the highest H₂ yield of 565.8 mL/g-VS. It suggests that other auxiliary processes (e.g., dilution, centrifugation, effective methanogen inhibition, etc.) need to be developed to further improve the H₂ production from WH via the UAA-DF-MEC process.

Mathematical modeling of dark fermentation of macroalgae for hydrogen and volatile fatty acids production

A mathematical model of H₂ and volatile fatty acids (VFAs) production via dark fermentation of particulate macroalgal substrates is presented. Carbohydrates, proteins, and lipids in the particulate substrate are convert to H₂, CO₂, and VFAs via disintegration/solubilization, hydrolysis, and acidogenesis. Hydrolysis is modeled using a combined surface-limiting model combined with a first-order reaction model to describe both microbial hydrolysis and physical solubilization. Experimental and published data obtained using Saccharina japonica as the substrate are used to calibrate and validate the model. The model prediction featured a good accuracy, with high R² of 0.912 - 0.976 for all end products. The physical solubilisation accounts for 28.4% of the total hydrolysis. By the model simulation, a H₂ production of 103.2 mL/g-VS and VFA production of 0.41 g/g-VS are found at optimum conditions of 20 g-TS/L (13.2 g-VS/L) of substrate concentration and 7.0 of initial pH.

Improvement of zero waste sustainable recovery using microbial energy generation systems: A comprehensive review

Microbial energy generation systems, i.e., bioelectrochemical systems (BESs) are promising sustainable technologies that have been used in different fields of application such as biofuel production, biosensor, nutrient recovery, wastewater treatment, and heavy metals removal. However, BESs face great challenges such as large-scale application in real time, low power performance, and suitable materials for their configuration. This review paper aimed to discuss the use of BES systems such as conventional microbial fuel cells (MFCs), as well as plant microbial fuel cell (P-MFC), sediment microbial fuel cell (S-MFC), constructed wetland microbial fuel cell (CW-MFC), osmotic microbial fuel cell (OsMFC), photo-bioelectrochemical fuel cell (PBFC), and MFC-Fenton systems in the zero waste sustainable recovery process. Firstly, the configuration and electrode materials used in BESs as the main sources to improve the performance of these technologies are discussed. Additionally, zero waste recovery process from solid and wastewater feedstock, i.e., energy recovery: electricity generation (from 12 to 26,680 mW m^-2) and fuel generation, i.e., H₂ (170 ± 2.7 L^-1 L^-1 d^-1) and CH₄ (107.6 ± 3.2 mL^-1 g^-1), nutrient recovery of 100% (PO₄³-P), and 13-99% (NH₄⁺-N), heavy metal removal/recovery: water recovery, nitrate (100%), sulfate (53-99%), and sulfide recovery/removal (99%), antibiotic, dye removal, and other product recovery are critically analyzed in this review paper. Finally, the perspective and challenges, and future outlook are highlighted. There is no doubt that BES technologies are an economical option for the simultaneous zero waste elimination and energy recovery. However, more research is required to carry out the large-scale application of BES, as well as their commercialization.

Impact factors and novel strategies for improving biohydrogen production in microbial electrolysis cells

Microbial electrolysis cell (MEC) system is an environmentally friendly method for clean biohydrogen production from a wide range of biowastes owing to low greenhouse gas emissions. This approach has relatively higher yields and lower energy costs for biohydrogen production compared to conventional biological technologies and direct water electrolysis, respectively. However, biohydrogen production efficiency and operating costs of MEC still need further optimization to realize its large-scale application.This paper provides a unique review of impact factors influencing biohydrogen production in MECs, such as microorganisms and electrodes. Novel strategies, including inhibition of methanogens, development of novel cathode catalyst, advanced reactor design and integrated systems, to enhance low-cost biohydrogen production, are discussed based on recent publications in terms of their opportunities, bottlenecks and future directions. In addition, the current challenges, and effective future perspectives towards the practical application of MECs are described in this review.

Macroalgae (Ulva reticulata) derived biohydrogen recovery through mild surfactant induced energy and cost efficient dispersion pretreatment technology

Currently identification of alternate fuel is the key area of research under progress to overcome the depletion of fossil fuels, meet the domestic and industrial requirements. Generation of hydrogen, which is a clean fuel gas can solve various environmental related problems. Extensive research is being carried out to increase production of hydrogen through different substrates. This study aims to increase the production of hydrogen from Ulva reticulata (a macroalgal biomass). Initially, the biomass is pretreated mechanically with disperser and a biosurfactant, namely rhamnolipid in order to increase the solubilization of the biomass. The rate of COD liquefaction increased from 14% to 25% with the addition of biosurfactant to the macroalgal biomass, which is further treated mechanically using a disperser. The disperser rotor speed of 12,000 rpm and the specific energy input of 1175 kJ/kg TS (Total Solids) with the disintegration time of 30 min and biosurfactant dosage of 0.075 g/g TS were considered as the optimum parameters for the effective liquefaction of the macroalgal biomass. Approximately 3500 mg/L of the biopolymers were released after the combinative pretreatment (using disperser and biosurfactant). About 80 mL biohydrogen/g COD (Chemical Oxygen Demand) was generated when the biomass was pretreated with both the disperser and biosurfactant while the biomass pretreated with the disperser alone generated just 30 mL biohydrogen/g COD and the untreated biomass generated 5 mL biohydrogen/g COD. Thus, it can be concluded that Ulva reticulata can be utilized effectively to generate biohydrogen.

Co-production of hydrogen and electricity from macroalgae by simultaneous dark fermentation and microbial fuel cell

In this study, a hybrid process of dark fermentation (DF) and microbial fuel cell (MFC), sDFMFC, was investigated for simultaneous H₂ and electricity production from Saccharina japonica in a single reactor. The sDFMFC exhibited a considerably enhanced energy recovery owing to simultaneous H₂/carboxylic acids (CAs) production by DF and electricity production by MFC consuming CAs. The co-production of H₂ and electricity was confirmed by a time course of CAs concentration in sDFMFC. An excellent energy recovery of 17.3% was obtained from S. japonica with H₂ yield of 110 mL/g-VS and maximum power density of 1.82 W/m². The sDFMFC showed a diverse microbial community for a desirable microbial conversion of organic substrates. The results indicate that sDFMFC can be a promising single reactor process to produce H₂ and electricity from various biomass feedstock with considerable cost savings while ensuring the strength of the individual DF and MFC process.

High-rate mesophilic hydrogen production from food waste using hybrid immobilized microbiome

This study examined the feasibility of dark fermentative biohydrogen production from food waste using hybrid immobilization in mesophilic condition. Among four different organic loading rates (OLRs), the highest average hydrogen production rate (HPR) of 9.82 ± 0.30 L/L-d was found at an OLR of 74.7 g hexose/L-d, which was higher than reported values from particulate feedstock in mesophilic condition. The average hydrogen yield (HY) at the condition was 1.25 ± 0.04 mol H₂/mol hexose_consumed. Whereas the average HPR and HY at an OLR 80 g hexose/L-d were 5.82 ± 0.12 L/L-d and 0.64 ± 0.02 mol H₂/mol hexose_consumed, respectively. Metabolic flux analysis showed the low HY was concurrent with the highest propionic acid and homoacetogenis. Bacterial population was shift from Clostridium sp. to non-hydrogen producers including Bifidobacterium, Bacteriodes, Olsenella, Dysgonomonas, and Dialister sp.