State-of-the-art technologies for continuous high-rate biohydrogen production

Pilot composite tubular bioreactor for outdoor photo-fermentation hydrogen production: From batch to continuous operation

A novel 70 L composite tubular photo-bioreactor was constructed, and its photo-fermentation hydrogen production characteristics of batch and continuous modes were investigated with glucose as the substrate in an outdoor environment. In the batch fermentation stage, the hydrogen production rate peaked at 37.6 mL H2/(L·h) accompanied by a high hydrogen yield of 7 mol H2/mol glucose. The daytime light conversion efficiency is 4 %, with 37 % of light energy from the sun. An optimal hydraulic retention time of 5 d was identified during continuous photo-fermentation. Under this condition, the stability of the cell concentration is maintained and more electrons can be driven to the hydrogen generation pathway while attaining a hydrogen production rate of 20.7 ± 0.9 mL H2/(L·h). The changes of biomass, volatile fatty acids concentration and ion concentration during fermentation were analyzed. Continuous hydrogen production by composite tubular photo-bioreactor offers new ideas for the large-scale deployment of photobiological hydrogen production.

A bibliometric analysis of the role of nanotechnology in dark fermentative biohydrogen production

Recently, nanoparticles have drawn a lot of interest as catalysts to enhance the effectiveness and output of biohydrogen generation processes. This review article provides a comprehensive bibliometric analysis of the significance of nanotechnology in dark fermentative biohydrogen production. The study examines the scientific literature from the database of The Web of Science© while the bibliometric investigation utilized VOSviewer© and Bibliometrix software tools to conduct the analysis. The findings revealed that a total of 232 articles focused on studying dark fermentation for hydrogen production throughout the entire duration. The extracted data was used to analyze publication trends, authorship patterns, and geographic distribution along with types and effects of nanoparticles on the microbial community responsible for dark fermentative biohydrogen production. The findings of this bibliometric analysis provide valuable insights into the advancements and achievements in the utilization of nanoparticles in the dark fermentation process used to produce biohydrogen.

Towards industrial biological hydrogen production: a review

Increased production of renewable energy sources is becoming increasingly needed. Amidst other strategies, one promising technology that could help achieve this goal is biological hydrogen production. This technology uses micro-organisms to convert organic matter into hydrogen gas, a clean and versatile fuel that can be used in a wide range of applications. While biohydrogen production is in its early stages, several challenges must be addressed for biological hydrogen production to become a viable commercial solution. From an experimental perspective, the need to improve the efficiency of hydrogen production, the optimization strategy of the microbial consortia, and the reduction in costs associated with the process is still required. From a scale-up perspective, novel strategies (such as modelling and experimental validation) need to be discussed to facilitate this hydrogen production process. Hence, this review considers hydrogen production, not within the framework of a particular production method or technique, but rather outlines the work (bioreactor modes and configurations, modelling, and techno-economic and life cycle assessment) that has been done in the field as a whole. This type of analysis allows for the abstraction of the biohydrogen production technology industrially, giving insights into novel applications, cross-pollination of separate lines of inquiry, and giving a reference point for researchers and industrial developers in the field of biohydrogen production.

Bioengineering of biowaste to recover bioproducts and bioenergy: A circular economy approach towards sustainable zero-waste environment

The inevitable need for waste valorisation and management has revolutionized the way in which the waste is visualised as a potential biorefinery for various product development rather than offensive trash. Biowaste has emerged as a potential feedstock to produce several value-added products. Bioenergy generation is one of the potential applications originating from the valorisation of biowaste. Bioenergy production requires analysis and optimization of various parameters such as biowaste composition and conversion potential to develop innovative and sustainable technologies for most effective utilization of biowaste with enhanced bioenergy production. In this context, feedstocks, such as food, agriculture, beverage, and municipal solid waste act as promising resources to produce renewable energy. Similarly, the concept of microbial fuel cells employing biowaste has clearly gained research focus in the past few decades. Despite of these potential benefits, the area of bioenergy generation still is in infancy and requires more interdisciplinary research to be sustainable alternatives. This review is aimed at analysing the bioconversion potential of biowaste to renewable energy. The possibility of valorising underutilized biowaste substrates is elaborately presented. In addition, the application and efficiency of microbial fuel cells in utilizing biowaste are described in detail taking into consideration of its great scope. Furthermore, the review addresses the significance bioreactor development for energy production along with major challenges and future prospects in bioenergy production. Based on this review it can be concluded that bioenergy production utilizing biowaste can clearly open new avenues in the field of waste valorisation and energy research. Systematic and strategic developments considering the techno economic feasibilities of this excellent energy generation process will make them a true sustainable alternative for conventional energy sources.

Enhanced anaerobic hydrogen production from cotton straws assisted by copper molybdate

Hydrogen production from dark fermentation has potential application due to its environmental friendliness, low production cost, and sustainability. However, there is still an obstacle to improving the efficiency of bioH₂ production to meet the requirements in practical applications. In this research, copper molybdates are synthesized under different pH conditions as additives to study their different influence processes during anaerobic hydrogen production from cotton straws with the pure cultural system. A series of results indicate that CuMoO₄ with appropriate experimental conditions has the highest H₂ yield at 191.3 mL/g straws at 37 °C, which is 236% higher than the control group. It can be shown that O. ethanolica 8KG-4 has an obvious accompanying with high stability and low cytotoxicity for this clean energy production system as well as the improvement of metabolic pathway. These results extend new thinking of obtaining higher H₂ yield as a biofuel in future production.

Recent updates in biohydrogen production strategies and life-cycle assessment for sustainable future

Biohydrogen (bio-H₂) is regarded as a clean, non-toxic, energy carrier and has enormous potential for transforming fossil fuel-based economy. The development of a continuous high-rate H₂ production with low-cost economics following an environmentally friendly approach should be admired for technology demonstration. Thus, the current review discusses the biotechnological and thermochemical pathways for H₂ production. Thermochemical conversion involves pyrolysis and gasification routes, while biotechnological involves light-dependent processes (e.g., direct and indirect photolysis, photo/ dark fermentation strategies). Moreover, environmentally friendly technologies can be created while utilizing renewable energy sources including lignocellulosic, wastewater, sludge, microalgae, and others, which are still being developed. Lifecycle assessment (LCA) evaluates and integrates the economic, environmental, and social performance of H₂ production from biomass, microalgae, and biochar. Moreover, system boundaries evaluation, i.e., global warming potential, acidification, eutrophication, and sensitivity analysis could lead in development of sustainable bioenergy transition with high economic and environmental benefits.

A comprehensive review on the biological conversion of lignocellulosic biomass into hydrogen: Pretreatment strategy, technology advances and perspectives

The globe has dependent on energy generation and utilization for many years; conversely, ecological concerns constrained the world to view hydrogen as an alternative for economic development. Lignocellulosic biomass is broadly accessible as a low-cost renewable feedstock and nonreactive nature; it has received a lot of consideration as a global energy source and the most attractive alternative to replace fossil natural substances for energy production. Pretreatment of lignocellulosic biomass is essential to advance its fragmentation and lower the lignin content for sustainable energy generation. This review's goal is to provide the different pretreatment strategies for enlarging the solubility and surface area of lignocellulosic biomass. The biological conversion of lignocellulosic biomass to hydrogen was reviewed and operational conditions and enhancing methods were discussed. This review summarizes the working conditions, parameters, yield percentages, techno-economic analysis, challenges, and future recommendations on the direct conversion of biomass to hydrogen.

Microbial electrolysis cells for the production of biohydrogen in dark fermentation - A review

To assess biohydrogen for future green energy, this review revisited dark fermentation and microbial electrolysis cells (MECs). Hydrogen evolution rate in mesophilic dark fermentation is as high as 192 m³ H₂/m³-d, however hydrogen yield is limited. MECs are ideal for improving hydrogen yield from carboxylate accumulated from dark fermentation, whereas hydrogen production rate is too slow in MECs. Hence, improving anode kinetic is very important for realizing MEC biohydrogen. Intracellular electron transfer (IET) and extracellular electron transfer (EET) can limit current density in MECs, which is proportional to hydrogen evolution rate. EET does not limit current density once electrically conductive biofilms are formed on anodes, potentially producing 300 A/m². Hence, IET kinetics mainly govern current density in MECs. Among parameters associated with IET kinetic, population of anode-respiring bacteria in anode biofilms, biofilm density of active microorganisms, biofilm thickness, and alkalinity are critical for current density.

Advances in the utilisation of carbon-neutral technologies for a sustainable tomorrow: A critical review and the path forward

Global industrialisation and overexploitation of fossil fuels significantly impact greenhouse gas emissions, resulting in global warming and other environmental problems. Hence, investigations on capturing, storing, and utilising atmospheric CO2 create novel technologies. Few microorganisms, microalgae, and macroalgae utilise atmospheric CO2 for their growth and reduce atmospheric CO2 levels. Activated carbon and biochar from biomasses also capture CO2. Nanomaterials such as metallic oxides, metal-organic frameworks, and MXenes illustrate outstanding adsorption characteristics, and convert CO2 to carbon-neutral fuels, creating a balance between CO2 production and elimination, thus zeroing the carbon footprint. The need for a paradigm shift from fossil fuels and promising technologies on renewable energies, carbon capture mechanisms, and carbon sequestration techniques that help reduce CO2 emissions for a better tomorrow are reviewed to achieve the world's sustainable development goals. The challenges and possible solutions with future perspectives are also discussed.

Deep eutectic solvent with Lewis acid for highly efficient biohydrogen production from corn straw

To boost saccharification and biohydrogen production efficiency from corn straw, Lewis acid enhanced deep eutectic solvent (DES) pretreatment using choline chloride/glycerol was developed. A notable enhancement of the enzymatic hydrolysis efficiency from 26.3 % to 87.0 % was acquired when corn straw was pretreated with aqueous DES at 100 °C for 5 h using 2.0 wt% AlCl₃. A maximum biohydrogen yield of 114.8 mL/g total solids (TS) was achieved in the sequential dark fermentation stage, which was 2.1 times higher than that of the raw feedstock (37.1 mL/g TS). The enhanced efficient conversion was ascribed to the effective removal of lignin and hemicellulose, which led to the bio-accessibility of the straw. This work provides new sights for the rational design of efficient AlCl₃-aided aqueous DES system toward biohydrogen production from lignocellulosic biomass.

Critical challenges and technological breakthroughs in food waste hydrolysis and detoxification for fuels and chemicals production

Organic waste has increased as the global population and economy have grown exponentially. Food waste (FW) is posing a severe environmental issue because of mismanaged disposal techniques, which frequently result in the squandering of carbohydrate-rich feedstocks. In an advanced valorization strategy, organic material in FW can be used as a viable carbon source for microbial digestion and hence for the generation of value-added compounds. In comparison to traditional feedstocks, a modest pretreatment of the FW stream utilizing chemical, biochemical, or thermochemical techniques can extract bulk of sugars for microbial digestion. Pretreatment produces a large number of toxins and inhibitors that affect bacterial fuel and chemical conversion processes. Thus, the current review scrutinizes the FW structure, pretreatment methods (e.g., physical, chemical, physicochemical, and biological), and various strategies for detoxification before microbial fermentation into renewable chemical production. Technological and commercial challenges and future perspectives for FW integrated biorefineries have also been outlined.

Membrane-based technologies for biohydrogen production: A review

Overcoming the existing environmental issues and the gradual depletion of energy sources is a priority at global level, biohydrogen can provide a sustainable and reliable energy reserve. However, the process instability and low biohydrogen yields are still hindering the adoption of biohydrogen production plants at industrial scale. In this context, membrane-based biohydrogen production technologies, and in particular fermentative membrane bioreactors (MBRs) and microbial electrolysis cells (MECs), as well as downstream membrane-based technologies such as electrodialysis (ED), are suitable options to achieve high-rate biohydrogen production. We have shed the light on the research efforts towards the development of membrane-based technologies for biohydrogen production from organic waste, with special emphasis to the reactor design and materials. Besides, techno-economic analyses have been traced to ensure the suitability of such technologies in bio-H₂ production. Operation parameters such as pH, temperature and organic loading rate affect the performance of MBRs. MEC and ED technologies also are highly affected by the chemistry of the membrane used and anode material as well as the operation parameters. The limitations and future directions for application of membrane-based biohydrogen production technologies have been individuated. At the end, this review helps in the critical understanding of deploying membrane-based technologies for biohydrogen production, thereby encouraging future outcomes for a sustainable biohydrogen economy.

Intensification of Acidogenic Fermentation for the Production of Biohydrogen and Volatile Fatty Acids—A Perspective

Utilising ‘wastes’ as ‘resources’ is key to a circular economy. While there are multiple routes to waste valorisation, anaerobic digestion (AD)—a biochemical means to breakdown organic wastes in the absence of oxygen—is favoured due to its capacity to handle a variety of feedstocks. Traditional AD focuses on the production of biogas and fertiliser as products; however, such low-value products combined with longer residence times and slow kinetics have paved the way to explore alternative product platforms. The intermediate steps in conventional AD—acidogenesis and acetogenesis—have the capability to produce biohydrogen and volatile fatty acids (VFA) which are gaining increased attention due to the higher energy density (than biogas) and higher market value, respectively. This review hence focusses specifically on the production of biohydrogen and VFAs from organic wastes. With the revived interest in these products, a critical analysis of recent literature is needed to establish the current status. Therefore, intensification strategies in this area involving three main streams: substrate pre-treatment, digestion parameters and product recovery are discussed in detail based on literature reported in the last decade. The techno-economic aspects and future pointers are clearly highlighted to drive research forward in relevant areas.

A 3D-Printed Customizable Platform for Multiplex Dynamic Biofilm Studies

Biofilms are communities of microbes that colonize surfaces. While several biofilm experimental models exist, they often have limited replications of spatiotemporal dynamics surrounding biofilms. For a better understanding dynamic and complex biofilm development, this manuscript presents a customizable platform compatible with off-the-shelf well plates that can monitor microbial adhesion, growth, and associated parameters under various relevant scenarios by taking advantage of 3D printing. The system i) holds any substrate in a stable, vertical position, ii) subjects samples to flow at different angles, iii) switches between static and dynamic modes during an experiment, and iv) allows multiplexing and real-time monitoring of biofilm parameters. Simulated fluid dynamics is employed to estimate flow patterns around discs and shear stresses at disc surfaces. A 3D printed peristaltic pump and a customized pH measurement system for real-time tracking of spent biofilm culture media are equipped with a graphical user interface that grants control over all experimental parameters. The system is tested under static and dynamic conditions with Streptococcus mutans using different carbon sources. By monitoring the effluent pH and characterizing biochemical, microbiological, and morphological properties of cultured biofilms, distinct properties are demonstrated. This novel platform liberates designing experimental strategies for investigations of biofilms under various conditions.

Novel strategies towards efficient molecular biohydrogen production by dark fermentative mechanism: present progress and future perspective

In the scenario of alarming increase in greenhouse and toxic gas emissions from the burning of conventional fuels, it is high time that the population drifts towards alternative fuel usage to obviate pollution. Hydrogen is an environment-friendly biofuel with high energy content. Several production methods exist to produce hydrogen, but the least energy intensive processes are the fermentative biohydrogen techniques. Dark fermentative biohydrogen production (DFBHP) is a value-added, less energy-consuming process to generate biohydrogen. In this process, biohydrogen can be produced from sugars as well as complex substrates that are generally considered as organic waste. Yet, the process is constrained by many factors such as low hydrogen yield, incomplete conversion of substrates, accumulation of volatile fatty acids which lead to the drop of the system pH resulting in hindered growth and hydrogen production by the bacteria. To circumvent these drawbacks, researchers have come up with several strategies that improve the yield of DFBHP process. These strategies can be classified as preliminary methodologies concerned with the process optimization and the latter that deals with pretreatment of substrate and seed sludge, bioaugmentation, co-culture of bacteria, supplementation of additives, bioreactor design considerations, metabolic engineering, nanotechnology, immobilization of bacteria, etc. This review sums up some of the improvement techniques that profoundly enhance the biohydrogen productivity in a DFBHP process.

Coupled Biohydrogen Production and Bio-Nanocatalysis for Dual Energy from Cellulose: Towards Cellulosic Waste Up-Conversion into Biofuels

Hydrogen, an emergent alternative energy vector to fossil fuels, can be produced sustainably by fermentation of cellulose following hydrolysis. Fermentation feedstock was produced hydrolytically using hot compressed water. The addition of CO2 enhanced hydrolysis by ~26% between 240 and 260 °C with comparable hydrolysis products as obtained under N2 but at a 10 °C lower temperature. Co-production of inhibitory 5-hydromethyl furfural was mitigated via activated carbon sorption, facilitating fermentative biohydrogen production from the hydrolysate by Escherichia coli. Post-fermentation E. coli cells were recycled to biomanufacture supported Pd/Ru nanocatalyst to up-convert liquid-extracted 5-HMF to 2,5-dimethyl furan, a precursor of ‘drop in’ liquid fuel, in a one-pot reaction. This side stream up-valorisation mitigates against the high ‘parasitic’ energy demand of cellulose bioenergy, potentially increasing process viability via the coupled generation of two biofuels. This is discussed with respect to example data obtained via a hydrogen biotechnology with catalytic side stream up-conversion from cellulose feedstock.

Simultaneous biogas upgrading and biogas slurry treatment by different microalgae-based technologies under various strigolactone analog (GR24) concentrations

In this research, the effects of exogenous strigolactone analog (GR24) on the growth rate, daily productivity and photosynthesis of symbiotes of Chlorella vulgaris (C. vulgaris)-Ganoderma lucidum (G. lucidum)-endophytic bacteria, C. vulgaris-G. lucidum-activated sludge and C. vulgaris-G. lucidum-multi-walled carbon nanotube, and the simultaneous treatment of biogas slurry and biogas were examined. The C. vulgaris-G. lucidum-endophytic bacteria symbiote achieved the best treatment effectiveness for biogas slurry and biogas, with removal efficiencies of chemical oxygen demand, total nitrogen, total phosphorus and CO₂ of 81.4 ± 7.6%, 79.6 ± 7.6%, 82.5 ± 8.2%, and 67.3 ± 6.3% under the optimal GR24 concentration of 10^-9 M. Moreover, the treatment effects were positively correlated with growth performance and photosynthesis efficiency of the symbiote. These findings advance the development and application of symbiotic systems in the field of wastewater treatment and biogas upgrading.

BioH2 from Dark Fermentation of OFMSW: Effect of the Hydraulic Retention Time and Organic Loading Rate

Food wastes represent one third of all food produced worldwide. It is crucial to both prevent the production of food waste and recover the wasted fraction with the aim to valorizing it. In this context, the conversion of the organic fraction of municipal solid wastes (OFMSW) into bioH2 by dark fermentation (DF) is an important technology to valorize these wastes into renewable fuel. Nevertheless, the DF of OFMSW needs to be optimized for critical operational parameters. The main purposes of this study were to investigate (i) the effect of HRT during continuous bioH2 production through DF and (ii) the effect of organic loading rate (OLR) ruled by HRT. In this work, three HRTs (4, 5, and 6 d) were tested in a mesophilic continuous stirred-tank reactor (CSTR). The HRTs of 4, 5, and 6 days, corresponding to OLRs of 23.6, 18.0, and 10.6 g volatile solids (VS)·L−1·d−1, respectively, showed bioH2 yields of 8.48, 18.2, and 1.64 L·kg−1 VSinfluent with an H2 content of approximately 25, 32, and 5% v/v, respectively. An accumulation of volatile fatty acids (VFAs) was registered with the decrease in HRT, causing a decrease in bioH2 production. The 5 d HRT was the most favorable condition.

Thermal Design of a Biohydrogen Production System Driven by Integrated Gasification Combined Cycle Waste Heat Using Dynamic Simulation

Utilizing biological processes for hydrogen production via gasification is a promising alternative method to coal gasification. The present study proposes a dynamic simulation model that uses a one-dimensional heat-transfer analysis method to simulate a biohydrogen production system. The proposed model is based on an existing experimental design setup. It is used to simulate a biohydrogen production system driven by the waste heat from an integrated gasification combined cycle (IGCC) power plant equipped with carbon capture and storage technologies. The data from the simulated results are compared with the experimental measurement data to validate the developed model’s reliability. The results show good agreement between the experimental data and the developed model. The relative root-mean-square error for the heat storage, feed-mixing, and bioreactor tanks is 1.26%, 3.59%, and 1.78%, respectively. After the developed model’s reliability is confirmed, it is used to simulate and optimize the biohydrogen production system inside the IGCC power plant. The bioreactor tank’s time constant can be improved when reducing the operating volume of the feed-mixing tank by the scale factors of 0.75 and 0.50, leading to a 15.76% and 31.54% faster time constant, respectively, when compared with the existing design.

Regulation and augmentation of anaerobic digestion processes via the use of bioelectrochemical systems

Anaerobic digestion (AD) is a biological process that can be used to treat a wide range of carbon-rich wastes and producerenewable, green energy. To maximize energy recovery from various resources while controlling inhibitory chemicals, notwithstanding AD's efficiency, many limitations must be addressed. As a result, bioelectrochemical systems (BESs) have emerged as a hybrid technology, extensively studied to remediate AD inhibitory chemicals, increase AD operating efficacy, and make the process economically viable via integration approaches. Biogas and residual intermediatory metabolites such as volatile fatty acids are upgraded to value-added chemicals and fuels with the help of the BES as a pre-treatment step, within AD or after the AD process. It may also be used directly to generate power. To overcome the constraints of AD in lab-scale applications, this article summarizes BES technology and operations and endorses ways to scale up BES-AD systems in the future.

Effects of temperature and total solid content on biohydrogen production from dark fermentation of rice straw: Performance and microbial community characteristics

Semi-continuous experiments were carried out in lab-scale continuous stirred tank reactors to evaluate the effects of fermentation temperature (37 ± 1 °C and 55 ± 1 °C) and total solids (TS) contents (3 %, 6 %, and 12 %) on biohydrogen production from the dark fermentations (DF) of rice straw (RS) and the total operation duration was 105 days. The experimental results show that biohydrogen production (0.46-63.60 mL/g VS_added) from the thermophilic (55 ± 1 °C) DF (TDF) was higher than the mesophilic (37 ± 1 °C) DF (MDF) (0.19-2.13 mL/g VS_added) at the three TS contents, and achieved the highest of 63.60 ± 2.98 mL/g VS_added at TS = 6 % in TDF. The pH, NH₄⁺-N and total volatile fatty acid of fermentation liquids in the TDF were all higher than those in the MDF. The high abundance of lactic acid-producing bacteria resulted in low biohydrogen produced at TS = 3 %. Under the TDF with TS = 6 %, the highest abundance of hydrolytic bacteria (Ruminiclostridium 54.24 %) led to the highest biohydrogen production. The increase of TS content from 6 % to 12 % induced degradation pathway changes from biohydrogen production to methane production. This study demonstrated that butyric acid fermentation was the main pathway to produce biohydrogen from RS in both DFs.

Emerging technologies for sustainable production of biohydrogen production from microalgae: A state-of-the-art review of upstream and downstream processes

Biohydrogen (BioH₂) is considered as one of the most environmentally friendly fuels and a strong candidate to meet the future demand for a sustainable source of energy. Presently, the production of BioH₂ from photosynthetic organisms has raised a lot of hopes in the fuel industry. Moreover, microalgal-based BioH₂ synthesis not only helps to combat current global warming by capturing greenhouse gases but also plays a key role in wastewater treatment. Hence, this manuscript provides a state-of-the-art review of the upstream and downstream BioH₂ production processes. Different metabolic routes such as direct and indirect photolysis, dark fermentation, photofermentation, and microbial electrolysis are covered in detail. Upstream processes (e.g. growth techniques, growth media) also have a great impact on BioH₂ productivity and economics, which is also explored. Technical and scientific obstacles of microalgae BioH₂ systems are finally addressed, allowing the technology to become more innovative and commercial.

Effect of genus Clostridium abundance on mixed-culture fermentation converting food waste into biohydrogen

This study examined the effect of various inocula on mixed-culture dark fermentative H₂ production from food waste. Heat-treated and frozen H₂-producing granular sludge (HPG) grown with monomeric sugars showed a higher H₂ yield, production rate, and acidogenic efficiency along with a shorter lag phase than heat-treated methanogenic sludge. Among three different methods of methanogenic sludge inoculation, inoculation after centrifugation showed better H₂ production performance. Propionic acid production and homoacetogenesis were regarded as major H₂-consuming pathways when methanogenic sludge was used, whereas only homoacetogenesis was found in HPG-inoculated fermentation. During fermentation, the abundance of Clostridium increased greater than 48-fold for methanogenic sludge and greater than 108-fold for HPG, respectively. The initial abundance of Clostridium showed a linear relationship with the H₂ production rate and lag-phase time. The use of inoculum with a high abundance of Clostridium is essential for H₂ production from food waste.

Renewable hydrogen production from biomass and wastes (ReBioH2-2020)

Growing consumption of fossil reserves to meet the rising demand of energy has led to climate deterioration and simultaneous waste generation, urging modern society to find sustainable energy resource that can meet the growing energy demands and reduce greenhouse gas emissions and carbon footprints. In this aspect, hydrogen (H₂) is one of the most promising sustainable clean fuels that has gained significant interest in recent years. This article highlights the major research progress on biohydrogen production from renewable bioresources such as organic wastes, lignocellulosic biomass, algal biomass, and industrial wastewaters. It summarizes the research highlights of manuscripts published in the special issue (VSI: ReBioH2-2020), which contains twenty-two articles, including seven critical reviews and fifteen research articles, focusing on biotechnological and thermochemical routes for biohydrogen production from renewable feedstocks. The major findings of the research works in this special issue can be used as a road-map for sustainable renewable hydrogen production from bioresources.

Electro-fermentation for biofuels and biochemicals production: Current status and future directions

Electro-fermentation is an emerging bioporcess that could regulate the metabolism of electrochemically active microorganisms. The provision of electrodes for the fermentation process that functions as an electron acceptor and supports the formation and transportation of electrons and protons, consequently producing bioelectricity and value-added chemicals. The traditional method of fermentation has several limitations in usability and economic feasibility. Subsequently, a series of metabolic processes occurring in conventional fermentation processes are most often redox misaligned. In this regard, electro-fermentation emerged as a hybrid technology which can regulate a series of metabolic processes occurring in a bioreactor by regulating the redox instabilities and boosting the overall metabolic process towards high biomass yield and enhanced product formation. The present article deals with microorganisms-electrode interactions, various types of electro-fermentation systems, comparative evaluation of pure and mixed culture electro-fermentation application, and value-added fuels and chemical synthesis.

Biohydrogen from Microalgae: Production and Applications

The need to safeguard our planet by reducing carbon dioxide emissions has led to a significant development of research in the field of alternative energy sources. Hydrogen has proved to be the most promising molecule, as a fuel, due to its low environmental impact. Even if various methods already exist for producing hydrogen, most of them are not sustainable. Thus, research focuses on the biological sector, studying microalgae, and other microorganisms’ ability to produce this precious molecule in a natural way. In this review, we provide a description of the biochemical and molecular processes for the production of biohydrogen and give a general overview of one of the most interesting technologies in which hydrogen finds application for electricity production: fuel cells.