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This review comprehensively examines the various applications of microalgae, focusing on their significant potential in producing biodiesel and hydrogen, serving as sustainable food sources, and their efficacy in treating both municipal and food-related wastewater. While previous studies have mainly focused on specific applications of microalgae, such as biofuel production or wastewater treatment, this review covers these applications comprehensively. It examines the potential for microalgae to be applied in various industrial sectors such as energy, food security, and environmental management. By bridging these different application areas, this review differs from previous studies in providing an integrated and multifaceted view of the industrial applications of microalgae. Since it is essential to increase the productivity of the process to utilize microalgae for various industrial applications, research trends in different microalgae cultivation processes, including the culture system (e.g., open ponds, closed ponds) or environmental conditions (e.g., pH, temperature, light intensity) to improve the productivity of biomass and valuable substances was firstly analyzed. In addition, microalgae cultivation technologies that can maximize the biomass and valuable substances productivity while limiting the potential for contamination that can occur when utilizing these systems have been described to maximize CO2 reduction. In conclusion, this review has provided a detailed analysis of current research findings and technological innovations, highlighting the important role of microalgae in addressing global challenges related to energy, food supply, and waste management. It has also provided valuable insights into future research directions and potential commercial applications in several bio-related industries, and illustrated how important continued exploration and development in this area is to realize the full potential of microalgae. [ABSTRACT FROM AUTHOR]

The development and implementation of innovative production technologies have a direct influence on the creation of new sources of pollution and types of waste. An example of this is the wastewater from soil-less agriculture and the effluent from microbial fuel cells. An important topic is the development and application of methods for their neutralisation that take into account the assumptions of global environmental policy. The aim of the present study was to determine the possibilities of utilising this type of pollution in the process of autotrophic cultivation of the biohydrogen-producing microalgae Tetraselmis subcordiformis. The highest biomass concentration of 3030 ± 183 mgVS/L and 67.9 ± 3.5 mg chl-a/L was observed when the culture medium was wastewater from soil-less agriculture. The growth rate in the logarithmic growth phase was 270 ± 16 mgVS/L-day and 5.95 ± 0.24 mg chl-a/L-day. In the same scenario, the highest total H2 production of 161 ± 8 mL was also achieved, with an observed H2 production rate of 4.67 ± 0.23 mL/h. Significantly lower effects in terms of biomass production of T. subcordiformis and H2 yield were observed when fermented dairy wastewater from the anode chamber of the microbial fuel cell was added to the culture medium. [ABSTRACT FROM AUTHOR]

The Gompertz model has been extensively employed in describing biohydrogen kinetics. In this study, the Gompertz model, including its origins, modifications, application for describing biohydrogen kinetics, and solving methods, was explored in detail. The Gompertz model has undergone modifications to enhance its applicability in biological processes. The Lay-modified Gompertz model, tailored explicitly for modeling bioproduction, demonstrates versatility in predicting crucial factors, contributing to a deeper understanding of production efficiency. The applications of this model in biohydrogen production were summarized. Additionally, the solving methods for the Gompertz model were presented for different software platforms, in which Microsoft Excel, Origin, SigmaPlot, and GraphPad Prism offer user-friendly interfaces. The MATLAB-based method is more versatile, allowing users to solve the Gompertz model without the need for relatively accurate initial parameter values. The Excel sheet and MATLAB file are provided in Supplementary Material. This study enhances the understanding and practical application of the Gompertz model in describing biohydrogen production kinetics. [Display omitted] • Origins/development of the Gompertz model are studied to illuminate its evolution. • Extension of the Gompertz model to biohydrogen production kinetics is explained. • User-friendly methods for solving the model are provided to enhance its accessibility. • Recent applications of the Gompertz model in biohydrogen kinetics are summarized. [ABSTRACT FROM AUTHOR]

Abstract Biofuel can be generated by different organisms using various substrates. The green alga Chlorococcum humicola OQ934050 exhibited the capability to photosynthesize carbonate carbon, maybe via the activity of carbonic anhydrase enzymes. The optimum treatment is C:N ratio of 1:1 (0.2 mmoles sodium carbonate and 0.2 mmoles sodium nitrate) as it induced the highest dry mass (more than 0.5 mg.mL−1). At this combination, biomass were about 0.2 mg/mL−1 carbohydrates, 0.085 mg/mL−1 proteins, and 0.16 mg/mL−1 oil of this dry weight. The C/N ratios of 1:1 or 10:1 induced up to 30% of the Chlorococcum humicola dry mass as oils. Growth and dry matter content were hindered at 50:1 C/N and oil content was reduced as a result. The fatty acid profile was strongly altered by the applied C.N ratios. The defatted leftovers of the grown alga, after oil extraction, were fermented by a newly isolated heterotrophic bacterium, identified as Bacillus coagulans OQ053202, to evolve hydrogen content as gas. The highest cumulative hydrogen production and reducing sugar (70 ml H2/g biomass and 0.128 mg/ml; respectively) were found at the C/N ratio of 10:1 with the highest hydrogen evolution efficiency (HEE) of 22.8 ml H2/ mg reducing sugar. The optimum treatment applied to the Chlorococcum humicola is C:N ratio of 1:1 for the highest dry mass, up to 30% dry mass as oils. Some fatty acids were induced while others disappeared, depending on the C/N ratios. The highest cumulative hydrogen production and reducing sugar were found at the C/N ratio of 10:1.

Biofuel can be generated by different organisms using various substrates. The green alga Chlorococcum humicola OQ934050 exhibited the capability to photosynthesize carbonate carbon, maybe via the activity of carbonic anhydrase enzymes. The optimum treatment is C:N ratio of 1:1 (0.2 mmoles sodium carbonate and 0.2 mmoles sodium nitrate) as it induced the highest dry mass (more than 0.5 mg.mL−1). At this combination, biomass were about 0.2 mg/mL−1 carbohydrates, 0.085 mg/mL−1 proteins, and 0.16 mg/mL−1 oil of this dry weight. The C/N ratios of 1:1 or 10:1 induced up to 30% of the Chlorococcum humicola dry mass as oils. Growth and dry matter content were hindered at 50:1 C/N and oil content was reduced as a result. The fatty acid profile was strongly altered by the applied C.N ratios. The defatted leftovers of the grown alga, after oil extraction, were fermented by a newly isolated heterotrophic bacterium, identified as Bacillus coagulans OQ053202, to evolve hydrogen content as gas. The highest cumulative hydrogen production and reducing sugar (70 ml H2/g biomass and 0.128 mg/ml; respectively) were found at the C/N ratio of 10:1 with the highest hydrogen evolution efficiency (HEE) of 22.8 ml H2/ mg reducing sugar. The optimum treatment applied to the Chlorococcum humicola is C:N ratio of 1:1 for the highest dry mass, up to 30% dry mass as oils. Some fatty acids were induced while others disappeared, depending on the C/N ratios. The highest cumulative hydrogen production and reducing sugar were found at the C/N ratio of 10:1. [ABSTRACT FROM AUTHOR]

Extremophilic microorganisms play a key role in understanding how life on Earth originated and evolved over centuries. Their ability to thrive in harsh environments relies on a plethora of mechanisms developed to survive at extreme temperatures, pressures, salinity, and pH values. From a biotechnological point of view, thermophiles are considered a robust tool for synthetic biology as well as a reliable starting material for the development of sustainable bioprocesses. This review discusses the current progress in the biomanufacturing of high-added bioproducts from thermophilic microorganisms and their industrial applications. [ABSTRACT FROM AUTHOR]

The biohydrogen production in Dark fermentation (DF) could be enhanced by ZnFe 2 O 4 nanomaterials (NPs). The optimum conditions were obtained by a response surface method. Eventually, a biohydrogen production of 2645 mL/L was obtained after 48 h of batch culture, which is 116% higher than control without ZnFe 2 O 4 NPs. The mechanism was investigated by a multi-scale method. In bioreactor scale, ZnFe 2 O 4 NPs could enhance the glucose metabolic ability of C. pasteurianum to promote cell growth and biohydrogen production. The metabolic pathways of biohydrogen production were shifted from the butyric acid-type to the ethanol-type. In cellular scale, ZnFe 2 O 4 NPs could reduce bacterial flagella assembly. In macromolecule scale, the activities of hydrogenase and ethanol dehydrogenase were increased. In genetic scale, the differentially expressed genes mainly involved in biohydrogen production, like those encoded Fe-only hydrogenase, ethanol dehydrogenase, and nitrogenase were up-regulated. The results could provide theoretical and technical supports for the development of commercial biohydrogen process. • ZnFe2O4 NPs can effectively promote biohydrogen production. • Optimal enhancement conditions determined through response surface optimization. • ZnFe2O4 NPs enhance glucose utilization by C. pasteurianum. • ZnFe2O4 NPs boost hydrogenase & ethanol dehydrogenase in C. pasteurianum. • Mechanism of NPs promoting biohydrogen production revealed by multi-scale analysis. [ABSTRACT FROM AUTHOR]

Anaerobic fermentation has attracted wide attention to effectively reduce carbon footprint and alleviate potential energy shortages, which is being regarded as a sustainable and promising technology to obtain high biohydrogen production from widespread organic wastes. However, biohydrogen commercial uptake is now dominantly inhibited by the low hydrogen yield and process instability. In this work, Al 2 O 3 /BaFe 2 O 4 nanoparticles (NPs) are successfully applied to anaerobic fermentation for investigating their effects on hydrogen yield, activity of bacteria and microbial community structure. The benefits of Al 2 O 3 /BaFe 2 O 4 NPs with respect to microbial metabolism, reactivity of enzymes and process optimization are systematically researched through batch experiments. In addition, various characterizations are used to verify the physical and chemical properties of Al 2 O 3 /BaFe 2 O 4 NPs. The results show that the activity of hydrogenases and microbe metabolism can be significantly inhibited by excess addition of Al 2 O 3 /BaFe 2 O 4 NPs (150 mg/L and 200 mg/L) while the optimum addition 100 mg/L of Al 2 O 3 /BaFe 2 O 4 NPs can boost the biohydrogen yield by 49% via facilitating microorganism growth and enhancing key enzymatic activities, which indicate that the Al 2 O 3 /BaFe 2 O 4 NPs display a beneficial influence on electron transfer efficiency and process stability. The existence of Fe3+, Al3+and Ba2+ derived from the corrosion of Al 2 O 3 /BaFe 2 O 4 NPs by organic acids synergistically improve the microbial transmembrane transportation and substrate utilization, which contribute to higher conversion rate of glucose into acetate, butyrate and H 2. Meanwhile, the complementary functions of Fe3+ and Al3+ can powerfully shorten the lag phase and promote the glycolysis, which finally accelerate the dark fermentation process. Compared with the control group, Clostridium _ sensu _ stricto _1 is selectively enriched by the addition of Al 2 O 3 /BaFe 2 O 4 NPs, which keep heavily involved in the synthesis of H 2. On balance, this study provides an effective strategy to enhance hydrogen productivity and maintain process stability, which offer the valuable information for the sustainable utilization of sewage sludge. [Display omitted] • Al 2 O 3 /BaFe 2 O 4 NPs are synthesized to enhance H 2 production. • Al 2 O 3 /BaFe 2 O 4 NPs show positive effects on activity of H 2 -producing bacteria. • The addition of Al 2 O 3 /BaFe 2 O 4 NPs can facilitate H 2 -producing bacteria growth. • Humic acids are reduced by addition of Al 2 O 3 /BaFe 2 O 4 NPs. • Firmicutes and Clostridium_sensu_stricto_ 1 are selectively enriched by Al 2 O 3 /BaFe 2 O 4 NPs. [ABSTRACT FROM AUTHOR]

The present work studied the effects of alkali pretreatment on the cellulosic biomass of rice straw. The improvement in the cellulose content and reduction in the lignin and hemicellulose percentage was observed with alkali pretreatment. Fourier transformation infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM) analysis confirm the modification in the surface structure of alkali rice straw. Further, the study investigated the potential of different types of seed sludge as inoculum sources for dark fermentative biohydrogen production. In comparison to other sludge samples (beverage industry, food industry, and sewage treatment plant sludge), the mixed culture of sewage treatment plant sludge had the highest cumulative volume of biohydrogen (90.52 mL), as well as the highest hydrogen production yield (0.75 moleH2/mole) with the substrate utilization of 86.72%. The results provide information on the best sludge source for enhancing biohydrogen production in the dark fermentation method. [ABSTRACT FROM AUTHOR]

Hydrogen is ideal for replacing fossil fuels because upon combustion it generates only water. Dark fermentation (DF) from lignocellulose might be a competitive process for hydrogen production at the industrial scale. However, lignocellulose must be pretreated to obtain fermentable sugars, which is costly and creates pollution. Microorganisms from bovine rumen efficiently degrade lignocellulose. Unfortunately, they have scarcely been explored for the production of hydrogen. Therefore, deeper studies on the culture conditions have to be undertaken to understand the behavior of microbial consortia from the rumen of bovines (MCRB) during hydrogen production. In this work, we evaluated the production of hydrogen by DF with MCRB by varying the incubation time, two culture media (MB and Rhodospirillaceae), headspace (40 and 80 mL), and thermal treatment. It was found that the production of hydrogen was maximum at 16 h MCRB incubation in MB. An amount of 80 mL headspace resulted in a threefold production of hydrogen as compared to 40 mL; the MCRB without heat treatment had a higher H2 yield. The production of hydrogen with 32 MCRB was highly variable, ranging between 21 and 696 mL. Our findings show a different perspective on the treatment of MCRB for the production of hydrogen and give insights on the impact of the culture conditions for increasing hydrogen production. [ABSTRACT FROM AUTHOR]

In the context of valorizing the organic fraction of urban solid waste (OFMSW) in megacities, dark fermentation emerges as a central strategy alongside composting and anaerobic digestion. This article focuses on assessing the environmental, technical, and energy viability of dark fermentation using life cycle assessment (LCA) and circular economy principles. Dark fermentation for biohydrogen production is an active and promising research field in the quest for sustainable biofuels. In this context, defining operational parameters such as organic loading and the substrate-inoculum ratio is relevant for achieving better production yields. Laboratory tests were conducted using organic loading values of 5, 10, and 15 g of volatile solids per liter (gVS/L) and with substrate-inoculum ratios (s/x) of 1, 0.75, and 0.5 g of volatile solids of substrate per gram of volatile solids of inoculum (gVSs/gVSi). The combination with the best performance turned out to be an initial organic loading of 10 gVS/L and an s/x of 1 gVSs/gVSi. From this result, it was determined that the s/x had a greater impact on production. Finally, a valorization plant was dimensioned with the scaled-up process, starting from the municipal solid waste generated by Bogotá projected for 2042. The scaling was demonstrated to be energetically sustainable, producing a power of 2,368,358.72 kWh per day. [ABSTRACT FROM AUTHOR]

Microbial electrolysis cells (MECs) are emerging sustainable power generation technologies that can be used for biohydrogen production and wastewater treatment. The prospect for hydrogen gas as a vehicle fuel suitable for the environment is enormous. MEC serves as a reactor for producing biohydrogen by mixing MFC with electrolysis. MECs are the most sustainable, clean, and effective ways to produce biohydrogen. Effective aspects impacting H 2 production, including microbial culture, electrodes, membrane, and substrate, have been explored for greater comprehension of creating MEC technology-based hydrogen generation. The present issues with effective scale-up include the costly production expenses of microbial electrolysis cells, their significant internal resistance, methanogenesis, and membrane/cathode biofouling. This review examines the various operational parameters in optimization studies that influence overall hydrogen generation. This paper also presents strategies to overcome the constraints listed above by creating effective architecture, including several reactor designs, biological, and physical properties, and the use of various operational conditions for improved hydrogen production. This study summarizes recent developments and several other operating factors (organic loading, ionic strength, hydraulic retention time, applied voltage, etc.) that affect hydrogen production in an MEC system. The paper outlines the present technical difficulties and offers practical future ideas for addressing the constraints. [Display omitted] • MEC has great efficiency in hydrogen recovery and concurrent waste conversion. • Microbial culture, electrodes, membrane, and substrate affect H 2 production in MEC. • Scale-up constraints: high costs, internal resistance, methanogenesis, and biofouling. • Modifying strain, nanoparticles, and reactor design can help in overcoming this. [ABSTRACT FROM AUTHOR]

Biohydrogen (H 2) production by green algae has great biotechnological potential. This study aimed to analyze photosynthetic pigment levels, photosynthetic systems activity, total phenolic/flavonoid content, and H 2 generation in Chlorella vulgaris IBCE C-19 and Parachlorella kessleri MDC6524 in response to sulfur (S) and nitrogen (N) deprivation. The results showed that S and N deficiency caused a growth rate decrease in both cultures that was accompanied by a decrease in the photosynthetic pigments levels, PS II activity, and polyphenols synthesis. In addition, S and N deprivation led to an increase in the H 2 generation. Moreover, the H 2 photoproduction by P. kessleri was higher compared to that of C. vulgaris under N- and S-deprived anaerobic conditions. DCMU inhibited the H 2 production by both algae showing the involvement of PS II in this process. The findings contribute to the ongoing research on the development of strategies to optimize algae cultivation for enhanced H 2 yield. • N and S deprivation leads to a decrease in pigments content and PS II activity. • N and S starvation increases H 2 generation in Parachlorella and Chlorella cultures. • P. kessleri produce more H 2 than C. vulgaris under N- and S-deprived conditions. • DCMU inhibited H 2 production by green algae under N- and S-deprived conditions. [ABSTRACT FROM AUTHOR]

This paper concerns the design, development, and building of a unique electro-bio-membrane reactor for concurrent bioH 2 production, desalination, and energy production by microorganisms in a single reactor. The effects of varying biomass amounts (5–50 g) and inoculum amounts (250–1500 mL) on the bioH 2 production efficiency are also investigated. The lowest cumulative bioH 2 yield of 24.2 mL/g is obtained using a biomass amount of 5 g, while it is 44.7 mL/g at a biomass amount of 50 g. The highest H 2 production from water electrolysis is also found as 0.719 mL/min at improved conditions. Furthermore, the highest power and current density values are 2794.5 mW/m2 and 2786.1 mA/m2 at 1500 mL-inoculum, biomass amount of 30 g, initial pH of 5.5, and temperature of 37 °C in the dark fermentation (DF) cell. Moreover, the desalination efficiency increases from 41.6 to 65.8% with decreasing inoculum amounts from 1500 to 250 mL. [Display omitted] [ABSTRACT FROM AUTHOR]

Hydrogen creates water during combustion. Therefore, it is expected to be the most promising environmentally friendly energy alternative in the coming years. This study used extract liquid obtained from the waste nigella sativa generated by the black cumin oil industry. The performance of biological hydrogen manufacturing via dark fermentation was investigated in the fluidized bed reactor (FBR) and completely stirred tank reactor (CSTR) under the operation conditions of pH 5.0, 4.0, and 6.0 and a hydraulic retention time (HRT) of 36 and 24 h. The performance of hydrogen manufacturing was determined to be good under an organic loading ratio (OLR) of 6.66 g.nigella sativa extract/L and pH 4.0. According to these conditions, the maximum amount of hydrogen in CSTR and FBR was found to be 20.8 and 7.6 mL H2/day, respectively. The operating process of the reactors displayed that a reduction in HRT augmented biohydrogen manufacturing. The work that used mixed culture found that the dominant microbial population at pH 4.0 involved Hydrogenimonas thermophila, Sulfurospirillum carboxydovorans, Sulfurospirillum cavolei, Sulfurospirillum alkalitolerans, and Thiofractor thiocaminus. No research on waste black cumin extract was found in biohydrogen studies, and it was determined that this substrate source is applicable for biological hydrogen manufacturing. [ABSTRACT FROM AUTHOR]

In order to deal with the environmental pollution problem caused by excessive emission of greenhouse gases, hydrogen energy, a green low-carbon secondary energy, acts as an important role in the process of energy transformation and the realization of global carbon neutrality goals. With the development of nuclear reactors of Generation IV, there is a new way using the high-temperature residual heat of nuclear reactors to couple with advanced chemical reaction in producing hydrogen. This research based on a small Fluoride-Salt-cooled high-Temperature Advanced Reactor (FuSTAR), gives a hydrogen production method derived by biomass. Exergy analysis of this method by Aspen HYSYS shows that the material exergy consumption (including physical exergy consumption and chemical consumption) is the main part affecting exergy losses. The energy utilization of a closed-loop heating system is better than that of an open system that directly heats gasification agents. Specifically, When the temperature reaches 700 °C, the mass flow rate of CO 2 and Biomass is 1:15 and the reaction finally reaches equilibrium, the total exergy consumption of the system is 1.47 × 109 kJ/h and the mole fraction of H 2 is 49.9 % in theory. In addition, the change of temperature mainly affects physical exergy consumption while the change of mass flow rate mainly affects chemical exergy consumption. Furthermore, when the system is coupled with Brayton cycle power generation system, in which a small amount of SCO 2 is drawn out as a high-temperature gasification agent for biomass hydrogen production, the exergy consumption is barely increased. • The concept of a biomass and nuclear hydrogen production system is presented. • Supercritical carbon dioxide acts as a gasification agent and heat-transfer medium. • Detailed exergy analysis on thermal-hydraulic parameters of FuSTAR. • Exergy consumption barely increases when coupled with the Brayton power cycle. • A reference for the optimal design of comprehensive utilization of nuclear energy. [ABSTRACT FROM AUTHOR]

Biohydrogen production through photofermentation has gained significant attention as it provides a sustainable solution for clean energy supply and addresses wastewater concerns by utilizing volatile fatty acids (VFA) which are produced in dark fermentation. In this study, response surface methodology via a Face-centered Central Composite Design (FCCD) was employed to optimize buffer solution pH, ferric citrate concentration, sodium glutamate concentration to maximize biohydrogen production by Rhodobacter sp. MAY2 with mixed VFA (acetate, propionate, butyrate) as substrates. Results showed that the concentrations of ferric citrate, sodium glutamate, and buffer solution pH positively impact the biohydrogen production of Rhodobacter sp. MAY2. The optimal conditions were shown to be 0.36 mM ferric citrate, 11 mM sodium glutamate, and buffer solution of pH 7. The predicted hydrogen production potential (HPP) at these conditions (661.1 mL/L) was within 2 % of the actual HPP (647.7 mL/L). Kinetic parameters using the modified Gompertz equation showed that the predicted values for maximum potential cumulative H 2 production (P), maximum hydrogen production rate (R m), and lag time (λ) are comparable to those reported in literature. Overall, the study highlighted the potential of a local isolate, Rhodobacter sp. MAY2, for biohydrogen production and the suitable fermentation conditions for its growth. • Optimized pH, ferric citrate, and sodium glutamate enhanced Rhodobacter sp. MAY2 biohydrogen production. • Buffer pH, ferric citrate, and sodium glutamate significantly influenced biohydrogen yield. • Rhodobacter sp. MAY2 exhibited high substrate consumption efficiency for volatile fatty acids. [ABSTRACT FROM AUTHOR]

Dark fermentation (DF) of kitchen waste (KW) is a promising technology for the production of renewable biohydrogen. It can be both a method of obtaining clean energy and a sustainable waste management. Despite its potential, this process requires further research to improve efficiency. The aim of the research was to test the effect of thermal pretreatment of the inoculum on H2 and volatile fatty acids (VFAs) production in the DF process. The process was carried out at 37 °C, in batch mode. The digested sludge from the Group Wastewater Treatment Plant in Lodz was used as inoculum. KW from households was used as substrate. The inoculum was pre-treated at 70 °C for 15 and 30 min. Two control reference experiments were also used. The first without the inoculum, and the second without heating the inoculum. The thermal pretreatment inhibited methane production and increased hydrogen production. After the thermal pretreatment, the amount of CO2 produced during the process decreased compared to the bioreactor without inoculum pretreatment. Additionally, the main VFAs in the samples with pretreated inoculum were acetic and butyric acids, which are associated with hydrogen production in the biochemical pathways of the DF process. However, the time of thermal pretreatment had no significant effect on H2 production. [ABSTRACT FROM AUTHOR]

Among multiple alternative clean and renewable energy sources, hydrogen is the most promising green fuel because of its high conversion efficiency, energy potentiality, and sustainability. In this review, green biohydrogen production by anoxygenic photosynthetic bacteria (APB) is summarized with the aim to enhance the present understanding of the underlying mechanisms and to gain a definite presentation of the current state of biohydrogen production. Mechanisms of biohydrogen derived from APB are briefly summarized, including the transformation of light energy into adenosine triphosphate, the metabolism of organic matter producing hydrogen ions, and photosynthetic bacteria coupled with reducing substances. In addition, factors affecting biohydrogen production by APB, including internal factors and external factors, are systematically described and discussed. Moreover, current methods for improving the hydrogen production efficiency from APB are presented. Promising applications ingratiating sustainable development goals are summarized, and both economic viability and environmental sustainability are reviewed. [Display omitted] • Anoxygenic photosynthetic bacteria (APB) do not evolve O 2 in hydrogen production. • APB consume organic substrates and produce hydrogen at high rates. • ATP serving as co-factor participate in nitrogenase-catalyzed hydrogen evolution. • APB can yield carotenoid as by-products during the process of hydrogen production. • More high-quality life cycle assessment studies should be performed in the future. [ABSTRACT FROM AUTHOR]

Seaweed biomass in Korea is rich in galactose following hydrolysis, and leveraging this resource for enhancing the biohydrogen production is the aim of this study. The study investigates the biohydrogen production potential of a newly isolated pure strain, Clostridium sp. JH03, utilizing galactose and seaweed biomass as renewable feedstocks. The strain could utilize galactose as the sole carbon source for biohydrogen production, with a maximum hydrogen yield of 1.61 mol H2/mol galactose. The parameters included pH, temperature, and initial galactose concentration, which were varied to determine the optimal conditions for maximum biohydrogen production. The optimal conditions for biohydrogen production were pH 9 and a temperature of 25 °C, with an initial galactose concentration of 10 g/L. Moreover, hydrogen production from seaweed hydrolysate by Clostridium sp. JH03 resulted in maximum production of 1.71 mol H2/mol galactose. The study also investigated that combining sludge, a common practice in dark fermentation, with JH03 increased biohydrogen production by up to 34%. By addressing the need for clean energy and reducing raw materials price using biomass, this study contributes to the advancement of sustainable and cost-compatible energy solutions. [ABSTRACT FROM AUTHOR]

The increasing consumption of energy and consequent fast depletion of fossil fuels and associated environmental challenges necessitate transformative innovations in the field of energy conversion. Owing to its exceptional energy density and zero emissions during combustion, Hydrogen is hailed as a promising source of clean and renewable energy that can replace fossil fuels in future energy conversion systems. Since Hydrogen is not readily available in the atmosphere, a variety of pathways have been followed for the evolution of Hydrogen from water and organic materials, which requires the involvement of catalysts to accelerate the reactions. Currently, noble metals and their alloys represent state-of-the-art materials for HER (Hydrogen Evolution Reaction), and the scarcity and high expense of such materials impose significant constraints on their widespread implementation in hydrogen production. In this context, nanocarbons and their composites for HER are worth exploring owing to their abundance, cost-effectiveness, eco-friendliness, exceptionally large surface-to-volume ratio, and excellent electrical and charge transfer properties. Here, three leading hydrogen production methods - biological, electrochemical, and photo-driven- are analyzed based on their characteristics, effectiveness, and limitations w.r.t. different nanocarbon materials. [Display omitted] • Nanocarbon-based biological methods for hydrogen production. • Brief outline of carbon nanomaterials in electrochemical hydrogen production. • Outlook on photo-driven hydrogen production based on nanocarbon materials. • Reported studies are critically compared and analyzed. • Future prospects of different hydrogen production methods. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract Palm oil decanter cake and crude glycerol, which are characterized by their highly biodegradable organic content and nutrient-rich composition, are attractive ingredients for biohydrogen production. In this experiment, we investigated (1) how to produce hydrogen more effectively by co-fermenting palm oil decanter cake and crude glycerol and (2) how to improve the quality of the hydrogen gas produced via chemical absorption technology. This study was divided into two parts. In the first part, the co-fermentation was conducted with a fixed decanter cake concentration of 1% total solids (TS) w/v and variable crude glycerol concentrations (0.25–2.0% w/v). The results showed that maximum biohydrogen production was achieved with 2.0% w/v crude glycerol, which had a hydrogen yield of 131 L kg−1 TSadded and a hydrogen productivity of 1310 mL L−1 d−1. In the second part of the experiment, biohydrogen purification was conducted using the chemical absorption technique by varying four different alkaline solutions: mono ethanolamine (MEA), ammonia (NH3), sodium hydroxide (NaOH), and potassium hydroxide (KOH). The highest hydrogen purity of 98.9% v/v was reached with the MEA solution at a 5 M concentration and a 280 mL min−1 feed mixed gas flow rate for an absorption time of 5 min. However, to achieve sustainable waste management in palm oil mill plants, the feasibility of integrating the biohydrogen production process with palm oil mill effluent from the biogas plants and applying a hydrogen gas quality improvement system need to be investigated further.

The effects of ultrasonic factors (acoustic power and sonication time) and substrate mixture (tomato waste and cow manure) on the lignocellulosic structure degradability, elimination of feedstock pollutants and solids, and bio-H2 fermentation improvement were studied using the integration of multiple regression modeling and structural equation modeling. Analyses indicated that (i) a mixture of substrates is needed for improving the feedstock quality and bio-H2 fermentation, (ii) highest feedstock solid removal was attained in 0.42 W/mL acoustic power at 15-min sonication time with mixture 75%:25% cow manure/tomato waste, (iii) highest feedstock pollutant removal was obtained in ultrasonic power of 0.34 W/mL at 15 min with higher amounts of tomato waste in the mixtures, (iv) highest lignin removal was achieved for ultrasonic power of 0.42 W/mL at 15 min with higher amounts of cow manure in the mixtures, and (v) highest amount of bio-H2 was produced in ultrasonic power of 0.1 W/mL at 25 min with mixtures 0–25%:75–100% or 75–100%:0–25% cow manure/tomato waste. In proper conditions of pretreatment and substrate mixture, the removal of solid, volatile solid, lignin, cellulose, and hemicellulose contents increased respectively by 3.58%, 17.95%, 57.67%, 24.38%, and 38.7% compared to the control system, leading to a 6% increase in bio-H2 production. [ABSTRACT FROM AUTHOR]

In the study, the best conditions for aflatoxin removal and the highest dissolved sugar were determined by applying microwave pretreatment (250-800W) to waste dried figs. Biohydrogen production performances of aflatoxin-free dried figs were evaluated by testing different substrate (11.8-118 g/L) and different organism concentrations (0.5-2.5 g/L). The optimum microwave of the microwave pretreatment process, giving the highest dissolved sugar concentration (89.7 g/L) from 100 g/L waste dried figs was 400 W and the treatment time was 10 minutes. Under these conditions, 46.2% hydrolysis of sugars and 77.8% aflatoxin removal were achieved. At the initial substrate concentration of 59 g/L, the highest cumulative volume of hydrogen gas, hydrogen gas production yield, hydrogen gas production rate were found as 161.9 mL, 207.5 mL H2/g total sugar, 1.75 mL/hour, respectively. Although lactic acid was produced in high amounts from organic acids produced in experiments using different substrate concentrations, it has been observed that it is converted into butyric acid in some experiments. This resulted as an increase in biohydrogen gas production. In different organism amount experiments, it was observed that sugar was consumed in all experiments and hydrogen gas was produced successfully. Butyric acid was the main organic acid in the experimental media where the highest hydrogen gas production yield was produced in 1 g/L as 124.28 mL H2/g total sugar. The specific hydrogen gas production rate (SHPR) decreased with increasing organism concentrations. The highest SHPR was obtained with 0.5 g/L organism concentration as 3.83 mL H2/g biomass hour. [ABSTRACT FROM AUTHOR]

Palm oil decanter cake and crude glycerol, which are characterized by their highly biodegradable organic content and nutrient-rich composition, are attractive ingredients for biohydrogen production. In this experiment, we investigated (1) how to produce hydrogen more effectively by co-fermenting palm oil decanter cake and crude glycerol and (2) how to improve the quality of the hydrogen gas produced via chemical absorption technology. This study was divided into two parts. In the first part, the co-fermentation was conducted with a fixed decanter cake concentration of 1% total solids (TS) w/v and variable crude glycerol concentrations (0.25–2.0% w/v). The results showed that maximum biohydrogen production was achieved with 2.0% w/v crude glycerol, which had a hydrogen yield of 131 L kg−1 TSadded and a hydrogen productivity of 1310 mL L−1 d−1. In the second part of the experiment, biohydrogen purification was conducted using the chemical absorption technique by varying four different alkaline solutions: mono ethanolamine (MEA), ammonia (NH3), sodium hydroxide (NaOH), and potassium hydroxide (KOH). The highest hydrogen purity of 98.9% v/v was reached with the MEA solution at a 5 M concentration and a 280 mL min−1 feed mixed gas flow rate for an absorption time of 5 min. However, to achieve sustainable waste management in palm oil mill plants, the feasibility of integrating the biohydrogen production process with palm oil mill effluent from the biogas plants and applying a hydrogen gas quality improvement system need to be investigated further. [ABSTRACT FROM AUTHOR]

Hydrogen is ideal for replacing fossil fuels because upon combustion it generates only water. Dark fermentation (DF) from lignocellulose might be a competitive process for hydrogen production at the industrial scale. However, lignocellulose must be pretreated to obtain fermentable sugars, which is costly and creates pollution. Microorganisms from bovine rumen efficiently degrade lignocellulose. Unfortunately, they have scarcely been explored for the production of hydrogen. Therefore, deeper studies on the culture conditions have to be undertaken to understand the behavior of microbial consortia from the rumen of bovines (MCRB) during hydrogen production. In this work, we evaluated the production of hydrogen by DF with MCRB by varying the incubation time, two culture media (MB and Rhodospirillaceae), headspace (40 and 80 mL), and thermal treatment. It was found that the production of hydrogen was maximum at 16 h MCRB incubation in MB. An amount of 80 mL headspace resulted in a threefold production of hydrogen as compared to 40 mL; the MCRB without heat treatment had a higher H2 yield. The production of hydrogen with 32 MCRB was highly variable, ranging between 21 and 696 mL. Our findings show a different perspective on the treatment of MCRB for the production of hydrogen and give insights on the impact of the culture conditions for increasing hydrogen production.

In the context of valorizing the organic fraction of urban solid waste (OFMSW) in megacities, dark fermentation emerges as a central strategy alongside composting and anaerobic digestion. This article focuses on assessing the environmental, technical, and energy viability of dark fermentation using life cycle assessment (LCA) and circular economy principles. Dark fermentation for biohydrogen production is an active and promising research field in the quest for sustainable biofuels. In this context, defining operational parameters such as organic loading and the substrate-inoculum ratio is relevant for achieving better production yields. Laboratory tests were conducted using organic loading values of 5, 10, and 15 g of volatile solids per liter (gVS/L) and with substrate-inoculum ratios (s/x) of 1, 0.75, and 0.5 g of volatile solids of substrate per gram of volatile solids of inoculum (gVSs/gVSi). The combination with the best performance turned out to be an initial organic loading of 10 gVS/L and an s/x of 1 gVSs/gVSi. From this result, it was determined that the s/x had a greater impact on production. Finally, a valorization plant was dimensioned with the scaled-up process, starting from the municipal solid waste generated by Bogotá projected for 2042. The scaling was demonstrated to be energetically sustainable, producing a power of 2,368,358.72 kWh per day.

Hydrogen can be a capable alternative to fossil fuels due to its carbon-free characteristics, in this content, biological hydrogen production is considered a practical approach because technology is green. Due to parameters affecting biohydrogen production, such as operating conditions, it is crucial to predict the process to see the proper yield. There are several conventional and unconventional models used in biohydrogen production prediction. This paper derived a triple first-order prediction model from a previously presented multi-scale kinetic model polynomial built upon the multi-stage growth hypothesis for bio-hydrogen production prediction. The original model was applied to batch and continuous stirred tank reactor studies for their model evaluation, this study evaluated the newly derived model for studies of membrane bioreactors. Due to their increased production yield, membrane bioreactors are an emerging field in biohydrogen production. Although the previous study was mainly applied for batch dark fermentations consisting of various microorganisms, the results presented in this study indicate that it is also applicable for continuous and photo fermentation systems. The original model results reported significant fitness accuracy among different datasheets compared to conventional models like the modified Gompertz model, considering essential factors impacting biohydrogen production suggested in the original model, this paper investigated eleven case studies of dynamic membrane bioreactors with modeling fitness of 99% for most cases. This study reports even higher fitness accuracy compared to the original model, even with different operating conditions. • Investigating biohydrogen production rate of membrane bioreactors (MBR). • A multi-scale kinetic model based on multi-stage growth hypothesis for MBRs. • Providing excellent data fitting for dark/photo fermentations in MBRs. • A flexible black-box data driven model proper for a range of processes. [ABSTRACT FROM AUTHOR]

In recent years, there has been a significant deal of interest in the photo-fermentation-based synthesis of biological hydrogen due to its unique advantages, such as high hydrogen yield and the use of renewable raw materials as substrates. This paper assesses biological hydrogen production by photo-fermentation using the purple non-sulfur bacteria Rhodobacter capsulatus and Rhodospirillum rubrum cultivated in Rhodobacter capsulatus V minimal (RCV) medium. Lactose was used as a carbon source at a starting concentration of 10 g/L. An investigation of the use Rhodobacter capsulatus and Rhodospirillum rubrum strains in mixed culture confirmed the viability of the use of a co-culture system in detriment of mono-culture systems. On average, co-cultured hydrogen responses resulted in 1.43- and 1.50-fold increases in hydrogen productivity and yield, respectively, between the two species. The experiments were also conducted in a 1.5-L stirred tank reactor using repeated batch cycles, with or without medium renewal. The medium renewal allowed for the removal of organic acids produced by cellular metabolism and ensured stable and long-term hydrogen production, reaching peak productivity 278.05 mmol H2/L/day and maximum yield 19.67 mol H2/mol lactose (82% of the theoretical yield). For comparative purposes, a subsequent assay was carried out in the same initial conditions without medium renewal. An accumulation of organic acids resulted in lower peak productivity of 104.47 mmol H2/L/day and lower peak hydrogen yield of 11.71 mol H2/mol lactose confirming viability of medium renewal strategy to improve hydrogen production in photo-fermentation. [ABSTRACT FROM AUTHOR]

More than 80% of the energy from fossil fuels is utilized in homes and industries. Increased use of fossil fuels not only depletes them but also contributes to global warming. By 2050, the usage of fossil fuels will be approximately lower than 80% than it is today. There is no yearly variation in the amount of CO2 in the atmosphere due to soil and land plants. Therefore, an alternative source of energy is required to overcome these problems. Biohydrogen is considered to be a renewable source of energy, which is useful for electricity generation rather than relying on harmful fossil fuels. Hydrogen can be produced from a variety of sources and technologies and has numerous applications including electricity generation, being a clean energy carrier, and as an alternative fuel. In this review, a detailed elaboration about different kinds of sources involved in biohydrogen production, various biohydrogen production routes, and their applications in electricity generation is provided. [ABSTRACT FROM AUTHOR]

H2‐producing microorganisms are a promising source of sustainable biohydrogen. However, most H2‐producing microorganisms are anaerobes, which are difficult to cultivate and characterize. While several methods for measuring H2 exist, common H2 sensors often require oxygen, making them unsuitable for anaerobic processes. Other sensors can often not be operated at high gas humidity. Thus, we applied thermal conductivity (TC) sensors and developed a parallelized, online H2 monitoring for time‐efficient characterization of H2 production by anaerobes. Since TC sensors are nonspecific for H2, the cross‐sensitivity of the sensors was evaluated regarding temperature, gas humidity, and CO2 concentrations. The systems' measurement range was validated with two anaerobes: a high H2‐producer (Clostridium pasteurianum) and a low H2‐producer (Phocaeicola vulgatus). Online monitoring of H2 production in shake flask cultivations was demonstrated, and H2 transfer rates were derived. Combined with online CO2 and pressure measurements, molar gas balances of the cultivations were closed, and an anaerobic respiration quotient was calculated. Thus, insight into the effect of medium components and inhibitory cultivation conditions on H2 production with the model anaerobes was gained. The presented online H2 monitoring method can accelerate the characterization of anaerobes for biohydrogen production and reveal metabolic changes without expensive equipment and offline analysis. [ABSTRACT FROM AUTHOR]

Generating hydrogen gas (H 2) using the dark fermentation method has attracted much attention due to its lower energy requirement and environmental friendliness. However, producing a high yield of bio-H 2 is as challenging as ever due to low energy conversion by microorganisms. In this respect, the advancement of genome editing tools including the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-Cas technology could overcome the established maximum ceiling of product yield. To date, CRISPR-Cas systems, particularly those based on Type II CRISPR-Cas9 and Type V CRISPR-Cas12, are widely used in manipulating novel bacteria to improve the yield of specific biofuel. However, studies using the CRISPR-Cas technology for improving bio-H 2 production remain scarce. Understanding the metabolic pathways of Clostridium spp. is essential for using the CRISPR-Cas technology Thus, this review highlighted the state-of-the-art in CRISPR-Cas systems for bacterial genome editing while paying attention to bioprocess optimization strategies for modulating the biohydrogen production. • Cas9, Cas12 and endogenous CRISPR-Cas can be used for genome editing in Clostridium. • Template vectors for easy deliveries of CRISPR-Cas components in Clostridium spp. • Overexpress butyrate and knockout acetate production pathway improve H 2 production. • Simultaneous repression of solvent and lactate pathway for efficient H 2 production. • Modulation of lignocellulose and sugar utilization genes to improve H 2 production. [ABSTRACT FROM AUTHOR]

Biohydrogen production with the utilization of thermophilic microorganisms is a green process contributing to the mitigation of fossil fuel dependency. This study reports an improved water-gas shift reaction (WGSR) methodology with isolation of thermophilic and anaerobic microorganisms from 5 different closely-located hot springs, employing enrichment and characterization techniques to evaluate their biohydrogen production capacities with 100% CO in the headspace. Enriched mixed and pure cultures were screened for biohydrogen production. An isolate from Doğanbey hot spring reached the highest H 2 yield of 0.43 mmol H 2 /mmol CO with a 43% CO conversion. Using growth profiling and morphologically with SEM imaging, this isolate was characterized biochemically, and was identified as an isolated bacilli shaped bacteria capable of producing hydrogen through WGSR. This is the first study to report potential thermophilic hydrogen producers in selected hot springs in the Izmir region. [Display omitted] • The ability of local isolates from five distinct hot springs to produce biohydrogen was investigated for the first time. • An isolation methodology was developed for CO fermenting bacteria. • Highest H 2 production was observed in Doğanbey hot spring, with a yield of 0.43 mmol H 2 /mmol CO. • Best H 2 producer culture was characterized by SEM imaging. • Growth profiling of the best producer including the assessment of gaseous and liquid by-products was conducted. [ABSTRACT FROM AUTHOR]

Biohydrogen (H2) is considered as a prospective energy source for altering of exhausting fossil fuel-based hydrogen in the coming years. Among biomaterials, lignocellulose is the most abundant renewable feedstock for the second generation biohydrogen production through many processes. The conventional microbial fermentation and the photocatalytic reforming have received considerable attention that could convert the monosugars (mainly glucose and xylose) of the lignocellulosic materials into biohydrogen. In general, to obtain these monosugars, the lignocellulosic materials must be pre-treated through various complicated processes. This review focuses on various integrated pre-treating lignocellulosic material techniques and their advantages and disadvantages, including pretreatment, hydrolysis, and detoxification methods to get monosugars. Additionally, the state-of-the-art accomplishments in the post-methods, including microbial fermentation (including photo-fermentation and dark fermentation), microbial electrolysis, and photocatalytic reforming, for further converting monosugars into sustainable biohydrogen, are favorably highlighted. Finally, the perspectives for material pre-treating techniques and future challenges for post-methods to enhance biohydrogen are also discussed and intensified. [ABSTRACT FROM AUTHOR]

Photo-fermentation biohydrogen production is an eye-catching and environmentally friendly route that can be excellently performed at ambient conditions. Nevertheless, light conversion efficacy and photo-fermentation hydrogen production performance are still low, and hence, numerous approaches are explored to enhance biohydrogen production. This review is intended at describing comprehensive characteristics and general mechanism of photo-fermentation biohydrogen production and highlights the advantages of this approach over other methods. Moreover, various pretreatment procedures of potential lignocellulosic biomass feedstocks for enhanced photo-fermentation biohydrogen production including physical, chemical, physical-chemical, and biological methods were elaborated thoroughly. Several crucial factors affecting photo-fermentation biohydrogen production such as the impact of pH, mixing, stirring, and lighting conditions, substrate concentration, different pretreatment conditions, and diverse fermentation modes were also discussed comprehensively. This aims to emphasize the recent advances in this field for further enhancement of biohydrogen production via photo-fermentation of lignocellulosic biomass. Additionally, the major challenge and prospects are also included to uncover the unexplored criteria of an effective and greener photo-fermentation biohydrogen production. [ABSTRACT FROM AUTHOR]

Hydrogen production with the use of biological processes and renewable feedstock may be considered an economical and sustainable alternative fuel. The high calorific value and zero emission in the production of biohydrogen make it the best possible source for energy security and environmental sustainability. Solar energy, microorganisms, and feedstock such as organic waste and lignocellulosic biomasses of different feedstock are the only requirements of biohydrogen production along with specific environmental conditions for the growth of microorganisms. Hydrogen is also named as 'fuel of the future'. This study presents different pathways of biohydrogen production. Because of breakthroughs in R&D, biohydrogen has been elevated to the status of a viable biofuel for the future. However, significant problems such as the cost of preprocessing, oxygen-hypersensitive enzymes, a lack of uniform light illumination for photobiological processes, and other expenses requiring intensification process limits are faced throughout the biohydrogen production process. Despite concerns regarding nanoparticle (NP) toxicity at higher concentrations, proper NP concentrations may improve hydrogen production dramatically by dissolving the substrates for bacterial hydrogen transformation. The data-driven Machine Learning (ML) model allows for quick response approximation for fermentative biohydrogen production while accounting for non-linear interactions between input variables. Scaling up biohydrogen production for future commercial-scale applications requires combining cost-benefit evaluations and life cycle effects with machine learning. • Biohydrogen synthesis from organic waste is a sustainable fuel production strategy. • Review on improvement in biohydrogen yield using nanoparticles. • Machine learning for process intensification and model-prediction. • Nanoparticles and machine learning help boost biohydrogen output. [ABSTRACT FROM AUTHOR]

Simultaneous bioproduction of hydrogen and ethanol from cheaper waste feedstock has the potential for the development of a more cost-effective biofuel generation process. Crude glycerol (CG), a by-product of the biodiesel industry, is a renewable resource, abundant, sold at low prices and available worldwide. However, the main CG limitations in fermentation processes are mainly related to the presence of impurities and the lack of nitrogen sources, both acting on microbial activity. In this study, a fermentation process with CG was improved using a highly specific microbial consortium called GlyCeroL (GCL). The process was developed in fed-batch fermentation mode using not diluted substrate and carried out under non-sterile conditions and at increasing amounts of the substrate (from 20 to 80 gL−1 of glycerol). The results showed higher H2 (from 6 to 8 LL−1) and EtOH (from 13 to 20 gL−1) production by increasing glycerol concentration from 20 to 40 gL−1. On the other hand, a decrease in glycerol degradation efficiency (from 75 to 56%) was observed. Then, the nitrogen sparging strategy was applied. Using CG of 40 gL−1, process improvement was achieved, leading to the increased production of hydrogen (10 LL−1) but not that of ethanol (20 gL−1). A further increase to 60 gL−1 of glycerol produced a slight increment of EtOH (21 gL−1) and H2 (11 gL−1) but a sharp decrease in glycerol degradation efficiency (41%). Acetate, as the main impurity of CG, was an additional carbon source for GCL microorganisms contributing to EtOH production and increasing that of lactic acid to restore the redox balance. The Denaturing Gradient Gel Electrophoresis (DGGE) fingerprint at the end of all fed-batch fermentations supported the robustness of GCL functional units and their adaptability to fermentation conditions. [ABSTRACT FROM AUTHOR]

This study aims to utilize magnetite nanoparticles (MNP) embedded in granular activated carbon (GAC) originating from coconut shells as microbial support carriers in thermophilic biohydrogen production. MNP can facilitate intracellular electron transportation while providing essential nutrition for microbial growth. Response Surface Methodology (RSM) with a Central Composite Design was used to investigate the simultaneous effect of three variables; Ni:Fe (0.25–0.80), MNP:GAC (0.01–0.03) and type of GAC (GAC-O or GAC-C) on the hydrogen productivity rate (HPR). Biohydrogen content in the biogas to range from 22.25 to 64.71%. The quadratic model was well fitted (R-squared>0.80) with a confidence level higher than 90%. The optimum magnetite GAC was GAC-O as the preferred GAC at Ni:Fe (0.53) and MNP:GAC (0.02), with HPR of 20.33 ± 0.32 ml H 2 /L.h. Magnetite GAC exhibited a better biohydrogen productivity rate by 63.99% compared to non-magnetite GAC. The developed magnetite GAC shown a high potential to improve biohydrogen production. [Display omitted] • Optimisation of magnetite granular activated carbon using response surface methodology. • The performance of magnetite granular activated carbon in biohydrogen production. • Evaluation of mathematical derived model and kinetic modelling. • Physio-chemical characteristics of the optimum magnetite granular activated carbon. [ABSTRACT FROM AUTHOR]

Hydrogen creates water during combustion. Therefore, it is expected to be the most promising environmentally friendly energy alternative in the coming years. This study used extract liquid obtained from the waste nigella sativa generated by the black cumin oil industry. The performance of biological hydrogen manufacturing via dark fermentation was investigated in the fluidized bed reactor (FBR) and completely stirred tank reactor (CSTR) under the operation conditions of pH 5.0, 4.0, and 6.0 and a hydraulic retention time (HRT) of 36 and 24 h. The performance of hydrogen manufacturing was determined to be good under an organic loading ratio (OLR) of 6.66 g.nigella sativa extract/L and pH 4.0. According to these conditions, the maximum amount of hydrogen in CSTR and FBR was found to be 20.8 and 7.6 mL H2/day, respectively. The operating process of the reactors displayed that a reduction in HRT augmented biohydrogen manufacturing. The work that used mixed culture found that the dominant microbial population at pH 4.0 involved Hydrogenimonas thermophila, Sulfurospirillum carboxydovorans, Sulfurospirillum cavolei, Sulfurospirillum alkalitolerans, and Thiofractor thiocaminus. No research on waste black cumin extract was found in biohydrogen studies, and it was determined that this substrate source is applicable for biological hydrogen manufacturing.

Dark fermentation (DF) of kitchen waste (KW) is a promising technology for the production of renewable biohydrogen. It can be both a method of obtaining clean energy and a sustainable waste management. Despite its potential, this process requires further research to improve efficiency. The aim of the research was to test the effect of thermal pretreatment of the inoculum on H2 and volatile fatty acids (VFAs) production in the DF process. The process was carried out at 37 °C, in batch mode. The digested sludge from the Group Wastewater Treatment Plant in Lodz was used as inoculum. KW from households was used as substrate. The inoculum was pre-treated at 70 °C for 15 and 30 min. Two control reference experiments were also used. The first without the inoculum, and the second without heating the inoculum. The thermal pretreatment inhibited methane production and increased hydrogen production. After the thermal pretreatment, the amount of CO2 produced during the process decreased compared to the bioreactor without inoculum pretreatment. Additionally, the main VFAs in the samples with pretreated inoculum were acetic and butyric acids, which are associated with hydrogen production in the biochemical pathways of the DF process. However, the time of thermal pretreatment had no significant effect on H2 production.

Under certain conditions, cyanobacteria can switch from photosynthesis to hydrogen production, which is a good energy carrier. However, the biological diversity of hydrogen-releasing cyanobacteria has a great unexplored potential. This study is aimed to investigate the ability of new strains of cyanobacteria Cyanobacterium sp. IPPAS B-1200, Dolichospermum sp. IPPAS B-1213, and Sodalinema gerasimenkoae IPPAS B-353 to release H 2 and to evaluate the effects of photosystem II inhibitor 3-(3,4-dichlorphenyl)-1,1-dimethylurea (DCMU) on H 2 production under light and dark conditions. The results showed that cultures treated with DCMU produced several times more H 2 than untreated cells. The highest rate of H 2 photoproduction of 4.24 μmol H 2 (mg Chl a h)−1 was found in a Dolichospermum sp. IPPAS B-1213 culture treated with 20 μM DCMU. [Display omitted] • The ability of three new cyanobacterial strains to release hydrogen was studied. • The highest H2 yield was in the Dolichospermum sp. IPPAS B-1213 strain under light anaerobic conditions. • Sodalinema gerasimenkoae IPPAS B-353 released hydrogen only in the dark. • H2 production rate increased in presence of photosynthesis inhibitor. [ABSTRACT FROM AUTHOR]

Biohydrogen possesses similar benefits as the other types of biofuels in terms of its capability to reduce fossil fuel dependency and greenhouse gas emission. This work investigates the economic potential of biohydrogen production using liquid pineapple waste as the feedstock. The economic assessment conducted includes total production cost, total annual sales, annual profit analysis, and cash flow analysis focusing on biohydrogen production via integrated dark and photo fermentation. The estimated Total Capital Investment involved in the production of 3000 metric tonnes of biohydrogen annually from liquid pineapple waste is RM114,994,456 with the net annual profit after tax of RM68,659,386. The plant would operate for 20 years with a depreciation of 10%. For 0% undiscounted cash flow, the payback period is 5.25 years while the expected rate of return is 68%. The economic analysis presented in this work supports the economic feasibility of biohydrogen production from liquid pineapple waste in large scale making it more desirable as another important player in achieving circular economy. [ABSTRACT FROM AUTHOR]

Process parameters were optimized for enzyme (textile‐grade enzymes) hydrolysis of Azolla, water hyacinth, and algae biomass for recovery of maximum sugar to be used as feed for biohydrogen production by Enterobacter cloacae strain DT‐1. Under optimum temperature and pH, the hydrogen yield in mole per mole of sugar from enzyme‐hydrolyzed water hyacinth biomass, Azolla biomass, and Spirulina and Scenedesmus biomass was determined with regard to cellulase, hemicellulase, amylase, pectinase, and xylanase. The maximum hydrogen yield was observed with hemicellulase‐treated Spirulina, Azolla, and Scenedesmus biomass. [ABSTRACT FROM AUTHOR]