Search Results (113)

Despite being recognized as toxic in anaerobic systems, sulfide’s potential to enhance hydrogen fermentation via microbial modulation remains underexplored. This study evaluated the combined effects of sulfide concentration (0–800 mg S/L) and heat pretreatment on hydrogen production during dark fermentation (DF). Without pretreatment, hydrogen yield reached 83 ± 2 mL/g COD at 0 mg S/L but declined with increasing sulfide, becoming negligible at 800 mg S/L. In contrast, heat-pretreated inocula showed markedly improved performance: peak cumulative production (4628 ± 17 mL) and yield (231 ± 1 mL/g COD) were attained at 200 mg S/L, while the maximum production rate (1462 ± 64 mL/h) occurred at 400 mg S/L. These enhancements coincided with elevated acetic and butyric acids, indicating a metabolic shift toward hydrogen-producing pathways. The microbial analysis of heat-pretreated samples revealed an enrichment of Clostridium butyricum (from 73.1% to 87.5%) and Clostridium perfringens, which peaked at 13.5% at 400 mg S/L. This species contributed to butyric acid synthesis. At 800 mg S/L, Clostridium perfringens declined sharply to 0.6%, while non-hydrogenogenic Levilinea saccharolytica proliferated, correlating with reduced butyric acid and hydrogen output. These findings indicate that sulfide supplementation, when combined with heat pretreatment, selectively restructures microbial communities and metabolic pathways, enhancing DF performance. Full article

Adequate treatment of the organic fraction of municipal solid waste (OFMSW) in co-digestion with sewage sludge (SS) through dark fermentation (DF) technologies has been widely studied and recognized. However, there is little experience with a high-solids approach, where practical and scalable conditions are established to lay the groundwork for further development of feasible industrial-scale projects. In this study, the biochemical hydrogen potential of OFMSW using a 7 L batch reactor at mesophilic conditions was evaluated. Parameters such as pH, redox potential, temperature, alkalinity, total solids, and substrate/inoculum ratio were adjusted and monitored. Biogas composition was analyzed by gas chromatography. The microbial characterization of SS and post-reaction percolate liquids was determined through metagenomics analyses. Results show a biohydrogen yield of 38.4 NmLH₂/gVS OFMSW, which forms ~60% of the produced biogas. Aeration was proven to be an efficient inoculum pretreatment method, mainly to decrease the levels of methanogenic archaea and metabolic competition, and at the same time maintain the required total solid (TS) contents for high-solids conditions. The microbial community analysis reveals that biohydrogen production was carried out by specific anaerobic and aerobic bacteria, predominantly dominated by the phylum Firmicutes, including the genus Bacillus (44.63% of the total microbial community), Clostridium, Romboutsia, and the phylum Proteobacteria, with the genus Proteus. Full article

The possibility of hydrogen (H₂) production from sizing waste, specifically starch-based substrates, was investigated through dark fermentation. Modified starch substrates produced less (up to 54% without heating and 18% after heating) H₂ than natural ones. However, heating modified starch samples led to 18% higher H₂ production than unheated ones, suggesting that high temperatures activate more favorable metabolic pathways. The highest H₂ production (215 mL/g_{TVS_substrate}) was observed with unheated natural starch, where the classic butyric–acetic fermentation pathway predominated. This variant also generated the highest CO₂ levels (250 mL/g_{TVS_substrate}), confirming the correlation between H₂ and CO₂ production in these pathways. Modified starch substrates shifted fermentation towards fatty acid chain elongation, reducing CO₂ production. The proportion of CO₂ in the fermentation gases correlated strongly with H₂ production across all variants. A decrease in total volatile solids (TVS) indicated effective organic matter conversion, while varying dissolved organic carbon (DOC) levels suggested different degradation rates. Nitrogen analysis (TN) revealed that the differences between variants were due to varying nitrogen processing mechanisms by microorganisms. These results highlight the potential of sizing waste as a substrate for bioH₂ production and offer insights for optimizing the process and developing industrial technologies for bioH₂ and other valuable products. Full article

This study investigates the potential of sugar beet pulp (SBP), a lignocellulosic by-product of sugar production, as a low-cost substrate for biohydrogen and biomass generation using Escherichia coli under dark fermentation conditions. Two strains—BW25113 wild-type and a genetically engineered septuple mutant—were employed. SBP was pretreated via thermochemical hydrolysis, and the effects of substrate concentration, dilution, and glycerol supplementation were evaluated. Hydrogen production was highly dependent on substrate dilution and nutrient balance. The septuple mutant achieved the highest H₂ yield in 30 g L⁻¹ SBP hydrolysate (0.75% sulfuric acid) at 5× dilution with glycerol, reaching 12.06 mmol H₂ (g sugar)⁻¹ and 0.28 mmol H₂ (g waste)⁻¹, while the wild type under the same conditions yielded 3.78 mmol H₂ (g sugar)⁻¹ and 0.25 mmol H₂ (g waste)⁻¹. In contrast, undiluted hydrolysates favored biomass accumulation over H₂ production, with the highest biomass yield (0.3 g CDW L⁻¹) obtained using the septuple mutant in 30 g L⁻¹ SBP hydrolysate without glycerol. These findings highlight the potential of genetically optimized E. coli and optimized hydrolysate conditions to enhance the valorization of agro-industrial waste, supporting future advances in sustainable hydrogen bioeconomy and integrated waste biorefineries. Full article

The present study investigates a two-stage process aimed at producing biogas from food waste leachates (FWL) through an experimental approach. The first stage involves biohydrogen production via dark fermentation (DF), while the second focuses on biomethane production through anaerobic digestion (AD). The substrate consists of leachates derived from fruit and vegetable waste, which are introduced into two continuous stirred-tank reactors (CSTR1) with two different inoculum-to-substrate ratios (ISR). Dark fermentation occurs in these reactors. The effluent from the CSTRs is then fed into two additional reactors for methanogenesis. All reactors operated under mesophilic conditions. During the DF stage, hydrogen yields were relatively low, with a maximum of 8.2 NmL H₂/g VS added (ISR = 0.3) and 6.1 NmL H₂/g VS added (ISR = 0.5). These results were attributed to limited biodegradation of volatile solids (VS), which reached only 21.9% and 23.6% in each respective assay. Similarly, the removal of organic matter was modest. In contrast, the AD stage demonstrated more robust methane production, achieving yields of 275.2 NmL CH₄/g VS added (ISR = 0.3) and 277.5 NmL CH₄/g VS added (ISR = 0.5). The system exhibited significant organic matter degradation, with VS biodegradability reaching 66%, and COD removal efficiencies of 50.8% (ISR = 0.3) and 60.1% (ISR = 0.5). The primary focus of the study was to monitor and quantify the production of the two biofuels, biohydrogen and biomethane. In conclusion, this study provides an assessment of the two biochemical conversion pathways, detailing the generation of two valuable and utilizable gaseous products. This research examines the process-specific operational conditions governing gas production, with a focus on optimizing process parameters to enhance yield and overall efficiency. Full article

This study examines the effect of inoculum (0.5–3 g/L) and substrate concentration (40–200 g/L) on butyric acid and biohydrogen production by batch dark fermentation at 37 °C. Clostridium pasteurianum DSM525 and Cheese Whey Powder (CWP) were used in the experiments. The results showed that biohydrogen and butyric acid production increased with a 1.5 g/L microorganism concentration and 80 g/L CWP. A Cumulative Hydrogen Formation (CHF) of 458 mL, butyric acid (BA) of 1.523 g/L, butyric acid to acetic acid (BA/AA) ratio of 3.07 g BA/g AA, hydrogen production yield (Y_H2/TS) of 1278.63 mL H₂/g TS, and butyric acid production yield (Y_BA/TS) of 0.37 g BA/g TS at 1.5 g/L inoculum concentration was achieved. The hydrogen (HPR) and butyric acid production rates (BAPR) were similarly the highest at 1.5 g/L. The maximum specific hydrogen (SHPR) and butyric acid rates (SBAPR) were obtained at 2 g/L and 1 g/L organism concentrations, respectively. In variations of substrate concentrations, 651.1 mL of CHF, 1.1 g/L of BA, 3.23 g BA/g AA of BA/AA ratio, 576 mL H2/g TS of YH2/TS, and 27.4 g BA/g TS of Y_BA/TS were accomplished. HPR and SHPR were the highest at 80 g/L CWP due to no substrate inhibition. The BAPR was at its maximum at 100 g/L, BA accumulation was faster, and the SBAPR was at maximum 40 g/L CWP. The results showed a good adaptation of C. pasteurianum to the butyric acid-derived hydrogen production pathway. This strategy could build a renewable and sustainable process with dual valuable outputs. Full article

Waste-based sustainable solutions proposed by scientific and industrial communities for energy production are an approach that can respond to the growing concerns regarding climate change and fossil resources depletion. This study investigates a two-phase bioprocess combining dark fermentation (DF) and photo-fermentation (PF) to enhance hydrogen yield while anaerobically treating urban organic food waste and sewage sludge. A key objective was to assess the effect of waste composition and temperature on hydrogen accumulation, with particular attention to the fermentation product and the role of zeolite in improving process efficiency. In the DF stage, the addition of zeolite significantly enhanced hydrogen production by increasing microbial activity and improving substrate bioavailability. As a result, hydrogen production increased up to 27.3 mmol H₂/(L d) under thermophilic conditions. After the suspended solids were removed from the dark fermentation broth, a photo-fermentation step driven by a pure strain of Rhodopseudomonas palustris was performed under permanent IR light and different substrate-to-inoculum [S/I] ratios. The maximum hydrogen production rate was 9.33 mmol H₂/(L d), when R. palustris was inoculated at the lowest [S/I] ratio (<20 COD/COD) and with 0.5 g VSS/L as the initial concentration. This condition in the photo-fermentation process led to an increase in the hydrogen yield up to 35% compared to values obtained from dark fermentation alone. Full article

This study explores biohydrogen production through dark fermentation, an alternative supporting sustainable hydrogen generation. Dark fermentation uses organic waste under anaerobic conditions to produce hydrogen in the absence of light. Key process parameters affecting hydrogen yield, including substrate type, microorganism selection, and fermentation conditions, were examined. Various substrates, such as organic wastes and carbohydrates, were tested, and the role of anaerobic and facultative anaerobic microorganisms in optimizing the process was analyzed. The research also focused on factors such as pH, temperature, and hydraulic retention time to enhance yields and scalability. Additionally, the study modelled the process using ASPEN Plus software 14. This simulation identifies the bottle necks of this process. Due to the lack of available data, modelling and simulation of the described processes in ASPEN Plus required certain approximations. The simulation provides insight into the key challenges that need to be addressed for hydrogen production. Future research should indeed explore current limitations, such as substrate efficiency, process scalability, and cost-effectiveness, as well as potential advancements like the genetic engineering of microbial strains and improved bioreactor designs. Full article

In the last five years, the use of hydrogen as an energy carrier has received rising attention because it can be used in internal combustion and jet engines, and it can even generate electricity in fuel cells. The scope of this work was to critically review the methods of H₂ production from renewable and non-renewable sources, with a focus on bio-H₂ production from the perennial grass giant reed (Arundo donax L.) due to its outstanding biomass yield. This lignocellulosic biomass appears as a promising feedstock for bio-H₂ production, with a higher yield in dark fermentation than photo-fermentation (217 vs. 87 mL H₂ g⁻¹ volatile solids on average). The H₂ production can reach 202 m³ Mg⁻¹ of giant reed dry matter. Assuming the average giant reed dry biomass yield (30.3 Mg ha⁻¹ y⁻¹), the attainable H₂ yield could be 6060 m³ ha⁻¹ y⁻¹. A synthetic but comprehensive review of methods of H₂ production from non-renewable sources is first presented, and then a more detailed analysis of renewable sources is discussed with emphasis on giant reed. Perspectives and challenges of bio-H₂ production, including storage and transportation, are also discussed. Full article

The global need for energy has risen sharply recently. A global shift to clean energy is urgently needed to avoid catastrophic climate impacts. Hydrogen (H₂) has emerged as a potential alternative energy source with near-net-zero emissions. In the African continent, for sustainable access to clean energy and the transition away from fossil fuels, this paper presents a new approach through which waste energy can produce green hydrogen from biomass. Bio-based hydrogen employing organic waste and biomass is recommended using biological (anaerobic digestion and fermentation) processes for scalable, cheaper, and low-carbon hydrogen. By reviewing all methods for producing green hydrogen, dark fermentation can be applied in developed and developing countries without putting pressure on natural resources such as freshwater and rare metals, the primary feedstocks used in producing green hydrogen by electrolysis. It can be expanded to produce medium- and long-term green hydrogen without relying heavily on energy sources or building expensive infrastructure. Implementing the dark fermentation process can support poor communities in producing green hydrogen as an energy source regardless of political and tribal conflicts, unlike other methods that require political stability. In addition, this approach does not require the approval of new legislation. Such processes can ensure the minimization of waste and greenhouse gases. To achieve cost reduction in hydrogen production by 2030, governments should develop a strategy to expand the use of dark fermentation reactors and utilize hot water from various industrial processes (waste energy recovery from hot wastewater). Full article

Lactic acid fermentation has recently been shown to be a robust storage strategy for food waste prior to conversion to biohydrogen through dark fermentation. However, the importance of initial microbial communities and, more particularly, exogenous microorganisms on the conversion of lactic acid-rich stored substrate is not yet fully elucidated. This study investigates the impact of introducing exogenous inoculum to lactic acid-rich stored food waste prior to biohydrogen production in dark fermentation. Results showed exogenous inoculation produced a statistically significant increase in biohydrogen production rate (R_m) by 199%, 250%, 137%, 130%, 19%, and 10% compared to non-inoculated stored food waste after food waste storage at 4 °C, 10 °C, 23 °C, 35 °C, 45 °C, and 55 °C, respectively. Interestingly, no impact on the maximum production yield (P_m) was observed, but exogenous inoculation increased the accumulation of acetate, up to 160% more compared to endogenous inoculum. The main hydrogen-producing bacteria (HPB) were affiliated with Clostridium sp., while Prevotella_9 sp., another known HPB, was found after the fermentation of the food waste stored at 23 °C. In this study, the interest of exogenous inoculation to convert food waste stored by lactic acid fermentation was demonstrated through an increase in production rate along with higher accumulation of co-products, e.g., acetate. Such findings are promising for further development of process coupling, combining storage and conversion by fermentation of complex food waste. Full article

Today, the world is increasingly concerned about energy and environmental challenges, and the search for renewable energy sources has become an unavoidable priority. In this context, Elaeis guineensis (better known as the African oil palm) has been placed in the spotlight due to its great potential and specific characteristics for the production of alternative fuels in the search for sustainable energy solutions. In the present study, bibliometric and co-occurrence analyses are proposed to identify trends, gaps, future directions, and challenges related to the production of bioethanol and hydrogen from oil palm rachis, using VOSviewer v.1.6.20 as a tool to analyze data obtained from SCOPUS. A mapping of several topics related to bioethanol and hydrogen production from oil palm bagasse or rachis is provided, resulting in contributions to the topic under review. It is shown that research is trending towards the use of oil palm rachis as a raw material for hydrogen production, consolidating its position as a promising renewable energy source. The field of hydrogen production from renewable sources has undergone constant evolution, and it is expected to continue growing and playing a significant role in the transition towards cleaner and more sustainable energy sources, potentially involving the adoption of innovative technologies such as solar-powered steam generation. From an economic point of view, developing a circular economy approach to bioethanol and hydrogen production from oil palm rachis and waste management will require innovations in material design, recycling technologies, and the development of effective life cycle strategies that can be evaluated through computer-assisted process simulation. Additionally, the extraction and purification of other gases during the dark fermentation method contribute to reducing greenhouse gas emissions and minimizing energy consumption. Ultimately, the sustainability assessment of bioethanol production processes is crucial, employing various methodologies such as life cycle assessment (LCA), techno-economic analysis, techno-economic resilience, and environmental risk assessment (ERA). This research is original in that it evaluates not only the behavior of the scientific community on these topics over the past 20 years but also examines a less-studied biofuel, namely bioethanol. Full article

The growing population and economic expansion have led to increased energy demand while presenting complex waste generation and management challenges, particularly in light of climate change. Green hydrogen, which is considered a major clean energy carrier, can also be generated from food waste through a process known as dark fermentation. The production of dark fermentative hydrogen from food waste and biomass residues, in general, is influenced by the type of feedstock, source of inoculum, and their pretreatment and handling strategies. Food waste is a suitable substrate for dark fermentation and has a variable and complex composition, which is a major factor limiting the hydrogen yield. This review critically assesses food waste sources, focusing on their physical and chemical composition, pretreatment methods, and strategies for optimizing dark fermentative hydrogen production. This paper also highlights and critically discusses various inoculum sources and innovations regarding the pretreatment and enrichment applications of inocula for dark fermentative hydrogen production. Based on the literature analysis, advanced research is required to develop more sustainable and specific pretreatment strategies that consider the properties of food waste and the source of the inoculum. This approach will aid in preventing inhibition and inefficiency during the dark fermentation process. Full article

The production of hydrogen via dark fermentation generates carbon dioxide, which needs to be separated and re-utilized to minimize the environmental impact. This research investigates the potential of utilizing algae for carbon dioxide sequestration in hydrogen production via dark fermentation. However, algae alone cannot fully use all the carbon dioxide produced, necessitating the implementation of a multistage separation process. This study proposes a purification approach that integrates membrane separation with a photobioreactor in a multistage design layout. Mathematical models were used to simulate the performance efficiency of multistage design layout using MATLAB 2015b (Version 9.3). A detailed parametric analysis and the key parameters influencing the separation efficiency were conducted for each stage. This study explores how reactor geometry, operational dynamics (such as gas transfer rates and light availability), and algae growth impact both CO₂ removal and hydrogen purity. An optimization strategy was used to obtain the set of optimal operating and design parameters. Our results have shown a significant improvement in hydrogen purity, increasing from 55% to 99% using this multistage separation process, while CO₂ removal efficiency rose from 35% to 85% over a week. This study highlights the potential of combining membrane technology with photobioreactors to enhance hydrogen purification, offering a more sustainable and efficient solution for hydrogen production. Full article

Sorghum distillers grains (SDGs) produced from a sorghum liquor company were used for generating biohydrogen via dark fermentation at pH 4.5–6.5 and 55 °C with a batch test, and the biohydrogen electricity generation potential was evaluated. The experimental results show that pH markedly affects hydrogen concentration, hydrogen production rate (HPR) and hydrogen yield (HY), in that high acidic pH values result in high values. The HPR and HY ranged from 0.76 to 3.2 L/L-d and 21.4 to 62.3 mL/g chemical oxygen demand, respectively. These hydrogen production values were used to evaluate bioelectricity generation using a newly developed gas/liquid-fuel engine. The results show a new and prospective biomass source for biohydrogen production, bioelectricity generation and simultaneously solving the problem of treating SDGs when producing kaoliang liquor. Applications of the experimental results are also discussed. Full article