Effects of biochar on ethanol-type and butyrate-type fermentative hydrogen productions

Application of exogenous electron mediator in fermentation to enhance the production of value-added products

Electron transfer is essential for the production efficiency of value-added products in anaerobic fermentation, such as butanol and ethanol as biofuels, and short-chain fatty acids (SCFAs) including butyric acid and acetic acid as platform chemicals. Electron mediators (EMs), also known as electron shuttles, can facilitate electron transfer to counter irreversible or slow redox reactions that limit fermentation. The addition of EMs has been shown to be an effective strategy to promote fermentation by various bacteria, particularly Clostridium species, for these valuable product syntheses. This paper reviews recent advancements in the application of exogenous electron mediators (EEMs) across various scenarios. Common EEM types, their characteristics, and mechanisms are summarized, and different application scenarios are discussed to elucidate the effect of EEMs. Key technical challenges and future directions for EEM application are also explored.

Effects of Fe/Mg-modified lignocellulosic biochar on in vitro ruminal microorganism fermentation of corn stover

This study investigated the effectiveness and synergistic mechanism of trace-element-modified biochar (BC) on in vitro ruminal fermentation of lignocellulose. Fe/Mg-modified BC containing Fe@BC, Mg@BC and Fe/Mg@BC were prepared, and their effects on in vitro ruminal fermentation of corn stover were assessed. Results indicate that Mg@BC achieved the highest reducing-sugar content (320.4 mg/L) with an additive dose of 12 g/L and a substrate load of 4 %, owing to the presence of enriched lignocellulolytic microorganisms like Treponema and Bacillus. Moreover, Mg@BC promoted the growth of acid-producing bacteria, including Bacteroides and Lachnospiraceae, resulting in the highest production of volatile fatty acid (3.2 g/L). Fe@BC increased the amount of hydrogenogens including Prevotellaceae_YAB2003 and Lachnospiraceae_NK3A20, contributing to the highest hydrogen production. Meanwhile, Fe/Mg@BC facilitated the growth of Succiniclasticum and Lactobacillus, which effectively produce succinic and lactic acids. These findings provide new insights into efficient lignocellulose bioconversion via in vitro ruminal fermentation with Fe/Mg-modified BC supplementation.

Promoting caproate production using anaerobically digested sludge-derived biochar: Performances, mechanisms, and environmental impacts

Carbon chain elongation offers a promising pathway for converting waste resources into caproate. However, challenges in yield and selectivity have limited its broader application. To address these limitations, anaerobically digested sludge-derived biochar (ADS-B) was incorporated into the carbon chain elongation process. The findings reveal that the addition of 20 g/L ADS-B resulted in the highest net caproate yield (6.5 g/L) and selectivity (61.1%). Further analysis highlighted that ADS-B's superior physicochemical properties enhanced the conversion of butyrate to caproate and facilitated the colonization of key microorganisms, such as Terrisporobacter and Clostridium, essential for caproate production. Additionally, a life cycle assessment indicated that ADS-B addition effectively reduced the environmental impact of caprate production, with additional potential for further mitigation through feedstock substitution. This study provides critical insights into the application of anaerobically digested sludge-derived biochar for enhancing carbon chain elongation, presenting an alternative approach for waste reutilization.

Influence of adding strategy of biochar on medium-chain fatty acids production from sewage sludge

Production of medium-chain fatty acids (MCFAs) from sewage sludge has dual effects on valuable sludge disposal and renewable energy generation, while low efficiency limits its application. Biochar addition is considered an effective method to improve MCFAs production. In this study, the influence of biochar adding strategies (i.e., adding biochar in acidification or chain elongation (CE) processes) on MCFAs production was explored. Results showed that by adding biochar in the acidification process, MCFAs accumulation increased by over 114%, accompanied by the highest carbon conversion efficiency (134.66%) and electron transfer efficiency of MCFAs (94.22%) by the terminal CE. Adding biochar before the acidification process better enriched CE bacteria (e.g., Paraclostridium) and strengthened the dominant metabolic pathway. In contrast, the biochar added before the CE process priorly enriched the bacteria capable of degrading organics, like unclassified_f__Dysgonomonadaceae, norank_f__norank_o__OPB41, and Acetobacterium. The differences in excessive ethanol oxidation and short-chain fatty acids accumulation induced by varied adding strategies might be responsible for this.

Potential mechanism of biochar enhanced degradation of oxytetracycline by Pseudomonas aeruginosa OTC-T

Extensive use of oxytetracycline (OTC) and the generation of its corresponding resistance genes have resulted in serious environmental problems. Physical-biological combined remediation is an attractive method for OTC degradation because of its high remediation efficiency, stability, and environmental friendliness. In this study, an effective OTC-degrading strain identified as Pseudomonas aeruginosa OTC-T, was isolated from chicken manure. In the degradation experiment, the degradation rates of OTC in the degradation systems with and without the biochar addition were 92.71-100 % and 69.11-99.59 %, respectively. Biochar improved the tolerance of the strain to extreme environments, and the OTC degradation rate increased by 20.25 %, 18.61 %, and 13.13 % under extreme pH, temperature, and substrate concentration conditions, respectively. Additionally, the degradation kinetics showed that biochar increased the reaction rate constant in the degradation system and shortened the degradation period. In the biological toxicity assessment, biochar increased the proportion of live cells by 17.63 % and decreased the proportion of apoptotic cells by 58.87 %. Metabolomics revealed that biochar had a significant effect on the metabolism of the strains and promoted cell growth and reproduction, effectively reducing oxidative stress induced by OTC. This study elucidates how biochar affects OTC biodegradation and provides insights into the future application of biochar-assisted microbial technology in environmental remediation.

An Overview of Microbial Fuel Cell Technology for Sustainable Electricity Production

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

Improved sequential production of hydrogen and caproate by addition of biochar prepared from cornstalk residues

This study proposes a new model in which ethanol and acetate produced by dark fermentation are processed by Clostridium kluyveri for chain elongation to produce caproate with an addition of biochar prepared from cornstalk residues after acid pretreatment and enzymatic hydrolysis (AERBC) in the dark fermentation and chain elongation processes. The results show a 6-25% increase in hydrogen production in dark fermentation with adding AERBC, and the maximum concentration of caproate in the new model reached 1740 mg/L, 61% higher than that in the control group. In addition, caproate was obtained by dark fermentation, using liquid metabolites as substrates with an initial pH range of 6.5-7.5. Finally, the electron balance and electron transfer efficiency in the new model were analyzed, and the role of AERBC in dark fermentation and chain elongation was investigated. This study provides a new reference for the use of dark-fermented liquid metabolites and cornstalk residue.

Biochar applications in microbial fermentation processes for producing non-methane products: Current status and future prospects

The objective of this review is to encourage the technical development of biochar-assisted microbial fermentation. To this end, recent advances in biochar applications for microbial fermentation processes (i.e., non-methane products of hydrogen, acids, alcohols, and biofertilizer) have been critically reviewed, including process performance, enhanced mechanisms, and current research gaps. Key findings of enhanced mechanisms by biochar applications in biochemical conversion platforms are summarized, including supportive microbial habitats due to the immobilization effect, pH buffering due to alkalinity, nutrition supply due to being rich in nutrient elements, promoting electron transfer by acting as electron carriers, and detoxification of inhibitors due to high adsorption capacity. The current technical limitations and biochar's industrial applications in microbial fermentation processes are also discussed. Finally, suggestions like exploring functionalized biochar materials, biochar's automatic addition and pilot-scale demonstration are proposed. This review would further promote biochar applications in microbial fermentation processes for the production of non-methane products.

Magnetic nitrogen-doped activated carbon improved biohydrogen production

Low biological hydrogen (bioH2) production due to non-optimal metabolic pathways occurs frequently. In this work, magnetic nitrogen-doped activated carbon (MNAC) was prepared and added into the inoculated sludge with glucose as substrate to enhance hydrogen (H2) yield by mesophilic dark fermentation (DF). The highest H2 yield appeared in 400 mg/L AC (252.8 mL/g glucose) and 600 mg/L MNAC group (304.8 mL/g glucose), which were 26.02% and 51.94% higher than that of 0 mg/L MNAC group (200.6 mL/g glucose). The addition of MNAC allowed for efficient enrichment of Firmicutes and Clostridium-sensu-stricto-1, accelerating the metabolic pathway shifted towards butyrate type. The Fe ions released by MNAC facilitated electron transfer and favored the reduction of ferredoxin (Fd), thereby obtaining more bioH2. Finally, the generation of [Fe-Fe] hydrogenase and cellular components of H2-producing microbes (HPM) during homeostasis was discussed to understand on the use of MNAC in DF system.

Molten salt strategy to activate biochar for enhancing biohydrogen production

Generally, dark fermentation (DF) of hydrogen (H₂) synthesis has low H₂ production from industrial-scale plant. In this study, campus greening wastes-ginkgo leaves were used to produce molten salt-modified biochar (MSBC) and nitrogen (N₂)-atmosphere BC (NBC) in molten salt and N₂ environment at 800 °C, respectively. MSBC showed excellent properties including high specific surface area and electron transfer ability. After supplementation with MSBC, H₂ yield rose by 32.4% compared to the control group without carbon material. Electrochemical analysis revealed MSBC improved the electrochemical properties of sludge. Furthermore, MSBC optimized the microbial community structure and increased the relative abundance of dominant microbes, thus promoting H₂ production. This work is provide the deep understanding of two carbons that play vital roles in increasing microbial biomass, supplementing trace element and favoring electron transfer in DF reactions. Salt recovery achieved 93.57% in molten salt carbonization, which has sustainability compared with N₂-atmosphere pyrolysis.

Performance and mechanism of different pretreatment methods for inoculated sludge in biohydrogen production

A comparison was conducted between pre-culture bacteria (PCB) and heat treatment anaerobic granular sludge (HTAGS) for hydrogen production, and it was found that hydrogen molar yield (HMY) of PCB was 21-35% higher than that of HTAGS. The addition of biochar increased hydrogen production in both cultivation methods by acting as an electron shuttle to enhance extracellular electron transfers of Clostridium and Enterobacter. On the other hand, Fe₃O₄ did not promote hydrogen production in PCB experiments but had a positive effect on HTAGS experiments. This was due to the fact that PCB was mainly composed of Clostridium butyricum, which could not reduce extracellular iron oxide, resulting in a lack of respiratory driving force. In contrast, HTAGS retained a significant amount of Enterobacter, which possess the ability of extracellular anaerobic respiration. Different pretreatment methods of inoculum resulted in significant changes in the sludge community, thus exerting a noticeable impact on biohydrogen production.

More effective application of biochar-based immobilization technology in the environment: Understanding the role of biochar

In recent years, biochar-based immobilization technology (BIT) has been widely used to treat different environmental issues because of its cost-effectiveness and high removal performance. However, the complexity of the real environment is always ignored, which hinders the transfer of the BIT from lab-scale to commercial applications. Therefore, in this review, the analysis is performed separately on the internal side of the BIT (microbial fixation and growth) and on the external side of the BIT (function) to achieve effective BIT performance. Importantly, the internal two stages of BIT have been discussed concisely. Further, the usage of BIT in different areas is summarized precisely. Notably, the key impacts were systemically analyzed during BIT applications including environmental conditions and biochar types. Finally, the suggestions and perspectives are elucidated to solve current issues regarding BIT.

Evaluating Bio-Hydrogen Production Potential and Energy Conversion Efficiency from Glucose and Xylose under Diverse Concentrations

Lignocellulose bioconversion to hydrogen has been proposed as a promising solution to augment the fossil fuel dominated energy market. However, little is known about the effects of the substrate concentration supplied on hydrogen production. Herein, the hydrogen producing bacteria Thermoanaerobacter thermosaccharolyticum W16 feeding with respective glucose, xylose, and glucose and xylose mixture (glucose–xylose) at different concentrations was evaluated, to study whether substrate concentration could impact the lignocellulose bioconversion to hydrogen and the associated kinetics. An average bio-hydrogen yield of 1.40 ± 0.23 mol H2·mol−1 substrate was obtained at an average substrate concentration of 60.89 mM. The maximum bio-hydrogen production rate of 0.25 and 0.24 mol H2·mol−1 substrate h−1 was achieved at a substrate concentration of 27.75 mM glucose and 30.82 mM glucose–xylose, respectively, while the value reached the high point of 0.08 mol H2·mol−1 xylose·h−1 at 66.61 mM xylose. Upon further energy conversion efficiency (ESE) analysis, a substrate of 10 g·L−1 (amounting to 55.51 mM glucose, 66.61 mM xylose or 60.55 mM glucose–xylose) provided the maximum ESE of 15.3 ± 0.3%, which was 15.3% higher than that obtained at a substrate concentration of 5 g·L−1 (amounting to 27.75 mM glucose, 33.30 mM xylose or 30.28 mM glucose–xylose). The findings could be helpful to provide effective support for the future development of efficient and sustainable lignocellulosic bio-hydrogen production.

Biohydrogen production from brown algae fermentation: Relationship between substrate reduction degree and hydrogen production

In this study, mannitol and mannitol-rich seaweed were fermented to investigate the relationship between substrate reduction degree and hydrogen production performance. The results showed that acetate was required in mannitol fermentation with an optimum acetate/mannitol mass ratio of 1:5. Hydrogen production and yield of mannitol fermentation reached 123.76 mL and 2.12 mol/mol-mannitol, respectively, 42.02 % and 26.95 % higher than that of glucose, respectively. The acetate was fully assimilated and the butyrate selectivity reached 100 % in the effluent. Redox potential and electron distribution showed that mannitol increased the overall electron input from mannitol and acetate, leading to the increase in hydrogen and butyrate generation. Hydrogen yield reached 2.33 mol/mol-mannitol with brown algae hydrolysate, which was the highest ever reported. This study demonstrated that substrate with a higher reduction degree could yield higher hydrogen and showed the great application potential of brown algae fermentation for the co-production of hydrogen and butyrate.

Microbial and physicochemical responses of anaerobic hydrogen-producing granular sludge to polyethylene micro(nano)plastics

Micro(nano)plastics is an emerging contaminant in wastewater that has showed significant impacts on various biological treatment processes. Nevertheless, the underlying effects of micro(nano)plastics with different concentrations and sizes on the anaerobic hydrogen-producing granular sludge (HPG) were still unclear. This work firstly attempted to illustrate the microbial and physicochemical responses of HPG to a shock load of polyethylene microplastics (PE-MPs) with varied concentrations and sizes. The results revealed that the PE-MPs inhibitory effect on hydrogen production by HPG was both concentration- and size-dependent. Specifically, the increase of PE-MPs concentration and the decline of PE-MPs size to nano-sized plastics (NPs) significantly decreased the hydrogen yield, downgraded to 79.9 ± 2.6% and 63.0 ± 3.9% (p = 0.001, and 0.0002) of control, respectively, at higher MPs concentration and the smaller MPs size (i.e., NPs). The higher PE-MPs concentration and PE-NPs also suppressed extracellular polymeric substances (EPS) generation more severely. The critical bio-processes involved in hydrogen production were disturbed by PE-MPs, with the extent of negative impacts depending on the dosage and size of PE-MPs. These adverse impacts further manifested as granule disintegration and loss of cellular activity. Mechanism analysis highlighted the roles of oxidative stress, leachate released from PE-MPs, interaction between PE-NPs and granules inducing physical crushing of HPG that led to possible direct contact between cells and toxic substances.

Advanced strategies for enhancing dark fermentative biohydrogen production from biowaste towards sustainable environment

As a clean energy carrier, hydrogen is a promising alternative to fossil fuel so as the global growing energy demand can be met. Currently, producing hydrogen from biowastes through fermentation has attracted much attention due to its multiple advantages of biowastes management and valuable energy generation. Nevertheless, conventional dark fermentation (DF) processes are still hindered by the low biohydrogen yields and challenges of biohydrogen purification, which limit their commercialization. In recent years, researchers have focused on various advanced strategies for enhancing biohydrogen yields, such as screening of super hydrogen-producing bacteria, genetic engineering, cell immobilization, nanomaterials utilization, bioreactors modification, and combination of different processes. This paper critically reviews by discussing the above stated technologies employed in DF, respectively, to improve biohydrogen generation and stating challenges and future perspectives on biowaste-based biohydrogen production.

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

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

Bioaugmentation combined with biochar to enhance thermophilic hydrogen production from sugarcane bagasse

In this study, Thermoanaerobacterium thermosaccharolyticum MJ2 and biochar were used to enhance thermophilic hydrogen production from sugarcane bagasse. MJ2 bioaugmentation notably increased the hydrogen production by 95.31%, which was further significantly improved by 158.10% by adding biochar. The addition of biochar promoted the degradation of substrate, improved the activities of hydrogenase and electron transfer system, and stimulated microbial growth and metabolism. Microbial community analysis showed that the relative abundance of Thermoanaerobacterium was significantly increased by bioaugmentation and further enriched by biochar. PICRUSt analysis showed that MJ2 combined with biochar promoted metabolic pathways related to substrate degradation and microbial metabolism. This study provides a novel enhancement method for hydrogen production of the cellulolytic microbial consortium by exogenous hydrogen-producing microorganism combined with biochar and deepens the understanding of its functional mechanism.

Trends in renewable energy production employing biomass-based biochar

Tremendous population growth and industrialization have increased energy consumption unprecedentedly. The depletion of fossil-based energy supplies necessitates the exploration of solar, geothermal, wind, hydrogen, biodiesel, etc. as a clean and renewable energy source. Most of these energy sources are intermittent, while bioelectricity, biodiesel, and biohydrogen can be produced using abundantly available organic wastes regularly. The production of various energy resources requires materials that are costly and affect the applicability at a large scale. Biomass-derived materials (biochar) are getting attention in the field of bioenergy due to their simple method of synthesis, high surface area, porosity, and availability of functional groups for easy modification. Biochar synthesis using various techniques is discussed and their use as an electrode (anodic/cathodic) in a microbial fuel cell (MFC), catalysts in transesterification, and anaerobic digestion for energy production are reviewed. Renewable energy production using biochar would be a sustainable approach to create an energy secure world.

Effects of feedstock and pyrolysis temperature of biochar on promoting hydrogen production of ethanol-type fermentation

Biochar has been shown to benefit fermentative hydrogen production. However, the influencing factors and key characteristics of its promoting function remained to be elucidated. This study investigated the effects of two crucial factors, feedstock and pyrolysis temperature, on the hydrogen production-promoting function of biochar in ethanol-type fermentation. The physicochemical characteristics and promoting effects of biochars prepared with five biomass wastes (coffee ground, corn stalk, Ginkgo biloba leaf, mealworm frass, and sugarcane bagasse) were determined. Sugarcane bagasse-derived biochar (SBBC) showed the best hydrogen production-promoting effect in ethanol-type fermentation. The physicochemical properties of biochar, such as pH, element composition and surface features, were significantly affected by pyrolysis temperature, but the promoting effects were not significantly changed. The hydrogen production-promoting effect of biochar in ethanol-type fermentation was mainly affected by feedstock instead of pyrolysis temperature. A potential promoting mechanism was proposed that biochar prepared at low temperature boosted the hydrogen production with redox activity, while that at high temperature achieved the promotion via cell growth enhancement. This study revealed the key promoting factor of biochar in ethanol-type fermentative hydrogen production, and provided novel insights for the promoting mechanism of biochar.

Tolerance of photo-fermentative biohydrogen production system amended with biochar and nanoscale zero-valent iron to acidic environment

Anaerobic fermentation system is easy to become acidic due to the generation of small molecular acids, which will affect the metabolism of bacteria. Therefore, it is necessary to improve the acid resistance of system. In this work, the tolerance of photo-fermentative biohydrogen production system amended with biochar, nanoscale zero-valent iron (nZVI) and biochar + nZVI to acidic environment was studied. Results showed that additives improved the stability and performance of the photo fermentation. The best increment of biohydrogen from 0 to 286.83 ± 2.77 mL was obtained by adding biochar and nZVI together at the original pH of 4.5. The additive reduced the oxidation-reduction potential and promoted the consumption of acetate and butyrate. At initial pH of 5, 6 and 7, the highest biohydrogen yield of 361.02 ± 10.11, 419.36 ± 10.70 and 382.67 ± 25.08 mL was obtained by adding nZVI, respectively, representing 42%-44.45% increase compared with the control group under the same conditions.

Mitigation of acidogenic product inhibition and elevated mass transfer by biochar during anaerobic digestion of food waste

Anaerobic digestion (AD) of food waste is widely accepted as a promising technology for both waste disposal and resource recovery. With the advancing of AD technology, to exploit the capacity of organic waste for maximum energy/resource recovery becomes the new focus and hence, improve the viability of this technology for practical application. Product inhibition and mass transfer are the common limitations encountered during AD of putrescible organic waste. Biochar materials have been widely used to promote AD process in recent years. This review summarizes the mechanism and regulation strategies of biochar and its modified derivatives in promoting AD of solid waste (mainly food waste) from the three aspects of hydrolysis, syntrophic acetogenesis, and methane production. At the same time, the relationship between carbon materials and electron transfer among anaerobic microbes is summarized from the perspective of microbial community. In addition, the market application of this technology was evaluated.

Biochar boosts dark fermentative H2 production from sugarcane bagasse by selective enrichment/colonization of functional bacteria and enhancing extracellular electron transfer

The influence of biochar (BC) on anerobic digestion (AD) of organic wastes have been widely studied. However, the effect of BC on rate-limiting step during AD of lignocellulosic waste, i.e. the hydrolysis and acidogenesis step, is rarely studied and the underlying mechanisms have not been investigated. In this study, the benefits of BC with respect to dark fermentative hydrogen production were explored in a fermentation system by a heat-shocked consortium from sewage sludge (SS) with pretreated sugarcane bagasse (PSCB) as carbon source. The results showed that biochar boosted biohydrogen production by 317.1% through stimulating bacterial growth, improving critical enzymatic activities, manipulating the ratio of NADH/NAD⁺ and enhancing electron transfer efficiency of fermentation system. Furthermore, cellulolytic Lachnospiraceae was efficiently enriched and electroactive bacteria were selectively colonized and the ecological niche was formed on the surface of biochar. Synergistic effect between functional bacteria and extracellular electron transfer (EET) in electroactive bacteria were assumed to be established and maintained by biochar amendment. This study shed light on the underlying mechanisms of improved performance of biohydrogen production from lignocellulosic waste during mesophilic dark fermentation by BC supplementation.

Renewable biohydrogen production from lignocellulosic biomass using fermentation and integration of systems with other energy generation technologies

Biohydrogen is a clean and renewable source of energy. It can be produced by using technologies such as thermochemical, electrolysis, photoelectrochemical and biological, etc. Among these technologies, the biological method (dark fermentation) is considered more sustainable and ecofriendly. Dark fermentation involves anaerobic microbes which degrade carbohydrate rich substrate and produce hydrogen. Lignocellulosic biomass is an abundantly available raw material and can be utilized as an economic and renewable substrate for biohydrogen production. Although there are many hurdles, continuous advancements in lignocellulosic biomass pretreatment technology, microbial fermentation (mixed substrate and co-culture fermentation), the involvement of molecular biology techniques, and understanding of various factors (pH, T, addition of nanomaterials) effect on biohydrogen productivity and yield render this technology efficient and capable to meet future energy demands. Further integration of biohydrogen production technology with other products such as bio-alcohol, volatile fatty acids (VFAs), and methane have the potential to improve the efficiency and economics of the overall process. In this article, various methods used for lignocellulosic biomass pretreatment, technologies in trends to produce and improve biohydrogen production, a coproduction of other energy resources, and techno-economic analysis of biohydrogen production from lignocellulosic biomass are reviewed.