Improve Biohydrogen Production Research Articles

Improved biohydrogen production from lactic acid bacteria contaminating substrates by enriched hydrogen-producing consortium with lactate-fermentation pathway

The hydrogen-producing consortium conveying the lactate-fermentation pathway was enriched and used as a co-inoculum with the non-enriched hydrogen-producing consortium for biohydrogen production in the presence of lactic acid bacteria (LAB). The co-inoculum treatment achieved superior hydrogen production performance compared to that of the non-enriched consortium treatment. The effects of enriched consortium concentration, initial pH, and glucose concentration were evaluated, and hydrogen production potential (HP) of 1,605 ± 161 mL-H2/L and a maximum hydrogen production rate (HPR) of 87.17 ± 15.85 mL-H2/L.h were achieved under optimal conditions. Biohydrogen production from food waste using the co-inoculum was 1,137 mL-H2/L from non-autoclaved food waste, corresponding to 56.85 mL-H2/g-VSadded. Metabolite product and microbial community analyses during food waste fermentation indicated positive cross-feeding activity of hydrogen producers, LAB, and acetogenic bacteria. This study provides valuable information on the use of an efficient, enriched hydrogen-producing consortium to improve biohydrogen production from LAB-contaminated feedstock.

Investigating the microbial community dynamics in biohydrogen production from palm oil mill effluent (POME) with molasses addition under mesophilic condition

Recently, there has been a surge in global demand for hydrogen as a sustainable and carbon dioxide-free energy carrier. As hydrogen is derived from biological processes, biohydrogen is gaining attention from economic and environmental perspectives because it can be produced from waste, such as palm oil mill effluent (POME). As a country with the largest palm oil industry in the world, Indonesia has the potential to utilize POME as a fermentation substrate for biohydrogen production. This study used local indigenous microorganisms from POME anaerobic pond sludge to produce biohydrogen. The experiment was conducted in an anaerobic batch fermenter under dark fermentation. Screening at initial pH and molasses addition were optimized to obtain the optimal fermentation substrate. A urea addition and heat shock pretreatment were compared to understand the relationship between biohydrogen production, COD reduction representing substrate value, and microbial community dynamics. As in field application, anaerobic process conditions were adjusted at the mesophilic temperature. The importance of comprehending what kind of microorganisms played a role in a consortium was analyzed by the 16S rRNA V3–V4 region using a next-generation sequencing (NGS) approach. Heat pretreatment exhibited the number of bacterial taxa order Thermoanaerobacterales increased significantly in direct proportion to the biohydrogen, up to 24.07% of the total volume gas produced. Notwithstanding, the mesophilic production process altered the microbial community, with Clostridiales as the predominant bacteria group, followed by Lactobacillales, Oscillospirales, and Lachnospirales. Understanding the dynamics and physiochemicals of the microbial community that affect microbial growth is targeted to improve biohydrogen production.

A Strategy to Enhance Photo-Algal Hydrogen Production Using External H+ Ions in a Dual Photobioreactor

The use of microalgae for direct biohydrogen energy generation exhibits significant promise as an alternative to traditional bio-energy production due to zero-emission of CO2. It is known that during photolysis, algae are capable of producing hydrogen (H2) gas instead of oxygen (O2) under enriched acetate conditions by algal fermentative metabolisms [1]. The utilization of acetate as a practical oxygen regulator in photosystem II (PSII), but the algal hydrogen production was relatively low due to the insufficient H+ ions available in the photobioreactor (PBR) [2]. Therefore, given that hydrogen ions from acetate contribute to H2 production, it is still unclear whether supplying additional external H+ ions can enhance H2 production.Here, we demonstrate a feasibility study on improving algal H2 production using a dual PBR system. This system enables the continuous transfer of H+ ions generated from photolysis to an algal H2 PBR through a proton exchange membrane (PEM), thereby enhancing photo-algal hydrogen production. The maximum H2 production of 108 µmol L-1 was obtained for Chlamydomonas reinhardtii in a single PBR for 15 days at a light intensity of 100 µmol m-2 s-1 [3]. However, by leveraging the external H+ ions supply, the dual PBR system increased photo-algal hydrogen production from 108 up to 760 µmol L-1 for the same period, which is 7 times greater compared to single chamber operation. This indicates that supplying external H+ ions in the operation of the dual PBR is one of the important parameters for improving biohydrogen production. Our findings contribute to the ongoing development of high-performance algal H2 production, offering valuable insights into optimizing the amount of H+ ions for enhanced hydrogen production.[1] Clemens KL, Force DA, Britt RD. Acetate binding at the photosystem II oxygen evolving complex: an S2-state multiline signal ESEEM study. J Am Chem Soc. 2002;124(36):10921-33.[2] Hwang J-H, Church J, Lim J, Lee WH. Photosynthetic biohydrogen production in a wastewater environment and its potential as renewable energy. Energy. 2018;149:222-9.[3] Hwang J-H, Lee WH. Continuous photosynthetic biohydrogen production from acetate-rich wastewater: Influence of light intensity. Int J Hydrogen Energy. 2021;46(42):21812-21.

Nanotechnology approaches for Enhancement in Biohydrogen Production

The rapid surge of renewable energy sources has been influenced by the high rate of energy consumption and the low sustainability of traditional energy sources. Being an excellent energy source, hydrogen does not leave any negative carbon footprint as it only produces water during the combustion process. It is carbon neutral which can be produced from a variety of waste feed stocks or biomass, making it the most efficient and environmentally friendly form of energy amid all biofuels. To meet the future hydrogen demand, biological processes like bacterial fermentation, are considered to be environmentally favourable option. Since biomass is abundant, cheap, and biodegradable it is considered profitable for biohydrogen production. Though photo-biological and dark fermentation methods are regarded as successful in generating biohydrogen, their lower yields pose significant challenges for its commercial production. Studies are being conducted to improve efficiency, and here is where nanomaterials come into play by influencing biological processes at the cellular level. They can act as catalysts speeding up the reactions that create hydrogen and making the process more sustainable. Owing to their distinct properties such as stability, crystalline nature, high ratio of surface to volume, adsorption ability, and increased electroconductivity significantly enhance hydrogen generation. In this paper, the applications of nanomaterials such as metals, metal alloys, metal oxides, nanocomposites, and inorganic nanoparticles to improve biohydrogen production have been studied.

Evaluating the feasibility of carbon fiber brush for improving biohydrogen production in acidogenic dark fermentation

Dark fermentation is a promising technology for biohydrogen (bioH2) production. Augmenting the dark fermentation process with conductive materials has drawn significant research interests improving the bioH2 yield. This study evaluated the feasibility of using carbon fiber brush (CB) as an additive to increase the efficiency of mesophilic dark fermentation using glucose as substrate and heat-shock pretreated anaerobic sludge as inoculum. Effect of electrode packing density on bioH2 yield, soluble metabolite product formation, and substrate degradation was investigated. Maximal bioH2 yield of 334.6 mL/g-glucose was obtained using medium-sized CB with 72.5% higher than the control (194 mL/g-glucose) and butyrate-type fermentation was the dominant metabolic pathway. Further, enhanced concentrations of proteins and polysaccharides on CB biofilm suggested the critical role of extracellular polymeric substances in microbial electron transfer. This was supported via electron transport activity in CB biofilm. Finally, microbial community analysis revealed a selective enrichment of the potentially electroactive Clostridium_sensu_stricto_1 on the CB (56.6%) compared to 40.9% abundance in control. Insights gained from this study demonstrated that CB aided dark fermentation can be an economical and environmentally benign strategy for improving bioH2 yield.

Improvement of biohydrogen production from rice straw hydrolysate by green-self-prepared nano-silica

Rice straw stands as a highly sustainable agricultural residue enriched in silica and carbohydrates. This study delves into the potential of rice straw, focusing on the impact of green-synthesized nano-silica particles on biohydrogen fermentation using Enterobacter aerogenes. Rice straw was subjected to three different leading pretreatments, i.e., organsolv, sulfuric acid, and sodium hydroxide, to decimate the lignocellulosic structure. In addition to these, sodium hydroxide was employed as a secondary pretreatment for the organosolv- and sulfuric acid-pretreated straw. Three distinct nano-silica particles were extracted from the liquor of alkali pretreatments and examined using XRD, XRF, FE-SEM, and DLS analysis. The solid fractions of pretreatment were enzymatically hydrolyzed and subjected to dark fermentation, achieving the maximum biohydrogen yield of 156.9 ± 2.0 mL per g total solids (TS) from the organosolv-sodium hydroxide pretreated straw. Further improvement of biohydrogen yield to 178.3 ± 4.2 mL per g TS was obtained by adding 200 ppm of nano-silica particles isolated from one-step sodium hydroxide pretreatment. Analyzing the metabolic products exhibited that nano-silica particles modified the metabolic pathway, leading to an increase in acetic acid production and a decrease in ethanol production. It was concluded that nano-silica particles isolated from untreated and treated rice straws have the potential to boost biohydrogen generation. However, the degree of improvement was dependent on the composition and structure of the nanoparticles.

Combining pretreatments and co-fermentation as successful approach to improve biohydrogen production from dairy cow manure

The present paper is focused on enhancing the production of biohydrogen (bioH2) from dairy cow manure (DCM) through dark fermentation (DF). Two enhancement production strategies have been tested: i) the combination of H2O2 with sonification as pretreatment and ii) the co-fermentation with cheese whey as co-substrate. Concerning the pretreatment, the best combination was investigated according to the response surface methodology (RSM) by varying H2O2 dosage between 0.0015 and 0.06 g/gTS and ultrasonic specific energy input (USEI) between 35.48 and 1419.36 J/gTS. The increase of carbohydrates concentration was used as target parameter. Results showed that the combination of 0.06 g/gTS of H2O2 with 1419.36 J/gTS of USEI maximized the concentration of carbohydrates. The optimized conditions were used to pretreat the substrate prior conducting DF tests. The use of pretreatment resulted in obtaining a cumulative bioH2 volume of 51.25 mL/L and enhanced the bioH2 production by 125% compared to the control test conducted using raw DCM. Moreover, the second strategy, i.e. co-fermentation with cheese whey (20% v/v) as co-substrate ended up to enhancing the DF performance as the bioH2 production reached a value of 334.90 mL/L with an increase of 1372% compared to the control DF test. To further improve the process, dark fermentation effluents (DFEs) were valorized via photo fermentation (PF), obtaining an additional hydrogen production aliquot.

Improvement of biohydrogen production from biomass using supercritical water gasification and CaO adsorption

Producing biohydrogen is a promising alternative to fossil fuels, sourced from renewable energy like wind, solar, and biomass, known for its eco-friendliness and minimal greenhouse gas emissions. This study focuses on the process design and simulation of producing biohydrogen from biomass (bagasse) gasification. New integration of the water gas shift reactor and CaO adsorption process is connected to biomass gasification with the steam/supercritical water agents for improving the hydrogen production process. Simulations show that steam gasification integrated with CaO adsorption (SG-CaO) is optimized at specific conditions, resulting in high-purity hydrogen at 99.95 %. Similarly, the supercritical water gasification integrated with CaO adsorption (SCWG-CaO) requires specific conditions, achieving exceptionally pure hydrogen at 99.99 %. In terms of energy analysis, SCWG-CaO outperforms SG-CaO, with higher hydrogen yield (14.16 % vs. 14.12 %) and greater energy efficiency (42.32 % vs. 40.26 %). It shows that the SCWG-CaO is a suitable and efficient approach for biohydrogen production, considering factors such as hydrogen purity, yield, and energy efficiency.

Biological production of hydrogen: From basic principles to the latest advances in process improvement

The development of net-zero emission fuels is a priority area of modern research due to the imminent reduction of fossil fuel reserves and environmental problems caused by their combustion. One of the promising fuels is hydrogen, which has a high heat of combustion and is eco-friendly, forms water as the only byproduct. Recently, methods of hydrogen production by microorganisms, which use directly the solar energy or utilize the organic waste during fermentation, have been intensively developed and applied. In this review, the basic principles of the main light-dependent (biophotolysis, photofermentation) and light-independent (dark fermentation and microbial electrolysis) methods of biological hydrogen production are discussed. Particular attention is paid to the advantages and disadvantages of these methods, the possibility of combining them into a single system, as well as various strategies for improving biohydrogen production aimed at transition from laboratory research to full-scale application.

Nanomaterials mediated valorization of agriculture waste residue for biohydrogen production

Hydrogen is consider as clean fuel with potential source of unlimited clean power. The global market for the hydrogen generation is expected to be $317.39 billion by 2030. The key factors responsible for hydrogen generation market includes high demand of conventional fuel in steel, cement and power generation industries and government initiatives for green and sustainable environment. It is of the utmost note that the major production of hydrogen is based on conversion from fossil fuels such as coal, petroleum etc. Among green hydrogen production method transformation of biomass to biohydrogen via anaerobic fermentation is considered as carbon neutral source of energy. However, the yield of hydrogen production is low and depends upon various factors such waste composition, bioreactor type, and microorganisms used its production, but production is limited due to shortage of raw materials. Since, the biomass such as agriculture waste residues are largely available as corn stover, sugar beet juice, beverage waste; water, wheat straw, rice straw, wood chips, sawdust, shrubs, and branches etc. The major hurdle in dark fermentation is lower biohydrogen yield due to inefficient conversion of carbohydrates into biohydrogen. Nanomaterials can help in valorization of agriculture residue for efficient biohydrogen production. Nano-technological application like increasing surface area, enzyme stability and saccharification efficiency of enzyme can contribute in biohydrogen production. Nanoparticles may result in a shift in the microbial community and the metabolic pathway for hydrogen production. This review explore the impending application of nanomaterial for valorization of agriculture biomass, biochemical pathways, and possible application of nanomaterial as individual or in composite to improve biohydrogen production.

Nickel-iron doped on granular activated carbon for efficient immobilization in biohydrogen production

Nickel-iron doped granular activated carbon (GAC-N) was used to enhance immobilization in biohydrogen production. The effect of the sludge ratio to GAC-N, ranged 1:0.5–4, was studied. The optimum hydrogen yield (HY) of 1.64 ± 0.04 mol H2/mol sugar consumed and hydrogen production rate (HPR) of 45.67 ± 1.00 ml H2/L.h was achieved at a ratio of 1:1. Immobilization study was performed at 2 d HRT with a stable HY of 2.94 ± 0.16 mol H2/mol sugar consumed (HPR of 83.10 ± 4.61 ml H2/L.h), shorten biohydrogen production from 66 d to 26 d, incrementing HY by 57.30 %. The Monod model resulted in the optimum initial sugar, maximum specific growth rate, specific growth rate, and cell growth saturation coefficient at 20 g/L, 2.05 h−1, 1.98 h−1 and 6.96 g/L, respectively. The dominant bacteria identified was Thermoanaerobacterium spp. The GAC-N showed potential as a medium for immobilization to improve biohydrogen production.

Improving Biohydrogen Production by Dark Fermentation of Milk Processing Wastewater by Physicochemical and Enzymatic Pretreatments.

Biohydrogen is considered an alternative energy reserve. Dark fermentation is one of the important green hydrogen production techniques that utilizes organic waste as raw material. It is a promising bioconversion, easy, not expensive, and cost-effective process. Milk processing wastewater (MPWW) is an organic effluent generated in large volumes on a daily basis and disposed directly into the environment. In this research, the study of biochemical hydrogen potential (BHP) test of MPWW was evaluated and used as substrate (S). A waste sludge was used as an inoculum (I) and source of bacteria. Both substrate and inoculum were analyzed and the study was based mainly on the ratio of volatile solids (VS) of inoculum and substrate subsequently, which was noted as I/S. Different substrate pretreatments were performed: ultrasonic, thermal, chemical, and enzymatic hydrolysis. The I/S ratio impact was investigated and evaluated the hydrogen production improvement. Modified Gompertz and modified Logistic kinetic models were employed for the kinetic modeling of cumulative hydrogen production values. Results show that I/S ratio of 1/4 gVS/gVS resulted from the best hydrogen production of 59.96mL during 30days of MPWW fermentation without pretreatment. It was also shown that all the adopted pretreatments enhanced hydrogen production, whereas ultrasonic pretreatment for 5min increased the production by only 14.84%. Heat pretreatment was more efficient, where the hydrogen production increased from 60 to 162mL (170% of improvement) using heat shock at 90°C for 30min. The impact of chemical pretreatment was different from a reagent to another. Pretreatment using calcium hydroxide resulted in the biggest hydrogen production of 165.3mL (175.5%) compared to the other chemical pretreatments. However, the best hydrogen production was given by the biological pretreatment using enzymatic hydrolysis (Lactase) resulting in 254mL of hydrogen production, which is equivalent to 323.62% of production improvement. Modified Gompertz and Logistic kinetic models fitted well with experimental data. Thus, the enzymatic hydrolysis of MPWW proved to be a promising technique for biohydrogen production enhancement.

Integrated process to produce biohydrogen from wheat straw by enzymatic saccharification and dark fermentation

In this study, different pretreatment methods, including lyophilization, hydrothermal pretreatment, and ultrasound combined with dilute alkali post-cooking, were investigated to enhance the efficiency of enzymatic saccharification and biohydrogen production of the wheat straw. All pretreatment methods could effectively remove lignin and hemicellulose while retaining cellulose, further enhancing the biomass accessibility for subsequently enzymatic saccharification and biohydrogen production. A reducing sugar concentration of 13.18 g/L was acquired when wheat straw was treated with ultrasound and dilute alkali cooking (RU). The sequential fermentative hydrogen yield of the substrate RU was 133.6 mL/g total solids (TS), which was 5.6-fold larger than that of the raw material (23.9 mL/g TS). The study confirmed that ultrasound combined with dilute alkali cooking was an effective method, which not only provided significant guideline for improving biohydrogen production but also presented helpful direction for the efficient pretreatment of other lignocellulosic biomass.

Metal-based nanoadditives for increasing biomass and biohydrogen production in microalgal cultures: A review

Microalgae have emerged as an interesting alternative for the generation of biofuels, including bioethanol, biodiesel, biomethane, biohydrogen and syngas. They are also used for the production of biofertilizers and other products of interest, while acting as a CO2 sink and favoring water purification by absorbing nutrients. However, the economic viability of large-scale microalgae cultivation for any of these purposes is not yet a reality. One of the main factors affecting this viability refers to the microalgae growing phase. In this scenario, nanoparticles, e.g. metallic, are emerging as possible alternatives to improve the cultivation and harvesting of microalgae. The addition of certain nanoadditives in microalgal cultures can improve light conversion in the photobioreactor, as well as CO2 absorption performance. However, the way in which these nanoparticles act or the concentration at which they maximize their positive effects on the culture are aspects that remain unclear. Thus, this paper critically reviews recent advances in nanoparticulate additives when they are used as a supplement in microalgae cultures, with the specific objective of improving biohydrogen production, but also analyzing their effect on algal growth, lipid accumulation and CO2 capture. The effects of nanoparticles on the selection of metabolic pathways of microalgae and their potential toxicity are also reviewed. The reported studies reveal that the toxicity of nanoadditives depends on their concentration, typology (chemical nature, particle size, crystalline structure) and species of microalgae. Furthermore, the supplementation of certain nanoparticles clearly increases the accumulation of intracellular compounds of interest and the growth of the algae. Additional studies should focus on aspects such as optimizing the dose of nanoparticles, designing strategies to minimize toxicity risks, or working with several additives simultaneously to create synergistic effects.

Design of experiment for hydrogen production from ethanol reforming: A state-of-the-art review

Hydrogen production from bioethanol has garnered significant research attention due to its renewability, sustainability, and net zero emission. This research aims to review two statistical optimization techniques, response surface methodology (RSM) and the Taguchi method, for hydrogen production from ethanol thermochemical conversion. The RSM model demonstrated that temperature increases hydrogen production, which peaked between 500 °C and 600 °C for ethanol steam reformation (ESR) and >700 °C for ethanol autothermal reforming (ATR) processes. Maximum hydrogen synthesis occurs at steam-to-ethanol (S/E) ratios of 3–5 mol.mol−1 for both ethanol steam and autothermal reforming. Adding oxygen, a characteristic parameter of autothermal reforming, reduces hydrogen production. Ethanol autothermal reforming may be less efficient than ethanol steam reforming for hydrogen production. The impacting parameters for ethanol reforming identified by Taguchi techniques are steam-to-carbon ratio, ethanol steam reforming temperature, and water–gas shift reaction temperature, where steam-to-carbon ratio and ethanol steam reforming regulate hydrogen production substantially. The Taguchi approach reveals that an ethanol flow rate of 2 cm3.min−1, a steam-to-carbon ratio of 5, and an ethanol steam reforming temperature of 500 °C are optimal reaction conditions. Optimization strategies improve biohydrogen production and make the following reaction more precise. For example, only optimization approaches can determine if a parameter should be reinforced or lowered.

Biohydrogen production with utilisation of magnetite nanoparticles embedded in granular activated carbon from coconut shell

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 H2/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.

Influence of Nanomaterials and Other Factors on Biohydrogen Production Rates in Microbial Electrolysis Cells—A Review

Microbial Electrolysis Cells (MECs) are one of the bioreactors that have been used to produce bio-hydrogen by biological methods. The objective of this comprehensive review is to study the effects of MEC configuration (single-chamber and double-chamber), electrode materials (anode and cathode), substrates (sodium acetate, glucose, glycerol, domestic wastewater and industrial wastewater), pH, temperature, applied voltage and nanomaterials at maximum bio-hydrogen production rates (Bio-HPR). The obtained results were summarized based on the use of nanomaterials as electrodes, substrates, pH, temperature, applied voltage, Bio-HPR, columbic efficiency (CE) and cathode bio-hydrogen recovery (C Bio-HR). At the end of this review, future challenges for improving bio-hydrogen production in the MEC are also discussed.

Application of nanomaterials in dark or light-assisted fermentation for enhanced biohydrogen production: A mini-review

Biohydrogen is regarded as the most promising new generation of green energy. However, the low yield and high cost of biohydrogen restrict its production on a large scale. Nanomaterials have demonstrated outstanding potential for improving biohydrogen production due to their unique photoelectrochemical properties. Some metal nanoparticles are used to promote biohydrogen production in dark fermentation (biohydrogen increased by 5.4–230 %). The state-of-the-art involves using metal or nonmetal photosensitizers to build extracellular or intracellular photo-biohybrid systems with microorganisms, which can be driven by light to efficiently produce biohydrogen (increased by 1.29–8.6 times). This review has summarized in detail the application status and working principle of metal nanoparticles in dark fermentation, the light-assisted biohydrogen production performance, and the mechanism of the extracellular and intracellular photo-biohybrid system. Next, the toxicity and biocompatibility modifications of nanoparticles were discussed. Finally, we proposed the key issues that should be prioritized in the long-term development of biohydrogen.

Improvement of Biohydrogen Production from Date Wastes by Thermotoga maritima Using a Continuous Anaerobic Membrane Bioreactor

Improvement of Biohydrogen Production from Date Wastes by Thermotoga maritima Using a Continuous Anaerobic Membrane Bioreactor

Simultaneous production of renewable biohydrogen, biobutanol and biopolymer from phytogenic CoNPs-assisted Clostridial fermentation for sustainable energy and environment

Considering the environmental impacts, rapid fossil fuel depletion and production costs, sustainable production of clean biofuels from alternative sources is required to meet the increasing demand for energy while avoiding environmental pollution. In this study, phytogenic cobalt nanoparticles (CoNPs)-assisted dark fermentation process was developed for the simultaneous production of biohydrogen, biobutanol and biopolymer from glucose using Clostridium acetobutylicum NCIM 2337. The maximum biohydrogen yield of 2.89 mol H2/mol glucose was achieved at 1.5 mg of CoNPs, which is 1.6 folds higher than that of the control experiment. The high level of soluble metabolites, specifically acetate and butyrate, confirmed the production of biohydrogen through acetate/butyrate pathways. The modified Gompertz model fitted well with experimental results of CoNPs-assisted biohydrogen production. The CoNPs could act as an electron carrier in intracellular metabolism to enhance the activity of ferredoxin and hydrogenase enzymes, thus improving biohydrogen production. Furthermore, biobutanol and biopolymer yields of 975 ± 2.5 mg/L and 1182 ± 1.4 mg/L were achieved, with 2.0 mg and 2.5 mg of CoNP, respectively, which were 1.27 and 1.19 folds higher than the control values. Hence, the inclusion of CoNPs in the fermentation medium seems to be a promising technique for the enhanced simultaneous production of biohydrogen, biobutanol and biopolymer. The environmental perspectives of the obtained renewable biohydrogen, biobutanol and biopolymer are also discussed.