Cumulative Hydrogen Production Research Articles

Bio-hydrogen production from crude glycerol: Optimisation through response surface methodology and artificial neural network approach

Crude glycerol (CG) is the main by-product of biodiesel production from the transesterification of vegetable or animal oils. The CG's high energy content makes it an effective carbon source for bio-hydrogen production. However, the purity of CG derived from the transesterification process may vary due to impurities such as methanol, soap, salt, etc., which influence the hydrogen production yield. The present study investigated the impacts of initial glycerol, methanol, and soap concentration of CG on the hydrogen production by dark fermentation, and the effect of various factors was evaluated and optimised with the response surface methodology (RSM) and artificial neural network (ANN) approach to maximise the yield of hydrogen production. Both the results of these approaches showed good fitting. The correlation coefficient between actual and predicted values from RSM and ANN models is closer to ∼1, and the lower error shows the applicability of these models. A maximum of 17.67 mmol/L of hydrogen production was obtained via RSM with optimum methanol, soap and glycerol concentrations of 2.75 g/L, 6.07 g/L, and 20.45 g/L, respectively. Besides, the 3-D response surface graphs illustrated the suppressive impact of increased initial concentration of methanol and soap, along with higher initial concentrations of glycerol, on hydrogen production. Further, the outcome of the controlled experiment shows that the presence of impurities (methanol and soap) in glycerol reduces the cumulative hydrogen production by 5 %–17 % compared to the control for over five days.

Increasing biohydrogen production from swine wastewater influenced by anaerobic consortium and nickel ferrite nanoparticles

Screening of efficient microbial consortia and supplementing nanoparticles for pure hydrogen gas evolution have recently become urgent issues in the field of wastewater-derived hydrogen production. In this study, a newly isolated anaerobic consortium combining with nickel ferrite (NiFe2O4) nanoparticles (NPs) was applied to increase the biohydrogen production from swine wastewater. The suitable swine-wastewater-to-rice-straw-hydrolysate proportion was determined as 2:3, which corresponded to a cumulative hydrogen production of 1560.4 ± 10.3 mL/L. The addition of 200 mg/L NiFe2O4 NPs was found to be the most favorable for hydrogen gas evolution, resulting in a cumulative hydrogen production that was 21.8 % higher than that of the control (0 mg/L). Moreover, with the optimal dose (200 mg/L) of NiFe2O4 NPs, butyric acid was converted to the dominant volatile fatty acid, the microbialcommunity was dominated by Clostridium_sensu_stricto and Rummeliibacillus, and the relative expression of hydrogenase gene increased 175.4 ± 31.7-fold after 24 h of fermentation. The changes in microbial metabolism, distribution, and hydrogenase gene expression are helpful to increase the biohydrogen production with the addition of optimal dose of NiFe2O4 NPs.

Investigation into the hydrogen production performance of a novel 5-kW hybrid-system composed of a solar steam generator directly connected with conventional solid oxide electrolysis cells

Coupling solar energy with solid oxide electrolysis cell has the potential to reduce electricity consumption and improve energy conversion efficiency. This study introduces a pioneering 5 kW direct-connected hybrid system that couples a solar steam generator with solid oxide electrolysis cells utilizing conventional electrical energy for the electrolysis process. The successful demonstration of hydrogen production showcases promising results. When the solar irradiation power is 2.26 kW, the inlet water flow rate is 1.23 kg/h under operations at 700 °C, the hydrogen production efficiency of the system reaches 95.2 %, and the steam conversion ratio approaches 92 %, giving a cumulative hydrogen production yield of 5,840 NL in 6.3 h. The solid oxide electrolysis system is further tested under different operating conditions of the stack and solar irradiation. The experimental results show that a greater operating temperature is conducive to more efficient hydrogen production, while more water vapor at the cathode leads to a larger steam conversion ratio. The results indicate that increasing the irradiation power is beneficial to hydrogen production while decreasing the irradiation power will lead to fluctuations of hydrogen yield. In addition, the system efficiency (45.3 %) is higher than that of a photovoltaic alkaline water electrolysis (12.6 %) or photovoltaic proton exchange membrane electrolysis (14.76 %) system at the same irradiation power. Under the same electrolysis power and cathode inlet temperature, the total power consumption of a traditional solid oxide electrolysis system is significantly greater than that of the proposed hybrid system. The comparison shows that the saved electricity of the proposed hybrid system can account for about 30 %. Therefore, the proposed hybrid system has significant efficiency and power savings advantages.

Unleashing solar energy's full potential: Synergetic thermo-photo catalysis for enhanced hydrogen production with metal-free carbon nitrides

Conventional photocatalytic hydrogen production processes are limited by their dependency on photons possessing energy levels surpassing the material's bandgap, thus restricting their ability to utilize the full solar spectrum. Conversely, in thermal catalysis, although the entire solar spectrum is accessible, high-energy photons remain underutilized, and reaction temperatures are often elevated. To address these issues, thermo-photo catalysis is proposed to effectively harness the full spectrum of solar energy under gentle conditions. In this study, a narrow-bandgap carbon nitride catalyst with a bandgap of 2.3 eV was synthesized for the specific purpose of hydrogen production from water through thermo-photo catalysis. Results revealed that under thermo-photo catalytic (TPC) conditions, impressive hydrogen generation rates of 3009.6 μmol·g−1·h−1 and 7090.7 μmol·g−1·h−1 were achieved without and with the application of an external heat source, respectively. Both of them substantially surpassed the cumulative hydrogen production rates achieved via photocatalytic (PC) and thermocatalytic (TC) pathways, demonstrating a remarkable synergy between photonic and thermal energies in the hydrogen evolution process. The synergetic factor with an external heat source applied (2.29) was lower than that without an external heat source (3.02), indicating that there is a better synergy between the photo energy and the thermal energy provided by photothermal conversion than the thermal energy supplied by external heat sources. The properties of photo-generated carriers under various temperature regimes were further examined by photoelectrochemically tests, and electron paramagnetic resonance experiments elucidated the pivotal influence of both photo and thermal energy on radical species, offering a microscopic understanding of the mechanism responsible for the enhanced hydrogen production rate in thermo-photo catalysis.

Polydimethyldiallylammonium chloride inhibits dark fermentative hydrogen production from waste activated sludge

Polydimethyldiallylammonium chloride (PDDA) is an excellent flocculant for wastewater purification and sludge dewatering, but whether it poses a threat to hydrogen production from waste activated sludge is not known. In this study, the effect and underlying mechanism of PDDA on the dark fermentation of sludge was investigated. The results showed that PDDA reduced cumulative hydrogen production from 3.8±0.1 to 2.4±0.1 mL/g volatile suspended solids at 40 g/kg total suspended solids. PDDA impeded the dark fermentation process by inhibiting the activity of key enzymes, presenting a stronger inhibitory effect on the hydrogen production process than the hydrogen consumption process. Additionally, PDDA inhibited Firmicutes by enriching other microorganisms, thereby impeding hydrogen production via the acetate pathway. This study deepens the understanding of the potential effects of PDDA on sludge treatment and provides a theoretical basis for alleviating the negative effects of quaternary ammonium-based cationic flocculants.

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.

Non-noble metal based nickel phosphate decorated CdS nanorods for persistent and efficient solar-to-hydrogen conversion

Solar-to-hydrogen conversion is a potential technology to help end our dependency on fossil fuels. The electron cloud structure of metal sulfide is more suitable than oxide for the preparation of photocatalytic materials. However, their low production rate has always been a limiting factor. Precious metal cocatalysts, such as Pt, Pd, Au, and Ru, are often introduced to tackle this problem. But in fact, their high price and scarcity limit their large-scale application in photocatalysis. At the same time, photooxidation corrosion has always been a problem in the application of metal sulfide. In the present study, we loaded cadmium sulfide (CdS) nanorods with noble metal-free nickel-based cocatalyst at room temperature. The reaction conditions were mild, making the process facile and easy to control. The nickel-based cocatalyst successfully prevented the oxidative photocorrosion of CdS, making the composite material stable for an extended time. The suggested non-noble metal-based cocatalyst had better performance than the traditional Pt cocatalyst. The hydrogen production rate was 58 mmol/g/h at the reaction time of 5 h, and the cumulative hydrogen production was kept up to 35 h with the same evolution rate. Overall, the results were striking to serve a new idea for efficient and persistent photocatalytic hydrogen generation using a non-noble metal-based photocatalyst.

Thermally modified tourmaline enhances hydrogen production by influencing hydrolysis acidification in two stages during dark fermentation of corn stover

This study investigated the influence of thermally modified tourmaline (Tur) on hydrogen production during the dark fermentation of corn stover. Single-factor experimental results revealed influencing factors of particle size, mass, and temperature. Optimization of the experimental process was achieved using the Box-Behnken design, reaching optimum at conditions of 407 °C, 910-mesh, and 6.2 g. The principle analysis experiment showed that the Tur-enhanced group (Tur_En) amplified cumulative hydrogen production by elevating hydrogen production during the sugar-production stage. The Tur_En group's cumulative hydrogen production was measured at 396.2 ± 40.3 (mL/g VS), marking a 34.2% increase compared to the control group. Analysis of microbial diversity indicated that Firmicutes and Bacteroidota emerged as dominant colonies in both stages. Tur facilitated hydrogen production by stimulating the activity of Firmicutes. This study suggests a highly effective Tur-enhanced technology for hydrogen production from corn stover and elucidates the principles underpinning this method from two stages.

Co-production of biohydrogen and biomethane utilizing halophytic biomass Atriplexcrassifolia by two-stage anaerobic fermentation process.

The excessive use of fossil has resulted in the drastic exhaustion of natural energy sources, leading to environmental challenges and energy crises. Owing to rising energy demand there is a dire need to shift towards renewable energies from lignocellulosic biomass. The present study assessed the co-production of biohydrogen (H2) and biomethane (CH4) by utilizing a less explored halophyte Atriplexcrassifolia. Various reaction parameters were evaluated for their effect on biohydrogen and biomethane production in batch experiments. One parameter at a time experimental strategy was chosen for production optimization. Hydrogen and methane yields along with their production rates were assessed at different incubation times, temperatures, pH, substrate concentrations, and inoculum sizes in acidogenesis and methanogenesis stages, respectively. In the first stage, maximum cumulative hydrogen production of 66 ± 0.02mL, with hydrogen yield of 13.2 ± 0.03mL/g, and hydrogen production rate (HPR) of 1.37 ± 0.05mL/h was attained when the reaction mixture (5g Atriplexcrassifolia and 10mL pretreated sewage sludge) was processed at 37°C and pH 5.5 after 48h of incubation. While in the second stage, maximum cumulative methane production, i.e., 343 ± 0.12mL, methane yield (MY) of 8.5 ± 0.07mL/mL, and methane production rate (MPR) of 0.8 ± 0.05mL/h was achieved after 18days of incubation of reaction mixture (40mL of hydrogenic slurry with 80mL inoculum) at 45°C and pH 8. Furthermore, a 51% and 24% rise in biohydrogen and biomethane production respectively were recorded when the gases were produced at these optimized reaction conditions. The results ensure halophyte Atriplexcrassifolia as an imperative renewable energy resource and proposed that effective optimization of the process further increased the coproduction of biohydrogen and biomethane.

Maximization of Energy Recovery from Starch Processing Wastewater by Thermophilic Dark Fermentation Coupled with Microbial fuel Cell Technology

Utilization of organic wastewater for hydrogen production has dual advantages of clean energy generation and bioremediation, which is sustainable for a longer period. To maximize the energy recovery from starch rich wastewater, a two stage system comprising of thermophilic dark fermentation coupled with microbial fuel cell was employed. A single parameter optimization strategy was implemented for the operation of the batch system. The maximum cumulative hydrogen production obtained was 2.56 L L−1 with a 48% reduction in COD under the optimal conditions of 35 g L−1 initial substrate concentration (COD), temperature 60 °C, and pH 6.5. The H2 yield and H2 production rate were 6.8 mol H2/kg CODreduced and 731.3 mL L−1 h−1, respectively. The effect of the organic loading rate (OLR) on H2 production rate was studied in a continuous stirred tank reactor (CSTR). A maximum hydrogen production rate of 913 mL L−1 h−1 was observed at an OLR of 5.6 g L−1 h−1. Effluent recycle played an important role in the improvement of H2 production. A maximum H2 production rate of 1224 mL L−1 h−1 was observed at a recycle ratio of 0.6. Power density of 4.2 W m−3 was observed with MFC using the dark fermentative spent media neutralized with carbonate buffer at an optimal pH of 7. A total COD reduction of 86% was observed.

Optimization and enhancement of biohydrogen production in a single-stage hybrid (dark/photo) fermentation reactor using Fe3O4 and TiO2 nanoparticles

The utilization of nanoparticles to enhance bacterial activity and boost hydrogen production in fermentation processes has gained significant attention due to their unique properties such as high specific surface area and quantum size. This research aimed to improve the biohydrogen yield from food waste by adding iron oxide nanoparticles (Fe3O4) at various concentrations (50, 75, 100, 150, and 200 mg/l) and titanium dioxide (TiO2) at different amounts (25–150 mg/l) to a single-stage hybrid (dark/photo) fermentation reactor. After obtaining the optimal amount of these two nanoparticles, the effect of synergic addition of nanoparticles on hydrogen production yield, was investigated at ratios of Fe3O4/TiO2 = 50/50 and 100/50 mg/mg. At the ratio of Fe3O4/TiO2 = 100/50, the cumulative hydrogen production and yield of hydrogen have increased from 1613 to 3392 ml and 101.60 to 213.66 mlH2/gVS, respectively, compared to the control experiment. We also found that the COD removal rate has enhanced from 28% to 40.1%. In the optimal value, the bacterial growth lag phase has also remarkably decreased from 8.19 to 4.81 h.

Green synthesis of nickel ferrite nanoparticles for efficient enhancement of lignocellulosic hydrolysate-based biohydrogen production

To improve the lignocellulosic hydrolysate-based production of biohydrogen, bimetallic nickel ferrite nanoparticles (NPs) with small particle size, cubic shape, high stability, and biocompatibility are synthesized using an Eichhornia crassipes extract at a low annealing temperature of 400 °C and added to the lignocellulosic hydrolysate fermentation by Klebsiella sp. WL1316. The optimal addition of 30 mg/L gsNiFe2O4 NPs accounts for the highest cumulative hydrogen production of 5544.86 ± 37.03 mL/L and improvement of 112.32% ± 1.86% at 24 h, while also resulting in the highest improvement of hydrogenase and formate-hydrogen lyase activities up to 102.11% ± 13.73% and 62.99% ± 4.66% compared to the Control treatment, respectively. Moreover, the conversion efficiencies of glucose, xylose, and substrate are enhanced upon addition of gsNiFe2O4 NPs, reaching values higher than 96% in the presence of 30 mg/L gsNiFe2O4 NPs. At the same time, the hydrogen yield converted from the substrate (Y(H2/S)) and biomass converted from the substrate (Y(B/S)) are also improved. In addition, the alteration of soluble metabolic products, especially significant changes in formic acid and ethanol concentrations compared to the control, increases the flux in the formate-hydrogen lytic pathway for hydrogen evolution, thereby promoting the substrate conversion level to hydrogen gas.

Impact of experimentally measured relative permeability hysteresis on reservoir-scale performance of underground hydrogen storage (UHS)

Underground Hydrogen Storage (UHS) is an emerging large-scale energy storage technology. Researchers are investigating its feasibility and performance, including its injectivity, productivity, and storage capacity through numerical simulations. However, several ad-hoc relative permeability and capillary pressure functions have been used in the literature, with no direct link to the underlying physics of the hydrogen storage and production process. Recent relative permeability measurements for the hydrogen-brine system show very low hydrogen relative permeability and strong liquid phase hysteresis, very different to what has been observed for other fluid systems for the same rock type. This raises the concern as to what extend the existing studies in the literature are able to reliably quantify the feasibility of the potential storage projects. In this study, we investigate how experimentally measured hydrogen-brine relative permeability hysteresis affects the performance of UHS projects through numerical reservoir simulations. Relative permeability data measured during a hydrogen-water core-flooding experiment within ADMIRE project is used to design a relative permeability hysteresis model. Next, numerical simulation for a UHS project in a generic braided-fluvial water-gas reservoir is performed using this hysteresis model. A performance assessment is carried out for several UHS scenarios with different drainage relative permeability curves, hysteresis model coefficients, and injection/production rates. Our results show that both gas and liquid relative permeability hysteresis play an important role in UHS irrespective of injection/production rate. Ignoring gas hysteresis may cause up to 338% of uncertainty on cumulative hydrogen production, as it has negative effects on injectivity and productivity due to the resulting limited variation range of gas saturation and pressure during cyclic operations. In contrast, hysteresis in the liquid phase relative permeability resolves this issue to some extent by improving the displacement of the liquid phase. Finally, implementing relative permeability curves from other fluid systems during UHS performance assessment will cause uncertainty in terms of gas saturation and up to 141% underestimation on cumulative hydrogen production. These observations illustrate the importance of using relative permeability curves characteristic of hydrogen-brine system for assessing the UHS performances.

Dynamic Operation of a Heat Exchanger in a Thermally Integrated Photovoltaic Electrolyzer

The outdoor operation of an up‐scaled thermally photovoltaic electrolyzer (PV EC), constructed using a heat exchanger (HE) made of low‐cost materials, compared to its nonintegrated counterpart to quantify heat transfer and its effects, is studied. Thermal coupling of the PV and EC can reduce the difference between their temperatures, benefitting device performance. Such devices can produce hydrogen at rooftop installations of small‐to‐medium‐sized nonindustrial buildings. The devices are tested outdoors using automated real‐time monitoring. Under ≈880 W m−2 peak irradiance, they produced hydrogen at ≈120 and ≈110 mL min−1 rate with and without HE, respectively, corresponding to about 8.5% and 7.8% solar‐to‐hydrogen efficiencies. During about 700 h of testing, the HE is beneficial at over ≈500 W m−2 due to cyclic device operation. Under lower irradiance levels, pumping previously heated electrolyte through the HE increases the PV and reduces the electrolyte temperature, reducing the device performance. The HE increases the cumulative hydrogen production (≈800 L from both devices), so even relatively modest heat transfer rates can improve the PV EC operation. Improving the HE should further increase the benefits, but additional measures may be needed to maximize the hydrogen production.

Biohydrogen and Biomethane Production from Acid Pretreated Water Hyacinth and Kinetics

In this study, several ratios of water hyacinth to acid solution were varied from 1:10, 1:20, 1:30, and 1:40, in order to find the optimum ratio for biohydrogen and biomethane production. The pretreated water hyacinth was used as substrates to produce hydrogen in the first stage anaerobic digestion. Then the residue from hydrogen production was used as substrate for methane production in the second stage. The results showed that cumulative hydrogen production slightly increased with the substrate to acid solution (2 % v/v H2SO4) ratio. The highest cumulative hydrogen produced (77.47 mL with 7.75 mL H2/gVS) at 1:40 substrate to acid solution, however the highest hydrogen content obtained at 1:20 (40.1 %). Hydrogen could not be produced from water hyacinth without acid pretreatment, only 4 mL hydrogen was detected from control case. In the second stage, methane was generated from the residue of first stage fermentation and found that the highest cumulative methane was obtained from 1:30 substrate to acid solution ratio. The methane content was not significantly different for control (53.68 %), 1:10 (54.45 %), 1:20 (53.46 %), and 1:30 (52.10 %) cases. The modified Gompertz, modified Logistic, and Cone model were best fit models for hydrogen production since the fermentation needed lag phase time before the hydrogen can be generated. The calculated lag phase time from modified Gompertz model increased from 0.0531 to 0.9775 day, and those from modified Logistic model increased from 0.3867 to 1.0305 day. On the other hand, the Cone model, first order model, and Transference function agreed very well with the second stage methane production data where lag phase time was nearly zero.
 HIGHLIGHTS
 
 Biohydrogen cannot be produced from water hyacinth without acid pretreatment
 The optimum substrate to acid solution ratio for pretreating water hyacinth for hydrogen production is at 1:20 with highest hydrogen content. Higher acid ratio produced more undesired gases
 Biomethane can be produced from water hyacinth without acid pretreatment. Only mechanical size reductionand heating pretreatment are enough to facilitate the process
 Hydrogen production were best described by the modified Gompertz, modified Logistic, and Cone model. On the other hand, second stage biomethane production were best described by the Cone model, first order model, and Transference function
 
 GRAPHICAL ABSTRACT

Enhancing Dark Fermentative Hydrogen Production from Problematic Substrates via the Co-Fermentation Strategy

The aim of the present paper is the improvement of dark fermentative hydrogen production from problematic substrates. In detail, the study is aimed at (i) investigating the inhibiting effect of two problematic biomasses (i.e., of olive mill wastewater, containing recalcitrant/toxic compounds and cheese whey, lacking pH buffering capacity) on the dark fermentation process, (ii) as well as verifying the possibility to apply a co-fermentation strategy to enhance the process. To investigate the inhibiting effect of the substrates, two experimental sets were conducted using olive mill wastewater and cheese whey alone, under different food-to-microorganism ratios (i.e., 1, 2.5, and 5). Further experiments were conducted to verify the possibility of improving hydrogen production via the co-fermentation strategy. Such experiments included two tests conducted using different volumetric percentages of olive mill wastewater and cheese whey (90% olive mill wastewater + 10% cheese whey and 80% olive mill wastewater + 20% cheese whey). Results show that using olive mill wastewater alone, the inhibiting effect increased at a higher food-to-microorganism ratio. Moreover, because of the occurrence of a metabolic shift, hydrogen was not produced using 100% cheese whey. Interestingly, compared to the 100% olive mill wastewater condition, the use of 20% cheese whey allowed to double the hydrogen yield, reaching the high cumulative hydrogen production of 2.08 LL−1. Obtained results confirm that the two investigated substrates exert inhibiting effects on microorganisms. Nevertheless, co-fermentation is an effective strategy to improve the dark fermentation process of problematic biomass.

Synergistic enhancement of biohydrogen production by supplementing with green synthesized magnetic iron nanoparticles using thermophilic mixed bacteria culture

The production of biohydrogen can be improved by focusing on the nutrients needed by fermentative bacteria like iron. Iron reacts with the [Fe-Fe]-hydrogenase enzyme within the mixed bacteria culture for optimum hydrogen release. Iron nanoparticles (NPs) are attractive due to its unique properties and high reactivity. It can be produced through green synthesis, a more eco-friendly and relatively lower cost process, by using iron salt as precursor and green coconut shell extracted by deep eutectic solvent (DES) as reducing agent. The coconut shell extract consists of phytochemicals that help in producing polydisperse magnetic iron oxide nanoparticles at ∼75 nm in size. The addition of optimum concentration of 200 mg Fe/L magnetic iron NPs resulted in the maximum cumulative hydrogen production, glucose utilization and hydrogen yield of 101.33 mL, 9.12 g/L and 0.79 mol H2/mol glucose respectively. Furthermore, the kinetic analysis on Gompertz model using the optimum magnetic iron NPs concentration showed that the hydrogen production potential (P) and hydrogen production rate (Rm) increased to 50.69 mL and 3.30 mL/h respectively and the lag phase time reduced about 7.12 h as compared with the control experiment (0 mg Fe/L). These results indicated the positive effects of magnetic iron NPs supplementation on fermentative biohydrogen production of mixed bacteria culture and proved the feasibility of adding the magnetic iron NPs as the micronutrient for enhancement of such hydrogen production system.

Fusion of Vermicompost and Sewage Sludge as Dark Fermentative Biocatalyst for Biohydrogen Production: A Kinetic Study

The present study explores the synergy between vermicompost and the anaerobic sewage sludge as inoculum for biohydrogen production using food waste as a substrate. Experiments were designed and performed in two phases of operation. In the first phase, the vermicompost (VC) was used as inoculum and food waste as substrate at three different organic loading rates of 10 gVS/L (VC1), 20 gVS/L (VC2), and 30 gVS/L (VC3). In the second phase of operation, the inoculums were combined with a proportion of 50% (VC+AS). The study showed an effective biohydrogen production of 20 gVS/L when the mixing ratio of vermicompost and anaerobic sludge was 50:50. The results inferred that effective synergy was observed between the combined consortia of the inoculum, which induces a more effective metabolic pathway for enhanced hydrogen production. H2 production was 33 mL/gVS (VC1), 48 mL/gVS (VC2), 35 mL/gVS (VC3), 46 mL/gVS (AS), and 50 mL/gVS (VC+AS). Heat pretreatment (100–120 °C) of the inoculum suppresses the methane-producing microorganisms and increases the hydrogen-producing microbes. In addition to hydrogen production, different metabolites are formed in the liquid phase, such as acetic acid, butyric acid, and propionic acid of 2.957 g/L, 4.286 g/L, and 2.123 g/L, respectively, with an energy content of 257 J/day with VC+AS. In addition, a kinetic model was studied for the cumulative hydrogen production curves using the modified Gompertz model, and the fit infers that the experimental data fitted well, with high coefficients of determination for VC+AS (R2 (G) > 0.99).

Continuous hydrogen production characteristics and environmental analysis of a pilot-scale hydrogen production system by photocatalytic water splitting

Hydrogen production by photocatalytic water splitting (HPPCWS) is a promising clean energy conversion technology. However, this technology lacks quantitative environmental impact information and comparison with other hydrogen production technologies. In the process of the technology scale-up, the environmental impact assessment of the whole life cycle is essential. Life cycle assessment (LCA) based on a pilot plant of HPPCWS constructed in China is conducted to evaluate the environmental performance using Simapro software. As the source of inventory, the continuous hydrogen production characteristics of the system are predicted by using local radiation data and reveal that the cumulative hydrogen production of the system is closely related to the local radiation data and the time intervals for replacing the reaction solution. The LCA results on environmental impact show that the construction stage of the system has a more significant impact. In contrast, the dismantling stage can offset part of the environmental impact due to partially recycling primary materials. Transportation and power consumption are the main factors affecting the environment during system operation. The value of the leading midpoint indicator, global warming potential (GWP), could be as low as 4.53 kg CO2 eq/kg H2 under suitable design conditions. Compared to other hydrogen production routes, this work has significant advantages on environmental impact, while there is no denying that the application of the system is facing opportunities and challenges. The results reflect the problems that should be paid attention to in the process of the technology scale-up from the aspects of material and energy utilization and environmental risk. This paper aims to provide credible data on the environmental impact of photocatalytic hydrogen production technology and supply a professional reference for industry decision-making on complete process control.

Peracetic acid promotes biohydrogen production from anaerobic dark fermentation of waste activated sludge

Peracetic acid (PAA), a widely used organic peroxide with strong disinfection and oxidizing effect, has recently attracted research interest in waste activated sludge (WAS) treatment to achieve sludge reduction and resource utilization. However, its impact on hydrogen accumulation from WAS dark fermentation has not been documented. This study therefore is intended to fill in this knowledge gap and clarify the underlying mechanism of PAA-promoted hydrogen generation. Batch experiments revealed that when raised PAA dosage from 0 to 8 mg/g TSS (total suspended solids), cumulative hydrogen production within 168 h fermentation increased from 1.3 to 14.2 mL/g VSS (volatile suspended solids), however, further increase PAA dosage to 10 mg/g TSS resulted in a slight decrease in hydrogen yield. Mechanism studies revealed that PAA was beneficial to sludge disintegration (10 mg/g TSS PAA increased SCOD (soluble chemical oxygen demand) by 254 %). Although PAA inhibited the activity of all microorganism involved in dark fermentation, the inhibitory effect on hydrogen consumers were much more serious than that on hydrogen producers (−45.8 % versus −5.1 % and − 7.3 %). The fermentation was found to shift from propionate type to acetate and butyrate type, favoring hydrogen production. Moreover, the methane production process was effectively inhibited by PAA, which meant less hydrogen consumption. Microbial community analysis results unveiled that PAA increased the abundances of hydrolytic bacteria (e.g., norank_f__Saprospiraceae) and hydrogen producers (e.g., Clostridium_sensu_stricto_10). These findings obtained in this work provide new insights into oxidants-involved sludge treatment process and might have important implication for WAS treatment and bioenergy production in the future.