Kinetic study of biological hydrogen production by anaerobic fermentation

The growth kinetics of hydrogen producing bacteria using three different substrates, namely sucrose, non-fat dry milk (NFDM), and food waste were investigated in dark fermentation through a series of batch experiments. The results showed that hydrogen production potential and hydrogen production rate increased with an increasing substrate concentration. The maximum hydrogen yields from sucrose, NFDM, and food waste were 234, 119, and 101 mL/g COD, respectively. The low pH (pH<4)$(\mathrm{pH}<4)$ inhibited hydrogen production and resulted in lower carbohydrate fermentation at high substrate concentration. Michaelis–Menten equation was employed to model the hydrogen production rate at different substrate concentrations. The equation gave a good approximation of the maximum hydrogen production rate and the half saturation constant (_Ks)$(K_{\mathrm{s}})$ with correlation coefficient (R²)$(R^2)$ over 0.85. The _Ks$K_{\mathrm{s}}$ values of sucrose, NFDM, and food waste were 1.4, 6.6, and 8.7 g COD/L, respectively. Based on _Ks$K_{\mathrm{s}}$ values, the substrate affinity of the enriched hydrogen producing culture was found to depend on carbohydrate content of the substrate. The substrate containing high carbohydrate showed a lower _Ks$K_{\mathrm{s}}$ value. The maximum hydrogen production rate was governed by the complexity of carbohydrates in the substrate.     

Biological hydrogen production in continuous stirred tank reactor systems with suspended and attached microbial growth

Fermentative H₂ production in continuous stirred tank reactor (CSTR) system with bacteria attached onto granular activated carbon (GAC) was designed to produce H₂ continuously. The H₂ production performances of CSTR with suspended and attached-sludge from molasses were examined and compared at various organic loading rates (8–40 g COD/L/d) at hydraulic retention time of 6 h under mesophilic conditions (35 °C). Both reactor systems achieved ethanol-type fermentation in the pH ranges 4.5–4.8 and 3.8–4.4, respectively, while ORP ranges from −450 to −470 mV and from −330 to −350 mV, respectively. The hydrogen production rate in the attached system was higher compared to that of the suspended system (9.72 and 6.65 L/d/L, respectively) while specific hydrogen production rate of 5.13 L/g VSS/d was higher in the suspended system. The attached-sludge CSTR is more stable than the suspended-sludge CSTR with regard to hydrogen production, pH, substrate utilization efficiency and metabolic products (e.g., volatile fatty acids and ethanol) during the whole test.     

乙酸对发酵产氢过程的抑制影响

以甲酸为发酵原料进行试验,控制发酵料液的pH在4.8左右,试验共分为10组,每组中分别含有不同浓度的乙酸作为抑制剂。采用批量发酵工艺,进行厌氧发酵产氢,研究乙酸在产氢过程中的抑制作用。由试验可知,当乙酸浓度≥7000mg/l时,抑制作用显著,使产气停止。     

Sustainable biohydrogen production by dark fermentation using carbon monoxide as the sole carbon and energy source

This study evaluated the kinetics of biomass growth, biohydrogen production and substrate utilization using carbon monoxide as the sole carbon and energy source. Experiments were conducted at different initial CO concentration in the range 1.8–5.12 mmol/L over a period of 144 h in order to assess the effect of CO concentration on biomass growth, substrate utilization and H₂ production. Complete utilization (100%) of CO was achieved up to an initial concentration of 3.8 mmol/L and it gradually decreased to 84.5% for 4.4 mmol/L and 83.7% for 5.12 mmol/L. The experimental results of CO utilization were fitted to substrate utilization kinetic models reported in the literature, and it followed a modified Gompertz model. A maximum yield of H₂ on CO was found to be 70.8% and a maximum H₂ production of 29.9 mmol/L was obtained for an initial CO concentration of 5.12 mmol/L. The experimental results on biohydrogen production matched well with the values predicted using the modified Gompertz model. Furthermore, the experimental data on specific growth rate of the ananerobic biomass at different H₂ concentration was fitted to different product inhibition models and the best fit was obtained with Aiba model. This study showed product inhibition on both specific growth rate of biomass and H₂ production due to H₂ accumulation in the gas phase. A very good correlation between the experimental specific growth rate and the Han-Levenspiel model predicted values were obtained with a high determination coefficient (R²) value of more than 0.96.     

Different feedback effects of aqueous end products on hydrogen production of Clostridium tyrobutyricum

Feedback inhibition is one of the main challenges of fermentative hydrogen production. In this study, the effects of butyrate and acetate on hydrogen production of Clostridium tyrobutyricum were investigated. Substrate consumption and hydrogen production were accelerated when acetate ≤15 g/L was fed. Exogenous acetate induced acetate assimilation and increased the metabolic flux of butyrate synthesis. Exogenous butyrate significantly decreased biomass formation, and slowed substrate consumption and hydrogen production. Metabolic and gene expression analyses showed that butyrate impaired glycolysis and acetate production pathway. The increased butyrate/acetate molar ratio was deemed as a strategy for cells to alleviate pH decrease and reduce the inhibition of undissociated butyric acid. Inhibition model analyses indicated butyrate was the main inhibitor in butyrate-type hydrogen production. This study demonstrates the different feedback effects of acetate and butyrate on hydrogen production of C. tyrobutyricum and provides strategies to relieve the feedback inhibition for efficient hydrogen production.     

A meta-analysis of research trends on hydrogen production via dark fermentation

This work provides a meta-analysis of the state-of-the-art research on H₂ and value-added products production from biomass, via Dark Fermentation (DF) between 2015 and 2019. The meta-analysis data clusters are created considering inputs (i.e., feedstocks, and microorganisms used in DF), process conditions (i.e., feedstock pretreatments, and temperature, pH, working volume, substrate concentration in DF), yield and productivity of H₂ and the most common by-products (i.e., acetic, lactic, butyric, propionic acids and ethanol). Agricultural and green residues were the most common feedstock (36.5%), followed by Aquatic biomass (29.8%). Pretreated feedstocks and mixed cultures were employed in 72% and 79% of the studies, respectively. The meta-analysis relates H₂ high productivity to 6 ≤ pH ≤ 6.8 and 35 °C ≤ T ≤ 37 °C and H₂ high yield to 5.5 ≤ pH ≤ 7.5 under mesophilic conditions. The paper elaborates on the production strategies tested at the laboratory scale for each of the DF-products mentioned above, highlighting the pros and cons towards improving yield and productivity and discussing what are the challenges to integrating DF in large-scale biorefining schemes for industrial production of H₂ and value-added products.     

Operational behavior of a hydrogen extractive membrane bioreactor (HEMB) during mixed culture acidogenic fermentation

Fermentative hydrogen production requires a continuous products-removal and effective upgrading steps to improve its general performance. Therefore, implementation of new technologies capable of achieving both requirements is essential. We present the operational behavior of a new process concept based on integration of membranes for gas separation and fermentation technology. This process, which we term as hydrogen extractive membrane bioreactor consists of coupling two dense polymeric membranes to a hydrogen producing culture. The process automatization of this system was essential to maintain the proper operational pressures in the membrane module and in the bioreactor-gas-phase. This system was able to extract and partially separate the hydrogen and carbon dioxide generated. The hydrogen partial pressure was reduced from 55.5 to 49 KPa, which means an increase of hydrogen yield of 16.3% (1.1–1.28 mol-H₂/mol-glucose). Simultaneously, the implemented system generated a final hydrogen stream 13% (v/v) more concentrated than a conventional process.     

Effect of fermentation conditions on biohydrogen production from lipid-rich food material

Among the basic components of organic materials, such as carbohydrate, protein, and lipid, the hydrogen yield of carbohydrate fermentation has been reported to be significantly higher than that of lipid. This study used lard as a model organic matter for lipid and investigated its H₂ production potential in batch anaerobic fermentation experiments under various combinations of stirring and CO₂-scavenging conditions. A significant increase in the hydrogen yield was observed in both CO₂-scavenging and stirring conditions; the CO₂-scavenging condition yield was 2.9 times higher than the stirring condition (116.7 and 40.3 mL H₂/g volatile solid [VS], respectively), which was much greater than reported previously. A maximal hydrogen yield of 185.8 mL H₂/g VS was obtained in the presence of both CO₂-scavenging and stirring, and the H₂ content of the total biogas was as high as 99% (v/v). In addition, there was less H₂ and more CH₄ production in the absence of CO₂-scavenging and/or stirring, which suggests that the consumption of H₂ and CO₂ for methanogenesis was the major mechanism of the poor hydrogen yield from lipid. The volatile fatty acids in all the tests consisted primarily of valeric (47.2–54.9%) and propionic acids (26.6–30.3%), and higher concentrations of these acids remained in the fermentation liquid without CO₂ removal. These results suggest that lipid-rich food waste is a potential source for H₂ production if the fermentation process is optimized to minimize the partial pressure of CO₂ and H₂ and restrain the activities of H₂-consuming bacteria.     

Comparison of magnetite/reduced graphene oxide nanocomposites and magnetite nanoparticles on enhancing hydrogen production in dark fermentation

Magnetite/reduced graphene oxide nanocomposites (Fe₃O₄-rGO NCs) and magnetite nanoparticles (Fe₃O₄ NPs) were added to enhance biohydrogen (bioH₂) production in dark fermentation. Concentration of supplements from 10 to 100 mg/L was appropriate to enhance bioH₂ production, and inhibition appeared once concentration exceeded 100 mg/L. The best bioH₂ yield was 198.30 mL/g glucose at 100 mg/L Fe₃O₄ NPs and 225.60 mL/g glucose at 100 mg/L Fe₃O₄-rGO NCs, which was 42.97% and 62.65% higher than that in the blank group, respectively. Both Fe₃O₄ NPs and Fe₃O₄-rGO NCs could intensify butyrate-type fermentation and change the hydrogen-producing microorganism cells morphology, but the enhancement effect of Fe₃O₄-rGO NCs was superior. Microbial community structure analysis showed that Clostridium-sensu-stricto-1 became more dominant ultimately by Fe₃O₄-rGO NCs.     

Different role of focA and focB encoding formate channels for hydrogen production by Escherichia coli during glucose or glycerol fermentation

The dependence of H₂ production on the formate channels, FocA and FocB, by Escherichia coli at pH 5.5, 6.5 and 7.5 was shown using focA and focB mutants and comparing with the wild type. Moreover, effect of exogenous addition of formate (10 mM) on H₂ production was allotted. The results acquired propose that during glucose fermentation formate import can occur through FocB at different pHs; external formate drives FocA to import direction. However, during glycerol fermentation formate might be imported through FocB, whereas formate is exported preferentially through FocA at pH 7.5.     

Additive manufactured bipolar plate for high-efficiency hydrogen production in proton exchange membrane electrolyzer cells

Additive manufacturing (AM) technology is capable of fast and low-cost prototyping from complex 3D digital models. To take advantage of this technology, a stainless steel (SS) plate with parallel flow field served as a combination of a cathode bipolar plate and a current distributor; it was fabricated using selective laser melting (SLM) techniques and investigated in a proton exchange membrane electrolyzer cell (PEMEC) in-situ for the first time. The experimental results show that the PEMEC with an AM SS cathode bipolar plate can achieve an excellent performance for hydrogen production for a voltage of 1.779 V and a current density of 2.0 A/cm². The AM SS cathode bipolar plate was also characterized by SEM and EDS, and the results show a uniform elemental distribution across the plate with very limited oxidization. This research demonstrates that AM method could be a route to aid cost-effective and rapid development of PEMECs.     

Enhancing the performance of dark fermentative hydrogen production using a reduced pressure fermentation strategy

The partial pressure of hydrogen is an extremely important factor for hydrogen generation. This study investigated the effect of reduced pressure (via vacuum) on hydrogen production in a CSTR reactor. The results show that the reduced pressure condition is more effective in enhancing H₂ production at lower HRT (e.g., 8–4 h) than at higher HRT (e.g., 12 h). The optimal hydrogen yield and overall hydrogen production efficiency occurred at a HRT of 6 h with a value of 4.50 mol H₂/mol sucrose and 56.2%, respectively. Meanwhile, at HRT 6 h the hydrogen production rate was 0.937 mol/L/d. In addition, the HPR could be further improved to 1.196 mol/L/d when the HRT was shortened to 4 h, obtaining a 37–271% increase in HPR when compared with that described in the relevant reports. For all experiments, butyrate and acetate were the two primary soluble metabolites, accounting for 85–99% of total soluble microbial products. Predominant production of acetate and butyrate demonstrates the efficient H₂ fermentation with reduced pressure processes.     

Effect of percolation frequency on biohydrogen production from fruit and vegetable wastes by dry fermentation

Organic solid wastes are the most abundant sources for biohydrogen production. Dry fermentation system has many advantages over continuously fed reactor systems for treatment of organic solid wastes. In this study the effect of percolation frequency on yield of biohydrogen production from fruit and vegetable wastes using dry fermentation system was examined. For this purpose 2 times percolation per day, 1 time percolation per day and 1 time percolation per 2 days frequency were compared and the hydrogen yields were observed as; 57 mL H₂/gVS_removed, 53 mL H₂/gVS_removed and 68 mL H₂/gVS_removed respectively. The percolation frequency didn't affect the overall yield but significantly affected the biohydrogen producing reactor of the dry fermentation system. 80% of the hydrogen was produced in percolation tank during 1 time per 2 days feeding and almost all hydrogen production was conducted in dry fermenter during 2 times per day percolation. Therefore the percolation frequency is found to be very important for system operation characteristics.     

Optimization of fermentative hydrogen production process using genetic algorithm based on neural network and response surface methodology

A central composite design was carried out to investigate the effect of temperature, initial pH and glucose concentration on fermentative hydrogen production by mixed cultures in batch test. The modeling abilities of the response surface methodology model and neural network model, as well as the optimizing abilities of response surface methodology and the genetic algorithm based on a neural network model were compared. The results showed that the root mean square error and the standard error of prediction for the neural network model were much smaller than those for the response surface methodology model, indicting that the neural network model had a much higher modeling ability than the response surface methodology model. The maximum hydrogen yield of 289.8 mL/g glucose identified by response surface methodology was a little lower than that of 360.5 mL/g glucose identified by the genetic algorithm based on a neural network model, indicating that the genetic algorithm based on a neural network model had a much higher optimizing ability than the response surface methodology. Thus, the genetic algorithm based on a neural network model is a better optimization method than response surface methodology and is recommended to be used during the optimization of fermentative hydrogen production process.     

Assessment of two ionic exchange membranes in a bioelectrochemical system for wastewater treatment and hydrogen production

Bioelectrochemical systems are devices where organic matter (e.g. wastewater) is oxidized through exoelectrogenic bacteria; this process is a new alternative to energy crisis and to mitigate climate change. If the products of such oxidation are electrons they are called microbial fuel cell (MFC), otherwise if the product is hydrogen these devices are called microbial electrolysis cells (MEC) Mostly, MEC's studies have reported double chamber designs, where the anode and cathode are separated by an ion exchange membrane. Nafion is a proton exchange membrane widely used to study bioelectrochemical devices; however, to our knowledge there are no reports of bipolar membranes (BPM) in these systems. In this study, a double-chambered MEC was constructed to evaluate the performance of the system using Nafion^® 117, and FUMASEP^®FBM bipolar membrane, separately. Biofilm formation was monitored by cyclic voltammetry and open circuit potential (OCP); maximum power for MFC-Nafion and MFC-BPM were 105.1 and 3.6 mW/m², respectively. Hydrogen yield and COD removal were significantly different for both MEC systems. Whereas COD removal for MEC-BPM was 44.8%; MEC-Nafion exhibited a COD removal of 87.4%. Solely the latter system produced hydrogen, with a yield of 7.6%.     

High hydrogen production rate in a submerged membrane anaerobic bioreactor

Batch cultivation of an anaerobic consortium fed with glucose as sole carbon source showed a sharp decrease of the hydrogen productivity when volatile fatty acids (VFA) concentration exceeded 12.5 g L^?1. To avoid VFA accumulation, fermentative batch cultures were thereafter carried out with a submerged membrane anaerobic bioreactor to continuously remove hydrogen fermentation co-products, while retaining the biomass. The membrane made it possible to separate the residence times of bacterial biomass and hydraulic part. With this technology, average and maximal productivities reached 0.75 and 2.46 L_H2 L^?1 h^?1, corresponding to an increase of 44 and 51% in comparison to the control, respectively. By removing the VFAs from the cultivation medium, H₂-producing pathways were favored, confirming the metabolic inhibitory effects of co-product accumulation in fermentation medium. Such hydrogen productivity is one of the highest values encountered in the literature. Readily implementable, such technology offers a good opportunity for further developing high rate hydrogen fermentation bioprocesses.     

Thermophilic dark fermentation of untreated rice straw using mixed cultures for hydrogen production

Biohydrogen production from untreated rice straw using different heat-treated sludge, initial cultivation pH, substrate concentration and particle size was evaluated at 55 °C. The peak hydrogen production yield of 24.8 mL/g TS was obtained with rice straw concentration 90 g TS/L, particle size <0.297 mm and heat-treated sludge S1 at pH 6.5 and 55 °C in batch test. Hydrogen production using sludge S1 resulted from acetate-type fermentation and was pH dependent. The maximum hydrogen production (P), production rate (R_m) and lag (λ) were 733 mL, 18 mL/h and 45 h respectively. Repeated-batch operation showed decreasing trend in hydrogen production probably due to overloading of substrate and its non-utilization. PCR-DGGE showed both hydrolytic and fermentative bacteria (Clostridium pasteurianum, Clostridium stercorarium and Thermoanaerobacterium saccharolyticum) in the repeated-batch reactor, which perhaps in association led to the microbial hydrolysis and fermentation of raw rice straw avoiding the pretreatment step.     

Experimental investigation on dyeing wastewater treatment and by-product hydrogen with a reverse electrodialysis flocculator

Hydrogen production and dye degradation can be achieved simultaneously in a hybrid system of reverse electrodialysis（RED）and electrocoagulation (EC), using current derived from the salinity gradient energy. Under the current, Fe electrode is used as the anode to produce Fe²⁺(subsequently oxidized to Fe³⁺) which combines with OH⁻ produced from the cathode to remove the dyes, while the hydrogen gas produced by the cathode is collected by a hydrogen collection device. The experiments are carried out to investigate the effects of different initial concentrations, pH, currents, electrode rinse solution (ERS) flow rates and the addition of chlorine on the degradation rate and hydrogen production. The results indicate that the degradation rate and hydrogen production could reach 98.3% and 150 m h⁻¹ at alkaline condition (pH = 11) and acidic condition (pH = 3) respectively, with a current of 0.4 A. The degradation rate and hydrogen production increase significantly with an increase in current.     

Opportunities and challenges for thermally driven hydrogen production using reverse electrodialysis system

Ongoing and emerging renewable energy technologies mainly produce electric energy and intermittent power. As the energy economy relies on banking energy, there is a rising need for chemically stored energy. We propose heat driven reverse electrodialysis (RED) technology with ammonium bicarbonate (AmB) as salt for producing hydrogen. The study provides the authors’ perspective on the commercial feasibility of AmB RED for low grade waste heat (333 K–413 K) to electricity conversion system. This is to our best of knowledge the only existing study to evaluate levelized cost of energy of a RED system for hydrogen production. The economic assessment includes a parametric study, and a scenario analysis of AmB RED system for hydrogen production. The impact of various parameters including membrane cost, membrane lifetime, cost of heating, inter-membrane distance and residence time are studied. The results from the economic study suggests, RED system with membrane cost less than 2.86 €/m², membrane life more than 7 years and a production rate of 1.19 mol/m²/h or more are necessary for RED to be economically competitive with the current renewable technologies for hydrogen production. Further, salt solubility, residence time and inter-membrane distance were found to have impact on levelized cost of hydrogen, LCH. In the present state, use of ammonium bicarbonate in RED system for hydrogen production is uneconomical. This may be attributed to high membrane cost, low (0.72 mol/m²/h) hydrogen production rate and large (1,281,436 m²) membrane area requirements. There are three scenarios presented the present scenario, market scenario and future scenario. From the scenario analysis, it is clear that membrane cost and membrane life in present scenario controls the levelized cost of hydrogen. In market scenario and future scenario the hydrogen production rate (which depends on membrane properties, inter-membrane distance etc.), the cost of regeneration system and the cost of heating controls the levelized cost of hydrogen. For a thermally driven RED system to be economically feasible, the membrane cost not more than 20 €/m²; hydrogen production rate of 3.7 mol/m²/h or higher and cost of heating not more than 0.03 €/kWh for low grade waste heat to hydrogen production.     

Biological hydrogen production via dark fermentation: A holistic approach from lab-scale to pilot-scale

Biohydrogen is considered as fuel of future owing to its distinctive attribute for clean energy generation, waste management and high energy content. Suitable feedstock play important role for achieving high rate hydrogen production via dark fermentation process. In this regard, different organic wastes such as cane molasses, distillery effluent and starchy wastewater were examined as potential substrates for biohydrogen production by Enterobacter cloacae IIT-BT 08. Groundnut deoiled cake (GDOC) was considered as additional nutritional supplement to enhance biohydrogen yields. The maximum hydrogen yield of 12.2 mol H₂ kg⁻¹ COD_removed was obtained using cane molasses and GDOC as co-substrates. To further ensure reliability of the process, bench (50 L) and pilot scale (10000 L) bioreactors were customized and operated. The pilot scale study achieved 76.2 m³ hydrogen with a COD removal and energy conversion efficiency of 18.1 kg m⁻³ and 37.9%, respectively. This study provides an extensive strategy in moving from lab to pilot scale biohydrogen production thereby, providing further opportunity for commercial exploitation.