Enhancement of batch biohydrogen production from prehydrolysate of acid treated oil palm empty fruit bunch

Carbohydrates from hydrolyzed biomass has been a potential feedstock for fermentative hydrogen production. In this study, oil palm empty fruit bunch (OPEFB) was treated by sulfuric acid in different concentrations at 120 °C for 15 min in the autoclave. The optimal condition for pretreatment was obtained when OPEFB was hydrolyzing at 6% (w/v) sulfuric acid concentration, which gave the highest total sugar of 26.89 g/L and 78.51% of sugar production yield. However, the best conversion efficiency of OPEFB pretreatment was 39.47 at sulfuric acid concentration of 4%. A series of batch fermentation were performed to determine the effect of pH in fermentation media and the potential of this prehydrolysate was used as a substrate for fermentative hydrogen production under optimum pretreatment conditions. The prehydrolysate of OPEFB was efficiently converted to hydrogen via fermentation by acclimatized mixed consortia. The maximum hydrogen production was 690 mL H₂ L⁻¹ medium, which corresponded to the yield of 1.98 molH₂/mol_xylose achieved at pH 5.5 with initial total sugar concentration of 5 g/L. Therefore, the results implied that OPEFB prehydrolysate is prospective substrate for efficient fermentative hydrogen conducted at low controlled pH. No methane gas was detected throughout the fermentation.     

Optimization of culture conditions for biohydrogen production from sago wastewater by Enterobacter aerogenes using Response Surface Methodology

Sago wastewater (SWW) causes pollution to the environment due to its high organic content. Annually, about 2.5 million tons of SWW is produced in Malaysia. In this study, the potential of SWW as a substrate for biohydrogen production by Enterobacter aerogenes (E. aerogenes) was evaluated. Response Surface Methodology (RSM) was employed to find the optimum conditions. From preliminary optimization, it was found that the most significant factors were yeast extract, temperature, and inoculum size. According to Face Centered Central Composite Design (FCCCD), the maximum hydrogen concentration and yield were 630.67 μmol/L and 7.42 mmol H₂/mol glucose, respectively, which is obtained from the sample supplemented with 4.8 g/L yeast extract concentration, 5% inoculum, and incubated at the temperature of 31 °C. Cumulative hydrogen production curve fitted by the modified Gompertz equation suggested that H_max, R_max, and λ from this study were 15.10 mL, 2.18 mL/h, and 9.84 h, respectively.     

Optimization of dilute acid and enzymatic hydrolysis for dark fermentative hydrogen production from the empty fruit bunch of oil palm

Pretreatment of the empty fruit brunch (EFB) from oil palm was investigated for H₂ fermentation. The EFB was hydrolyzed at various temperatures, H₂SO₄ concentrations, and reaction times. Subsequently, the acid-hydrolysate underwent enzymatic saccharification under various temperature, pH, and enzymatic loading conditions. Response surface methodology derived the optimum sugar concentration (SC), hydrogen production rate (HPR), and hydrogen yield (HY) as 28.30 g L⁻¹, 2601.24 mL H₂ L⁻¹d⁻¹, and 275.75 mL H₂ g⁻¹ total sugar (TS), respectively, at 120 °C, 60 min of reaction, and 6 vol% H₂SO₄, with the combined severity factor of 1.75. Enzymatic hydrolysis enhanced the SC, HY, and HPR to 34.52 g L⁻¹, 283.91 mL H₂ g⁻¹ TS, and 3266.86 mL H₂ L⁻¹d⁻¹, respectively, at 45 °C, pH 5.0, and 1.17 mg enzyme mL⁻¹. Dilute acid hydrolysis would be a viable pretreatment for biohydrogen production from EFB. Subsequent enzymatic hydrolysis can be performed if enhanced HPR is required.     

Enhancement of hydrogen production rate by high biomass concentrations of Thermotoga neapolitana

The objective of this study was to enhance the hydrogen production rate of dark fermentation in batch operation. For the first time, the hyperthermophilic pure culture of Thermotoga neapolitana cf. Capnolactica was applied at elevated biomass concentrations. The increase of the initial biomass concentration from 0.46 to 1.74 g cell dry weight/L led to a general acceleration of the fermentation process, reducing the fermentation time of 5 g glucose/L down to 3 h with a lag phase of 0.4 h. The volumetric hydrogen production rate increased from 323 (±11) to 654 (±30) mL/L/h with a concomitant enhancement of the biomass growth and glucose consumption rate. The hydrogen yield of 2.45 (±0.09) mol H₂/mol glucose, the hydrogen concentration of 68% in the produced gas and the composition of the end products in the digestate, i.e. 62.3 (±2.5)% acetic acid, 23.5 (±2.9)% lactic acid and 2.3 (±0.1)% alanine, remained unaffected at increasing biomass concentrations.     

Optimization of media composition for hydrogen gas production from hydrolyzed wheat starch by dark fermentation

Effects of N/C, P/C and Fe(II)/C ratios in fermentation medium on biohydrogen production by dark fermentation of acid-hydrolyzed wheat starch was investigated. The powdered wheat was autoclaved at pH = 3 and 90 °C for 15 min and the resulting sugar solution was fermented after external addition of N, P and Fe(II) to overcome nutrient limitations. Box–Wilson statistical experiment design was used by considering the N/C (0–0.05, w w⁻¹), P/C (0–0.02) and Fe(II)/C (0–0.03) ratios as the independent variables while the hydrogen yield and specific hydrogen production rate (SHPR) were the objective functions to be optimized. A quadratic response function was used to correlate the response functions with the independent variables. Low levels of the variables (N/C < 0.02, P/C < 0.01, Fe(II)/C < 0.01) resulted in low hydrogen yield and SHPR due to nutrient limitations and high levels of nutrients caused inhibitions. The optimum conditions yielding the maximum hydrogen yield (Y = 2.84 mol H₂ mol⁻¹ glucose) were N/C = 0.02, P/C = 0.008 and Fe(II)/C = 0.015. The maximum SHPR (96 mL H₂ g⁻¹ biomass h⁻¹) was obtained at N/C = 0.025, P/C = 0.008 and Fe(II)/C = 0.015 (w w⁻¹).     

Metal nanoparticle-embedded super porous poly(3-sulfopropyl methacrylate) cryogel for H2 production from chemical hydride hydrolysis

Poly(3-sulfopropyl methacrylate) (p(SPM)) cryogel was prepared under cryogenic conditions (T = −18 °C) and used as template for in situ metal nanoparticle preparation of Co, Ni and Cu. These metal nanoparticle-containing super macroporous cryogel composites were tested for H₂ production from hydrolysis of sodium borohydride (NaBH₄) and ammonia borane (AB). It was found that amongst p(SPM)-M (M: Co, Ni, and Cu) composite catalyst systems, the catalytic performances of Co- and Ni-containing p(SPM) cryogel composite catalyst systems were the same, however in hydrolysis of NH₃BH₃, the order of performance of the catalysts was Co > Ni > Cu. Interestingly, p(SPM)-Co cryogel composite demonstrated better catalytic performances in salt environments e.g., faster H₂ production rate in sea and tap water compared to DI water, and almost no effect of ionic strength of the solution medium was observed, but the salt types were found to affect the H₂ generation rate. Other parameters that affect H₂ production rate such as metal type, temperature, water source, salt concentration, amount of metal nanocatalyst and reusability were investigated. It was found that the hydrogen generation rate (HGR) was increased to 2836 ± 90 from 1000 ± 53 (ml H₂)(g of Co min)⁻¹ by multiple loading and reduction cycles of Co catalyst. Also, it was found that TOF values are highly temperature dependent, and increased to 15.1 ± 0.8 from 2.4 ± 0.1 (mol H₂)(mol catalyst min)⁻¹ by increasing the temperature from 30 to 70 °C. The activation energy, activation enthalpy and activation entropy were determined as 40.8 kJ (mol)⁻¹, 37.23 kJ (mol K)⁻¹, and −170.87 J (mol K)⁻¹, respectively, for the hydrolysis reaction of NaBH₄ with p(SPM)-Co catalyst system, and 25.03 kJ (mol)⁻¹, 22.41 kJ (mol K)⁻¹, and −182.8 J (mol K)⁻¹, respectively, for AB hydrolysis catalyzed by p(SPM)-Co composite system.     

Dark fermentative biohydrogen production using pretreated Scenedesmus obliquus biomass under an integrated paradigm of biorefinery

In recent times, biohydrogen production from microalgal feedstock has garnered considerable research interests to sustainably replace the fossil fuels. The present work adapted an integrated approach of utilizing deoiled Scenedesmus obliquus biomass as feedstock for biohydrogen production and valorization of dark fermentation (DF) effluent via biomethanation. The microalgae was cultivated under different CO₂ concentration. CO₂-air sparging of 5% v/v supported maximum microalgal growth and carbohydrate production with CO₂ fixation ability of 727.7 mg L^?1 d^?1. Thereafter, lipid present in microalgae was extracted for biodiesel production and the deoiled microalgal biomass (DMB) was subjected to different pretreatment techniques to maximize the carbohydrate recovery and biohydrogen yield. Steam heating (121 °C) in coherence with H₂SO₄ (0.5 N) documented highest carbohydrate recovery of 87.5%. DF of acid-thermal pretreated DMB resulted in maximum H₂ yield of 97.6 mL g^?1 VS which was almost 10 times higher as compared to untreated DMB (9.8 mL g^?1 VS). Subsequent utilization of DF effluent in biomethanation process resulted in cumulative methane production of 1060 mL L^?1. The total substrate energy recovered from integrated biofuel production system was 30%. The present study envisages a microalgal biorefinery to produce biohydrogen via DF coupled with concomitant CO₂ sequestration.     

Identification of factors that accelerate hydrogen production by Clostridium butyricum RAK25832 using casamino acids as a nitrogen source

The ability of Clostridium butyricum RAK25832 to use casamino acids as a nitrogen source was investigated. Strain RAK25832 showed the capacity to utilize different types of carbon sources. With glucose as a carbon source (10 g/L), the preferred final concentration of casamino acids was 26.67 g/L, with a cumulative hydrogen production, production rate, and yield of 2505 mL H₂/L, 160 mL/h, and 1.81 mol H₂/mol glucose, respectively. Eighteen metal elements were screened to identify the most important metals for biohydrogen production, and four elements were optimized. The optimal medium composition was MgCl₂·6H₂O (0.1 g/L), K₂HPO₄·3H₂O (6.67 g/L), NaHCO₃ (2.6 g/L), and FeCl₂·4H₂O (0.002 g/L). Vitamin supplementation of the medium showed no significant effect on hydrogen production. Under the optimized conditions, cumulative hydrogen production reached 3074 mL H₂/L. This is the first study to demonstrate the use of casamino acids as a nitrogen source by C. butyricum.     

Simulation and optimization of hydrogen production by steam reforming of natural gas for refining and petrochemical demands in Lebanon

Steam reforming of natural gas produces the majority of the world's hydrogen (H₂) and it is considered as a cost-effective method from a product yield and energy consumption point of view. In this work, we present a simulation and an optimization study of an industrial natural gas steam reforming process by using Aspen HYSYS and MATLAB software. All the parameters were optimized to successfully run a complete process including the hydrogen production zone units (reformer reactor, high temperature gas shift reactor HTS and low temperature gas shift reactor LTS) and the purification zone units (absorber and methanator). Optimum production of hydrogen (87,404 MT/year) was obtained by fixing the temperatures in the reformer and the gas shift reactors (HTS & LTS) at 900 °C, 500 °C and 200 °C respectively while maintaining a pressure of 7 atm, and a steam to carbon ratio (S/C) of 4. Moreover, ~99% of the undesired CO₂ and CO gases were removed in the purification zone and a reduction of energy consumption of 77.5% was reached in the heating and cooling units of the process.     

Catalyst modification strategies to enhance the catalyst activity and stability during steam reforming of acetic acid for hydrogen production

A high energy content (∼122 MJ/kg H₂) and presence of hydrogen-bearing compounds abundance in nature make hydrogen forth runner candidate to fulfill future energy requirements. Biomass being abundant and carbon neutral is one of the promising source of hydrogen production. In addition, it also addresses agricultural waste disposal problems and will bring down our dependency on fossil fuel for energy requirements. Biomass-derived bio-oil can be an efficient way for hydrogen production. Acetic acid is the major component of bio-oil and has been extensively studied by the researchers round the globe as a test component of bio-oil for hydrogen generation. Hydrogen can be generated from acetic acid via catalytic steam reforming process which is thermodynamically feasible. A number of nickel-based catalysts have been reported. However, the coke deposition during reforming remains a major challenge. In this review, we have investigated all possible reactions during acetic acid steam reforming (AASR), which can cause coke deposition over the catalyst surface. Different operating parameters such as temperature and steam to carbon feed ratio affect not only the product distribution but also the carbon formation during the reaction. Present review elaborates effects of preparation methods, active metal catalyst including bimetallic catalysts, type of support and microstructure of catalysts on coke resistance behavior and catalyst stability during reforming reactions. The present study also focuses on the effects of a combination of a variety of alkali and alkaline earth metals (AAEM) promoters on coke deposition. Effect of specially designed reactors and the addition of oxygen on carbon deposition during AASR have also been analyzed. This review based on the available literature focuses mainly on the catalyst deactivation because of coke deposition, and possible strategies to minimize catalyst deactivation during AASR.