Biohydrogen production from thermochemically pretreated corncob using a mixed culture bioaugmented with Clostridium acetobutylicum

Bovine ruminal fluid (BRF) bioaugmented with Clostridium acetobutylicum (Clac) was assessed for hydrolyzing cellulose and produce biohydrogen (BioH₂) simultaneously from pretreated corncob in a single step, without the use of external hydrolytic biocatalysts. The corncob was pretreated using three thermochemical methods: H₂SO₄ 2%, 160 °C; NaOH 2%, 140 °C; NaOCl 2%, 140 °C; autohydrolysis: H₂O, 190 °C. Subsequently, BioH₂ production was carried out using the pretreated material with the highest digestibility applying a Taguchi experimental array to identify the optimal operating conditions. The results showed a higher glucose released from pretreated corncob with H₂SO₄ (134.7 g/L) compared to pretreated materials by autohydrolysis, NaOH and NaOCl (123 g/L, 89.8 g/L and 52.9 g/L, respectively). The mixed culture was able to hydrolyze the pretreated corncob and produce 575 mL of H₂ (at 35 °C, pH 5.5, 1:2 ratio of BRF:Clac and 5% of solids loading) equivalent to 132 L H₂/Kg of biomass.     

Screening and optimization of pretreatments in the preparation of sugarcane bagasse feedstock for biohydrogen production and process optimization

This work evaluated the effects of individual alkaline, sodium carbonate (Na₂CO₃ denoted as; NaC), sodium sulfide (Na₂SO₃ denoted as; NaS) and combination of NaC + NaS pretreatment for the saccharification of sugarcane bagasse (SCB). The effects of different pretreatments on chemical composition and structural complexity of SCB in relation with its saccharification were investigated. For enzymatic hydrolysis of pretreated SCB we have utilized the produced crude enzymes by Streptomyces sp. MDS to make the process more cost effective. A enzyme dose of 30 filter paperase (FPU) produced a maximum reducing sugar (RS) 592 mg/g with 80.2% hydrolysis yield from NaC + NaS pretreated SCB under optimized conditions. The resulted enzymatic hydrolysates of each pretreated SCB were applied for hydrogen production using Clostridium beijerinckii KCTC1785. NaC + NaS pretreated SCB hydrolysates exhibited maximum H₂ production relative to other pretreatment methods. Effects of temperature, initial pH of culture media and increasing NaC + NaS pretreated SCB enzymatic hydrolysates concentration (2.5–15 g/L) on bioH₂ production were investigated. Under the optimized conditions, the cumulative H₂ production, H₂ production rate, and H₂ yield were 1485 mL/L, 61.87 mL/L/h and 1.24 mmol H₂/mol of RS (0.733 mmol H₂/g of SCB), respectively. The efficient conversion of the SCB hydrolysate to H₂ without detoxification proves the viability of process for cost-effective hydrogen production.     

Vanadium-ceria catalysts for H2S abatement from biogas to feed to MCFC

Vanadium-based catalysts supported on ceria were studied for the direct and selective oxidation of H₂S to sulphur and water at low temperature.Catalysts with two vanadium loading (20–50 wt% of V₂O₅) were prepared, characterized and tested at temperature of 150–200 °C in order to identify the best catalytic formulation. The most promising catalyst was the sample with the 20 wt% of V₂O₅ that showed 99% of sulphur selectivity and equilibrium H₂S conversion at 150 °C.The effect of the components of a typical biogas stream (CH₄, CO₂ and H₂O) was studied at 150 °C in order to investigate the possible formation of secondary products such COS, CS₂. No significant effect was observed in terms of H₂S conversion (99%) and selectivity to SO₂ (<1%) by adding CH₄ and CO₂ to the feed stream. Furthermore, the effect of the H₂S inlet concentration, temperature, contact time and molar feed ratio (O₂/H₂S) were also investigated at a reaction temperature of 80 °C.Finally, time on stream tests of 30 h were performed at 80 and 120 °C, in order to examine the catalyst stability.     

Experimental investigation of ignition and combustion characteristics of single coal and biomass particles in O2/N2 and O2/H2O

Oxy-steam combustion is a potential new-generation option for CO₂ capture and storage. The ignition and combustion characteristics of single coal and biomass particles were investigated in a flow tube reactor in O₂/N₂ and O₂/H₂O at various oxygen concentrations. The ignition and combustion processes were recorded using a CCD camera, and the two-color pyrometry was used to estimate the volatile flame temperature and char combustion temperature. In O₂/N₂ and O₂/H₂O, coal ignites heterogeneously at <O₂> = 21–50%. In O₂/N₂, biomass ignites homogeneously at <O₂> = 21–30%, while it ignites heterogeneously at <O₂> = 40–50%. In O₂/H₂O, biomass ignites homogeneously at <O₂> = 21–50%. With increasing oxygen concentration, the ignition delay time, volatile burnout time and char burnout time are decreased, and the volatile flame temperature and char combustion temperature are increased. At a certain oxygen concentration in both atmospheres, the ignition delay time, volatile burnout time and char burnout time of biomass are shorter than those of coal. Moreover, biomass has a higher volatile flame temperature but a lower char combustion temperature than coal. The ignition delay time, volatile burnout time and char burnout time in O₂/H₂O are lower than those in O₂/N₂ for coal and biomass. The presence of H₂O can improve the combustion rates of coal and biomass. The volatile flame shows a lower temperature in O₂/H₂O than in O₂/N₂ at <O₂> = 21–50%. The char combustion shows a lower temperature in O₂/H₂O than in O₂/N₂ at <O₂> = 21–30%, while this behavior is switched at <O₂> = 40–50%. The results contribute to the understanding of the ignition and combustion characteristics of coal and biomass in oxy-steam combustion.     

Effect of inoculum pre-treatment on mesophilic hydrogen and methane production from food waste using two-stage anaerobic digestion

Two-stage anaerobic digestion of food waste was performed using four different inoculum pre-treatment methods to enrich hydrogen (H₂) producing bacteria from sludge. The pretreatments used in this study included heat shock, alkaline treatment, aeration, and a novel pretreatment using waste frying oil (WFO). Alkaline pretreatment and aeration did not completely inhibit methanogens in the first stage while no methane (CH₄) was detected in the reactors cultivated either with heat shock or WFO-pretreated inocula. The highest H₂ and CH₄ yields (76.1 and 598.2 mL/gVS, respectively) were obtained using the inoculum pretreated with WFO. The highest total energy yield (21.96 kJ/gVS) and total organic carbon (TOC) removal efficiencies (95.77%) were obtained using inoculum pretreatment with WFO. The total energy yield trend obtained using the different pretreatments was as follows: WFO > alkaline > heat > aeration > control.     

Optimization of various pretreatments condition of kenaf core (Hibiscus cannabinus) fibre for sugar production: Effect of chemical compositions of pretreated fibre on enzymatic hydrolysability

In this work, the effects of various pretreatments’ parameters on kenaf core fibre were analyzed statistically and optimized using Response Surface Methodology based on the total glucose yield. The chemical compositions of the pretreated fibres were examined to discuss the effect of pretreatment on the fibre hydrolysability comprehensively. The results showed that estimation model for each pretreatment of kenaf core fibre were polynomial equations. The optimum conditions for water, acid and alkali pretreatments were 170 °C for 45 min, 120 °C for 90 min in 2.0% H₂SO₄ solution and 140 °C for 60 min in 3.0% NaOH solution, respectively. Among the three pretreatments, water pretreatment achieved the highest total glucose yield (25.5%), followed by acid (20.0%) and alkali (18.2%) pretreatments. Based on chemical compositions analysis, both water and acid pretreatments were capable of eliminating almost 100% of hemicellulose with negligible removal of lignin while the alkali pretreatment removed both the lignin and hemicellulose more than 60%. This result revealed that the removal of hemicellulose showed greater influential in enhancing the enzymatic accessibility and hence, hydrolysability of kenaf core fibre.     

Pyrolysis of sugarcane bagasse pretreated with sulfuric acid

Pyrolysis is a promising technique for the recovery of useful gas, tar, and solid products from biomass waste. However, the low tar yields obtained from lignocellulosic biomass are a significant drawback. To enhance tar yields, sugarcane bagasse, which is the most abundant agricultural waste in Fiji, was pretreated at ambient temperature and atmospheric pressure using various sulfuric acid (H₂SO₄) concentrations. Here, the ether bonds of cellulose, hemicellulose, and lignin were partially hydrolyzed. The pretreated samples were then pyrolyzed at 500 °C, and it was confirmed that H₂SO₄-pretreatment disrupted the bagasse cell structure, with the thermogravimetry and differential thermogravimetry results confirming that decomposition occurred at lower temperatures after pretreatment. In addition, tar yields were significantly enhanced from 5.6 wt% to 13.4 wt% for the untreated and 3 M H₂SO₄-pretreated samples respectively. The main components detected in this tar product were levoglucosan, andcellulose-and hemicellulose-derived products, whose proportions were increased following pretreatment. Thus, our work demonstrates that dilute acid pretreatment enhances tar production from sugarcane bagasse due to the production of shorter chain components via the partial hydrolysis of ether bonds.     

Detailed investigation of NO mechanism in non-premixed oxy-fuel jet flames with CH4/H2 fuel blends

This study systematically investigates the detailed mechanism of nitrogen oxides (NO_x) in CH₄ and CH₄/H₂ jet flames with O₂/CO₂ hot coflow. After comprehensive validation of the modeling by experiments of Dally et al. [Proc. Combust. Inst. 29 (2002) 1147–1154]; the effects of CO₂ replacement of N₂, mass fraction of oxygen in the coflow (Y_O2), and mass fraction of hydrogen in the fuel jet (Y_H2) on NO formation and destruction are investigated in detail. For methane oxy-fuel combustion, the NNH route is found to control the NO formation at Y_O2 ≤ 3%, while both NNH and N₂O-intermediate routes dominate the NO production at 3% < Y_O2 < 10%. When Y_O2 ≥ 10%, NO is obtained mainly from thermal mechanism. Moreover, in the oxy-combustion of methane and hydrogen fuel blends with Y_O2 = 3%, with hydrogen addition the contribution of the NNH and prompt routes increases, while that of the N₂O-intermediate route decreases. Furthermore, the chemical effect of CO₂ is significant in reducing NO in both oxy-combustion of methane with Y_O2 ≤ 3% and combustion of methane and hydrogen fuel blends with Y_H2 ≤ 10%.     

Fuel cell operation on landfill gas at Penrose Power Station

This demonstration test successfully demonstrated the operation of a commercial phosphoric acid fuel cell (FC) on landfill gas (LG) at the Penrose Power Station in Sun Valley, CA. Demonstration output included operation up to 137 kW; 37.1% efficiency at 120 kW; exceptionally low secondary emissions (dry gas, 15% O₂) of 0.77 ppmV CO, 0.12 ppmV NO_x, and undetectable SO₂; no forced outages with an adjusted availability of 98.5%; and a total of 707 h of operation on LG. The LG pretreatment unit (GPU) operated for a total of 2297 h, including the 707 h with the FC, and documented total sulfur and halide removal to much lower than the specified <3 ppmV for the FC. The GPU flare safely disposed of the removed LG contaminants by achieving destruction efficiencies greater than 99%.     

Micro and nano-architectures of Co3O4 on Ni foam for electro-oxidation of methanol

Spinel Co₃O₄ material with different morphologies is directly grown on Ni foam by simple hydrothermal method and subsequent calcination processes. The direct growth of binder free active phase of Co₃O₄ on Ni foam is an effective approach to enhance the electrocatalytic activity of the material. The morphologies of Co₃O₄ strongly depend on the anion of the precursor salt used. Microflowers, microspheres and nanograss morphologies of Co₃O₄ are obtained using chloride, sulfate and acetate salts of cobalt, respectively. The BET surface areas of these cobalt oxide materials are found to increase in the order of microflower-Co₃O₄ (53 m² g^?1) < nanograss-Co₃O₄ (65 m² g^?1) < microsphere-Co₃O₄ (100 m² g^?1). The electrocatalytic activity of these Co₃O₄ materials has been tested for methanol oxidation by cyclic voltammetry and chronoamperometry. All three samples show low onset potentials (0.32–0.34 V) for methanol oxidation. The vanodic peak current of methanol oxidation is found to increase in the order of microflower-Co₃O₄ (28 A g^?1) < nanograss-Co₃O₄ (34.9 A g^?1) < microsphere-Co₃O₄ (36.2 A g^?1) at 0.6 V. This study highlights the significance of the morphology of cobalt oxide in the development of oxide based non-precious electrocatalysts for methanol oxidation.     

Effect of acid passivation and H2 sputtering pretreatments on the adhesive strength of sol–gel derived Hydroxyapatite coating on titanium surface

In this study, in order to increase the adhesive strength of a Hydroxyapatite (HA) coating, deposited on the surface of commercially pure titanium, acid passivation and hydrogen sputtering pretreatments were used. The pure titanium surfaces were passivized by acid solution and treated by hydrogen sputtering, at a temperature of 300 °C for 1 h. Ca(NO₃)₂·4H₂O and NH₄H₂PO₄ were chosen as starting precursors for Ca and P sources. HA coatings on the titanium surface were deposited using the sol–gel method and sintered in air at the temperatures of 750^oC-900 °C for 1 h. XRD, SEM, EDS and AFM analysis techniques were used for structural and morphological characterization. Scratch test was performed for determining the adhesion of HA coatings. The experimental results indicated that compact and crack free HA coating, which has a Ca/P ratio of 1:6, was formed on pure Titanium (Ti) surface. The adhesive strength values of the HA coating, pretreated with H₂ sputtering and acid passivation were found to be 72.84 MPa and 55.83 MPa at temperature of 900 °C, respectively. It was observed that H₂ plasma sputtering pretreatment, improved the adhesive strength of the HA coatings compared to pretreatment with acid passivation.     

Identifying the roles of MFe2O4 (M=Cu,Ba, Ni,and Co) in the chemical looping reforming of char,pyrolysis gas and tar resulting from biomass pyrolysis

Biomass chemical looping gasification (BCLG), which employs oxygen carriers (OCs) as the gasification agent, is drawing more attention for its low cost and environmental friendliness. However, the complex products of biomass pyrolysis and the reactions between OCs and the pyrolysis products constrain its development. In this study, MFe₂O₄ (M = Cu, Ba, Ni and Co) ferrites synthesized via the sol-gel method were investigated as OCs in BCLG for hydrogen-rich syngas production. The properties of the as-prepared and spent OCs were characterized by X-ray diffraction (XRD), H₂-temperature programmed reduction (TPR), scanning electron microscopy (SEM), and automatic surface area porosimetry (BET). The three-phase products (char, pyrolysis gas and toluene) derived from biomass pyrolysis were employed as the reactants to investigate the reactivity of the ferrites. Then, BCLG experiments using biomass were conducted on the four ferrites to further determine their performance. The characterization results suggested that the four ferrites are all attractive for the chemical looping process, exhibiting good oxygen transferability and wide distributions of metal cations because of their metal synergistic effects in the spine structure. Reactions with pyrolysis gas and biomass char indicated that BaFe₂O₄ has a higher reactivity via a solid-solid reaction but a lower reactivity with pyrolysis gas, which make it very favorable for the production of hydrogen-rich syngas. Furthermore, BaFe₂O₄ showed excellent performance for toluene catalytic cracking with small amounts of carbon deposition. The synergetic effects between Ba and Fe metals considerably enhanced selective oxidation to produce 26.72% more H₂ than CoFe₂O₄ and 13.79% more H₂ than NiFe₂O₄ and CuFe₂O₄ for biomass gasification. The hydrogen yield produced by BaFe₂O₄ with the assistance of steam for biomass gasification can reach 41.8 mol/kg of biomass.     

Dilute-acid pretreatment of barley straw for biological hydrogen production using Caldicellulosiruptor saccharolyticus

The main objective of this study was to use the fermentability test to investigate the feasibility of applying various dilute acids in the pretreatment of barley straw for biological hydrogen production. At a fixed acid loading of 1% (w/w dry matter) 28–32% of barley straw was converted to soluble monomeric sugars, while at a fixed combined severity of −0.8 30–32% of the straw was converted to soluble monomeric sugars. With fermentability tests at sugar concentrations 10 and 20 g/L the extreme thermophilic bacterium Caldicellulosiruptor saccharolyticus showed good hydrogen production on hydrolysates of straw pretreated with H₃PO₄ and H₂SO₄, and to a lesser extent, HNO₃. The fermentability of the hydrolysate of straw pretreated with HCl was lower compared to the other acids but equally high as that of pure sugars. At sugar concentration 30 g/L the fermentability of all hydrolysates was low.     

Evaluation of Bunsen reaction at elevated temperature and high pressure in continuous co-current reactor in iodine-sulfur thermochemical process

Bunsen reaction is one of the three reaction steps of iodine-sulfur process. In present study, Bunsen reaction is carried out in co-current reactor to identify effect of different operating conditions on concentrations of Bunsen reaction product mixture. Bunsen reaction studies have been done in tubular reactor, which is made of tantalum tube and stainless steel jacket, in 50–80 °C temperature range, 2–6 bar (g) pressure range. Feed flow rates are varied for HIx (mixture of hydroiodic acid, water and iodine) 1.2 l/h - 3 l/h, SO₂ 0.02 g/s – 0.24 g/s and O₂ 0.008 g/s ?0.016 g/s. It has been observed that, increasing SO₂ feed flow rate and pressure results in increased mole fraction of HI in HIx phase and H₂SO₄ in sulfuric acid phase. Increase in temperature increased the mole fraction of HI in HIx phase but decreased the mole fraction of H₂SO₄ in sulfuric acid phase. Increase in feed I₂/H₂O ratio and HIx feed flow rate, decreased the mole fraction of HI in HIx phase. Higher pressure improved the conversion of Bunsen reactants to products.     

Gaseous products evolution during microwave pyrolysis of tire powders

Microwave pyrolysis of tire powders were run in a laboratory scale microwave oven (2.45 GHz). A special attention was dedicated to the yields of gaseous products during the microwave pyrolysis at different powers (300, 500, and 700 W). Triple-channel refinery gas chromatograph was used to quickly detect the gas composition of tire pyrolysis and its evolution during the process. H₂, CO, and CH₄, up to 90% of the total volume of pyrolytic gases, were the most predominant gaseous products. As the pyrolysis proceeded, the composition exhibited a significantly changes, e.g., more H₂ was produced and less CH₄ was generated. As the power increased, the content of CH₄ + CO₂ decreased, while the fractions of H₂ + CO rapidly increased at the intense stage of the microwave pyrolysis. The maximum yields of gaseous and liquid products and the maximum conversion of tires were obtained at 500 W.     

Effects of alumina powder characteristics on H2 and H2O2 production yields in γ-radiolysis of water and 0.4 M H2SO4 aqueous solution

The effects of powder characteristics on H₂ and H₂O₂ productions in ⁶⁰Co γ-radiolysis were studied in pure water and in 0.4 M H₂SO₄ aqueous solutions containing alumina powders. In 0.4 M H₂SO₄ solution, the H₂ yields strongly depended on alumina structures and decreased in the order of α > θ > γ-alumina, although the specific surface areas increased as α < θ < γ. The yields increased with increasing specific surface area when compared among α-alumina. In pure water, similar dependence was observed but not as strong as that for 0.4 M H₂SO₄ solution. The H₂O₂ yields were strongly decreased by adding the alumina powders in both water and 0.4 M H₂SO₄ aqueous solution, although the amounts of decrease were almost neither correlated with specific surface areas nor structures. The enhancing H₂ production was discussed in terms of the electron supply from alumina to aqueous solution as well as the adsorption of OH radicals on alumina surfaces.     

Enhanced hydrogen production in catalytic pyrolysis of sewage sludge by red mud: Thermogravimetric kinetic analysis and pyrolysis characteristics

The catalytic mechanism of red mud (RM) on the pyrolysis of sewage sludge was investigated. The thermogravimetric data were used to study the kinetic characteristics by using a discrete distributed activation energy model (DAEM) to clarify the effects of three main components (Fe₂O₃, Al₂O₃, SiO₂) in the RM on the pyrolysis of organic matters in sewage sludge. The modeling results showed that the pyrolysis of organic matters, especially at the higher temperature stage, was promoted by Fe₂O₃ and Al₂O₃ in the RM. Adding Fe₂O₃ or the RM alone could reduce the mean activation energy of sewage sludge pyrolysis by 13.9 and 20.1 kJ mol^?1, respectively. The modeling results were validated by pyrolysis experiments of raw sludge with different additives at 600, 700, 800, and 900 °C. The experimental results showed that the addition of Al₂O₃, Fe₂O₃ or the RM could produce more gas than the addition of SiO₂, especially at high temperatures. Fe₂O₃ and Al₂O₃ acted as catalysts in the tar decomposition by in-situ catalyzing the cracking of CC and CH bonds to produce more gases. Especially, Fe₂O₃ and Al₂O₃ increased the H₂ yield from sewage sludge pyrolysis at 700, 800, and 900 °C by 268.5 and 50.7%, 111.1 and 56.0%, 10.9 and 10.3%, respectively. The char obtained from pyrolysis of sewage sludge with the RM possessed magnetic property, which has various potential applications. The research indicates that the RM is an efficient catalyst in the pyrolysis of sewage sludge.     

Hydrogen-rich gas production from pyrolysis of wet sludge in situ steam agent

A series of wet sludge samples with different moisture contents were pyrolyzed in situ steam in a bench-scale fixed bed reactor in order to examine the influence of moisture and temperature on product distribution and gas composition. The results demonstrated that inherent moisture in wet sludge had a great effect on the product yield. The pyrolysis of wet sludge (43.38% moisture content) at 800 °C exhibited maximum H₂ yield (7.76 mol kg^?1 dry basis wet sludge) and dry gas yield (0.61 Nm³ kg^?1) and H₂ content of 42.13 vol%. When the moisture exceeded 43.38%, H₂ yield and gas yield both tended to decline. It was also shown that the elevated temperature exhibited a significant influence on gas content increase and tar reduction; at the same time, H₂ yield and H₂ content were increased from 1.83 mol kg^?1 dry basis wet sludge and 16.67 vol% to 9.15 mol kg^?1 dry basis wet sludge and 45.67 vol%, respectively, as temperature increased from 600 °C to 850 °C. LHV of fuel gas varies from 15.49 MJ Nm^?3 to 11.65 MJ Nm^?3 because of decrease in CH₄ and C₂H₄ content as temperature increasing. In conclusion, hydrogen rich gas production by pyrolysis of wet sludge which avoided pre-drying process and utilized in situ steam agent from wet sludge is an economic method.     

Steam reforming of model bio-oil compounds 2-butanone, 1-methoxy-2-propanol,ethyl acetate and butyraldehyde over Ni/Al2O3

Oil derived from fast pyrolysis of biomass (or bio-oil) is a candidate renewable feedstock for producing hydrogen (H₂). In this work, the steam reforming of model oxygenates present in the bio-oil aqueous fraction was studied in a fixed-bed reactor. Using Ni/Al₂O₃ catalyst, the reactions with 2-butanone, 1-methoxy-2-propanol, ethyl acetate and butyraldehyde were studied. To study the efficacy of the chosen catalyst for H₂ production, experiments were performed in the 623–773 K range using varying steam/carbon ratios in feed (15–25 mol/mol). The conversion of the various feeds was of the order: butyraldehyde > ethyl acetate > 1-methoxy-2-propanol > 2-butanone. The catalyst was characterized using SEM, XRD, TPR/TPD and TGA methods. It showed high stability for 7 h of time-on-stream.     

Improvement of gaseous bioenergy production from spent coffee grounds Co-digestion with pulp wastewater by physical/chemical pretreatments

Two steps of hydrolysis and anaerobic biogas production processes was investigated in this study. In the first step, subcritical water (SBW) hydrolysis and chemical (acid/alkali) pretreatments were carried out to enhance hydrolysis efficiency by obtaining and analyzing the total volatile fatty acids (TVFA), chemical oxygen demand (COD), and total sugar productions from spent coffee grounds (SCG) hydrolysate. The subcritical water (SBW) hydrolysis under the condition of temperature 150 °C for 30 min can greatly improve the organic matter breakdown and reached the COD concentration of 1010 g/L which was 30% higher than the untreated raw SCG. For chemical pretreatments, it was found that the alkaline hydrolysis of SCG resulted in the greatest total sugar concentration of 181 g/L whereas the operation conditions were 2.0 M NaOH at 60 °C for 1 h. The peak of TVFA concentration 3725 mg/L was found at the acid hydrolysis of SCG with 1.0 M H₂SO₄ acid, 60 °C for 1 h. The optimal biomethane yield of 115 mL/g COD was obtained when 1.0 M H₂SO₄ acid hydrolysate co-digestion with pulp wastewater which increase methane yield production 8 times of raw pulp wastewater. The pretreatment process was confirmed in this study can significant improve the converting of the biowastes to bioenergy efficiency.