Effect of temperature on fermentative hydrogen production by mixed cultures

Effect of temperatures ranging from 20 °C to 55 °C on fermentative hydrogen production by mixed cultures was investigated in batch tests. The experimental results showed that, at initial pH 7.0, during the fermentative hydrogen production using glucose as substrate, the substrate degradation efficiency and hydrogen production potential increased with increasing temperatures from 20 °C to 40 °C. The maximal substrate degradation efficiency was 98.1%, the maximal hydrogen production potential was 269.9 mL, the maximal hydrogen yield was 275.1 mL/g glucose and the shortest lag time was 7.0 h. The temperature for fermentative hydrogen production by mixed cultures was optimized to be 40 °C. The expanded Ratkowsky models could be used to describe the effect of temperatures on the hydrogen production potential, maximum hydrogen production rate and the lag time during fermentative hydrogen production.     

Characterization of microbial community in the two-stage process for hydrogen and methane production from food waste

The structure of a microbial community in the two-stage process for H₂ and CH₄ production from food waste was investigated by a molecular biological approach. The process was a continuous combined thermophilic acidogenic hydrogenesis and mesophilic (RUN1) or thermophilic (RUN2) methanogenesis with recirculation of the digested sludge. A two-phase process suggested in this study effectively separate H₂-producing bacteria from methanogenic archaea by optimization of design parameters such as pH, hydraulic retention time (HRT) and temperature. Galore microbial diversity was found in the thermophilic acidogenic hydrogenesis, Clostridium sp. strain Z6 and Thermoanaerobacterium thermosaccharolyticum were considered to be the dominant thermophilic H₂-producing bacteria. The hydrogenotrophic methanogens were inhibited in thermophilic methanogenesis, whereas archaeal rDNAs were higher in the thermophilic methanogenesis than those in mesophilic methanogenesis. The yields of H₂ and CH₄ were in equal range depending on the characteristics of food waste, whereas effluent water quality indicators were different obviously in RUN1 and RUN2. The results indicated that hydrolysis and removal of food waste were higher in RUN2 than RUN1.     

A novel integrated process for hydrogen production from biomass

A novel process, which integrated with biomass pyrolysis, gas–solid simultaneous gasification and catalytic reforming processes, was utilized to produce hydrogen. The effects of gasification temperature and reforming temperature on hydrogen yield and carbon conversion efficiency were investigated. The results showed that both higher gasification temperature and reforming temperature led to higher hydrogen yield and carbon conversion efficiency. Compared with the two-stage pyrolysis-catalytic reforming process, hydrogen yield and carbon conversion efficiency were greatly increased from 43.58 to 75.96 g H₂/kg biomass and 66.18%–82.20% in the integrated process.     

Effect of substrate concentration on fermentative hydrogen production from sweet sorghum extract

The aim of the present study was to assess the influence of substrate concentration on the fermentative hydrogen production from sweet sorghum extract, in a continuous stirred tank bioreactor. The reactor was operated at a Hydraulic Retention Time (HRT) of 12 h and carbohydrate concentrations ranging from 9.89 to 20.99 g/L, in glucose equivalents. The maximum hydrogen production rate and yield were obtained at the concentration of 17.50 g carbohydrates/L and were 2.93 ± 0.09 L H₂/L reactor/d and 0.74 ± 0.02 mol H₂/mol glucose consumed, corresponding to 8.81 ± 0.02 L H₂/kg sweet sorghum, respectively. The main metabolic product at all steady states was butyric acid, while ethanol production was high at high substrate concentrations. The experiments showed that hydrogen productivity depends significantly on the initial carbohydrate concentration, which also influences the distribution of the metabolic products.     

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.     

Constructing a new business model for fermentative hydrogen production from wastewater treatment

The development of hydrogen energy as a sustainable energy resource is essential for mitigating climate change. The primary challenge to the commercialization of hydrogen energy, relative to that of petrochemical fuels, is cost. Therefore, an innovative business model that converts the costs of procuring biomass into revenue via the production of hydrogen was developed. Profitable hydrogen production can typically be realized by lowering costs through continuous technological development and increasing scale. Feedstock procurement costs, however, limit the cost/benefit reduction flexibility. This study employs biowaste material as feedstock for biological fermentative hydrogen production. This model extends the hydrogen production value chain to include the income from biomass hydrogen production as well as the revenue from processing biowaste and reduced fuel source costs. This study investigates the costs involved in the commercialization of the hydrogen fermentation process, develops an innovative business model, and presents a case study to describe this model.     

Semi-pilot scale production of hydrogen from Organic Fraction of Solid Municipal Waste and electricity generation from process effluents

The production of hydrogen from Organic Fraction of Solid Municipal Waste (OFSMW) was studied on a semi-pilot scale. The potential of generating electricity using the process effluents was further assessed using a two-chambered Microbial Fuel Cell. A maximum hydrogen fraction of 46.7% and hydrogen yield of 246.93 ml H₂ g⁻¹ Total Volatile Solids was obtained at optimum operational setpoints of 7.9, 30.29 °C and 60 h for pH, temperature and hydraulic retention time (HRT) respectively. A maximum electrical power density of 0.21 W m^-2 (0.74 A m⁻²) was recorded at 500 Ω and the chemical oxygen demand (COD) removal efficiency of 50.1% was achieved from the process. The process economics of energy generation from organic wastes could be significantly improved by integrating a two-stage process of fermentative hydrogen production and electricity generation.     

接种量对易腐垃圾发酵产氢和产甲烷的影响研究

试验研究了不同接种量对易腐垃圾厌氧消化的影响.在垃圾投加量为发酵容积的25%,接种量为发酵容积的12.5%～75%时,垃圾发酵的产氢量与接种量无明显的相关性;当接种量由发酵容积的12.5%提高到37.5%,垃圾的TS降解量、VS降解量、产沼气总量、产甲烷量分别提高了4.2倍、1.6倍、7.9倍、1 972.3倍;当接种量由发酵容积的37.5%提高到75%时,垃圾的TS降解量与VS降解量、产沼气总量及产甲烷量无较大变化,但反应的抑制期从25 d缩短至15 d.试验结果表明,为稳定易腐垃圾厌氧发酵产气,接种量不宜低于发酵容积的37.5%.     

Effects of potential inhibitors present in dilute acid-pretreated corn stover on fermentative hydrogen production by Escherichia coli

This study reports the inhibitory compounds present in dilute sulfuric acid-pretreated corn stover for fermentative hydrogen production by Escherichia coli. The E. coli W3110-derived strain deficient in lactate and succinate production pathways was used. When dilute acid-treated corn stover liquor containing 175 mM acetate, 21 mM furfural, and 2.6 mM 5-hydroxymethylfurfural was added at fourfold dilution to the xylose-containing culture medium, the microbial growth and hydrogen production were almost completely inhibited. The addition of acetate, furfural, or 5-hydroxymethylfurfural, at up to 200, 80, or 40 mM, respectively, to the xylose- or glucose-containing medium led to dose-dependent inhibition of fermentative hydrogen production. No synergistic inhibition by furfural with acetate or 5-hydroxymethylfurfural at concentrations based on the corn stover hydrolysate was observed. Altogether, these results suggest that the inhibition of the E. coli-based hydrogen production by the corn stover hydrolysate is primarily attributed to acetate under the conditions used.     

Enhancement effect of zero-valent iron nanoparticle and iron oxide nanoparticles on dark fermentative hydrogen production from molasses-based distillery wastewater

This study investigates the effect of two different iron compounds (zero-valent iron nanoparticle: nZVI and iron oxide nanoparticles: nIO) and pH on fermentative biohydrogen production from molasses-based distillery wastewater. The nZVI and nIO of optimum particle sizes of 50 nm and 55 nm respectively were synthesized and applied for fermentative hydrogen (H₂) production. The addition of nIO & nZVI at (0.7 g/L, pH: 6) resulted in the highest H₂ yield, H₂ production rate, H₂ content and COD reduction. Moreover, the kinetic parameters of H₂ production potential (P) and H₂ production rate (R_m) increased to 387 mL, and 22.2 mL/h, respectively for nZVI, these values were 363 mL and 21.8 mL/h for nIO. The results obtained indicated the positive effect of nZVI and nIO addition on enhanced fermentative H₂ production. The addition of nZVI & nIO resulted in 71% and 69.4% enhancement in biohydrogen production respectively.     

Effects of biomass,COD and bicarbonate concentrations on fermentative hydrogen production from POME by granulated sludge in a batch culture

Effects of three selected variables viz. biomass concentration, initial chemical oxygen demand (COD) concentration and initial bicarbonate alkalinity (BA) on biological hydrogen production from palm oil mill effluent (POME) using the granulated sludge in batch culture were investigated. The experimental results were analyzed and modeled using a central composite design (CCD) of response surface methodology (RSM). In order to carry out a comprehensive analysis of the biohydrogen production process, indicative parameters namely hydrogen yield (Y_H), specific hydrogen production rate (SHPR), and COD removal efficiency were studied as the process responses. Maximum hydrogen yield (124.5 mmol H₂/g COD_removed) and specific hydrogen production rate (55.42 mmol H₂/g VSS.d) were achieved at COD_in 3000 and 6500 mg/l, MLVSS 4000 and 2000 mg/l, and initial BA 1100 mg CaCO₃/l, respectively.     

A modified method for production of hydrogen from methane

The steam–methane‐reformation (SMR) reaction has been modified by including sodium hydroxide in the reaction. It is found that the reaction: 2NaOH+CH₄+H₂O = Na₂CO₃+4H₂ takes place at much lower temperatures (300–600°C) than the SMR reaction (800–1200°C). The reaction rate is enhanced with a nickel catalyst. We have studied the effect of variously ball‐milled nickel on the reaction rate and determined the optimum particle size of the catalyst. Best results were achieved by grinding the catalyst for 2 h. Prolonged ball milling caused the nickel platelets to coalesce and grow in size decreasing the reaction rate. Copyright © 2011 John Wiley & Sons, Ltd.     

Characteristics of fermentative hydrogen production with Klebsiella pneumoniae ECU-15 isolated from anaerobic sewage sludge

Klebsiella pneumoniae ECU-15 (EU360791), which was isolated from anaerobic sewage sludge, was investigated in this paper for its characteristics of fermentative hydrogen production. It was found that the anaerobic condition favored hydrogen production than that of the micro-aerobic condition. Culture temperature and pH of 37 °C and 6.0 were the most favorable for the hydrogen production. The strain could grow in several kinds of monosaccharide and disaccharide, as well as the complicated corn stalk hydrolysate, with the best results exhibited in glucose. The maximum hydrogen production rate and yield of 482 ml/l/h and 2.07 mol/mol glucose were obtained at initial glucose concentration of 30 g/L and 5 g/L, respectively. Fermentation results in the diluent corn stalk hydrolysate showed that cell growth was not inhibited. However, the hydrogen production of 0.65 V/V was relatively lower than that of the glucose (1.11 V/V), which was mainly due to the interaction between xylose and glucose.     

A two-stage modelling and optimization of biohydrogen production from a mixture of agro-municipal waste

A two-stage modelling and optimization of biohydrogen production is reported. A mixture design was used to determine the optimum proportions of bean husk (BH), corn stalk (CS), and organic fraction of solid municipal waste (OFSMW). The optimum operational setpoints for substrate concentration, pH, temperature and hydraulic retention time (HRT) were further investigated using the box-behnken design. The quadratic polynomial model from the mixture design had a coefficient of determination (R²) of 0.9427 and the optimized mixtures were in the ratio of OFSMW:BH:CS = 30:0:0 and OFSMW:BH:CS = 15:15:0 with yields of 56.47 ml H₂/g TVS and 41.16 ml H₂/g TVS respectively. Optimization on physico-chemical process parameters on the improved substrate gave the setpoints of 40.45 g/l, 7.9, 30.29 °C, 86.28 h for substrate concentration, pH, temperature and HRT respectively having a predicted H₂ yield of 57.73 ml H₂/g TVS. Model validation gave 58.62 ml H₂/g TVS, thus an improvement of 3.8% on the optimized mixture. Biohydrogen production can be significantly enhanced by a suitable mixture of agro-municipal waste and operational optimal setpoints.     

Comprehensive study on a two-stage anaerobic digestion process for the sequential production of hydrogen and methane from cost-effective molasses

Two-stage anaerobic digestion process has been frequently applied to the sequential production of hydrogen and methane from various organic substrates/wastes. In this study, a cost-effective byproduct of food industry, molasses, was used as a sole carbon source for the two-stage biogas-producing process. The two-stage process consisted of two reactor parts named as the first-stage hydrogenic reactor (HR) operated at pH 5.5 and 35°C and the second-stage methanogenic reactor (MR) at pH 7.0 and 35°C. Microbial community analysis revealed that Clostridium butyricum was the major hydrogen-producing bacteria and methanogens consisted of hydrotrophic bacteria like Methanobacterium beijingense and acetotrophic bacteria like Methanothrix soehngenii. In the first-stage process, hydrogen could be efficiently produced from diluted molasses with the highest production rate of 2.8 (±0.22) L-H₂/L-reactor/d at the optimum HRT of 6 h. In the second-stage process, methane could be also produced from residual sugars and VFAs with a production rate of 1.48 (±0.09) L-CH₄/L-reactor/d at the optimum HRT of 6 d, at which overall COD removal efficiency of the two-stage process was determined to be 79.8%. Finally, economic assessment supported that cost-effective molasses was a potent carbon source for the sequential production of hydrogen and methane by two-stage anaerobic digestion process.     

Inhibitory effect of chloroform on fermentative hydrogen and methane production from lipid-extracted microalgae

To improve the sustainability of microalgae as a bioenergy feedstock, lipid-extracted microalgae (LEM) are often further treated by anaerobic digestion (AD). However, the residual chloroform used for extracting lipids as a solvent could inhibit this process, an aspect that has not been studied to date. In this study, the inhibitory effect of chloroform on H₂ and CH₄ production was investigated by performing batch tests. To prepare the feedstock, Chlorella vulgaris was ultrasonicated and the supernatant was discarded after centrifugation. In case of H₂ production, it was found that the H₂ yield fell to almost half that of the control (15.6 mL H₂/g COD_added) at 100 mg CHCl₃/L. The reason for the decrease of the H₂ yield with the increase of chloroform level was due to the change of metabolites from acetate and butyrate to lactate via a non-hydrogenic reaction. In comparison with H₂ production, a much more severe inhibitory effect of chloroform on CH₄ production was observed. The inhibitor concentration (IC_{30, 60, and 90}) on H₂ production was 138, 319, and 622 mg CHCl₃/L, respectively, while concentrations of 15, 37, and 86 mg CHCl₃/L were obtained on CH₄ production. When the chloroform concentration was ≥25 mg/L on CH₄ production, more than 2 g COD/L of organic acids remained, resulting in a decrease of CH₄ yield. These findings indicate that the residual chloroform in LEM should be seriously considered to prevent possible microbial inhibition when designing a process for additional energy recovery from microalgae via AD.     

Energy optimisation from co-digested waste using a two-phase process to generate hydrogen and methane

The total energy produced from co-digested food waste and sewage sludge was compared for single phase mesophilic anaerobic digestion producing methane and two-phase hydrogen production followed by methane production. Both single and two-phase reactors were operated at close to optimum conditions. The single phase methaniser had a methane yield of 0.48 m³ methane/kg VS destroyed. The two-phase system had a hydrogen yield of 0.13 m³ hydrogen/kg VS destroyed, and a methane yield of 0.67 m³ methane/kg VS destroyed. Introduction of a hydrogen producing, pre-treatment phase increased the overall VS destruction 69-89%, however the total energy yield decreased by 13.4% due to the low hydrogen yield obtained in the first stage. The release of ammonia in the hydrogeniser was low and so with less alkalinity available, pH control was necessary. It was much higher in the methaniser and adequate to buffer any pH change. This also ensures more nitrogen in the digestate to enhance its value for recycling. The two-stage process is an attractive option where solids destruction is an important consideration but further optimisation of the hydrogen production stage is still required.     

Design of integrated laboratory‐scale iodine sulfur hydrogen production cycle at INET

The iodine sulfur (IS) thermochemical water‐splitting process, which has various merits, is considered as one of the most promising nuclear hydrogen production methods and has been intensively studied by many institutions. At the Institute of Nuclear and New Energy Technology of Tsinghua University in China, a proof‐of‐concept closed IS facility was built, and a closed‐cycle experiment was conducted. Currently, as a prospective research item of the high‐temperature gas‐cooled reactor demonstration plant project, an integrated laboratory‐scale IS facility (IS‐100) that aims to achieve long‐term stable operation of IS cycle is being developed, and the design and optimization of the flowsheet for the IS cycle are conducted. The specifications of the facility are presented along with simulation models. Mass balance and compositions of the streams in the Bunsen, sulfuric acid, and HI sections are calculated using Aspen Plus software with OLI database and embedded self‐made models. Based on the comparison between mass of recycled streams and heat requirements as well as sensitivity analysis, the optimized flowsheet and the operational parameters are proposed. In addition, the preliminary closed cycle experiment results on IS‐100 were presented, and the efficiency of the IS process and the R&D efforts to improve its efficiency are discussed. Copyright © 2016 John Wiley & Sons, Ltd.     

Hydrogen and methane potential based on the nature of food waste materials in a two-stage thermophilic fermentation process

The purpose of this study is to investigate the biological H₂ and CH₄ potential based on the nature of organic waste materials in a two-stage thermophilic fermentation process. Three varieties of actual waste specifically potato, kitchen garbage and bean curd manufacturing waste (okara) were selected. The production rates for H₂ and CH₄ were as follows: potato, 2.1 and 1.2 l/l/d; garbage, 1.7 and 1.5 l/l/d; okara, 0.4 and 1.4 l/l/d in the continuous processes. The H₂ and CH₄ yields were 20–85 ml H₂/g VS_added and 329–364 ml CH₄/g VS_added, respectively. The H₂ yield increased and the CH₄ yield decreased in the order of potato, kitchen garbage and okara. The H₂ yield was shown to be not only dependent on the proportion of carbohydrate but also on the hydrolysis pH of the organic waste, which was influenced by the nature of the organic waste materials. Higher yields of H₂ or CH₄ were obtained when the hydrolysis pH of the organic waste was close to the optimum pH range of H₂-producing bacteria or methanogenic archaea in the two-stage fermentation processes.     

Continuous fermentative hydrogen and methane production from Laminaria japonica using a two-stage fermentation system with recycling of methane fermented effluent

In this study, a two-stage fermentation system to produce H₂ and CH₄ from Laminaria japonica was developed. In the first stage (dark fermentative H₂ production, DFHP), response surface methodology (RSM) with a Box-Behnken design (BBD) was applied for optimization of operational parameters, including cycle-frequency, HRT, and substrate concentration, using an intermittent-continuously stirred tank reactor (i-CSTR). Overall performance revealed that the degree of importance of the three variables in terms of H₂ yield is as follows: cycle-frequency > substrate concentration > HRT. In the confirmation test, H₂ yield of 113.1 mL H₂/g dry cell weight (dcw) was recorded, corresponding with 96.3% of the predicted response value under desirable operational conditions (cycle-frequency of 17 hr, HRT of 2.7 days, and substrate concentration of 31.1 g COD/L). In the second stage, an anaerobic sequencing batch reactor (ASBR) and an up-flow anaerobic sludge blanket reactor (UASBr) were employed for CH₄ production from H₂ fermented solid state (HFSS) and H₂ fermented liquid state (HFLS), respectively. The CH₄ producing ASBR and UASBr showed a stable CH₄ yield and COD removal until a HRT of 12 days and OLR of 3.5 g COD/L/d, respectively. Subsequently, for recycling of CH₄ fermented effluent from the UASBr (MFE_UASBr) as diluting water in DFHP, the tap water and MFE_UASBr mixing ratio (T/M ratio) was optimized (a T/M ratio of 5:5) in a batch test using heat pretreated MFE_UASBr at 90 °C for 20 min, resulting in the best performance. Although slight decreases of H₂ yield (7.6%) and H₂ production rate (3.5%) were recorded, 100% reduction of alkali addition was possible, indicating potential to maximize economic benefits. However, a drastic decrease of H₂ productivity and a change of liquid-state metabolites were observed with the use of non-heat pretreated MFE_UASBr. These results coincided with those of the microbial analysis, where non-H₂ producing bacteria, such as Selenomonas sp., were detected. The results indicate that pretreatment of MFE_UASBr may be required in order to recycle it in DFHP.