Ozone pretreatment of wheat straw for enhanced biohydrogen production

Ozonation was tested as a pretreatment method for enhanced biohydrogen production from wheat straw. Ozone pretreatment effectively degraded wheat straw lignin, and the delignification increased with increase in the applied ozone dose. Results of reducing sugar measurement showed that under our experimental conditions ozone pretreatment significantly increased reducing sugar yields. A simultaneous enzyme hydrolysis and dark fermentation experiment was then conducted using a mixed anaerobic consortium, and the results demonstrated that ozone pretreatment significantly increased biohydrogen production. Compared to the untreated one, hydrogen production in the samples ozonated for 15, 30, 45 and 90 min increased 107%, 134%, 158% and 138%, respectively. Slight inhibitory effect on the dark fermentation was observed with the sample ozonated for 90 min, and the inhibitory effect was due to prolonged ozonation. These results proved that enhancement of biohydrogen production from lignocellulosic biomass using ozone as a pretreatment method is technically feasible.     

Development of a method for biohydrogen production from wheat straw by dark fermentation

Lignocellulosic biomass contains approximately 70-80% carbohydrates. If properly hydrolyzed, these carbohydrates can serve as an ideal feedstock for fermentative hydrogen production. In this research, batch tests of biohydrogen production from acid-pretreated wheat straw were conducted to analyze the effects of various associated bioprocesses. The objective of the pretreatment phase was to investigate the effects of various sulfuric acid pretreatments on the conversion of wheat straw to biohydrogen. When sulfuric acid-pretreated solids at a concentration of 2% (w/v) were placed in an oven for 90 min at 120 °C, they degraded substantially to fermentative gas. Therefore, wheat straw that is pre-treated under the evaluated conditions is suitable for hydrolysis and fermentation in a batch test apparatus. Five different conditions were evaluated in the tests, which were conducted in accordance with standard batch test procedures (DIN 38414 S8): fresh straw, pre-treated straw, supernatants derived from acid hydrolyzation, Separate Hydrolysis and Fermentation (SHF) and Simultaneous Saccharification and Fermentation (SSF). The SSF method proved to be the most effective and economical way to convert wheat straw to biohydrogen. The hydrogen yield by this method was 1 mol H₂/mol glucose, which resulted from 5% carbon degradation (η_{C, gas}) or the equivalent of 64% of the hydrogen volume that was produced in the reference test (glucose equivalent test). This method also proved to have the shortest lag phase for gas production. The supernatants derived from acid hydrolysis were very promising substances for continuous tests and presented excellent characteristics for the mass production of biohydrogen. For example, a 1.19 mol H₂/mol glucose (76% glucose equivalent) yield was achieved along with a 52% carbon degradation.     

Effect of enzyme addition on fermentative hydrogen production from wheat straw

Wheat straw is an abundant agricultural residue which can be used as raw material to produce hydrogen (H₂), a promising alternative energy carrier, at a low cost. Bioconversion of lignocellulosic biomass to produce H₂ usually involves three main operations: pretreatment, hydrolysis and fermentation. In this study, the efficiency of exogenous enzyme addition on fermentative H₂ production from wheat straw was evaluated using mixed-cultures in two experimental systems: a one-stage system (direct enzyme addition) and a two-stage system (enzymatic hydrolysis prior to dark fermentation). H₂ production from untreated wheat straw ranged from 5.18 to 10.52 mL-H₂ g-VS⁻¹. Whatever the experimental enzyme addition procedure, a two-fold increase in H₂ production yields ranging from 11.06 to 19.63 mL-H₂ g-VS⁻¹ was observed after enzymatic treatment of the wheat straw. The high variability in H₂ yields in the two step process was explained by the consumption of free sugars by indigenous wheat straw microorganisms during enzymatic hydrolysis. The direct addition of exogenous enzymes in the one-stage dark fermentation stage proved to be the best way of significantly improving H₂ production from lignocellulosic biomass. Finally, the optimal dose of enzyme mixture added to the wheat straw was evaluated between 1 and 5 mg-protein g-raw wheat straw⁻¹.     

Optimization of biogas production from wheat straw stillage in UASB reactor

In the present study, thermophilic anaerobic digestion of wheat straw stillage was investigated. Methane potential of stillage was determined in batch experiments at two different substrate concentrations. Results showed that higher methane yields of 324 ml/g-(volatile solids) VS_added were obtained at stillage concentrations of 12.8 g-VS/L than at 25.6 g-VS/l. Continuous anaerobic digestion of stillage was performed in an up-flow anaerobic sludge blanket (UASB) reactor at 55 °C with 2 days hydraulic retention time. Results showed that both substrate concentration and organic loading rate (OLR) influenced process performance and methane yields. Maximum methane yield of 155 ml CH₄/g-COD was obtained at stillage mixtures with water of 25% (v/v) in the feed and at an OLR of 17.1 g-COD/(l.d). Soluble chemical oxygen demand (SCOD) removal at this OLR was 76% (w/w). Increase in OLR to 41.2 g-COD/(l.d) and/or stillage concentration in the feed to 33–50% (v/v) resulted in low methane yields or complete process failure. The results showed that thermophilic anaerobic digestion of wheat straw stillage alone for methane production is feasible in UASB reactor at an OLR of 17.1 g-COD/(l.d) and at substrate concentration of 25% in the feed. The produced methane could improve the process energy and economics of a bioethanol plant and also enable to utilize the stillage in a sustainable manner.     

Cladophora sp. as a sustainable feedstock for dark fermentative biohydrogen production

Macroalgae are rich in carbohydrates which can be used as a promising substrate for fermentative biohydrogen production. In this study, Cladophora sp. biomass was fermented for biohydrogen production at various inoculum/substrate (I/S) ratios against a control of inoculum without substrate in laboratory-scale batch reactors. The biohydrogen production yield ranged from 40.8 to 54.7 ml H₂/g-VS, with the I/S ratio ranging from 0.0625 to 4. The results indicated that low I/S ratios caused the overloaded accumulation of metabolic products and a significant pH decrease, which negatively affected hydrogen production bacteria's metabolic activity, thus leading to the decrease of hydrogen fermentation efficiency. The overall results demonstrated that Cladophora sp. biomass is an efficient fermentation feedstock for biohydrogen production.     

Techno-economic evaluation of biohydrogen production from wastewater and agricultural waste

The world is facing serious climate change caused in part by human consumption of fossil fuel. Therefore, developing a clean and environmentally friendly energy resource is necessary given the depletion of fossil fuels, the preservation of the earth's ecosystem and self-preservation of human life. Biological hydrogen production, using dark fermentation is being developed as a promising alternative and renewable energy source, using biomass feedstock. In this study, beverage wastewater and agricultural waste were examined as substrates for dark fermentation to produce clean biohydrogen energy.     

Review on fermentative biohydrogen production from water hyacinth,wheat straw and rice straw with focus on recent perspectives

Hydrogen (H₂) is often considered as the best option to store energy coming from renewable sources. Hydrogen production from lignocellulosic biomass via fermentation offers low cost and environmental friendly method in terms of energy balance and provides a sustainable pathway for utilization of huge amount of unused biomass. In this regard, special attention on potential of different lignocellulosic biomass is required. In this paper, the fermentative hydrogen production from three carbohydrates-rich biomass: water hyacinth, wheat straw and rice straw is comprehensively reviewed. In other point of view, usage of H₂ has a 10% growth annually that will reach to 8–10% of total energy in 2025. Furthermore, research on recent trends of fermentative hydrogen production is crucial and vital. However, the majority of the published researches in the last decade confirmed that some challenges exists which are the process optimization, effecting parameters and commercialization aspects.     

Improvement of biohydrogen production from glycerol in micro-oxidative environment

Glycerol is a highly available by-product generated in the biodiesel industry. It can be converted into higher value products such as hydrogen using biological processes. The aim of this study was to optimize a continuous dark fermenter producing hydrogen from glycerol, by using micro-aerobic conditions to promote facultative anaerobes. For that, hydrogen peroxide (H₂O₂) was continuously added at low but constant flow rate (0.252 mL/min) with three different inlet concentrations (0.2, 0.4, and 0.6% w/w). A mixture of aerobic and anaerobic sludge was used as inoculum. Results showed that micro-oxidative environment significantly enhanced the overall hydrogen production. The maximum H₂ yield (403.6 ± 94.7 mmolH₂/molGly_consumed) was reached at a H₂O₂ concentration of 0.6% (w/w), through the formate, ethanol and butyrate metabolic pathways. The addition of H₂O₂ promoted the development of facultative anaerobic microorganisms such as Klebsiella, Escherichia-Shigella and Enterococcus sp., likely by consuming oxygen traces in the medium and also producing hydrogen. Despite the micro-oxidative environment, strict anaerobes (Clostridium sp.) were still dominant in the microbial community and were probably the main hydrogen producing species. In conclusion, such micro-oxidative environment can improve hydrogen production by selecting specific microbial community structures with efficient metabolic pathways.     

Recent insights into consolidated bioprocessing for lignocellulosic biohydrogen production

Biohydrogen production via dark fermentation using fermentable sugars from biomass materials is a sustainable way of procuring biohydrogen. Lignocellulosic biomass is a potential renewable feedstock for dark fermentation, but its use is challenged by the recalcitrant nature and generation of certain fermentation inhibitors resulting in compromised fermentation performance. Consolidated bioprocessing (CBP), the successful integration of hydrolysis and fermentation of lignocellulosic biomass to desirable products, has received tremendous research attentions in recent years to boost renewable fuel production in an economically feasible way. A microbial strain capable of both biomass hydrolysis and hydrogen fermentation is critical for successful CBP-based hydrogen fermentation. This review provides comprehensive information on dark fermentation for hydrogen production using lignocellulosic biomass as a potential feedstock with a CBP approach. Consolidated bioprocessing of lignocellulosic biomass for biohydrogen production via native and recombinant microbial strains is discussed in detail. Potential bottlenecks in the above mentioned processes are critically analyzed and future research perspectives are presented.     

Enhancement of fermentative biohydrogen production from textile desizing wastewater via coagulation-pretreatment

A real textile desizing wastewater (TDW) was coagulation-pretreated to enhance its potential of biohydrogen production. Batch fermentation showed that the hydrogen production was efficiently enhanced (550 and 120% increments for hydrogen production rate and hydrogen yield, respectively) and the production performance was substrate-concentration dependent. A peak hydrogen production rate of 3.9 L/L-d and hydrogen yield of 1.52 mol/mol hexose were obtained while using coagulant GGEFloc-653 at a dosage of 1 g/L to pretreat TDW with the concentration of 15 g total sugar/L. The coagulation-pretreatment could have butyrate-type fermentation with high biohydrogen production and the removed some toxic materials that might drive the metabolic pathways to those not favoring biohydrogen production. Based on the data obtained, strategies to operate the coagulation and biohydogen fermentation are suggested. Moreover, fermentation effluent utilization such as for two-stage biogas production and further biohythane (a mixture of H₂ and CH₄) generation are also elucidated.     

The effect of HRT on biohydrogen production from acid hydrolyzed waste wheat in a continuously operated packed bed reactor

Biohydrogen production in a continuously operated up flow packed bed reactor was investigated at different hydraulic retention time (HRT) varying between 2 h and 13 h scouring sponge pad. The substrate was sugar solution obtained from hydrolysis of waste wheat at pH = 2 and 90 °C in an autoclave for 15 min. Experimental results indicated that hydrogen production volume and yield increases with decreasing HRT. The highest volumetric hydrogen production rate and yield were obtained as VHPR = 1.75 L H₂/L d and Y_H2 = 1.6 moL H₂/mol TS, respectively, at HRT = 2 h. Yields and rates at HRT = 2 h were almost two times of that obtained at HRT = 13 h. It can be concluded that metal mesh covered plastic scouring sponge pad is a suitable microorganism support particle to obtain high hydrogen yield and rate at short HRTs by dark fermentation.     

A pilot-scale high-rate biohydrogen production system with mixed microflora

A pilot-scale high-rate dark fermentative hydrogen production plant has been established in the campus of Feng Chia University to develop biohydrogen production pilot-plant technology. This pilot-plant system is composed of two feedstock storage tanks (0.75 m³ each), a nutrient storage tank (0.75 m³), a mixing tank (0.6 m³), an agitated granular sludge bed fermentor (working volume 0.4 m³), a gas-liquid-solid separator (0.4 m³) and a control panel. The seed mixed microflora was obtained from a lab-scale agitated granular sludge bed bioreactor. This pilot-scale fermentor was operated for 67 days at 35 °C, an organic loading rate (OLR) of 40-240 kg COD/m³/d, and the influent sucrose concentration of 20 and 40 kg COD/m³. Both biogas and hydrogen production rates increased with increasing OLR. However, the biomass concentration (volatile suspended solids, VSS) only increased with an increasing OLR at an OLR range of 40-120 kg COD/m³/d, whereas it decreased when OLR was too high (i.e., 240 kg COD/m³/d). The biogas consisted mainly of H₂ and CO₂ with a H₂ content range of 23.2-37.8%. At an OLR of 240 kg COD/m³/d, the hydrogen content in biogas reached its maximum value of 37% with a hydrogen production rate (HPR) of 15.59 m³/m³/d and a hydrogen yield of 1.04 mol H₂/mol sucrose. This HPR value is much higher than 5.26 m³/m³/d (fermented molasses substrate) and 1.56 m³/m³/d (glucose substrate) reported by other pilot-scale systems. Moreover, HPR was also greatly affected by pH. At an optimal pH of 5.5, the bacterial community became simple, while the efficient hydrogen producer Clostridium pasteurianum was dominant. The factors of energy output compared with the energy input (E_f) ranged from 13.65 to 28.68 on biohydrogen, which is higher than the E_f value on corn ethanol, biodiesel and sugarcane ethanol but in the similar range of cellulosic ethanol.     

Application of nanotechnology in dark fermentation for enhanced biohydrogen production using inorganic nanoparticles

Fermentation is an important innovation by mankind and this process is used for converting organic substrate into useful products. Using natural conditions, specifically, light and dark conditions, photo-fermentation and dark fermentation techniques can be developed and operated under controlled conditions. Generally, products such as biofuels, bioactive compounds and enzymes have been produced using the dark fermentation method. However, the major requirement for today's industralized world is biofuels in its clean and pure forms. Biohydrogen is the most efficient and cleanest form of energy produced using dark fermentation of organic substrates. Nevertheless, the quantity of biohydrogen produced via dark fermentation is low. In order to increase the product quantity and quality, several internal and external stress or alterations are made to conventional fermentation conditions. In recent times, nanotechnology has been introduced to enhance the rate of dark fermentation. Nanoparticles (NPs), specifically, inorganic NPs such as silver, iron, titanium oxide and nickel have increased the production rate of biohydrogen. Therefore, the present review focuses on exploring the potential of nanotechnology in the dark fermentation of biohydrogen production, the mechanisms involved, substrates used and changes to be made to increase the production efficiency of dark fermentation.     

Optimized model of fermentable sugar production from Napier grass for biohydrogen generation via dark fermentation

Biohydrogen is a fossil-fuel alternative. Lignocellulosic biomass is a complex part of cellulose-to-simple sugar production. Napier grass, one of the lignocellulosic biomasses, is best for biofuels or biochemicals. The dark fermentation process of Napier grass for biohydrogen proved both cost-effective and environmentally friendly. This grass contains cellulose, hemicellulose and lignin were 35.44 ± 2.01, 20.05 ± 1.55, and 28.473 ± 1.34, respectively. Sodium hydroxide was used in different concentrations to delignify lignocellulose and improve grass glucose recovery. Fermentative hydrogen production from grass biomass processing by microflora was optimized in terms of pH (4.5–7.0) and mesophilic condition (35 ± 2 °C). In this study, mesophilic conditions favored maximum hydrogen production (763.34 ml), indicating that pH 5.5 was suitable for dark-fermentative hydrogen production; study results showed Napier grass could be used successfully for dark fermentation to produce biohydrogen.     

Dark fermentative biohydrogen production from confectionery wastewater in continuous-flow reactors

The production of biohydrogen from industrial wastewater through the dark fermentation (DF) process has attracted increased interest in recent years. To implement a DF process on a large scale, a thorough knowledge of laboratory scale process control is required. The operating parameters and design features of the reactors have a great influence on the efficiency of the process. In this work, the possibility of continuous production of biohydrogen from confectionery wastewater was evaluated. The DF process was carried out at 37 ± 1 °C in two different reactors: an upflow anaerobic filter (AF) and a fluidized bed reactor (AFB). Polyurethane foam (PU) was used to immobilize the biomass. The DF process was studied at four hydraulic retention times (HRT) (1.5, 2.5, 7.5 and 15 days) and the corresponding organic loading rates (OLR) (9.21, 6.12, 2.04 and 1.02 g COD_init/(L day)). The highest hydrogen yield (HY) (44.73 ml/g COD_init) and hydrogen production rate (HPR) (92.5 ml/(L day)) was observed in AFB at HRT of 7.5 days and 2.5 days, respectively. The highest concentration of hydrogen in biogas was 34% in AF and 36% in AFB at HRT of 7.5 days. In contrast to AF, the COD removal efficiency in AFB increased with increasing HRT. The pH of the effluent was low (3.95–4.38). However, due to the use of PU for biomass immobilization, it is possible that there were local zones in the reactor that were optimal for the functioning of not only acidogens, but also methanogens. This was evidenced by a rather high content of methane in biogas (2.5% in AF and 9.6% in AFB at HRT of 15 days). These results provide valuable data for optimizing the continuous DF of wastewater from confectionery and other food industries to produce biohydrogen or biohythane.     

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.     

Mathematical modelling for biohydrogen production by Clostridium beijerinckii

Hydrogen is an energy source that can be produced by Clostridium sporogenes microorganism. In the present work, modeling of dark fermentation using Clostridium beijerinckii and dextrose as substrate was performed to evaluate how the gases and liquid by-products affect the biological process. A mathematical model was developed according to ADM1. The developed model takes into account biochemical reactions, physicochemical equilibrium as well as mass transfer processes during dark fermentation. Findings revealed that Clostridium beijerinckii reached a yield as high as 3.58 mol of H₂/mol of dextrose and generates by-products in the aqueous phase that may either be used as raw materials in a chemical process. Clostridium beijerinckii is very sensitive to acid media (pH < 5.0) and shows a low rate of biohydrogen production (even the absence of metabolic activity) at pH lower than 4.5. The developed model is able to predict (R² > 0.95) dextrose consumption profile, cumulative biohydrogen production and the maximum concentrations of liquid by-products.     

Enhancement of biohydrogen production from palm oil mill effluent (POME): A review

Palm oil mill effluent (POME), a wastewater from the most significant agricultural industry in Southeast Asia is produced in tremendous amounts that requires proper management to mitigate its negative environmental effects. The feasibility of treating POME in a closed dark fermentation (DF) system to replace the existing inefficient open ponding treatment has been thoroughly investigated. Theoretically, the maximum H₂ yield obtained by DF process is 4 mol_H2/mol_glucose, however, it is not achievable due to the nature of POME. In this study, several enhancement methods for increasing H₂ yield and DF process stability were discussed. An apprehension into the different pre-treatment methods on POME including physicochemical, chemical and biological and their effects on the characteristics of POME including pH, temperature, sugar content, solid content, viscosity, nutrients and by-product toxicity on the biohydrogen production and effluent quality were reviewed. Various bioreactor designs were used for biohydrogen from POME, the modifications applied on the system design to increase the stability and productivity of POME treatment have been examined. Moreover, higher biohydrogen productivity could be obtained with the addition of nanoparticle nutrients and introducing genetically modified H₂-producing bacteria. Finally, further investigation in the future shall focus on the development of a more inclusive and efficient POME treatment via DF process that favours biohydrogen production, environmental benign and economically viable.     

Whey waste as potential feedstock for biohydrogen production

In-house isolate Clostridium sp. IODB-O3 was exploited for biohydrogen production using cheese whey waste in batch fermentation. Analysis of cheese whey shows, it is enriched with lactose, lactic acid and protein components which were observed most favourable for biohydrogen production. Biohydrogen yield by IODB-O3 was compared with the cultures naturally occurring in waste solely or in combinations, and found that Clostridium sp. IODB-O3 was the best producer. The maximum biohydrogen yield obtained was 6.35 ± 0.2 mol-H₂/mol-lactose. The cumulative H₂ production (ml/L), 3330 ± 50, H₂ production rate (ml/L/h), 139 ± 5, and specific H₂ production (ml/g/h), 694 ± 10 were obtained. Clostridium sp. IODB-O3 exhibited better H₂ yield from cheese whey than the reported values in literature. Importantly, the enhancement of biohydrogen yield was observed possibly due to absence of inhibitory compounds, presence of essential nutrients, protein and lactic acid fractions which supported better cell growth than that of the lactose and glucose media. Carbon balance was carried out for the process which provided more insights in IODB-O3 metabolic pathway for biohydrogen production. This study may help for effective utilization of whey wastes for economic large scale biohydrogen production.     

Impact of pretreatment on food waste for biohydrogen production: A review

Food waste (FW) can be utilized as a raw material to produce energy such as hydrogen via fermentation, which is a more attractive and environmentally friendly approach compared to incineration and land-filling. Food waste must be pretreated before being used in various biological processes. The choice of the pretreatment method usually depends on the composition of the food waste. Therefore, various pretreatment methods generally employed to treat FW, including physical, physiochemical, chemical and biological pretreatments, are summarized in this review. The different pretreatment methods are compared in terms of their efficiency and biohydrogen yield. Additionally, the energy efficiencies of the various pretreatment methods are compared, thereby leading to the selection of the most efficient pretreatment method.