Continuous production of biohydrogen from oil palm empty fruit bunch hydrolysate in tubular photobioreactors

Production of hydrogen by the photosynthetic bacterium Rhodobacter sphaeroides was compared in continuously operated tubular photobioreactors illuminated by natural outdoor sunlight (0.15–66 klux; diurnal cycle) and constant indoor artificial light (10 klux; tungsten lamps). In both cases the operating temperature was 35 °C and the organic carbon source was an acid hydrolysate of oil palm empty fruit bunch (EFB), an agroindustrial waste. In the outdoor photobioreactor, under the best production conditions, the daytime feeding rate of the mixed carbon substrate was 48 mL h^?1 and the average pseudo-steady state hydrogen production rate was 36 mL H₂ L^?1 medium h^?1. The cumulative hydrogen production was 430 mL H₂ L^?1 medium. For the indoor photobioreactor fed at the same rate as the outdoor system, the steady state average hydrogen production rate was 43 mL H₂ L^?1 h^?1 and the cumulative hydrogen production was 517 mL H₂ L^?1 medium. Reducing the feed rate to less than 48 mL h^?1, enhanced the biomass concentration, but reduced hydrogen production in both bioreactors. The sunlight-based cumulative hydrogen production was only about 17% less compared to the artificially lit system, but required only 22% of the electrical energy.     

Biohydrogen production from pentose-rich oil palm empty fruit bunch molasses: A first trial

Oil palm empty fruit bunch (OPEFB) was pretreated by local plantation industry to increase the accessibility towards its fermentable sugars. This pretreatment process led to the formation of a dark sugar-rich molasses byproduct. The total carbohydrate content of the molasses was 9.7 g/L with 4.3 g/L xylose (C₅H₁₀O₅). This pentose-rich molasses was fed as substrate for biohydrogen production using locally isolated Clostridium butyricum KBH1. The effect of initial pH and substrate concentration on the yield and productivity of hydrogen production were investigated in this study. The best result for the fermentation performed in 70 mL working volume was obtained at the initial reaction condition of pH 9, 150 rpm, 37 °C and 5.9 g/L total carbohydrate. The maximum hydrogen yield was 1.24 mol H₂/mol pentose and the highest productivity rate achieved was 0.91 mmol H₂/L/h. The optimal pH at pH 9 was slightly unusual due to the presence of inhibitors, mainly furfural. The furfural content decreased proportionally as pH was increased. The optimal experiment condition was repeated and continued in fermentation volume of 200 mL. The maximum hydrogen yield found for this run was 1.21 mol H₂/mol pentose while the maximum productivity was 1.1 mmol H₂/L/h. The major soluble metabolites in the fermentation were n-butyric acid and acetic acid.     

The effect of particle size of CaO and MgO as catalysts for gasification of oil palm empty fruit bunch to produce hydrogen

Finely ground and dried palm oil empty fruit bunch (EFB) was gasified using a temperature-programmed technique which online with mass spectrometer. Temperature-programmed gasification (TPG) was done under 5% oxygen in helium to determine the production of hydrogen, as well as CO, CO₂ and CH₄. TPG was performed from 50–700 °C at the heating rate of 10 °C min⁻¹. The temperature was held for 1 h at the final temperature. The effect of mass ratio of metal oxide:EFB was also investigated. Different particle size of calcium oxide and magnesium oxide were chosen as the catalysts. Bulk calcium oxide has shown to enhance the evolution of hydrogen. Nanosized calcium oxide enhanced the production of hydrogen compared to the bulk one and consequently reduced the production of carbon dioxide. Interestingly, when the mass ratio of metal oxide:EFB was changed to 1:2, nanosized MgO showed very significant increase of H₂ production. All the used catalysts were analyzed by XRD to show the transformation of both bulk and nanosized metal oxides to metal carbonates.     

Photofermentive production of biohydrogen from oil palm waste hydrolysate

Oil palm empty fruit bunch (OPEFB) was hydrolyzed with dilute sulfuric acid (6% v/v; 8 mL acid per g dry OPEFB) at 120 °C for 15-min to release the fermentable sugars. The hydrolysate contained xylose (23.51 g/L), acetic acid (2.44 g/L) and glucose (1.80 g/L) as the major carbon components. This hydrolysate was used as the sole carbon source for photofermentive production of hydrogen using a newly identified photosynthetic bacterium Rhodobacter sphaeroides S10. A Plackett–Burman experimental design was used to examine the influence of the following on hydrogen production: yeast extract concentration, molybdenum concentration, magnesium concentration, EDTA concentration and iron concentration. These factors influenced hydrogen production in the following decreasing order: yeast extract concentration > molybdenum concentration > magnesium concentration > EDTA concentration > iron concentration. Under the conditions used (35 °C, 14.6 W/m² illumination, initial pH of 7.0), the optimal composition of the culture medium was (per L): mixed carbon in OPEFB hydrolysate 3.87 g, K₂HPO₄ 0.9 g, KH₂PO₄ 0.6 g, CaCl₂⋅2H₂O 75 mg, l-glutamic acid 795.6 mg, FeSO₄⋅7H₂O 11 mg, Na₂MoO₂⋅2H₂O 1.45 mg, MgSO₄⋅7H₂O 2.46 g, EDTA 0.02 g, yeast extract 0.3 g). With this medium, the lag period of hydrogen production was 7.65 h, the volumetric production rate was 22.4 mL H₂/L medium per hour and the specific hydrogen production rate was 7.0 mL H₂/g (xylose + glucose + acetic acid) per hour during a 90 h batch culture of the bacterium. Under optimal conditions the conversion efficiency of the mixed carbon substrate to hydrogen was nearly 29%.     

Effect of kaolin addition on ash characteristics of palm empty fruit bunch (EFB) upon combustion

Palm empty fruit bunch (EFB), a by-product of the palm oil industry, is being recognized as one of the most potential kinds of biomass for energy production in Thailand. However, it has been reported that, in combusting EFB in boilers, some compounds evolving from abundant alkali metals in EFB into gas-phase condense and deposit on low-temperature surfaces of heat exchange equipment, causing fouling and corrosion problems. To come up with a solution to impede the deposition, kaolin, which is abundant in kaolinite (Al₂Si₂O₅(OH)₄), is employed to capture the alkali metal vapours eluding from the combustion region. The experiments were designed to simulate the combustion situations that may take place when kaolin is utilized in two different approaches: premixing of kaolin with EFB prior to combustion and gas-phase reaction of volatiles from EFB with kaolin. The amounts of kaolin used were 8% and 16% by weight based on dry weight of EFB, which were equivalent to one and two times of the theoretical kaolin requirement to capture all potassium originally present in the EFB. The furnace temperatures used for EFB combustion were 700–900 °C and ashes were analyzed by XRF and XRD. The results revealed that, under the kaolin premixing condition, 8% kaolin addition was sufficient to capture the potassium compounds at low temperature, i.e. 700 and 800 °C. However, when the temperature was increased to 900 °C, 16% kaolin addition was needed to completely capture the potassium compounds. The results from gas-phase experiments showed that kaolin can capture volatile potassium at maximum 25% at 900 °C. The XRD results showed, for both experimental cases, the evidence of formation of the high melting temperature potassium-alumino-silicates, which confirmed the reaction of potassium compounds with kaolin. The study also suggests that the premixing method is better than the other because of its higher overall capture efficiency.     

Optimum conditions for maximising pyrolysis liquids of oil palm empty fruit bunches

As production of palm oil is expanding, a more efficient use of oil palm biomass to obtain more energy from oil palm plantations is investigated. The work was carried out on a fluidised bed bench scale fast pyrolysis unit, with the objective of determining the important conditions and key variables which are required to maximise the liquid yield and its quality. The investigation on the impact of reactor temperature, varying residence time by changing the nitrogen flow rate and combined impact of ash content and particle size on the product yields is presented. The properties of the liquid product were analysed and compared with wood derived bio-oil and petroleum fuels. It was found that in all cases the liquid product separated into two phases presenting difficulties for fuel applications, which are critically discussed. Potential solutions are also proposed which include upgrading of the liquid for fuel applications and other useful applications.     

Potential for using enriched cultures and thermotolerant bacterial isolates for production of biohydrogen from oil palm sap and microbial community analysis

A limited number of bacteria can convert oil palm (Elaeis guineensis) sap to hydrogen with satisfactory yield and productivity. In this study, a total of 18 fermentative enriched cultures and 36 newly isolated thermotolerant bacterial strains were compared for hydrogen production from oil palm (OP) sap. The new isolates were obtained from hot springs, palm oil mill effluent and oil palm sap. The test was conducted in three steps: (i) a test for hydrogen production from mixed substrates (cellulose, starch, xylose, and glucose) and OP sap; (ii) a test for substrate concentration tolerance; and (iii) a test for thermotolerance. Five enriched candidates for each of the hydrogen producers were selected according to the criteria defined for the screening test. The hydrogen production of these selected bacterial strains from hot springs were cultivated in batch fermentation of oil palm sap at room temperature (30 ± 2 °C). Five enriched cultures, namely 81RN1, OPS, 85RN5, 89SR3-2 and 112YL1 were found to give high cumulative hydrogen formation of 1085, 1009, 994, 983 and 778 mL H₂/L-OP sap, respectively, with the hydrogen content of 29.8, 29.4, 28.7, 27.1 and 27.5%, respectively. PCR–DGGE profiling showed that all these five enriched cultures consisted of species closely related to the genus Clostridium sp. based on the 16S rRNA gene. For pure cultures, the top five hydrogen producers were the isolates encoded as PS-3, PS-4, PS-5, PS-7 and PS-8 exhibiting the hydrogen production of 1973, 1774, 1335, 1170 and 1070 mL H₂/L-OP sap, respectively, with the hydrogen content of 33.7, 29.6, 32.5, 31.5 and 26.4%, respectively. Identification of these high hydrogen producers using 16S rRNA sequence matching showed that the isolates PS-3 and PS-8 belonged to Clostridium beijerinckii, while the isolate PS-7 belonged to Clostridium acetobutylicum and the isolates PS-4 and PS-5 belonged to Klebsiella sp. and Klebsiella pneumoniae, respectively. Therefore, the pure culture C. beijerinckii PS-3 exhibited 1.8 folds higher hydrogen production (1973 mL H₂/L-OP sap) than the enriched cultures of 81RN1 (1085 mL H₂/L-OP sap).     

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.     

Mesophilic biohydrogen production from calcium hydroxide treated wheat straw

The use of Ca(OH)₂ pre-treatment to improve fermentative biohydrogen yields, from wheat straw was investigated. Wheat straw was pre-treated with 7.4% (w/w) Ca(OH)₂ at ambient temperature (20 °C) for 2, 5, 8, and 12 days, prior to 35 °C fermentation with sewage sludge inoculum. Biohydrogen yields were evaluated during dark fermentation and simultaneous saccharification fermentation (SSF) of total pre-treated straw material and compared to those from separated solid and hydrolysate fractions. Ca(OH)₂ pre-treatment followed by SSF, exhibited a synergetic relationship. On average, 58.78 mL-H₂ g-VS⁻¹ was produced from SSF of pre-treated and filtered solids. This was accompanied by approximately a 10-fold increase in volatile fatty acid production, compared to the untreated control. By omitting pre-treatment hydrolysate liquors from SSF, H₂ production increased on average by 35.8%, per VS of harvested straw. Additional inhibition studies indicated that CaCO₃, formed as a result of pre-treatment pH control, could promote homoacetogenesis and reduce biohydrogen yields.     

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.     

Start-up study of biohydrogen production from palm oil mill effluent in a lab-scale up-flow anaerobic sludge blanket fixed-film reactor

A start-up study of lab-scale up-flow anaerobic sludge blanket fixed-film reactor (UASFF) was conducted to produce biohydrogen from palm oil mill effluent (POME). The reactor was fed with POME at different hydraulic retention time (HRT) and organic loading rate (OLR) to obtain the optimum fermentation time for maximum hydrogen yield (HY). The results showed the HY, volumetric hydrogen production rate (VHPR), and COD removal of 0.5–1.1 L H₂/g COD_consumed, 1.98–4.1 L H₂ L^?1 day^?1, and 33.4–38.5%, respectively. The characteristic study on POME particles was analyzed by particle size distribution (PSD), Scanning electron microscopy (SEM), and Energy-dispersive X-ray spectroscopy (EDX). The microbial Shannon and Simpson diversity indices and Principal Component Analysis assessed the alpha and beta diversity, respectively. The results indicated the change of bacterial community diversity over the operation, in which Clostridium sensu stricto 1 and Lactobacillus species were contributed to hydrogen fermentation.     

Feasibility of biohydrogen production from Gelidium amansii

The feasibility of hydrogen production from red algae was investigated. Galactose, the main sugar monomer of red algae, was readily converted to hydrogen by dark fermentation. The maximum hydrogen production rate and yield of galactose were 2.46 L H₂/g VSS/d and 2.03 mol H₂/mol galactose_added, respectively, which were higher than those for glucose (0.914 L H₂/g VSS/d and 1.48 mol H₂/mol galactose_added). The distribution of soluble byproducts showed that H₂ production was the main pathway of galactose uptake. 5-HMF, the main byproduct of acid hydrolysis of red algae causes noncompetitive inhibition of H₂ fermentation. 1.37 g/L of 5-HMF decreased hydrogen production rate by 50% compared to the control. When red algae was hydrolyzed at 150 °C for 15 min and detoxified by activated carbon, 53.5 mL of H₂ was produced from 1 g of dry algae with a hydrogen production rate of 0.518 L H₂/g VSS/d. Red algae, cultivable on vast tracts of sea by sunlight without any nitrogen-based fertilizer, could be a suitable substrate for biohydrogen production.     

Optimization of batch dilute-acid hydrolysis for biohydrogen production from red algal biomass

Marine algae are promising alternative sources for bioenergy including hydrogen. Their polymeric structure, however, requires a pretreatment such as dilute-acid hydrolysis prior to fermentation. This study aimed to optimize the control variables of batch dilute-acid hydrolysis for dark hydrogen fermentation of algal biomass. The powder of Gelidium amansii was hydrolyzed at temperatures of 120–180 °C, solid/liquid (S/L) ratios of 5–15% (w/v), and H₂SO₄ concentrations of 0.5–1.5% (w/w), and then fed to batch hydrogen fermentation. Among the three control variables, hydrolysis temperature was the most significant for hydrogen production as well as for hydrolysis efficiency. The maximum hydrogen production performance of 0.51 L H₂/L/hr and 37.0 mL H₂/g dry biomass was found at 161–164 °C hydrolysis temperature, 12.7–14.1% S/L ratio, and 0.50% H₂SO₄. The optimized dilute-acid hydrolysis would enhance the feasibility of the red algal biomass as a suitable substrate for hydrogen fermentation.     

Analysis of syngas production rate in empty fruit bunch steam gasification with varying control factors

Biomass gasification is a prevailing approach for mitigating irreversible fossil fuel depletion. In this study, palm empty fruit bunch (EFB) was steam-gasified in a fixed-bed, batch-fed gasifier, and the effect of four control factors—namely torrefaction temperature for EFB pretreatment, gasification temperature, carrier-gas flow rate, and steam flow rate—on syngas production were investigated. The results showed that steam flow rate is the least influential control factor, with no effect on syngas composition or yield. The gasification temperature of biomass significantly affects the composition of syngas generated during steam gasification, and the H₂/CO ratio increases by approximately 50% with an increase in temperature ranging from 680 °C to 780 °C. The higher H₂/CO ratio at a lower gasification temperature increased the energy density of the combustible constituents of the syngas by 3.43%.     

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.     

Repeated-batch production of hydrogen using Rhodobacter sphaeroides S10

Photofermentation of acid hydrolyzed oil palm empty fruit bunch is reported for hydrogen production in repeated-batch fermentations using the bacterium Rhodobacter sphaeroides S10. Photofermentations were carried out at 35 °C at an incident light level of 10 klux. At specified times, different specified volumes of the culture broth were removed and replaced with an equal volume of the fresh medium. The initial mixed carbon (glucose, xylose, acetic acid) content in the medium of the repeated-batch reactors was adjusted to 20 mM. The kinetics of hydrogen production were evaluated in repeated-batch fermentations carried out in various ways: different volume exchange levels, different switch times from batch to repeated-batch operation, and different cycle times.     

Ultrasonic pretreatment of palm oil mill effluent: Impact on biohydrogen production,bioelectricity generation,and underlying microbial communities

Substrate bioavailabity is one of the critical factors that determine the relative biohydrogen (bioH₂) yield in fermentative hydrogen production and bioelectricity output in a microbial fuel cell (MFC). In the present undertaking, batch bioH₂ production and MFC-based biolectricity generation from ultrasonically pretreated palm oil mill effluent (POME) were investigated using heat-pretreated anaerobic sludge as seed inoculum. Maximum bioH₂ production (0.7 mmol H₂/g COD) and COD removal (65%) was achieved at pH 7, for POME which was ultrasonically pretreated at a dose of 195 J/mL. Maximum value for bioH₂ productivity and COD removal at this sonication dose was higher by 38% and 20%, respectively, than unsonicated treatments. In batch MFC experiments, the same ultrasound dose led to reduced lag-time in bioelectricity generation with concomitant 25% increase in bioelectricity output (18.3 W/m³) and an increase of COD removal from 30% to 54%, as compared to controls. Quantitative polymerase chain reaction (qPCR) tests on sludge samples from batch bioH₂ production reflected an abundance of gene fragments coding for both clostridial and thermoanaerobacterial [FeFe]-hydrogenase. Fluorescence in situ hybridization (FISH) tests on sludge from MFC experiments showed Clostridium spp. and Thermoanaerobacterium spp. as the dominant microflora. Results suggest the potential of ultrasonicated POME as sustainable feedstock for dark fermentation-based bioH₂ production and MFC-based bioelectricity generation.     

Ferric oxide/date seed activated carbon nanocomposites mediated dark fermentation of date fruit wastes for enriched biohydrogen production

Biohydrogen production from biomass waste, not only addresses the energy demand in a renewable manner but also resolves the safe disposal issues associated with these biowastes. Also, scalable and low-cost techniques to enhance biohydrogen production have gained more attraction and are highly explored. In this research work, date-palm fruit wastes have been studied for their biohydrogen production potential using Enterobacter aerogenes by dark fermentation. Hydrogen yield and productivity were improved through the addition of iron oxide nanoparticles (Fe₃O₄ NPs) and its date seed activated carbon nanocomposites (Fe₃O₄/DSAC) to the fermentation media. Studies on discrete inclusions of these NPs showed that the appropriate dosage of NPs promoted, while higher dosages repressed the hydrogen production performance. Optimal dosage and fermentation time was observed as 150 mg/L and 24 h for both the additives. Fe₃O₄/DSAC nanocomposites showed better hydrogen production enhancement than Fe₃O₄ NPs. Maximum hydrogen yield of 238.7 mL/g was obtained for the 150 mg/L nanocomposites, which was 65.7% higher than that of the standalone Fe₃O₄ NPs and three folds higher than the yield of the control run without any NPs inclusion (78.4 mL/g). Metabolites analysis showed that the hydrogen evolution followed the ethanol-acetate pathway. Formation levels of longer chain propionate and butyrate co-metabolites were significantly low in the presence of Fe₃O₄/DSAC than Fe₃O₄. The carbon support in the nanocomposites acted as an adsorbent-buffer, which favored the medium pH in-addition to the stimulatory effects of Fe₃O₄ NPs. Cell growth and specific hydrogenase activity analysis were also performed to supplement the hydrogen production results. Gompertz and modified Logistic kinetic models were employed for kinetic modeling of experimental hydrogen production values. The Fe₃O₄/DSAC nanocomposites exhibited significant application potential for the production of biohydrogen from date fruit wastes.     

Microbial community analysis of thermophilic mixed culture sludge for biohydrogen production from palm oil mill effluent

The microbial community structure of thermophilic mixed culture sludge used for biohydrogen production from palm oil mill effluent was analyzed by fluorescence in situ hybridization (FISH) and 16S rRNA gene clone library techniques. The hydrogen-producing bacteria were isolated and their ability to produce hydrogen was confirmed. The microbial community was dominated by Thermoanaerobacterium species (∼66%). The remaining microorganisms belonged to Clostridium and Desulfotomaculum spp. (∼28% and ∼6%, respectively). Three hydrogen-producing strains, namely HPB-1, HPB-2, and HPB-3, were isolated. 16S rRNA gene sequence analysis of HPB-1 and HPB-2 revealed a high similarity to Thermoanaerobacterium thermosaccharolyticum (98.6% and 99.0%, respectively). The Thermoanaerobacterium HPB-2 strain was a promising candidate for thermophilic fermentative hydrogen production with a hydrogen yield of 2.53 mol H₂ mol⁻¹hexose from organic waste and wastewater containing a mixture of hexose and pentose sugars. Thermoanaerobacterium species play a major role in thermophilic hydrogen production as confirmed both by molecular and cultivation-based analyses.     

Optimization of particle number,substrate concentration and temperature of batch immobilized reactor system for biohydrogen production by dark fermentation

Immobilized cell bioreactor was operated in batch mode for biohydrogen generation by dark fermentation from acid hydrolyzed waste wheat powder. It was aimed to optimize the fermentation conditions with the purpose of obtaining the highest hydrogen yield (Y_H2) and production rate (HPR) by applying Box–Wilson statistical experimental design method. Particle number (PN = 120–240; X₁), initial total sugar concentration (TS₀ = 10–30 g/l; X₂) and fermentation temperature (T = 35–55 °C; X₃) were selected as independent variables. Polyester fibers with particle diameter “Dp” = 0.5 cm were used as support material to immobilize microorganisms with heat-pretreated sludge. Quadratic equations for production yield and rate were developed by using experimental results. The maximum Y_H2 (3.21 mol H₂/mol glucose) and HPR (73.3 ml H₂/h) were predicted at the optimum conditions of PN = 240, TS₀ = 10 g/l and T = 44.9 °C. Also, analysis of variance, as well as sum of ranking difference test results demonstrated that fitting models were statistically significant.