Enhancement of biohydrogen production in industrial wastewaters with vinasse pond consortium using lignin-mediated iron nanoparticles

The aim of this work was the enhancement of biohydrogen production by an anaerobic bacterial consortium with incorporation of lignin-mediated iron nanoparticles in the fermentation medium. Lignin magnetic nanoparticles (LMNP), identified as magnetite by XRD, exhibited spherical shape and average particle size of 8.6 nm, while lignin non-magnetic nanoparticles (LNMNP) exhibited high agglomeration and an amorphous nature in TEM and XRD, respectively. The fermentation medium (pH 7) was composed of 88% soft drink wastewater (SDW) and 12% corn steep liquor (CSL) and supplemented with NaHCO₃ (1.0 g/L) and cysteine-HCl (0.5 g/L). Under optimal conditions, BioH₂ production was 17.67 ± 0.54 mL, after 48 h of fermentation at 37 °C. Addition of LMNP and LNMNP increased BioH₂ production in 91.0 and 74.3%, respectively. Additionally, 200 mg/L of LMNP and LNMNP in the fermentation medium improved the BioH₂ yields (mL H₂/g COD_removed) in 2.8- and 2.3-fold, respectively.     

Consolidated bioprocessing of hydrogen production from agave biomass by Clostridium acetobutylicum and bovine ruminal fluid

The biological production of H₂ represents a renewable and eco-friendly energy alternative compared to fossil fuels. However, its production from lignocellulose involves the use of expensive enzymatic complexes. In the present work, the production of H₂ from pretreated agave biomass was evaluated by means of a Consolidated Bioprocess (CBP). This strategy was carried through the interaction of cellulose-degrading microorganisms obtained from bovine ruminal fluid (BRF) capable of enhancing H₂ production by Clostridium acetobutylicum. The results obtained show the capacity of BRF to hydrolyze the acid pretreated agave, improving the production of H₂ in the experiments where the inoculum of Clostridium was greater. According to the results, production of H₂ is significantly affected by the increase of the solids loading, obtaining a maximum H₂ production at a 10% of solids loading, pH 5.5 and 35 °C, representing a yield of 150 L of H₂ per Kg of biomass in 264 h.     

Biohydrogen production from sugarcane bagasse hydrolysate by elephant dung: Effects of initial pH and substrate concentration

Pre-heated elephant dung was used as inoculum to produce hydrogen from sugarcane bagasse (SCB) hydrolysate. SCB was hydrolyzed by H₂SO₄ or NaOH at various concentrations (0.25-5% volume) and reaction time of 60 min at 121 °C, 1.5 kg/cm² in the autoclave. The optimal condition for the pretreatment was obtained when SCB was hydrolyzed by H₂SO₄ at 1% volume which yielded 11.28 g/L of total sugar (1.46 g glucose/L; 9.10 g xylose/L; 0.72 g arabinose/L). The maximum hydrogen yield of 0.84 mol H₂/mol total sugar and the hydrogen production rate of 109.55 mL H₂/L day were obtained at the initial pH 6.5 and initial total sugar concentration 10 g/L. Hydrogen-producing bacterium (Clostridium pasteurianum) and non hydrogen-producing bacterium (Flavobacterium sp.) were dominating species in the elephant dung and in hydrogen fermentation broth. Sporolactobacillus sp. was found to be responsible for a low hydrogen yield obtained.     

Hydrogen,alcohols and volatile fatty acids from the co-digestion of coffee waste (coffee pulp,husk, and processing wastewater) by applying autochthonous microorganisms

The objective of this study was to screen the factors that affect H₂, organic acids and alcohols production from coffee waste pretreated in a hydrothermal reactor applying consortium of bacteria and fungi (indigenous from coffee waste) with hydrolytic and fermentative activity. The effects of pH (4.0–7.0), temperature (30–50 °C), agitation (0–180 rpm), headspace (50–70%), percentage of bioaugmentation (without microbial consortium to 20%), concentration of coffee pulp and husk (2–6 g/L), coffee processing wastewater (7-30 gCOD/L) and yeast extract (0–2 g/L) were evaluated using a Plackett-Burman design. The highest H₂ production potential (82 ml H₂) was obtained under the following conditions: 30 °C, 180 rpm, 50% headspace, without bioaugmentation, 2 g/L pulp and husk coffee, 30 gCOD/L coffee processing wastewater and 2 g/L yeast extract. The main soluble products were acetic acid (1956 mg/L), lactic acid (786 mg/L) and ethanol (816 mg/L). Lactobacillus sp., Clostridium sp., Saccharomyces sp. and Kazachstania sp. were the main autochthonous microorganisms identified. Through metagenome functional analysis, enzymes related to lignin, phenol, cellulose, lignocellulose, and pectin degradation were identified, as well as acidogenesis, and H₂ production.     

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.     

Fermentable sugars recovery from grape stalks for bioethanol production

Three different processes were investigated for the recovery of fermentable sugars from grape stalks: autohydrolysis at 121 °C before and after a pre-washing step and acid hydrolysis (2% H₂SO₄ w/w) after a pre-washing step. Moreover, optimal conditions of a charcoal-based purification process were determined by experimental design. All hydrolysates, with their corresponding synthetic liquors were used as fermentation substrates for the production of metabolites by the yeast: Debaryomyces nepalensis NCYC 1026. The main fermentation product was ethanol, where a maximum production of 20.84 g/l, a conversion yield of 0.35 g ethanol/g monomeric sugars and a productivity of 0.453 g/l h were obtained from non-purified autohydrolysate liquor. In all cases, ethanol production and cell growth were better in non-purified liquors than in synthetic liquors. These results could be influenced by the presence of other sugars in the hydrolysates, with higher concentration in non-purified ones.     

A novel staggered hybrid SSF approach for efficient conversion of cellulose/hemicellulosic fractions of corncob into ethanol

The following study reports bioconversion of corncob into ethanol using hybrid approach for co-utilization of dilute acid hydrolysate (pentose rich stream) and hexose rich stream obtained by enzymatic saccharification employing commercial cellulase Cellic CTec2 as well as in-house cellulase preparations derived from Malbranchea cinnamomea, Scytalidium thermophilium and a recombinant Aspergillus strain. Acid hydrolysis (1% H₂SO₄) of corncob at 1:15 solid liquid ratio led to removal of 80.5% of hemicellulosic fraction. The solid glucan rich fraction (63.5% glucan, 8.3% pentosans and 27.9% lignin) was hydrolysed at 10% substrate loading rate with different enzymes for 72 h at 50 °C resulting in release of 732 and 535 (mg/g substrate) total sugars by Cellic CTec2 and M. cinnamomea derived enzymes, respectively. The fermentation of enzyme hydrolysate with co-culture of Saccharomyces cerevisiae and Pichia stipitis added in sequential manner resulted in 3.42 and 2.50% (v/v) ethanol in hydrolysate obtained from commercial Cellic CTec2 and M. cinnamomea, respectively. Employing a hybrid approach, where dilute acid hydrolysate stream was added to solid residue along with enzyme Cellic CTec2 during staggered simultaneous saccharification and fermentation at substrate loading rate of 15% resulted in 252 g ethanol/kg corncob.     

Influence of alkaline peroxide assisted and hydrothermal pretreatment on biodegradability and bio-hydrogen formation from citrus peel waste

The effect of pretreatments by hydrothermolysis (180 °C; 15 min) and alkaline delignification (NaOH 5M; H₂O₂ 1%; 24 h) in citrus peel waste (CPW) was evaluated, as well as the effect on H₂, organic acids and alcohols production, in addition to characterization of the microbial community involved in fermentation. Batch reactors at 37 °C were operated with 3 gTVS/L of CPW with allochthonous consortium (UASB reactor sludge; 2 gTVS/L) and autochthonous of CPW (1.5 gTVS/L) as inocula. H₂ production was higher in reactors with in natura CPW (13.31 mmol/L) compared to hydrothermolysis (8.19 mmol/L) and alkaline delignification (7.27 mmol/L). The acetogenic pathway was predominant in the in natura CPW (4,355 mg/L acetic acid). The most abundant genera in the in natura CPW and after hydrothermolysis were Clostridium (18.97 and 12.90%, respectively) and Ruminiclostridium (16.65 and 1.04%, respectively) commonly related to cellulolytic bacteria and/or H₂ production.     

Effect of cornstalk hydrolysis on photo-fermentative hydrogen production by R. capsulatus

Cornstalk is a typical cellulose material, which can be used by photo-fermentative H₂ production after pretreatment. However, the pretreatment methods have different influence on photo fermentation. In this study, 25.0 g cornstalk was pretreated by HCl/NaOH/cellusase. The hydrolysis rates increased from 45.51% by ddH₂O-treatment to 60.79% by diluted HCl-treatment and 51.6% by NaOH-treatment. The corresponding reducing sugar yields were 0.13 g/g, 0.42 g/g and 0.01 g/g, respectively. Enzymatic treatment enhanced the corresponding cornstalk hydrolysis rates to 50.81%, 67.60% and 64.10% with reducing sugar yields of 0.22 g/g, 0.62 g/g and 0.26 g/g. The sorts and concentrations of carbon source for H₂ production vary among different hydrolysates. Photo-fermentative H₂ production of strain R. capsulatus JL1 and mutant JL1601 (cheR2^-) with hydrolysates were investigated. The maximum H₂ yield of 123.8 ± 14.2 mL/g by strain JL1 was obtained from alkali-enzyme pretreated cornstalk, while the H₂ yield of 224.9 ± 5.2 mL/g by mutant JL1601 (cheR2^-) was obtained with acid-enzyme hydrolysate as the substrates. Meanwhile, the alkali pretreated cornstalk was the worst for photo-fermentation of both strain JL1 and mutant JL1601 (cheR2^-). Nevertheless, the highest substrate conversion efficiencies for both strains were obtained from ddH₂O-pretreated hydrolysate. Two-step pretreated hydrolysates were more beneficial to H₂ production for mutant JL1601 (cheR2^-) but not for strain JL1.     

Biohydrogen production from paper industry wastes by SSF: A study of the influence of temperature/enzyme loading

The present work focused in assessing the hydrogen production from pretreated wastes of the paper industry (PIW) by simultaneous saccharification and fermentation (SSF) using anaerobic biofilms developed in natural fibers (ixtle) at different conditions. Anaerobic sludge from brewery wastewater treatment was used for biofilms and they were developed in plastic spheres covered with fiber cord from ixtle. The solid wastes of paper industry were previously pretreated with H₂SO₄ at 2.5% (v/v) at 120 °C by 30 min. The solids pretreated were hydrolyzed and fermented in batch reactors. All reactors were kept at an initial pH of 5.0 and three levels of enzyme loadings (10, 40 and 70 FPU/mL) and temperatures (35, 45, 55 °C) were assessed. The maximum hydrogen obtained (60.75 mmol/h*g volatile solids) was at 45 °C and 70 FPU/mL, moreover, no methane was detected in all cases.     

Production of crude bio-oil via direct liquefaction of spent K-Cups

Spent K-Cups were liquefied into crude bio-oil in a water-ethanol co-solvent mixture and reaction conditions were optimized using response surface methodology (RSM) with a central composite design (CCD). The effects of three independent variables on the yield of crude bio-oil were examined, including the reaction temperature (varied from 255 °C to 350 °C), reaction time (varied from 0 min to 25 min) and solvent/feedstock mass ratio (varied from 2:1 to 12:1). The optimum reaction conditions identified were 276 °C, 3 min, and solvent/feedstock mass ratio of 11:1, giving a mass fraction yield of crude bio-oil of 60.0%. The overall carbon recovery at the optimum conditions was 93% in mass fraction. The effects of catalyst addition (NaOH and H₂SO₄) on the yield of crude bio-oil were also investigated under the optimized reaction conditions. The results revealed that the presence of NaOH promoted the decomposition of feedstock and significantly enhanced the bio-oil production and liquefaction efficiency, whereas the addition of H₂SO₄ resulted in a negative impact on the liquefaction process, decreasing the yield of crude bio-oil.     

Enzymatic saccharification of pretreated rice straw by cellulase produced from Bacillus carboniphilus CAS 3 utilizing lignocellulosic wastes through statistical optimization

A marine bacterium, Bacillus carboniphilus CAS 3 was subjected to optimization for cellulase production utilizing cellulosic waste through response surface methodology. Plackett – Burman and Central composite design was employed and the optimal medium constituents for maximum cellulase production (4040.45 U/mL) were determined as rice bran, yeast extract, MgSO₄·7H₂O and KH₂PO₄ at 6.27, 2.52, 0.57 and 0.39 g/L, respectively. The cellulase produced was purified to the specific activity of 434.94 U/mg and 11.46% of recovery with the molecular weight of 56 kDa. The optimum temperature, pH and NaCl for enzyme activity was determined as 50 °C, 9 and 30% and more than 70% of its original activity was retained even at 80 °C, 12 and 35% respectively. Further, enzymatic saccharification of pretreated rice straw yielded about 15.56 g/L of reducing sugar at 96 h, suggesting that the purified cellulase could be useful for production of reducing sugars from cellulosic biomass into ethanol.     

Study of factors involved in the behavior of biofilms formed by biohydrogen-producing microflora identified by molecular biology using dairy wastewater

Batch tests were carried out to investigate the production of H₂ considering the effects of: substrate concentration in a range of 3–25 g-COD/L; Initial pH: from 4 to 7 and 11 and temperatures of: 20, 35, 45 and 55 °C. The optimal substrate was 25 g-COD/L, with a reduction of COD of 73% and a yield of H₂ of 5.95 mM/gCOD; and the optimal initial pH was 11.0, with a 70% of COD reduction and a H₂ yield of 4236 mM/gCOD. The optimum temperature for pH = 11 was 35 °C, with a COD reduction of 69.8% and H₂ yield of 6.3 mM/gCOD. Escherichia, Acinetobacter, Alcaligenes, Brevibacterium, Clostridium and Mycobacterium were isolated from pretreated inoculum samples and identified by 16S rDNA sequencing. The results suggest that biofilm reactors developed on a natural support such as Opuntia imbricata have good potential for hydrogen production from dairy wastewater.     

Vegetable waste as substrate and source of suitable microflora for bio-hydrogen production

Self-fermentation of cellulosic substrates to produce biohydrogen without inoculum addition nor pretreatments was investigated. Dark fermentation of two different substrates made of leaf-shaped vegetable refuses (V) and leaf-shaped vegetable refuses plus potato peels (VP), was taken in consideration. Batch experiments were carried out, under two mesophilic anaerobic conditions (28 and 37 °C), in order to isolate and to identify potential H₂-producing bacterial strains contained in the vegetable extracts. The effect of initial glucose concentration (at 1, 5 and 10 g/L) on fermentative H₂ production by the isolates was also evaluated.H₂ production from self-fermentation of both biomasses was found to be feasible, without methane evolution, showing the highest yield for V biomass at 28 °C (24 L/kg VS). The pH control of the culture medium proved to be a critical parameter. The isolates had sequence similarities ≥98% with already known strains, belonging to the family Enterobacteriaceae (γ-proteobacteria) and Streptococcaceae (Firmicutes). Four genera found in the samples, namely Pectobacterium, Raoultella, Rahnella and Lactococcus have not been previously described for H₂ production from glucose. The isolates showed higher yield (1.6–2.2 mol H₂/mol glucose_added) at low glucose concentration (1 g/L), while the maximum H₂ production ranged from 410 to 1016 mL/L and was obtained at a substrate concentration of 10 g/L. The results suggested that vegetable waste can be effectively used as both, substrate and source of suitable microflora for bio-hydrogen production.     

Evaluating biohydrogen production by Clostridium hydrogenum sp. nov. strain CUEA01 isolated from mangrove sediments in Thailand

The hydrogen (H₂) fermentative Clostridium hydrogenum sp. nov. strain CUEA01 was isolated from a mangrove sediment in Thailand. Genome sequencing and analysis revealed a genome size of 5,501,482 bp that encoded for 3,292 predicted protein coding genes with annotated functional assignments and many genes associated with carbon utilization and H₂ evolution. The H₂ production performance was evaluated in batch fermentation, and revealed that this strain can grow and produce H₂ at a broad range of temperatures (15–40 °C), pH (4–10), and initial glucose concentrations (5–60 g/L). The maximum H₂ yield (3.11 mol_H2/mol_glucose) was obtained at 37 °C, pH 8, and an initial glucose concentration of 10 g/L. Furthermore, this strain could utilize various carbon sources, including xylose, xylan, starch, mannose, glycerol, and avicel cellulose, amongst others. Additionally, CUEA01 was compatible with agro-industrial wastes and could achieve a maximum CHP of 4639 mL/L and 4024 mL/L from sugarcane molasses and cassava pulp, respectively. This demonstrates that CUEA01 has a potential for H₂ fermentation from complex organic wastes since it can secrete enzyme cocktails that consolidate the fermentation process.     

Biohydrogen production from palm oil mill effluent (POME) by two stage anaerobic sequencing batch reactor (ASBR) system for better utilization of carbon sources in POME

The production of biohydrogen through dark fermentation of palm oil mill effluent (POME) was evaluated in two-stages of biohydrogen in an anaerobic sequencing batch reactor (ASBR) system using enriched mixed culture for the first time. This study attempts to examine the effect of HRT and its interaction behavior with the solid retention time (SRT), and the sugar consumption. The effluent after discharged from the thermophilic reactor contained 7.61 g/L TC and 22.87 g/L TSS was fed to the secondary mesophilic reactor system. Results indicated that the overall sugar consumption reached 88.62% at the optimum HRT of 12 h with the SRT set to 20 h. The optimum hydrogen yield and HPR in the thermophilic stage were 2.99 mol H₂/mol-sugar and 8.54 mmol H₂/L·h respectively, while for the mesophilic stage were 1.19 mol H₂/mol-sugar and 1.47 mmolH₂/L·h respectively. The overall HPR showed an improvement and increase from 8.54 mmol H₂/L·h to 10.34 mmol H₂/L.h. Microbial community analysis of mixed culture in the two-stage thermophilic (55.0 °C) and mesophilic (37.0 °C) ASBR reactor was dominated by Thermoanaerobacterium sp. based on the PCR-DGGE technique.     

Effect of aluminium sulphate-catalysed hydrolysis process on furfural yield and cellulose degradation of Cannabis sativa L. shives

Commercially, furfural is produced from pentosan-rich biomass using mineral acids as homogeneous catalysts. This study investigated a novel hydrolysis method that allows to obtain furfural from hemp shives with high yield and also to preserve the cellulose in the remaining biomass for other bioconversion processes. To date, hemp shives have not been investigated for furfural production. Cannabis sativa L. (“Bialobrzeskie” variety) shives were used as a feedstock due to the high content of pentosan (17.6% of oven-dried biomass). It means that the theoretically possible amount of furfural was 12.8% of oven-dried hemp shives. The effect of temperature (140–180 °C), the amount of catalyst (3–7% of oven-dried biomass) and the treatment time (10–90 min) on the furfural formation were studied. Whereas, the effect of the same temperature and the amount of catalyst on the changes of lignocellulose were studied after 90 min treatment time. Al₂(SO₄)₃*18H₂O was used as a catalyst for the conversion of C5-sugars to furfural. To show the catalytic properties of Al₂(SO₄)₃*18H₂O, autocatalysis was performed as a reference process using the same parameters. The highest yield of furfural, 73.7% of the theoretical yield, was obtained at 180 °C, 5% Al₂(SO₄)₃*18H₂O of oven-dried mass and 90 min. From the biorefinery perspective, the optimal hydrolysis parameters were 160 °C, 5% Al₂(SO₄)₃*18H₂O of oven-dried mass and 90 min. With these parameters, the yield of furfural was 62.7% of the theoretical yield, 99.2% of hemicelluloses were removed and 95.8% of cellulose was preserved and slightly depolymerized.     

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.     

Enhanced photocatalytic performance of NiFe2O4 nanoparticle spinel for hydrogen production

The spinel NiFe₂O₄, prepared from nitrates precursors, was characterized by thermal analyses, X-Ray Diffraction, UV-Vis diffuse reflectance, Scanning electron microscopy, X-Ray Fluorescence spectrometry, X-ray photoelectron spectroscopy and photo-electrochemistry measurements. The X-ray diffrcation analysis of the powder indicates a cubic phase with a lattice constant of 8.327(8) Å and crystallite size of 19 nm. The X-Ray Fluorescence spectrometry indicates a stoichiometry, very close to NiFe₂O₄ catalyst calcined at 900 °C The X-ray photoelectron spectroscopy analysis confirmed the valences and crystallographic sites of the transition elements. The direct optical gap of NiFe₂O₄ (1.78 eV), due to the crystal field splitting of the 3d orbital in the octahedral site, is well suited for the solar spectrum and attractive for photo-electrochemical H₂ production. The flat band potential (E_fb = 0.47 V_SCE) was obtained from the capacitance-potential (C^?2 - E) characteristic in NaOH (0.1 M) electrolyte. A conduction band of ?1.11 V_SCE, more cathodic than the H₂ level (?0.8 V_SCE), enabled the use of NiFe₂O₄ for the water reduction into hydrogen. The H₂ evolution rate of 46.5 μmol g^?1 min^?1 was obtained under optimal conditions (1 mg of catalyst/mL, NaOH and 50 °C) in the presence of SO₃^2? (10^?3 M) as hole scavenger under visible light flux of 23 mW cm^?2. A deactivation effect of only 1% was obtained.     

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.