Fermentative H2 Research Articles

Potential and characteristics of bio-H2 production from the garden waste of ornamental plant Malus prunifolia fruit: Comparison between ethanol-type and butyrate-type fermentations

Edible fruit waste has been studied and considered to be the ideal substrates for low-cost bio-H2 production. However, the garden waste of ornamental plant fruits, which has similar components to edible fruit, is rarely studied. In this study, the potential and characteristics of fermentative bio-H2 production from the campus ornamental plant fruit of Malus prunifolia (MP) in both ethanol- and butyrate-types were investigated. Ethanoligenens harbinense B49 and Clostridium neuense G1 were employed as the inoculums for the ethanol- and butyrate-type fermentations, respectively. The results indicated that the fruit of MP is rich in fructose and sucrose, both of strains B49 and G1 could grow well with MP powder as the carbon source for fermentation. However, a higher H2 yield of 1.77 mol-H2/mol-hexose was obtained in the butyrate-type fermentation with strain G1, which was 1.4 times of that with strain B49. C. neuense G1 was more suitable for the H2 fermentation with MP as substrate, and a H2 yield of 0.55 mol-H2/mol-hexose by strain B49 was observed in the test of buffer system exchanging from ethanol-type to the butyrate-type. In summary, garden wastes such as fruits of ornamental plants should be given more attention as low-cost fermentation substrate candidates for bio-H2 production.

Fermentative production of 3-hydroxypropionic acid by using metabolically engineered Klebsiella pneumoniae strains

3-Hydroxypropionic acid (3-HP) is an industrially important platform chemical for super-absorbent or biodegradable polymers. Its production via biological methods is expected to be more competitive than chemical methods. Klebsiella pneumoniae is the most promising host due to its innate capabilities for 3-HP and vitamin-B12 production, ease of culture, and ease of engineering. In this study, step-by-step metabolic engineering and fermentation technologies were used to enhance the production of 3-HP. K. pneumoniae-derived ydcW gene was overexpressed using a plasmid after screening candidate genes. Major competing pathways encoded by dhaT, yqhD, ldhA, glpK, poxB, and pta-ackA were blocked. Additionally, it was demonstrated that simultaneous reinforcement of two native aldehyde dehydrogenase encoded by the ydcW gene preferring NADPH and the puuC gene preferring NADH, synergistically improved 3-HP production. Additional reinforcement of the acs gene to reduce acetate accumulation resulted in 93.7 g/L of 3-HP with a yield of 0.42 g/g·glycerol over a 72-h fed-batch fermentation. This performance is deemed sufficient for industrial applications.

The intracellular accumulation of iron coincides with enhanced biohydrogen production by Thermoanaerobacterium thermosaccharolyticum

The aim of this study was to investigate the effects of different doses (10–200 mg/L) of magnetite (FeO·Fe2O3), Fe0, Ni0, and FeCl3 on the efficiency of dark fermentative H2 production from cheese whey using Thermoanaerobacterium thermosaccharolyticum SP-H2. Energy conversion efficiency and hydrogen yield increased significantly by 22.7 % and 34.8 %, respectively, when 10 mg/L of magnetite was added, and hydrogenase activity increased by 23.6 % when 100 mg/L of Fe0 was added compared to the control (p < 0.001). Using scanning electron microscopy and energy dispersive X-ray spectroscopy, it was found that during the early exponential phase of hydrogen evolution, T. thermosaccharolyticum cells accumulated up to 11.2 times more Fe (up to 2.8 wt%) in the presence of optimal concentrations of Fe additives compared to the control. Intracellular iron accumulation and hydrogen yield were positively correlated with acetate concentration (p < 0.001), suggesting an efficient acetate pathway for dark fermentation. During the stationary growth phase, with almost no H2 production, the intracellular iron content decreased by up to 67.9 %. The phenomenon of changes in the amount of metal in cells, depending on the phase of hydrogen production, was demonstrated for the first time. The findings suggest that intracellular metals can be used in cell metabolism to produce H2, and the mechanisms behind this process need further investigation. Overall, this study provides valuable insights into the optimal forms and doses of metals for enhancing biohydrogen production, as well as possible research directions for the potential use of metals by microorganisms during additive-assisted dark fermentation of carbohydrate-rich wastes.

ARTP mutagenesis of Aureobasidium pullulans RM1603 for high pullulan production and transcriptome analysis of mutants.

Pullulan is a microbial exopolysaccharide produced by Aureobasidium spp. with excellent physical and chemical properties, resulting in great application value. In this study, a novel strain RM1603 of Aureobasidium pullulans with high pullulan production of 51.0 ± 1.0g·L- 1 isolated from rhizosphere soil was subjected to atmospheric and room temperature plasma (ARTP) mutagenesis, followed by selection of mutants to obtain pullulan high-producing strains. Finally, two mutants Mu0816 and Mu1519 were obtained, with polysaccharide productions of 58.7 ± 0.8 and 60.0 ± 0.8g∙L- 1 after 72-h fermentation, representing 15.1 and 17.6% increases compared with the original strain, respectively. Transcriptome analysis of the two mutants and the original strain revealed that the high expression of α/β-hydrolase (ABHD), α-amylase (AMY1), and sugar porter family MFS transporters (SPF-MFS) in the mutants may be related to the synthesis and secretion of pullulan. These results demonstrated the effectiveness of ARTP mutagenesis in A. pullulans, providing a basis for the investigation of genes related to pullulan synthesis and secretion.

Rheological and Structural Characterization of Carrageenans during Depolymerization Conducted by a Marine Bacterium Shewanella sp. LE8.

Carrageenans were widely utilized as thickening and gelling agents in the food and cosmetic industries, and their oligosaccharides have been proven to possess enhanced physicochemical and biological properties. In this study, Shewanella sp. LE8 was utilized for the depolymerization of κ-, ι-, and λ-carrageenan under conditions of fermentation. During a 24-h fermentation at 28 °C, the apparent viscosity of κ-, ι-, and λ-carrageenan decreased by 53.12%, 84.10%, and 59.33%, respectively, accompanied by a decrease in storage modulus, and loss modulus. After a 72-h fermentation, the analysis of methylene blue and molecular weight distribution revealed that ι-carrageenan was extensively depolymerized into smaller polysaccharides by Shewanella sp. LE8, while exhibiting partial degradation on κ- and λ-carrageenan. However, the impact of Shewanella sp. LE8 on total sugars was found to be limited; nevertheless, a significant increase in reduced sugar content was observed. The ESIMS analysis results revealed that the purified components obtained through ι-carrageenan fermentation for 72 h were identified as tetrasaccharides, while the two purified components derived from λ-carrageenan fermentation consisted of a hexasaccharide and a tetrasaccharide, respectively. Overall, the present study first reported the depolymerization of ι-and λ-carrageenan by Shewanella and suggested that the Shewanella could be used to depolymerize multiple carrageenans, as well as complex polysaccharides derived from red algae, to further obtain their oligosaccharides.

Solid-state fermentation of Limosilactobacillus fermentum and lysine addition to improve the cooking and eating quality of high-fiber rice noodles

The incorporation of polysaccharides can effectively lower the glycemic index (GI) of rice noodles but may also negatively impact their cooking and eating quality. This study explores the use of solid-state fermentation with Limosilactobacillus fermentum and the addition of lysine to enhance the cooking and eating quality of high-fiber rice noodles (HFRN). Optimal fermentation conditions—10% Limosilactobacillus fermentum inoculum, 30 °C fermentation temperature, and 72-h fermentation time—along with a 3% lysine addition, were identified. The results revealed a significant increase in cooking quality and sensory characteristics of the rice noodles under these conditions. Compared to the control, the treated rice noodles exhibited higher sensory scores (increased by 17%), lower broken strip rates (reduced by 77.99%), and superior textural properties. Further analysis using Fourier Transform Infrared Spectroscopy (FTIR), rapid viscometer analyzer (RVA), and differential scanning calorimetry (DSC) demonstrated that fermentation and lysine addition inhibited starch granule swelling, leading to decreased pasting properties (viscosity drop of 22.77–29.94% in all stages). Additionally, the retrogradation rates were reduced, and thermal stability was markedly increased (ΔH increased by 190.90%). These findings suggest that solid-state fermentation combined with lysine supplementation offers a promising strategy for enhancing the cooking and eating quality of HFRN.

Antibiotic fermentation residue for biohydrogen production: Inhibitory mechanisms of the inherent antibiotic

Antibiotic fermentation residue, which is generated from the microbial antibiotic production process, has been a troublesome waste faced by the pharmaceutical industry. Dark fermentation is a potential technology to treat antibiotic fermentation residue in terms of renewable H2 generation and waste management. However, the inherent antibiotic in antibiotic fermentation residue may inhibit its dark fermentation performance, and current understanding on this topic is limited. This investigation examined the impact of the inherent antibiotic on the dark H2 fermentation of Cephalosporin C (CEPC) fermentation residue, and explored the mechanisms from the perspectives of bacterial communities and functional genes. It was found that CEP-C in the antibiotic fermentation residue significantly inhibited the H2 production, with the H2 yield decreasing from 17.2 mL/g-VSadded to 12.5 and 9.6 mL/g-VSadded at CEP-C concentrations of 100 and 200 mg/L, respectively. CEP-C also prolonged the H2-producing lag period. Microbiological analysis indicated that CEP-C remarkably decreased the abundances of high-yielding H2-producing bacteria, as well as downregulated the genes involved in hydrogen generation from the“pyruvate pathway” and“NADH pathway”, essentially leading to the decline of H2 productivity. The present work gains insights into how cephalosporin antibiotics influence the dark H2 fermentation, and provide guidance for mitigating the inhibitory effects.

Evaluation of structure, quality, physicochemical properties, and phenolics content of pea proteins: A novel strategy through the incorporation of fermentation.

The utilization of pea proteins (PPs) is limited due to their relatively low protein digestibility (∼81%) compared to animal-based proteins, such as whey. The present investigation involved the fermentation of PPs at a concentration of 1% (w/v) using 5% (w/v) water kefir for 60h at 25°C to improve the functional properties of PPs. The results showed a significant (p<0.05) increase in lactic acid and acetic acid production during fermentation. These findings suggest that PPs can be effectively fermented using water kefir as a starter culture for the increased protein digestibility of PPs. The PP conformation underwent modifications, including secondary and tertiary protein structure alterations. The total phenolic compounds increased throughout the fermentation, reaching around 695.32±15mg gallic acid equivalent/100g after 24h of fermentation. Furthermore, the fermentation process has culminated in significant (p<0.05) changes in the surface charge and hydrophobic properties of the fermented PPs, from -38.1 to -45.73 and 362.7 to 550.2, respectively. Fermentation using water kefir is a promising technique for improving the digestibility, protein structure, and nutritional values of PPs.

Evaluation of direct-fed microbials on in vitro ruminal fermentation, gas production kinetic, and greenhouse gas emissions in different ruminants’ diet

IntroductionThree in vitro experiments were conducted to evaluate the effects of increasing levels of Enterococcus faecium and Saccharomyces cerevisiae (DFM1) and increasing levels of Bacillus licheniformis and Bacillus subtilis (DFM2) on in vitro ruminal fermentation parameters in three different dietary scenarios.MethodsFor Exp. 1, the basal diet consisted of 25:75 roughage:concentrate ratio (R:C) and was composed by 5 treatments: control (no additive), 2 levels of DFM1 (1X = 1.9 mg and 5X = 9.0 mg), and 2 levels of DFM2 (1X = 3.8 mg and 5X = 19 mg). The Exp. 2 consisted of a 41:59 R:C diet and was composed by 5 treatments: control (no additive) and 2 levels of DFM1 (1X = 3.8 mg and 5 X = 19 mg) and 2 levels of DFM2 (1X = 5.6 mg and 5X = 28 mg). The Exp. 3 consisted of a 100:0 R:C diet [Brachiaria (syn. Urochloa brizantha)] and was composed by the same treatments described in Exp. 1. The DFM1 contained 3.5 × 109 CFU per g of Enterococccus faecium and Saccharomyces cerevisiae, whereas the DFM2 contained Bacillus licheniformis and Bacillus subtilis at 3.2 × 109 CFU per g. In each Exp., an in vitro gas production (GP) system with 43-bottles (AnkomRF) was used in four consecutive 48 or 72-h fermentation batches to evaluate total GP (TGP), kinetics and fermentation profiles, methane (CH4), and carbon dioxide (CO2).ResultsFor Exp 1, DFM1 increased quadratically TGP at 24 and 48-h, which reflected in a greater in vitro organic matter digestibility (IVOMD). The concentrations of ammonia-N, CH4, and CO2 (mmol/g of IVOMD) reduced quadratically as DFM1 increased. For Exp. 2, DFM1 inclusion reduced butyrate concentration and acetate to propionate ratio. Regarding GHG emissions, DFM1 and DFM2 quadratically reduced CH4 and CO2 emission per IVOMD (mmol/g of IVOMD). For Exp. 3, DFM1 increased quadratically TGP at 48h with no impact on IVOMD. Otherwise, DFM2 increased linearly TGP at 24 and 48h which reflected in a greater IVOMD. The inclusion of DFM1 increased linearly iso-valerate and branched-chain volatile fatty acids (BCVFA) concentration and DFM2 addition increased BCVFA quadratically.DiscussionOverall, addition of DFM1 [Enterococccus faecium (5 × 109 CFU per g) + Saccharomyces cerevisiae (5 × 109 CFU per g)] or DFM2 [Bacillus licheniformis + Bacillus subtilis (3.2 × 109 CFU per g)] might enhance the fermentation process in the rumen and decrease greenhouse gas emissions in a dose-dependent manner, though the results are contingent on the specific type of diet.

Continuous dark-photo fermentative H2 production from synthetic lignocellulose hydrolysate with different photoheterotrophic cultures: Sequential vs. co-culture processes

Integration of dark and photo-fermentation is a promising strategy to efficiently produce renewable hydrogen from different types of waste biomass. In this study, sequential and co-culture dark-photo fermentations were evaluated and compared during continuous operation using synthetic lignocellulose hydrolysate as a substrate. Mixed dark-fermentative bacterial consortium was combined with two different photo-fermentative bacterial cultures: pure culture of Rhodobacter sphaeroides (RSC) and mixed photoheterotrophic consortium (MPC). The sequential process showed higher total H2 yields compared to co-culture fermentation for both RSC and MPC. The highest yield of 4.15 mol H2/molsugar was obtained for the sequential process with RSC at an HRT of 3.5 days and pH 7.5. For the co-culture process, the yield reached 2.88 mol H2/molsugar at pH 7.0 and an HRT of 3.5 days. Complete sugar utilization was observed for dark fermentation. RSC preferred acetate as a carbon source, while MPC preferred butyrate. Photoheterotrophic bacteria, Rhodopseudomonas pseudopalustris and Rhodoplanes piscinae, present in the MPC inoculum were outcompeted by undesirable microorganisms during the continuous process, resulting in low HPR. On the other hand, in both sequential and co-culture processes, a high relative abundance of R. sphaeroides (>40%) was observed in the RSC, indicating effective cooperation between dark and photo bacteria.

Integrated biorefinery strategy for poly(3-hydroxybutyrate) accumulation in Cupriavidus necator DSM 545 using a sugar rich syrup from cereal waste and acetate from gas fermentation

Poly(3-hydroxybutyrate) (PHB) is one of the most well-known biodegradable and biocompatible biopolymers produced by prokaryotic microorganisms. It belongs to the family of polyhydroxyalkanoates (PHAs), and it has gained significant attention in recent years due to its potential as a sustainable alternative to traditional petroleum-based plastics. Cupriavidus necator has been identified as a potential producer of PHB for industrial applications due to its ability to produce high amounts of the polymer under controlled conditions, using a wide range of waste substrates. In this study, the ability of Cupriavidus necator DSM 545 strain to produce PHB was tested in a fed-batch strategy providing two different organic substrates. The first is a sugar-based syrup (SBS), derived from cereal waste. The second is an acetate-rich medium obtained through CO2 -H2 fermentation by the acetogenic bacterium Acetobacterium woodii. The carbon sources were tested to improve the accumulation of PHB in the strain. C. necator DSM 545 proved to be able to grow and to perform high accumulation of biopolymer on waste substrates containing glucose, fructose, and acetate, reaching about 10 g/L of PHB, 83% of biopolymer accumulation in cell dry mass, in 48 h of fed-batch fermentation in 0.6 L working volume in a bioreactor. Moreover, a Life Cycle Assessment analysis was performed to evaluate the environmental impact of the process converting the sugar syrup alone and the integrated one. It demonstrated that the integrated process is more sustainable and that the most impactful step is the PHB production, followed by the polymer extraction.

Cleaner production of biohydrogen using poplar leaves: Experimental and optimization studies

Biohydrogen (bioH2) is recognized as a potential carbon-neutral energy vector, and developing novel methods has received increasing attention with a prime goal of producing H2 more efficient and cost effective manner. This study aimed to develop a unique reactor to investigate dark fermentative H2 production from poplar biomass using commercially available and inexpensive microorganism cultures. Therefore, six factors of the Box-Behnken design (BBD) were performed to evaluate the individual and combined effects of operational parameters: acid concentration (2–10%), biomass concentration (2–10 g), initial pH (5–8), temperature (30–40 °C), mixing ratio (150–350 rpm), and microorganism concentration (2–6 g) on bioH2 production. Among the operational parameters, the acid concentration was the most effective parameter on bioH2 production. The bioH2 production increased from 11.33 to 18.15 mg/g biomass with increasing acid concentration from 6 to 10%. Moreover, the optimum levels of operational variables were as follows: acid concentration of 9.9%, biomass amount of 2 g, pH of 6.56, temperature of 35 °C, mixing ratio of 345 rpm, and microorganism amount of 4.5 g for the highest bioH2 production of 20 mg/g-biomass according to the experimental design. Consequently, the bioH2 production performance of the dark fermentation process showed that bioH2 production from poplar biomass using commercially available microorganisms had a competitive advantage.

Comparative Evaluation of Unpeeled Cassava (Manihot esculenta) and Tacca (Tacca involucrata) Tuber Flours as Substrates for Bioethanol Production

The ever-increasing demand for alternatives to fossil fuel due to its negative impacts on the environment and high prices have resulted in the search for feedstock for bioethanol production. Cassava is one of the major staple foods that is processed into various preservative forms in Nigeria, while tacca is a plant growing in the wild and is eaten by a few people during scarcity of food. Unpeeled cassava and tacca tubers were processed into flour. The flour was hydrolyzed using Aspergillus niger and Saccharomyces cerevisiae, separately. The bioethanol potentials of tuber flours were evaluated using a single-step process. Hydrolysis of 10g of cassava tuber flour separately by Aspergillus niger and Saccharomyces cerevisiae produced (g/100mL) 0.720 and 0.765 of sugar, respectively, while hydrolysis of 10g of tacca tuber flour separately by Aspergillus niger and Saccharomyces cerevisiae produced (g/100mL) 0.392 and 0.367 of sugar respectively. Evaluation of the effect of time during hydrolysis of cassava tuber flour for 24h by Aspergillus niger and Saccharomyces cerevisiae separately produced (g/100mL) 1.44 and 0.737 of sugar, while hydrolysis of tacca tuber flour for 24h produced (g/100mL) 0.768 and 0.493 of sugar. Evaluation of the effect of varying pH values during hydrolysis of the tuber flours revealed that pH 5.6 produced the highest concentration of sugar (0.240g/100mL) and (0.803g/100mL) when Aspergillus niger and Saccharomyces cerevisiae were separately used to hydrolyze cassava tuber flour. When Aspergillus niger and Saccharomyces cerevisiae were separately used to hydrolyze tacca tuber flour at pH 5.6, 0.626g and 0.436g of sugar was produced. Fermentation of cassava tuber flour by mixed culture of Aspergillus niger and Saccharomyces cerevisiae for 48h produced 3.851%(w/v) bioethanol at 24h of fermentation, while fermentation of tacca tuber flour by mixed culture of Aspergillus niger and Saccharomyces cerevisiae produced 3.236% (w/v) bioethanol at 48h. Cassava tuber flour produced a higher concentration of bioethanol than tacca tuber flour. These results have shown that tacca tuber is a potential feedstock for bioethanol production, hence exploitation of nonfood materials such as tacca tuber for bioprocesses can reduce the over _dependence on cassava tuber.

Development of a novel biochar-made porous monolith for enhanced C1 and H2 fermentation

Biochar is a carbonaceous porous material that is produced through the thermal processing of biomass under oxygen-limited environment. Nevertheless, biochar is known to be an inexpensive and sustainable raw material with a wide range of possible applications. Recently, biochar has been discovered as an efficient biological catalyst for anaerobic conversion, mainly due to its highly porous structure with micro and macro channels, which procures a viable living area for attached-grown microorganisms. Whereas it is never applied to improve the biological conversion of gas substances such as C1 (e.g., CO, CO2) and H2, which is a promising research area with increasing commercial interest. However, considering that biological reaction is limited by the target water solubility of gas substrates, special attention is required when combining biochar for gas fermentation. The goal was to create a novel gas sparger where the biofilm grows on biochar, thus improving the interaction with the gaseous substrate. For this purpose, polystyrene foam and powdered biochar were compounded to form a mouldable composite, which was then cast as a porous monolith.•Biochar-made sparger (BS) was investigated for the homoacetogenic conversion of H2 gas via microbial mixed cultures as opposed to a control test equipped with a stone sparger.•BS showed a significantly better performance in terms of biological gas fixation rate (36% more than control) and productivity (8.5 gCOD L−1 d−1).

Isolation and identification of protease-producing Bacillus amyloliquefaciens LX-6 and its application in the solid fermentation of soybean meal.

Soybean meal (SM) is considered an ideal substitute for fish meal; however, its application is mainly limited because of its antigen proteins, glycinin and β-conglycinin. To improve the value of SM in the aquaculture industry, we employed an aerobic bacterial strain (LX-6) with protease activity of 1,390.6 ± 12.5 U/mL. This strain was isolated from soil samples and identified as Bacillus amyloliquefaciens based on morphological and physiological biochemical characteristics and 16S rDNA gene sequence analyses. Subsequently, we quantified the extent of glycinin and β-conglycinin degradation and the total protein and water-soluble protein content after SM fermentation with B. amyloliquefaciens LX-6. At 24h of fermentation, the macromolecular antigen proteins of SM were almost completely degraded; the maximum degradation rates of glycinin and β-conglycinin reached 77.9% and 57.1%, respectively. Accordingly, not only did the concentration of water-soluble proteins increase from 5.74% to 44.45% after 48h of fermentation but so did the concentrations of total protein and amino acids compared to those of unfermented SM. Field emission scanning electron microscopy revealed that the LX-6 strain gradually disrupted the surface structure of SM during the fermentation process. In addition, B. amyloliquefaciens LX-6 exhibited broad-spectrum antagonistic activity and a wide pH tolerance, suggesting its application in SM fermentation for fish meal replacement.

Applying metabolic flux analysis to hydrogen fermentation using a metabolic network constructed for anaerobic mixed cultures

In this study, a mixed-cultural metabolic network for anaerobic digestion that included the concept of a “universal bacterium” was constructed, and metabolic flux analysis (MFA) applying this network was conducted to evaluate the flow of electrons and materials during H2 fermentation under various conditions. The MFA results from two H2 fermenters feeding glucose with (GP) or without (GA) the addition of peptone suggest that hydraulic retention time (HRT) presents a significant impact on hydrogen production, and the reversed trends could be observed at HRTs below and above 4 h. From the MFA results of lactate/acetate-fed H2 fermenter, the highest flux of H2 production is associated with more significant acetate consumption and the following pathways toward the anaplerotic reactions cycle that produces NADH. The occurrence of acetogenesis in the H2 fermenters using various types of bioethanol-fermented residues (BEFRs) was also identified according to the MFA results. By analyzing the MFA results of all 49 sets of data from H2 fermenters via Pearson's correlation, it was revealed that the flux of H2 production positively correlates to the reduction of ferredoxin with pyruvate oxidation, acetate formation, and acetate emission when lactate was produced in the system. On the contrary, negative relationships were found between the flux of H2 production and these three fluxes. The extended application of MFA provides additional information, including the fluxes between intracellular metabolites, and the information has the potential to be used in decision-making systems during the future operation of anaerobic processes by connecting operational parameters.

Continuous dark-fermentative H2 production using carbon components of lignocellulose hydrolysates: Insight into the difference between mixed and single substrates

Hydrogen produced from lignocellulosic biomass via dark fermentation is a promising alternative to fossil fuels. This study assessed fermentative H2 production from single sugars and sugar mixtures mimicking real lignocellulose hydrolysates during a continuous process. The highest hydrogen production rate (HPR) was obtained with pentose sugars, reaching 8.80 and 8.09 L/L-d for arabinose and xylose, respectively. Glucose showed the lowest HPR (6.19 L/L-d), while in the case of sugar mixtures (glucose, cellobiose, xylose, arabinose), HPR was approximately 7.3 L/L-d and was lower than expected from calculations. Thus, cofermentation reduced the H2 production potential. It was shown that pentose sugars are preferred for hydrogen production, but their utilization is limited by the presence of glucose, which is utilized preferentially in sugar mixtures. Xylose, arabinose and sugar mixtures showed similar H2 yields (approximately 0.29 mol H2/mol C), so the efficiency of substrate conversion into H2 was comparable for these substrates. The microbial community distribution showed that the Clostridium genus was dominant regardless of the substrate, with Clostridium beijerinckii and Clostridium guangxiense being the main bacterial species. Different substrates did not significantly affect the type of microorganisms present in the microbiome and changed only their relative abundance.

Exploring the feasibility of biological hydrogen production using seed sludge pretreated with agro-industrial wastes

The effect of applying agro-industrial waste (AIW), such as potash extract (PE), cassava-steep wastewater (CSWW), and corn-steep liquor (CSTL), as an alternative material to pretreat digested cattle slurry (DCS) for biological hydrogen production was examined. In this study, the pretreated (PT) DCS was employed for H2 fermentation in batch cultures utilising glucose and sucrose as substrates. The result showed that, at 55 °C and pH 5.5, the pretreated DCS's daily volumetric hydrogen production (VHP) was higher than the untreated DCS. Although heat-shocked DCS produced a higher daily VHP of 135 NmL H2 g−1 VS on the second day using glucose as substrates, it is followed by PE-PT DCS, which gave a peak daily VHP of 115 NmL H2 g−1 VS but at a shorter time. When sucrose was the carbon source, the highest peaks were recorded in all the laboratory reactors on day two, with the highest daily VHP of 211 NmL H2 g−1 VS achieved in PE-PT DCS digesters. After the different DCS PT studies, the dominant phylum Firmicutes, represented by the Clostridium and Ruminococcus, were the most abundant bacteria compared to the untreated DCS, which was more diverse. Further research is required to optimise the conditions for AIW DCS pretreatment.

Hydrogen production from Brewer's spent grain hydrolysate by dark fermentation

The aim of this study was to evaluate the production of H2 by dark fermentation of brewer's spent grain (BSG) hydrolysate. The process was evaluated under different conditions of temperature, initial pH, and inoculum ratio. The maximum cumulative H2 production (PH2), H2 production rate (RH2), and H2 yield (YH2) was 4160 mL/L of working volume, 760 mL/L.h, and 5154.26 mL/gglucose cons, respectively. The assay with initial pH 7.5, inoculum 30%, and 35 °C, resulted in the highest PH2, and assay with initial pH 7.5, inoculum 30%, and 45 °C resulted in the highest RH2 and YH2. It is observed that PH2 and RH2 were statistically influenced by the initial pH, showing the negative effect of low pH. The initial concentration of furfural (<0.0047 g/L) and 5-(hydroxymethyl)furfural (<0.0220 g/L) were low. Therefore, BSG hydrolysate would be a suitable substrate for dark fermentative H2 production.

Dark fermentative hydrogen production from cassava starch: A comprehensive evaluation of the effects of starch extrusion and enzymatic hydrolysis

Hydrolysis could be rate-limiting for the dark fermentative H2 production from cassava starch (CS) due to its semicrystalline nature. Therefore, the effects of CS extrusion and enzymatic hydrolysis on improving dark fermentation (DF) were studied. Preliminary DF experiments were conducted to investigate the effects of inoculum (sludge) heat-pretreatment, which increased H2 production from untreated-CS by over 154%. Likewise, 15 g/L starch was considered best for H2 production. Extruded-CS presented a maximum H2 yield of 1.58 mol H2/mol glucose with a 76% reduction in the fermentation adaptive phase and 43% increase in maximum H2 productivity compared to untreated-CS. Meanwhile, extruded-CS hydrolysate presented a maximum H2 yield of 1.8 mol H2/mol glucose with a 63% reduction in the fermentation adaptive phase and 18% increase in H2 productivity. A comprehensive assessment of the H2 yield, process time, production rate, and process simplification revealed extruded-CS as the most promising feedstock under the evaluated conditions.