Akerke Toleugazykyzy

The work is devoted to the study of inhibitory factors limiting the yield of biohydrogen during the processing of lignocellulosic biomass (LCB). In this context, dark fermentation is considered one of the most promising biological methods for producing hydrogen, since it does not require an external energy source, is compatible with modern reactor technologies and allows the use of a wide range of substrates. The main barrier to its industrial application remains the accumulation of toxic compounds formed during the pretreatment of LCB and during fermentation. The work summarizes information on the composition and action of the main inhibitors. The results of the analysis showed that the yield of H₂ during TF reaches 2-4 mol/mol sugar (maximum ~3.8 mol/mol hexose), but drops significantly in the presence of: (i) furans (furfural 0.03-8.23 g/l; 5-HMF 0.09-1.59 g/l), (ii) phenolic compounds of lignin (vanillin, syringaldehyde), (iii) organic acids (formic, acetic, levulinic), (iv) inorganic ions and heavy metals (Zn, Cu, Cr, Ni, etc.), (v) ammonia and sulfates. Dosedependent effects and changes in microbial community composition are also discussed, such as the effect of pH, the reduction in Clostridium abundance due to furfural, or the increase in Clostridium and Ruminococcaceae abundance with the addition of 5-HMP. Thus, understanding the mechanisms of action of inhibitors and finding ways to reduce their impact are key areas for improving the efficiency of dark fermentation and its implementation as a sustainable technology for converting lignocellulosic biomass into biohydrogen.

In this study acid‐hydrolyzed mixed vegetable waste was investigated as a sole carbon source for anaerobic fermentative growth and biohydrogen (H ₂ ) production by Escherichia coli . E. coli BW25113 wild type and a septuple mutant lacking key hydrogenase and fermentative enzymes were cultivated during anaerobic conditions using vegetable waste hydrolysates (VWHs) prepared at substrate concentrations of 5%–20% (w/v) and varying dilution levels. Both strains were able to grow anaerobically on VWHs, confirming the effective release of fermentable substrates during acid pretreatment. Maximum biomass formation by the wild‐type strain reached 0.46 g cell dry weight (g CDW) L ⁻¹ in undiluted 20% VWH, while the septuple mutant exhibited improved growth only upon dilution, indicating higher sensitivity to hydrolysate derived inhibitory compounds. Fermentable carbon removal efficiency (CRE) and H ₂ production were strongly dependent on substrate concentration and dilution level. H ₂ production was completely suppressed in undiluted VWHs but was restored upon dilution, with the highest cumulative H ₂ production (406 NmL) observed for the septuple mutant grown on 20% VWH at two‐fold dilution. The corresponding H ₂ yield reached approximately 2.4 NL H ₂ g ⁻¹ (consumed) carbohydrate g ⁻¹ biomass or 355 NmL per gram initial carbohydrate. These results demonstrate that VWH can support both biomass formation and competitive H ₂ production by E. coli , highlighting their potential as a sustainable platform for waste valorization and bioenergy generation.

Conventional solvents remain the most used media for lignocellulosic biomass valorization. However, these solvents exhibit many limitations and have a negative environmental impact. In the last decade, Deep Eutectic Solvents (DESs) have emerged as a multifaceted tool in biomass valorization, with a promising perspective in the application of lignocellulosic biomass valorization. DESs have gained attention in the last decade as an alternative solvent in biomass valorization and biorefinery processes due to their high efficiency; eco-friendliness; low cost; and numerous other advantages, such as recyclability, non-volatility, and stability. This paper discusses the latest research on the potential applications of DESs in the valorization of secondary lignocellulosic biomass.

Various pretreatment methods for the valorization of sunflower husks (SHs) for H₂ gas generation through fermentation by Escherichia coli were investigated. We analyzed thermal treatment (TT), acid hydrolysis (AH), and alkaline hydrolysis (AlkH) at different substrate concentrations (50 g L⁻¹, 75 g L⁻¹, 100 g L⁻¹, and 150 g L⁻¹) and dilution levels (undiluted, 2× diluted, and 5× diluted). A concentration of 75 g L⁻¹ SH that was acid-hydrolyzed and dissolved twice in the medium yielded optimal microbial growth, reaching 0.3 ± 0.1 g cell dry weight (CDW) L⁻¹ biomass. The highest substrate level enabling effective fermentation was 100 g L⁻¹, producing 0.37 ± 0.13 (g CDW) × L⁻¹ biomass after complete fermentation, while 150 g L⁻¹ exhibited pronounced inhibitory effects. It is worth mentioning that the sole alkaline treatment was not optimal for growth and H₂ production. Co-fermentation with glycerol significantly enhanced both biomass formation (up to 0.42 ± 0.15 (g CDW) × L⁻¹)) and H₂ production. The highest H₂ yield was observed during batch growth at 50 g L⁻¹ SH hydrolysate with 5× dilution, reaching up to 5.7 mmol H₂ (g sugar)⁻¹ with glycerol supplementation. This study introduces a dual-waste valorization strategy that combines agricultural and biodiesel industry residues to enhance clean energy generation. The novelty lies in optimizing pretreatment and co-substrate fermentation conditions to maximize both biohydrogen yield and microbial biomass using E. coli, a widely studied and scalable host.

This article discusses various methods of extracting valuable components from grape pomace, a byproduct of winemaking. Special attention is given to the effectiveness of traditional and innovative extraction methods, including solvent extraction, as well as new technologies such as solid-liquid extraction, supercritical fluid extraction, ultrasound-assisted extraction, accelerated solvent extraction, and pressurized liquid extraction. For example, supercritical fluid extraction is a relatively new technique for extracting target analytes from solid matrices. Ultrasound-Assisted Extraction is based on the phenomenon of cavitation, where pressure ultrasound waves propagate, and the transfer of extractants is enhanced by high shear forces. Pressurized Liquid Extraction involves using 100% water as the solvent. The research results confirm the high potential of using grape pomace as a raw material for obtaining functional products with antioxidant and anti-inflammatory properties. The process of extracting bioactive compounds, such as polyphenols, proteins, lignin, pectins, and oils, from food waste and by-products of winemaking is becoming an important alternative strategy. The most promising, efficient, sustainable, and environmentally friendly methods are supercritical extraction and ultrasound-assisted extraction.

This study investigates the potential of sugar beet pulp (SBP), a lignocellulosic by-product of sugar production, as a low-cost substrate for biohydrogen and biomass generation using Escherichia coli under dark fermentation conditions. Two strains—BW25113 wild-type and a genetically engineered septuple mutant—were employed. SBP was pretreated via thermochemical hydrolysis, and the effects of substrate concentration, dilution, and glycerol supplementation were evaluated. Hydrogen production was highly dependent on substrate dilution and nutrient balance. The septuple mutant achieved the highest H₂ yield in 30 g L⁻¹ SBP hydrolysate (0.75% sulfuric acid) at 5× dilution with glycerol, reaching 12.06 mmol H₂ (g sugar)⁻¹ and 0.28 mmol H₂ (g waste)⁻¹, while the wild type under the same conditions yielded 3.78 mmol H₂ (g sugar)⁻¹ and 0.25 mmol H₂ (g waste)⁻¹. In contrast, undiluted hydrolysates favored biomass accumulation over H₂ production, with the highest biomass yield (0.3 g CDW L⁻¹) obtained using the septuple mutant in 30 g L⁻¹ SBP hydrolysate without glycerol. These findings highlight the potential of genetically optimized E. coli and optimized hydrolysate conditions to enhance the valorization of agro-industrial waste, supporting future advances in sustainable hydrogen bioeconomy and integrated waste biorefineries.