Biohydrogen and carboxylic acids production from wheat straw hydrolysate

Production of acetic acid from wheat bran by catalysis of an acetoxylan esterase

In this study, a gene encoding for acetylxylan esterase was cloned and expressed in E. coli. A single uniform band with molecular weight of 31.2 kDa was observed in SDS-PAGE electrophoresis. Served as the substrate, p-nitrophenol butyrate was employed to detect the recombinant enzyme activity. It exhibited activity at a wide temperature range (30-100 °C) and pH (5.0-9.0) with the optimal temperature of 70 °C and pH 8.0. Acetylxylan esterase showed two substrates' specificities with the highest Vmax of 177.2 U/mg and Km of 20.98 mM against p-nitrophenol butyrate. Meanwhile, the Vmax of p-nitrophenol acetate was 137.0 U/mg and Km 12.16 mM. The acetic acid yield of 0.39 g/g was obtained (70 °C and pH 8.0) from wheat bran pretreated using amylase and papain. This study showed the highest yield up to date and developed a promising strategy for acetic acid production using wheat bran.

Biohythane production from food processing wastes - Challenges and perspectives

The food industry generates enormous quantity of food waste (FW) either directly or indirectly including the processing sector, which turned into biofuels for waste remediation. Six types of food processing wastes (FPW) such as oil, fruit and vegetable, dairy, brewery, livestock and finally agriculture based materials that get treated via dark fermentation/anaerobic digestion has been discussed. Production of both hydrogen and methane is daunting for oil, fruit and vegetable processing wastes because of the presence of polyphenols and essential oils. Moreover, acidic pH and high protein are the reasons for increased concentration of ammonia and accumulation of volatile fatty acids in FPW, especially in dairy, brewery, and livestock waste streams. Moreover, the review brought to forefront the enhancing methods, (pretreatment and co-digestion) operational, and environmental parameters that can influence the production of biohythane. Finally, the nature of feedstock's role in achieving successful circular bio economy is also highlighted.

A review of research trends in the enhancement of biomass-to-hydrogen conversion

Different types of biomass are being examined for their optimum hydrogen production potentials and actual hydrogen yields in different experimental set-ups and through different chemical synthetic routes. In this review, the observations emanating from research findings on the assessment of hydrogen synthesis kinetics during fermentation and gasification of different types of biomass substrates have been concisely surveyed from selected publications. This review revisits the recent progress reported in biomass-based hydrogen synthesis in the associated disciplines of microbial cell immobilization, bioreactor design and analysis, ultrasound-assisted, microwave-assisted and ionic liquid-assisted biomass pretreatments, development of new microbial strains, integrated production schemes, applications of nanocatalysis, subcritical and supercritical water processing, use of algae-based substrates and lastly inhibitor detoxification. The main observations from this review are that cell immobilization assists in optimizing the biomass fermentation performance by enhancing bead size, providing for adequate cell loading and improving mass transfer; there are novel and more potent bacterial and fungal strains which improve the fermentation process and impact on hydrogen yields positively; application of microwave irradiation and sonication and the use of ionic liquids in biomass pretreatment bring about enhanced delignification, and that supercritical water biomass processing and dosing with metal-based nanoparticles also assist in enhancing the kinetics of hydrogen synthesis. The research areas discussed in this work and their respective impacts on hydrogen synthesis from biomass are arguably standalone. Thence, further work is still required to explore the possibilities and techno-economic implications of combining these areas for developing robust and integrated biomass-to-hydrogen synthetic schemes.

Bio-immobilization of dark fermentative bacteria for enhancing continuous hydrogen production from cornstalk hydrolysate

Mycelia pellets were employed as biological carrier in a continuous stirred tank reactor to reduce biomass washout and enhance hydrogen production from cornstalk hydrolysate. Hydraulic retention time (HRT) and influent substrate concentration played critical roles on hydrogen production of the bioreactor. The maximum hydrogen production rate of 14.2mmol H₂L^-1h^-1 was obtained at optimized HRT of 6h and influent concentration of 20g/L, 2.6 times higher than the counterpart without mycelia pellets. With excellent immobilization ability, biomass accumulated in the reactor and reached 1.6g/L under the optimum conditions. Upon further energy conversion analysis, continuous hydrogen production with mycelia pellets gave the maximum energy conversion efficiency of 17.8%. These results indicate mycelia pellet is an ideal biological carrier to improve biomass retention capacity of the reactor and enhance hydrogen recovery efficiency from lignocellulosic biomass, and meanwhile provides a new direction for economic and efficient hydrogen production process.

Recent insights into the cell immobilization technology applied for dark fermentative hydrogen production

The contribution and insights of the immobilization technology in the recent years with regards to the generation of (bio)hydrogen via dark fermentation have been reviewed. The types of immobilization practices, such as entrapment, encapsulation and adsorption, are discussed. Materials and carriers used for cell immobilization are also comprehensively surveyed. New development of nano-based immobilization and nano-materials has been highlighted pertaining to the specific subject of this review. The microorganisms and the type of carbon sources applied in the dark hydrogen fermentation are also discussed and summarized. In addition, the essential components of process operation and reactor configuration using immobilized microbial cultures in the design of varieties of bioreactors (such as fixed bed reactor, CSTR and UASB) are spotlighted. Finally, suggestions and future directions of this field are provided to assist the development of efficient, economical and sustainable hydrogen production technologies.