Research progress of additives in photobiological hydrogen production system to enhance biohydrogen

Rumen fluid pretreatment promotes anaerobic methane production: revealing microbial dynamics driving increased acid yield from different concentrations of corn straw

In this work, the corn straw (CS) with concentrations of 3%, 6%, and 9% (w/v) were pretreated by rumen fluid (RF) and then used for batched mesophilic biogas production. The results showed that after a 6-day pretreatment, volatile fatty acid (VFAs) production of 3.78, 8.27, and 10.4 g/L could be found in 3%, 6%, and 9%, respectively. When concerning with biogas production, the highest accumulative methane production of 149.1 mL CH4/g volatile solid was achieved by 6% pretreated CS, which was 22% and 45% higher than 3% and 9%, respectively. Also, it was 3.6 times higher than the same concentration of unpretreated CS. The results of the microbial community structure analysis revealed that the 6% CS pretreatment not only maintained a microbial community with the highest richness and diversity, but also exhibited the highest relative abundance of Firmicutes (45%) and Euryarchaeota (3.9%). This high abundance was conducive to its elevated production of VFAs and methane. These findings provide scientific reference for the utilization of CS and support the development of agricultural waste resource utilization and environmental protection.

Enhancement of biohydrogen production by photo-fermentation of corn stover via visible light catalyzed titanium dioxide/activated carbon fiber

In this study, titanium dioxide/activated carbon fiber (TiO2/ACF) was synthesized by liquid-phase deposition method and the effect of TiO2/ACF on the performance of photo-fermentation biohydrogen production (PFHP) from corn stover under visible light catalysis was discussed. Results show the maximum cumulative hydrogen yield (CHY) obtained under the optimal conditions was 74.0 ± 1.3 mL/g TS with TiO2/ACF addition of 100 mg/L, which was twice that without TiO2/ACF addition (36.9 ± 1.0 mL/g TS). Initial pH value had the most significant effect on CHY. The addition of TiO2/ACF promoted the metabolic pathway of nitrogenase to reduce H+ produced by consuming acetic acid and butyric acid to hydrogen, and also shortened the photo-fermentation period. By scanning electron microscopy and X-ray diffraction analysis, the morphology and phase structure of TiO2/ACF after PFHP did not change significantly. This study laid the foundation for the reuse of TiO2 and its practical application in PFHP.

The Gompertz model and its applications in microbial growth and bioproduction kinetics: Past, present and future

The Gompertz model, initially proposed for human mortality rates, has found various applications in growth analysis across the biotechnological field. This paper presents a comprehensive review of the Gompertz model's applications in the biotechnological field, examining its past, present, and future. The past of the Gompertz model was examined by tracing its origins to 1825, and then it underwent various modifications throughout the 20th century to increase its applicability in biotechnological fields. The Zwietering-modified version has proven to be a versatile tool for calculating the lag-time and maximum growth rate/quantity in microbial growth. In addition, the present applications of the Gompertz model to microbial growth kinetics and bioproduction (e.g., hydrogen, methane, caproate, butanol, and hexanol production) kinetics have been comprehensively summarized and discussed. We highlighted the importance of standardized citations and guidance on model selection. The Zwietering-modified Gompertz model and the Lay-modified Gompertz model are recommended for describing microbial growth kinetics and bioproduction kinetics, recognized for their widespread use and provision of valuable kinetics information. Finally, in response to the current Gompertz models' focus on internal mortality, the modified Makeham-Gompertz models that consider both internal/external mortality were introduced and validated for microbial growth and bioproduction kinetics with good fitting performance. This paper provides a perspective of the Gompertz model and offers valuable insights that facilitate the diverse applications of this model in microbial growth and bioproduction kinetics.

Hydrothermal carbon microspheres and their iron salt modification for enhancing biohydrogen production

Dark fermentation (DF) for hydrogen (H₂) evolution is often limited to industrial application due to its low H₂ yield. In this work, hydrothermal carbon microspheres (HCM) and iron modified HCM (Fe-HCM) were prepared by hydrothermal process using waste corn cob. Subsequently, HCM and Fe-HCM were used in DF for more H₂. The highest H₂ yields amended with HCM and Fe-HCM at 600 mg/L were achieved to be 119 and 154 mL/g glucose (0.87 and 1.2 mol H₂/mol glucose), respectively, being 24% and 59% higher than that of control yield. Soluble metabolites revealed HCM and Fe-HCM promoted butyric acid-based DF. Microbial composition depicted that HCM and Fe-HCM improved the abundance level of Firmicutes from 35% to 41% and 56%, while the abundance level of Clostridium_sensu_stricto_1 rose from 25% to 38% and 51%, respectively. This provides valuable guidance for hydrothermal carbon used in biofuel production.

Critical review of biochemical pathways to transformation of waste and biomass into bioenergy

In recent years, biofuel or biogas have become the primary source of bio-energy, providing an alternative to conventionally used energy that can meet the growing energy demand for people all over the world while reducing greenhouse gas emissions. Enzyme hydrolysis in bioethanol production is a critical step in obtaining sugars fermented during the final fermentation process. More efficient enzymes are being researched to provide a more cost-effective technique during enzymatic hydrolysis. The exploitation of microbial catabolic biochemical reactions to produce electric energy can be used for complex renewable biomasses and organic wastes in microbial fuel cells. In hydrolysis methods, a variety of diverse enzyme strategies are used to promote efficient bioethanol production from various lignocellulosic biomasses like agricultural wastes, wood feedstocks, and sea algae. This paper investigates the most recent enzyme hydrolysis pathways, microbial fermentation, microbial fuel cells, and anaerobic digestion in the manufacture of bioethanol/bioenergy from lignocellulose biomass.