Optimization of photo fermentation in corn stalk through phosphate additive

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.

Pretreatment of corn stover by torrefaction for improving reducing sugar and biohydrogen production

The torrefaction pretreatment technology with different temperature varying from 160℃ to 240℃ was utilized to enhance the enzymatic saccharification and hydrogen production potential of corn stover. The composition characteristics, Crystal Intensity (CrI), reducing sugars yield and hydrogen production of the pretreated corn stover were detected to explore the torrefaction pretreatment effectiveness. Results revealed that the reducing sugar yield and hydrogen production from corn stover were improved significantly through torrefaction pretreatment, both the maximum reducing sugar yield of 427.86 ± 19 mg/g Total solid(TS) and hydrogen yield of 123.72 mL/g TS were obtained at 200 ℃, increased by 46.41% and 70.79%, respectively. The kinetic parameters from Gompertz model showed torrefaction pretreatment could shorten the lag phase time of enzymatic saccharification and hydrogen production. The reducing sugar data can be fitted well by fractal-like kinetic model and Gompertz model.

Study on Comparisons of Bio-Hydrogen Yield Potential and Energy Conversion Efficiency between Stem and Leaf of Sweet Potato by Photo-Fermentation

The source of raw materials for hydrogen production can be expanded by using vine waste as a substrate. Likewise, the effectiveness of vine waste can also be improved. However, plant parts such as stems and leaves often differ in physicochemical properties, which significantly affects the effectiveness of biochemical transformation. In this research, sweet potato was used as substrate in photo-fermentative hydrogen production (PFHP) to evaluate differences in bio-hydrogen production yield potential and energy conversion efficiency for its stem and leaf. Physicochemical properties were determined using the following techniques: elementary analysis, SEM, and X-ray diffraction. The Gompertz model was adopted to analyze the kinetic parameters, and energy conversion efficiency was calculated. The results showed that stem samples with loose structures produced more hydrogen, with a total cellulose and hemicellulose content of 44.6%, but crystallinity was only 29.67%. Cumulative bio-hydrogen yield of stem was 66.03 mL/g TS, which was 3.59 times higher than that of leaf. An increase of 258.93% in energy conversion efficiency was obtained when stem was used for PFHP. In conclusion, stem samples were more suitable for PFHP than leaf samples.

Effect of citrate buffer on hydrogen production by photosynthetic bacteria

The effect of citrate buffer on biohydrogen production using photosynthetic bacteria was studied. The study was performed in two steps. First, specific concentrations of citrate and sodium citrate as buffers were mixed into batch cultures, and the effects of these buffers on fermentation broth characteristics and biohydrogen production were analyzed. The maximum overall biohydrogen yield of 411.4 mL, which was 42% higher to the control group, was obtained with 0.05 mol/L citrate buffer. Then, the effect of 0.05 mol/L citrate buffer on biohydrogen yield at different pH values (5.5-7.5) were explored. The maximum biohydrogen yield of 429.82 mL was obtained at pH 6, and the final pH values were effectively controlled. The findings indicated that citrate buffer seriously affected the pH of the reaction liquid. The results provide technical support to stabilize the pH of photo-fermentation broth and improve biohydrogen production performance.

Enhancing photo-fermentation biohydrogen production from corn stalk by iron ion

This study aimed to investigate the enhancement of iron ion on growth, metabolic pathway, and biohydrogen production performance of biohydrogen producing bacteria HAU-M1. Different concentrations of Fe²⁺ and Fe³⁺ were respectively added into fermentation broth of photo-fermentation biohydrogen production (PFHP) from corn stalk. Regular sampling test was used to measure the characteristics of fermentation broth and gas, metabolic pathway, energy conversion efficiency, and kinetic of PFHP. The analysis of experimental data showed that the maximum hydrogen yield of 70.25 mL/g was observed at 2500 μmol/L Fe²⁺ addition, with an energy conversion efficiency of 5.21%, which was 19.98% higher over no-addition. However, the maximum hydrogen content of 51.41% and the maximum hydrogen production rate of 17.82 mL/h were observed at 2000 μmol/L Fe²⁺ addition. The experimental results revealed that iron ion played a key role in PFHP, which provided a technical support for improving the performance of PFHP.

Tolerance of photo-fermentative biohydrogen production system amended with biochar and nanoscale zero-valent iron to acidic environment

Anaerobic fermentation system is easy to become acidic due to the generation of small molecular acids, which will affect the metabolism of bacteria. Therefore, it is necessary to improve the acid resistance of system. In this work, the tolerance of photo-fermentative biohydrogen production system amended with biochar, nanoscale zero-valent iron (nZVI) and biochar + nZVI to acidic environment was studied. Results showed that additives improved the stability and performance of the photo fermentation. The best increment of biohydrogen from 0 to 286.83 ± 2.77 mL was obtained by adding biochar and nZVI together at the original pH of 4.5. The additive reduced the oxidation-reduction potential and promoted the consumption of acetate and butyrate. At initial pH of 5, 6 and 7, the highest biohydrogen yield of 361.02 ± 10.11, 419.36 ± 10.70 and 382.67 ± 25.08 mL was obtained by adding nZVI, respectively, representing 42%-44.45% increase compared with the control group under the same conditions.

Enhancement of the biohydrogen production performance from mixed substrate by photo-fermentation: Effects of initial pH and inoculation volume ratio

Co-digestion of substrates can improve hydrogen yield (HY) by adjusting carbon nitrogen ratio (C/N) of fermentation substrates. This study evaluated the enhancement of hydrogen production from co-digestion of duckweed and corn straw via photo-fermentation. The maximum HY of 78.0 mL/g Total solid (TS) was obtained from the mixed ratio of 5:1 (C/N of 13.2), which was 25.4% and 29.6% higher than those of single substrate of duckweed and corn straw, respectively. The effects of initial pH and inoculation volume ratio (IVR) on co-digestion photo-fermentative hydrogen production (CD-PFHP) from duckweed and corn straw were further studied. A maximum HY of 85.6 mL/g TS was achieved under the optimal condition (initial pH 8, IVR 20%, mix ratio of duckweed and corn straw of 5:1). Additionally, both mix ratio and initial pH showed statistical difference (p < 0.05). Acetic acid and butyric acid were found to be the main metabolic by-products during CD-PFHP.

Enhancement of pH values stability and photo-fermentation biohydrogen production by phosphate buffer

The main aim of this study was to investigate the effects of the initial pH values of the buffer on photo-fermentation biohydrogen production. Hydrogen production and the kinetics of it under different initial pH values were analyzed. Effects of initial pH values on reducing sugar consumption, hydrogen production rate, and byproduct production were evaluated at initial pH values of 5–7. The results showed that initial pH values of phosphate buffer had a significant effect on biohydrogen production via photo-fermentation. With the initial pH value of phosphate buffer at 6.0, the cumulative hydrogen production reached its maximum, 569.6 mL. The maximum hydrogen production rate was 23.96 mL/h at the initial pH value of 6.5. With the initial pH values at 5.0 and 7.5, the maximum hydrogen production rates were becoming lower, only 5.59 mL/h and 5.42 mL/h, respectively. And with the increase in pH values, the peak period of hydrogen production was gradually delayed, indicating that the alkaline environment had a negative effect on the ability of photosynthetic bacteria. This study revealed the influence of phosphate buffer initial pH values on the biohydrogen production via photo-fermentation and aimed to provide a scientific reference for further improving the theory and technology for biohydrogen production from biomass.