The team has also shown the production of cellulosic ethanol of 234.1 mg/g-total volatile solid (TVS) and of hydrogen (66.9 mL/g-TVS) in a two-stage process from enzymatic-treated cornstalk. (Pan et al., 2009). In this study, the team used dairy manure for hydrogen production in this two stage process; the hydrogen was produced from the effluent of the first, cellulosic ethanol stage by mixed culture.

Based on prior work that had shown hydrogen production potential of 89.2 mL/g-TS using microbes from cow manure and 109.0 mL/g-TS using microbes from lesser panda manure, the researchers opted to use lesser panda manure in the hydrogen study reported in the Chinese Science Bulletin.

During the optimal period of H2 production, the ORP (oxidation-reduction potential) values stayed in the lower level ranging from 445 mV to 455 mV. The results, said the researchers, show that the bio-pretreatment of the raw materials played a vital role in the effective conversion of corn stalk by mixed culture.

The researchers examined the influences of three pretreatment methods on the yields of soluble saccharides (SS) and H₂:

1. Dilute acid pretreatment: The yields of soluble saccharides (SS) and H₂ were significantly dependent on the acid types and acid concentration. The maximum SS yields of 212 mg/g-TS at lactic acid concentration of 0.4%; 343 mg/g-TS at HCl concentration of 1.0%; and 350 mg/g-TS at H₂SO₄ concentration of 2.0% were observed. Maximum H₂ yields of 125 mL/g-TS at 0.4% lactic acid 0.4%; 129 mL/g-TS at 1.0% HCl concentration; 151 mL/g-TS at H₂SO₄ 1.5% concentration were observed.

   With further increases in acid concentration, the trend was reversed. The results are consistent with the team’s previous studies, in which higher anion concentrations of Cl^- and SO₄^2- inhibited heavily the growth of the hydrogen-producing bacteria and led to the decrease of bio-hydrogen production capacity.

2. Acid-enzyme coupling pretreatment: The anaerobic atmosphere is beneficial to the enzymatic hydrolysis of corn stalk and the hydrogen production. The yields of SS and H₂ increased rapidly with the increase in the enzyme dosage from 348 mg/g-TS and 134 mL/g-TS at 1.1 IU/g to maximum 468 mg/g-TS and 165 mL/g-TS at 17.6 IU/g.

3. Solid bio-pretreatment: The process of the bio-pretreatment was accompanied by the generation of lactic acid, the microbe additive loading significantly effected the yields of SS and lactic acid in bio-pretreated corn stalk. An increase of the SS yield could be observed in the range of dosage 2.5 g/kg to 7.5 g/kg, the maximum SS yield of 212 mg/g-TS occurred at dosage 7.5 g/kg, and then with further increase in microbe additive dosage the trend was reversed.

   Furthermore, the mechanism studies of hydrogen production from pretreated corn stalk indicated that the enhanced H₂ yield related to the direct bio-degradation of the hemi-cellulose and cellulose besides the contribution of the generated SS and lactic acid in the bio-pretreated corn stalk during the bio-hydrogen fermentation.

The verification tests were performed in a 5-liter continuously stirred anaerobic bioreactor (CSABR) with 3-liter mixture at fixed bio-pretreated corn stalk of 15 g/L, pH 5.5, 36 °C and HRT for 10 h.

The maximal H₂ yield, H₂ content and H₂ production rate was observed at 175.6 mL/g-TS, 57.2% and 14.5 mL/g-TS•h^-1, respectively. During the optimal bio-hydrogen production period, the ORP value stayed in the range of -445 mV to -455 mV, which was consistent with that in previous reports.

During H₂ fermentation progresses, butyric acid, acetic acid and alcohol as main metabolic by-products were left at the reactor, during which butyrate and acetate accounted for about 70-80% of VFAs, and there was no significant methane observed in the CSABR. The CSABR operated steadily for 170 h with higher H₂ yield and lower H₂ partial pressure level, and the pH value could be easily adjusted by online control system, the researchers said.

Resources

• Xing Y, Ma H C, Fan Y T, et al. (2009) Cellulose-hydrogen production from corn stalk biomass by anaerobic fermentation. Chinese Sci Bull, 54(8): 1434-1441, doi: 10.1007/s11434-009-0147-x

• Pan CM, Zhang ML, Fan YT, Xing Y, Hou HW. (2009) Production of Cellulosic Ethanol and Hydrogen from Solid-State Enzymatic Treated Cornstalk: A Two-Stage Process. J. Agric. Food Chem., 57(7):2732-2738 doi: 10.1021/jf803779b