Abstract
The normal maximum H2 yield in mesophilic biohydrogen (bioH 2) fermentation is ∼2 mol of H2/(mol of glucose). Thermodynamics could be the most fundamental control for bioH2 formation, since proton reduction is strongly energy consuming (+79.4 kJ/(mol of H2)). However, most of the electron equivalents in glucose do not accumulate in H2 but in a range of organic acids and alcohols. Thus, evaluating the hypothesis of thermodynamic control requires the full stoichiometry of the fermentation. We carried out batch bioH2 reactions with a range of pH values that yielded H2 yields from 0 to ∼2 mol of H2/(mol of glucose). We constructed complete electron equivalent (e- equiv) balances for high or low H2 yield by measuring all e- sinks. The highest H2 yield occurred with pH ∼4 and was coincident with major butyrate accumulation; ethanol or lactate correlated to reduced H2 yields at pH 7 and 10, respectively. Although the Gibb's free energies for all overall reactions were similar (-10.6 to -11.2 kJ/(e- equiv)), thermodynamics controlled the H 2-producing reaction coupled to ferredoxin; this reaction was favorable at acidic pH but thermodynamically blocked at pH 10. Also, butyrate formation was the most thermodynamically favorable reaction that produced ATP after glycolysis.
Original language | English (US) |
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Pages (from-to) | 2401-2407 |
Number of pages | 7 |
Journal | Environmental Science and Technology |
Volume | 42 |
Issue number | 7 |
DOIs | |
State | Published - Apr 1 2008 |
ASJC Scopus subject areas
- Chemistry(all)
- Environmental Chemistry