which was much slower than that of cellobiose. Analysis of
the residual solids at the end of 90 h indicated that the cellulose
component of the added lignocellulose was totally
consumed. Based on the consumption of either cellulose or
cellobiose, the hydrogen molar yield was 1.67 mol/molglucose
for the corn stover lignocellulose, and 1.64 mol/molglucose
for the cellobiose. The ratio of H2 to CO2 was slightly
larger for cellobiose (0.93) than for lignocellulose (0.85), but
both results are within the range reported for fermentation of
a-cellulose and delignified wood [23].
Both fermentation reactions yielded acetic acid and
ethanol as the major by products along with minor amounts
of formic, lactic, and succinic acids (Table 1). However, the
original lignocellulose feed contained sugars and acetic acid
derived from hemicellulose (see Materials and Methods),
although C. thermocellum was unable to metabolize them [21].
As a result, 17% (2.4 mM) of the 14 mM acetic acid in the
fermentation effluent was present in the fermentation
influent for the lignocellulose substrate.
3.2. Volumetric hydrogen production in MECs
Hydrogen production using an inoculum acclimated to the
synthetic fermentation effluent and the synthetic fermentation
effluent (FEI-Syn) declined over successive cycles (Fig. 2A).
However, when the combined inoculum from the MFCs
acclimated to individual substrates was used in MEC tests
(SSI-Syn), there was more consistent gas production over