3.3. Hydrogen yields in MECs
Hydrogen yields were calculated on the basis of COD removal
and molar conversion for defined substrates (pure chemicals,
cellobiose and synthetic effluents). For the individual
substrates, acetic acid produced the most hydrogen with
1400 170 mL-H2/g-COD, with a range of 810 260 mL-H2/
g-COD (formic acid) to 1100 130 mL-H2/g-COD (succinic acid)
for the other single substrates (Fig. 3A). The molar yield was
highest for acetic acid based on the maximum possible
percent yield (3.6 mol/mol, or 90% conversion) (Fig. 4A), but
there were apparent larger molar yields produced with succinic
(4.8 mol/mol or 68.5%) and lactic acids (4 mol-H2/mol or
68%) but a lower overall conversion efficiency relative to the
possible percent yields.
The hydrogen yield with the synthetic effluent was higher
(980 110 mL-H2/g-COD) using the combined inoculum from
the individual substrates (SSI), than that obtained without the
special acclimation procedure (FEI) (800 290 mL-H2/g-COD)
(Fig.3B). Basedonthecomposition of thesynthetic effluent,and
the results achieved withthe individual substrates in theMECs,
we expected a hydrogen yield of 1200 mL-H2/g-COD. Thus, the
FEI-Syn produced 33%less hydrogen than expected.Onamolar
basis, we obtained an average of 3.2 mol-H2/mol-substrate
using the SSI inoculum, and 2.6 mol-H2/mol-substrate using
the FEI inoculum with the synthetic effluent (Fig. 4B).
3.3. Hydrogen yields in MECs
Hydrogen yields were calculated on the basis of COD removal
and molar conversion for defined substrates (pure chemicals,
cellobiose and synthetic effluents). For the individual
substrates, acetic acid produced the most hydrogen with
1400 170 mL-H2/g-COD, with a range of 810 260 mL-H2/
g-COD (formic acid) to 1100 130 mL-H2/g-COD (succinic acid)
for the other single substrates (Fig. 3A). The molar yield was
highest for acetic acid based on the maximum possible
percent yield (3.6 mol/mol, or 90% conversion) (Fig. 4A), but
there were apparent larger molar yields produced with succinic
(4.8 mol/mol or 68.5%) and lactic acids (4 mol-H2/mol or
68%) but a lower overall conversion efficiency relative to the
possible percent yields.
The hydrogen yield with the synthetic effluent was higher
(980 110 mL-H2/g-COD) using the combined inoculum from
the individual substrates (SSI), than that obtained without the
special acclimation procedure (FEI) (800 290 mL-H2/g-COD)
(Fig.3B). Basedonthecomposition of thesynthetic effluent,and
the results achieved withthe individual substrates in theMECs,
we expected a hydrogen yield of 1200 mL-H2/g-COD. Thus, the
FEI-Syn produced 33%less hydrogen than expected.Onamolar
basis, we obtained an average of 3.2 mol-H2/mol-substrate
using the SSI inoculum, and 2.6 mol-H2/mol-substrate using
the FEI inoculum with the synthetic effluent (Fig. 4B).
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