Page 59 - Biofuels Refining and Performance

42 Chapter One

using hydrogen, and the excess hydrogen is spilled out. Higher con-
centration of formate reduced hydrogen production.

HCOOH ↔ CO H 2
2
Facultative anaerobes.
1. Enterobacter: Enterobacter aerogenes, as an example, can use varied
and mixed nutrients, i.e., glucose, fructose, galactose, mannose, pep-
tones, and salts (pH 4.0, 40 C); and may show activity for about a
month in a continuous culture; evolution of hydrogen was about 120
mL/h/L of medium; 0.8 mol/mol of glucose. Accumulation of acetic,
lactic, or succinic acids is likely to cause antimetabolic suppression
in older cultures.
and
2. Escherichia coli: Anaerobically, it can use formate to produce CO 2
H . Carbohydrates as nutrient sources usually end up with mixed
2
products, i.e., ethanol, acetate, hydrogen, formate, carbon dioxide and
succinate.

Various anaerobes.
1. Ruminococcus albus mostly converts cellulose to CO , H , HCOOH,
2
2
C H OH, CH , and COOH. Pyruvatelyase may be functional in the
5
2
3
(237 mol/mol of glucose). Further details are not
production of H 2
available.
2. P. furiosus (thermophilic archeon) possesses nickel-containing hydro-
genase and produces hydrogen using carbohydrate and peptone, at
100 C. The metabolic system seems to be uncommon to those of non-
thermophiles.
3. Methanobacterium (Methanotrix) soehngenii (methanogens) can grow
on acetate and salts media, but can split formate into hydrogen and
carbon dioxide. M. barkeri, in the presence of bromoethane sulphonate,
has suppressed methane production; instead, hydrogen, carbon dioxide,
carbon monoxide, and water were produced.
4. Methylomonas albus BG8 and Methylosinus trichosporium OB3b
(methylotrophs) used various substrates, i.e., methane, methanol,
formaldehyde, formate, pyruvate, and so forth. But formate was
found to be most useful for production of hydrogen under anaerobic
conditions.
5. C. butyricum, C. welchii, C. pasturianum, C. beljerinscki, and so forth
are very efficient in utilizing different carbohydrate sources and even
effluents to produce hydrogen (see Fig. 1.14). Immobilization of these
cells has also been successful.