Page 47 - Biofuels Refining and Performance

30 Chapter One

known in the Indian Subcontinent as the gobargas plant, and will be dis-
cussed subsequently.
Sargassum tenerrimum, an abundant variety of marine algae found
on the Indian coast of the Arabian Sea, shows promising results in lab-
oratory experiments by anaerobic digestion. A mixed culture of marine
bacteria and methanogens happens to be a better choice. In a prototype
experiment, the partially treated marine algal biomass mixed with
cattle dung could be the initial feed for a digester. In a mixed culture,
the entire process is a complex one. The organisms which are very effi-
cient in cellulolytic activities degrade higher-carbohydrate materials
and less fre-
into simpler products as lower organic acids, including CO 2
quently H , along with other products, but very seldom show a significant
2
amount of reduction reactions. In absence of methanogens, they usually
produce H , CO (even CO), formate, acetate, and less favorably other
2
2
fatty acids and alcohols. It has been established that many methanogens

utilize NH as their nitrogen source, either H S or cysteine for their
2
4
sulfur requirement, and other growth-stimulating amino acids, vita-
mins, and some trace minerals.
Uncommon in many other anaerobic organisms, methanogens have
shown presence of a cofactor (coenzyme) named CoM, identified as
HSCH CH SO (2-mercapto-ethanesulfonic acid), and also another low-
2
2
3
molecular-weight factor called F 420 , as of yet unidentified. This F 420 in
an oxidized state fluoresces at 420 nm but loses all optical activity when
reduced. This compound is neither a ferredoxin nor can it be substituted
by ferredoxin. Another interesting part is its dependence on Co II
(NADP) and it cannot be substituted by Co I (NAD system). Occurrence
of oxidative or substrate-level phosphorylation in methanogens could not
be established, and the presence of quinines or cytochrome b/c systems
could not be observed. The involvement of methylcobalamin also could
not be substantiated. So, a large part of the information is yet to be
derived by the next-generation scientists. It will be useful to summarize
some of the metabolic steps, so far understood (see Fig. 1.10).
The ecologic role of biogas is manifold. Chemical anoxic transforma-
tion reduces the BOD value of the organic residues, which in turn are
enriched, proportionately in its C, N, P, and mineral ratios. In lignocel-
lulosics, after the anoxic process, enrichment of lignin occurs and may
lead to peat formation. This may be the origin of coal; natural gas and
coal deposits are likely to be found within a reasonable stretch. This is
a built-in machinery of nature for BOD and pollution control.

1.13 Gobargas
As already mentioned in the preceeding section of biogas, gobargas is
an extended version of the biogas. Usually, when cattle excreta (gobar)