Page 44 - Biofuels Refining and Performance

Energy and Its Biological Resources 27

exists on the noncyclic hydrogen production by these microbes unin-
hibited by nitrogen. Dilute wastes can be utilized by the photosynthetic
bacteria, which is an added advantage over those of the methane fer-
mentors. The conventional fermentation of organic substrates to
methane or hydrogen is theoretically limited to 80% and 20%, and prac-
tically to 65% and 15%. The difference is accounted for by the synthesis
of ATP and cell biomass. ATP is produced in presence of light and reac-
tions are driven at its expense, if hydrogen is produced by nitrogenase.

1.10.3 Methane production
The biology of an “oxidation pond” is not well understood. The algae-versus-
bacterial growth needs to be controlled, and anaerobicity and temperature
need to be maintained properly. The carbonaceous matter tends to ferment,
and methane is produced instead of carbon dioxide. The end product,
methane, can be used either as a direct fuel or through a suitably designed
fuel cell. Microbial methane and hydrogen production are discussed later.

1.11 Plant Hydrocarbons
While a significant number of scientists are assessing the future of
renewable and nonrenewable sources of energy, and their potential use-
fulness and costs, a few of them are busy exploring existing storehouses
of nature and modifying the renewable resources into direct conventional
fuels. Prof. Melvin Calvin and his group at the University of California at
Berkeley emphasize the importance of a group of plants which, in addi-
tion to producing polysaccharide, also produce polyisoprenes (rubber)
and similar associated products [4]. While the Hevea produces rubber,
different euphorbiacea produce polyhydrocarbons that have molecular
weights lower than 10% of that of average natural rubber. It is likely
that chemical manipulation may yield liquid fuels similar to that of
conventional gasoline or diesel out of these products.
The interesting aspect of these plants is that rubber plants demand
good insolation and high moisture content in soil as well as in the atmos-
phere. But many subspecies of Euphorbia can grow comfortably in sunny
semiarid lands, where standard cultivations are not economically viable
[5]. This leads us to two major considerations: (1) soil conservation, eco-
logic improvement, and increase in P/R (productivity/respiratory) ratio; (2)
production of hydrocarbon and biomass, both of which have energy value.
Avalois is the North Brazil variety, and Euphorbia tirucalli is the
Southern Californian equivalent of the plant. Both of them usually con-
tain 30% hydrocarbon in their latex. Similar or parallel plants in the
Indian Subcontinent are not yet well known. But like rubber plantation,
which successfully migrated from Brazil to Malaysia, one may try a few