Page 46 - Advances in Eco-Fuels for a Sustainable Environment

Ecofuel feedstocks and their prospects 23

nutrient recovery from wastewater. It also means that, considering the CO 2 footprint,
the environmental cost of algae-base biofuel is much higher than biofuel from other
sources. This single major disadvantage means that large-scale production of algal
biofuel will not occur for a long time: in 2013, Exxon Mobil, after about an investment
of about $600 million, came to the conclusion that algae-based biofuels would not be
viable for at least 25 years from a strictly economical perspective, without considering
the yet-to-be-solved environmental impacts. Recent progress by this company and
Synthetic Genomics, a synbio startup, however, developed a new variety of these
organisms based on genetic modifications of Nannocholoropsis gaditana that are
capable of converting 55% of carbon into lipids in laboratory settings, against a nor-
mal conversion of about 20% [17, 18]. Although not yet ready for generalized produc-
tion, this development could give a final push to third-generation, large-scale fuel
production.
Another minor drawback is that algal biofuels tend to be less stable than biodiesel
from other sources, due to the highly unsaturated, more volatile oil found in the algae
that is, particularly at high temperatures, more prone to degradation. Unlike the nutri-
ent issue, however, this problem already has potential industrial mitigating solutions.

2.3 Biofuel types

A biofuel is any fuel whose energy is obtained through a process of biological carbon
fixation, the process that takes inorganic carbon (like CO 2 ) and converts it into organic
forms. In practice, any hydrocarbon produced from organic matter (living or once liv-
ing) in a short (not geologic) period of time is considered a biofuel. In contrast, fossil
fuels, although still originating from the same basic processes, took millions of years
to form.
Biofuels need not be made by a living organism; they can also be made through
chemical reactions, in a laboratory or industrial setting, from organic matter. The only
actual requirements for a biofuel are that the starting material must be CO 2 that was
fixed by a living organism, and the final product must be produced quickly, and not in
millions of years. The chemical structure of biofuels can differ the same way that the
chemical structure of fossil fuels can differ. Current industrial interest is in biofuels
that are easy to transport and store so they can be used as needed, when needed, in the
quantity needed. Biofuels can assume different states: gaseous (biogas), liquid (bio-
diesel, bioethanol, etc.), solid, and different chemical forms such as alcohols, ethers,
gases, liquids, and solid. These may have had different uses from those we are accus-
tomed to today: Rudolf Diesel, father of the diesel engine, initially designed its inven-
tion to run on vegetable oil, and ran it on peanut oil at its demonstration at the World
Exhibition in Paris in 1897.
Because biofuel can be any renewable biological material used as fuel, it becomes
clear that even substances such as wood, sawdust, leaves, and even dried animal dung
constitute biofuels. Wood and derivatives (charcoal, chips, sawdust) constituted the
largest fuel source for millennia, first in the form of firewood and recently, mechan-
ically pelletized wood biomass (a large source of particulate pollution in urban areas,