Integrated Environmental Biotechnology - Environmental Biotechnology: Theory and Application - page 245

Kassel on a range of plants, including cabbage, carrots, potatoes and tomatoes has
found that the use of compost was associated with an improved nitrate to vitamin
C ratio in the final product. Moreover, in structurally deficient soils especially,
compost appears to produce better results than it is possible for artificial fertilisers
alone to achieve. Even so, most investigations have concluded that while high
application rates generally tend to give relatively big increases in crop yield, at
lower levels the effect is less significant, being very largely attributable to the
compost's humus enhancing effect.
Biodiesel
Returning to the central consideration of bioenergy, it would be wrong to dis-
cuss this topic without at least some passing reference to biodiesel, even though
since it revolves around a chemical refining process, it is not strictly produced
by biotechnology. Like the increasing number of mineral oil substitutes currently
available or under development, biodiesel is derived from vegetable oils. Modern
diesel engines demand a clean-burning fuel of uniform quality which can function
under all expected operating conditions. One of the main advantages of biodiesel
is that it can be used directly, in unmodified engines, with the additional bonus
that it can perform as a single, pure fuel, or as part of a mix with its traditional
counterpart, in any ratio desired. While there remains some disagreement as to the
scale of the environmental benefits to be gained, especially in respect of carbon
dioxide discharges, there is good evidence that particulate emissions are signifi-
cantly reduced. In addition, biodiesel is claimed to have better lubricant properties
and to improve the biodegradability of the conventional diesel component of a
blended fuel. Various studies have concluded that biodiesel exhaust is generally
less harmful to both human health and the planet. Specifically, it contains sig-
nificantly lower levels of polycyclic aromatic hydrocarbons (PAHs) and nitrited
polycyclic aromatic hydrocarbons (nPAHs), which is of great importance, since
both groups have been identified as potential carcinogens. In laboratory tests,
PAHs were reduced by between 75 and 85% (excepting benzo(a)anthracene for
which the figure was around 50%) and nPAHs were also dramatically lessened.
Most of the targeted nPAH compounds were present only as traces, while the
highest levels reported, 2-nitrofluorene and 1-nitropyrene, were found to repre-
sent a 90% reduction over typical conventional diesel releases. Objective views
of the performance of a 'new' fuel depend on such information and the National
Biodiesel Board was congratulated by representatives of the House Energy and
Power subcommittee for being the first industry to complete the rigorous health
effects testing of the Clean Air Act.
It is not entirely without irony that in 1894, when Rudolf Diesel invented the
engine which bears his name, he produced a design specifically suitable for a
range of fuels, including coal dust and vegetable oil, as well as the petroleum
product which is automatically associated with the device. In many respects,
the current resurgence of interest in the potential of a fuel source so deeply