Environmental Engineering Reference
In-Depth Information
2004; Schmidt, 2004). Although NO
x
emissions from vehicles using bio-
diesel are found to be generally higher than from those using conventional
diesel, studies have shown that this can be reduced by a slight modii cation
of the diesel engine (Schmidt, 2004; Booth et al., 2005). A major drawback
in using biodiesel compared with conventional diesel seems to be the higher
emission of N
2
O, both from production processes (that is, from feed-
stock production) and vehicle emissions, which has stratospheric ozone-
depleting potential (Franke and Reinhardt, 1998; Poitrat, 1999). Although
Poitrat (1999) contests this drawback, stating that the overall greenhouse
ef ect of biodiesel is four or i ve times less than that of conventional diesel,
Franke and Reinhardt (1998, p. 1037) are more cautious and state that this
drawback actually favours conventional diesel over RME given the 'high
to very high ecological importance' of this ozone depletion potential.
Many dif erent studies have come up with dif erent i gures as to the
level of emissions and emission reductions for various gases and particu-
late matters when using biodiesel. While Ryan et al. (2006) state that for
biodiesel the CO
2
equivalent emissions savings could range from 36 per
cent to 83 per cent compared with conventional diesel, Mortimer et al.
(2003) conclude that savings in total CO
2
emissions of 72 per cent to 86 per
cent are possible by using biodiesel derived by conventional and modii ed
production respectively compared with ultra low sulphur diesel. Similarly,
net energy balance (measured as NER - Net Energy Ratio) for biodiesel
use has been reported to be from between 1.59 and 2.08 (Turley et al.,
2002) through to between 1.9 and 2.7 (Poitrat, 1999).
Feedstocks, comprising mainly oilseed rape and other competitor oils
like soybean, sunl ower and palm oil, are the main input in the production
of biodiesel fuel. The production of these feedstocks could have two major
environmental impacts, namely an impact on land use and an impact on
biodiversity. The general consensus in terms of the potential impacts of
biodiesel feedstock production on the environment is that there would be
little or no negative impact if the feedstock were grown on existing agri-
cultural land (Anderson et al., 2004). However, Puppan (2002) warns of
dangers to the environment from large monoculture oilseed farms, as well
as land and water pollution from excess use of fertilizers and pesticides
in commercial oilseed plantations. In terms of the impact of biodiesel
feedstock production on biodiversity, Anderson et al. (2004) argue that
production of oilseed rape could have a positive impact on biodiversity,
especially for farmland bird species that feed on seeds and invertebrate
(that is insect) species within the crop. However, they warn against using
large areas of set-aside land for oilseed production, as that could have
negative impacts on the birds inhabiting such land (Anderson et al., 2004;
Anderson and Ferguson, 2006).
