Environmental Engineering Reference
In-Depth Information
pioneered the large-scale production of sugar cane-based ethanol with its Programa
Nacional do Álcool, which was launched in 1975 and eventually led to more than
half of Brazilian cars using anhydrous ethanol, whose lower heating value of ethanol
is only 21 MJ/L, compared to 32 MJ/L for gasoline (Smil 2010a).
The U.S. production of corn-based ethanol began in 1980, but rapid expansion
of output began only in the year 2002: by 2005 the shipped volume had nearly
doubled, to 15 GL, and by 2009 it had surpassed 40 GL, with the maximum volume
mandated at 136 GL of ethanol by the year 2022. That goal implies a 17-fold
expansion of ethanol output in 20 years, but even if gasoline demand remained
stable at the 2010 level of about 520 GL, biofuel would supply only about 17%
of the 2022 demand. Low power densities of corn-derived ethanol (averaging
only about 0.25 W/m
2
) limit its eventual contribution. Even if the entire U.S.
corn harvest (averaging 280 Mt/year between 2005 and 2010) were converted to
ethanol, the country would produce some 2.4 EJ of biofuel, or just 13% of its total
gasoline consumption in 2010. Moreover, corn-based ethanol has many negative
consequences.
Studies of energy costs of corn-derived ethanol have shown values ranging from
a signii cant energy loss (Pimentel 2003) to a substantial energy gain after taking
credits for by-products of fermentation used for animal feeding (Kim and Dale
2002). But these accounts ignore the environmental degradation inherent in any
intensii ed and expanded corn cultivation: the perpetuation of a massive crop mono-
culture, an increased demand for irrigation water, the leaching of nitrates and the
ensuing eutrophication of streams, and the extension of the anoxic dead zone in the
coastal waters of the Gulf of Mexico (Smil 2010a). And the post-2002 expansion
has taken place only thanks to the substantial government subsidies needed to make
the fuel competitive with gasoline (Steenblik 2007).
Sugarcane is a much better choice as a feedstock for ethanol fermentation: the
entire process has a power density of nearly 0.5 W/m
2
, and according to Macedo,
Leal, and da Silva (2004), typical cultivation and fermentation practices in the state
of São Paulo have an energy return of 8.3, and the best operations may have rates
just in excess of 10. But de Oliveira, Vaughan, and Rykiel (2005) found those cal-
culations underestimate the energy cost of sugarcane cultivation, and they put the
net energy return at less than 4. But the return is a secondary matter compared to
the availability of suitable land: no other large populous country is as land-rich as
Brazil, and this puts limits on the mass-scale production of cane ethanol (box 9.3).
And even the United States and Brazil would have to deal with higher food prices
if they embarked on the large-scale cultivation of biofuel crops, a policy that the
