Bioenergy Makes Heavy Demands On Scarce Water Supplies

4.6.2009 (Science Daily)

The ‘water footprint’ of bioenergy, i.e. the amount of water required to cultivate
crops for biomass, is much greater than for other forms of energy. The generation
of bioelectricity is significantly more water-efficient in the end, however –
by a factor of two – than the production of biofuel.

By establishing the water footprint for thirteen crops, researchers at the University
of Twente were able to make an informed choice of a specific crop and production
region. They published their results in the Proceedings of the National Academy of Sciences (PNAS) of 2 June.

In their article, the researchers show the water footprint of thirteen crops:
the volume of water – rainwater and irrigation – required per gigajoule of energy
production.   In respect of various applications of biomass, the researchers present
the impact that cultivation of the crops has on water consumption.

By linking the water consumption to the location and climate data, it is possible
to select the optimum production region for each crop.   This makes it easier to
prevent biomass cultivation from jeopardizing food production in regions where
water is already in short supply, according to the researchers.

This lends an extra dimension to the bioenergy debate: until now, the discussion
has mainly focused on the question of whether it should be allowed to use food
crops for fuel.

But underlying this is the question of how we should deploy our limited supplies
of fresh water.   Water that is used for bioenergy – whether it be for a food crop
such as maize or a non-food crop such as jatropha – cannot be used for food production,
for drinking water or for maintaining natural eco-systems.   The water footprint,
developed by Prof. Arjen Hoekstra, one of the authors of the PNAS article, is
a powerful tool for surveying this.

1 litre of diesel, 14,000 litres of water

An example is biodiesel, which is made from rapeseed, soya or jatropha. On average,
it takes 14,000 litres of water to produce one litre of biodiesel from rapeseed
or soya. However, the water footprint for rapeseed in Western Europe is significantly
smaller than in Asia.   For soya, India has a large water footprint, while the
figures for countries such as Italy and Paraguay are more favourable.  Jatropha,
which is increasingly used for biomass production, has an even less favourable
water footprint of 20,000 litres of water on average for one litre of biodiesel.

Whole plant

The research shows that generation of bioelectricity has a smaller water footprint
than the production of biofuels. A significant cause is that in the case of the
former, the whole plant is used and in the case of the latter, only the sugar,
starch or oil from the seeds is used. As regards the new generation of biofuels,
ethanol can also be made from the stalk and leaves; this will have a favourable
effect on the water consumption.

Sugar beet a favourite

In the generation of bioelectricity, too, there are big differences between the
crops: sugar beet has by far the smallest water footprint – jatropha is 10 times
less water-efficient. For the production of bioethanol, sugar beet is again by
far the favourite: one litre of bioethanol made from sugar beet takes 1,400 litres
of water, as against 2,500 litres for sugarcane, which is widely cultivated   in

Adapted from materials provided by University of Twente


see also


Is Biofuel Policy Harming European Biodiversity?

25.4.2009       Science Daily