Science - April 23, 2012

More biodiesel from elephant grass

Second generation biofuels are much more sustainable than crops such as rapeseed and sugar beet cultivated for the production of biodiesel and ethanol in Europe. So says Sander de Vries, who compared energy and environmental scores of cultivation systems in the German federal state of Brandenburg. Elephant grass, in particular, is a good alternative for food crops.

Elephant grass can grow up to 3 metres tall.
A hectare of elephant grass (Miscanthus) can produce 90 gigajoules of biodiesel or 71 gigajoules of ethanol, while a hectare of sugar beet and a hectare of rapeseed produce 51 and 32 gigajoules respectively. Unlike food crops, processing grass requires hardly any fossil energy and has a more favourable CO 2 score. The cultivation of Robinia for producing biodieselis is also more sustainable than cultivating rapeseed. Earlier research had already shown that producing biofuels from European food crops is relatively bad for the environment. 
The situation is different for second generation energy crops which make fuels out of cellulose, says De Vries. These crops produce much more energy than that used up during cultivation, transport and processing. Furthermore, they require less (chemical-)fertilisers than food crops, produce less greenhouse gases and grow well on marginal soils, thus interfering less with food production. Therefore, cultivating them - elephant grass, in particular - shows promise. Miscanthus does have one disadvantage, though: early sowing can result in plants freezing to death in harsh winters, as was the case in Brandenburg. 
Currently, the production of biofuels out of elephant grass is not cost-effective, says De Vries. This is largely because the conversion of fibres into biofuel is not yet done optimally. For the time being, higher returns are still to be had from burning the woody crop in a power station, resulting in more energy produced per hectare and better scores with regard to the greenhouse effect.
De Vries had already proven in earlier research that tropical crops such as oil palm and sugarcane score much better environmentally and energy-wise than food crops in temperate regions.
Sander de Vries obtained his PhD degree on 20 April from Martin van Ittersum,  Professor holding a personal chair, and Professor Ken Giller, both attached to the Plant Production Systems Group.