Rotting tomatoes, brown bananas and overripe cherries -- the waste
from wholesale marts usually ends on the compost heap. But
fermenting this food waste produces methane, also known as biogas,
which can be compressed into high-pressure cylinders and used as
fuel for vehicles, according to new research.
Natural gas is kinder on the wallet, but it is also a fossil fuel.
Researchers at Fraunhofer Institute for Interfacial Engineering
and Biotechnology (IGB), Germany, have now developed an
alternative from fruit and vegetable waste generated by wholesale
In early 2012, researchers will begin operating a pilot plant
adjacent to Stuttgart's wholesale market. It will use various
micro organisms to generate sought-after methane from food waste
in a two-stage digestion process that lasts just a few days.
"The waste contains a lot of water and has a very low
lignocellulose content, so it's highly suitable for rapid
fermentation," said Ing. Ursula Schlie▀mann, head of department at
IGB, according to a university statement.
But it still presents a challenge because its precise composition
varies every day. Sometimes it has a high proportion of citrus
fruits, while at other times there are more cherries, plums and
On days with a higher citrus fruit content, the researchers have
to adjust the pH value through substrate management because these
fruits are very acidic.
"We hold the waste in several storage tanks, where a number of
parameters are automatically calculated -- including the pH
value," said Schlie▀mann.
"An indicator for acidity or alkalinity is known as the pH value.
A pH value of seven means a substance is neutral. The lower value
indicates acidity, and a higher value is a sign of alkalinity,"
"The specially designed management system determines exactly how
many litres of waste from which containers should be mixed
together and fed to the micro organisms," explained Schlie▀mann.
Another advantage of the new plant lies in the fact that
absolutely everything it generates can be utilised - the biogas,
the liquid filtrate and even the sludgy residue that cannot be
broken down any further.