Leftover
fruit and vegetables from markets don’t always have to end up on the compost
heap. Researchers in Stuttgart are developing a new system aims to turn that
waste into biogas for cars.
In affluent
countries like Germany, food doesn't always land on people's plate - quite
often it ends up in the trash instead. A recent study found that Germans throw
away an incredible 11 metric tons (around 12 million short tons) of food each
year.
In
Stuttgart, Germany's de facto automobile capital, researchers are trying to
feed some of this waste from the local fruit and vegetable market directly into
a biogas plant. They're even building a service station for cars to tank up
with the gas directly at the plant itself.
With the
rising prices of petrol, biogas made from food waste could be an attractive -
and more sustainable - alternative.
From the
market into the tank
Stuttgart's
wholesalers market is the third biggest in Germany. Titus Steiger, head of a
busy fruit and vegetable trading company, is one of hundreds of traders and
farmers based at there.
Leafy
vegetables have to be sold quickly, he told DW, within three days. "After
that we have to give them away. With herbs we only have two days," Steiger
said.
The
Stuttgart market produces 2,000 kilograms (2,200 pounds) of green waste, or
biowaste, every year. Currently, these food scraps are collected by the city
and composted.
In many
regions of Germany, biogas from organic waste is increasingly being used to run
heating systems and produce electricity.
The new
project in Stuttgart is being run by the Frauenhofer Institute for Interfacial
Engineering and Biotechnology and is set to show that energy from food waste
can also be used to run cars. The experiment is part of a project called
Etamax, which received 6 million euros ($8 billion) from Germany's Federal
Research Ministry.
 |
| In this gleaming facility, food waste is transformed into fuel |
In the
pilot phase, the project will be collecting leftover fruit and vegetables from
the nearby central market and several cafeterias, and then fermenting it into
methane.
In a
two-stage process, which lasts several days, various microorganisms digest the
waste, which produces biological methane. After being pressurized, it can be
used to fuel vehicles that normally run on compressed natural gas.
"Food
waste has high water content and low lignin and lignocellulose content. That
makes it ideal for this digestive process," Ursula Schliessman, a
Fraunhofer scientist, said.
Lettuce or
lemons: the right mix
Karl
Kübler, who heads up Stuttgart's market, said the kind of food waste can
fluctuate wildly according to season.
If it's
melon season, for example, and "suddenly we have a cold spell, no one buys
the melons and then we have a huge quantity of melons that are thrown out all
at the same time," Kübler said.
The waste
even varies from day to day. Sometimes there will be more lettuce thrown away,
sometimes citrus fruits - which contain a lot of acid.
This means
the scientists have to balance the pH of the material for it to be digested in
the fermenter. To do this, different kinds of biowaste are stored in separate
containers, where the pH and other parameters are measured.
"Then
we have a specially developed system to calculate how many liters of waste have
to be taken from which containers and then put in with the
microorganisms," said Schliessmann.
The correct
balance has to be maintained so that the microorganisms have a consistent
environment in which to carry out their digestion.
Nothing is
wasted
After the
biogas is produced, fluid residue and any bits that cannot be fermented are put
to use in other projects.
The water
from the digestion process, which contains nitrogen and phosphorous, is used as
a nutrient for algae, which can produce oil for use in diesel engines.
The
remaining residue is turned into methane using another process - so that the
organic waste is completely re-used.
The next
step is to get the gas into cars.
Avoiding
demand for waste
Since the
system runs on food waste, it does not compete in any way with the actual
production of food, as is the case when the biofuel ethanol is made from maize
or other crops.
Ethanol has
been the subject of a lot of criticism, especially because it uses up valuable
land which could be used for growing food crops. Many also question whether it
takes more energy to grow the crops than is produced.
But organic
leftovers are just that. Right now in the best scenario they are composted, but
for biogas proponents they represent considerable source of untapped energy.
Environment
groups like Friends of the Earth Germany (BUND), say it makes sense to use food
waste for biogas.
 |
| Culture of waste: Worldwide, half of all food prodcued ends up in the trash |
However,
Berthold Friess, who heads the organization in the German state of
Baden-Württemberg where the new fermenter is located, warns that technology of
this kind should not be allowed to create an artificially high demand for food
waste.
Studies
have indicated that around half the world's food already ends up being thrown
away. "The aim should really be to make sure as little food as possible is
thrown away at markets," Friess said.
He also
calls for the development of lighter, more economical cars and the improvement
of public transport, to reduce the use of limited natural resources like oil
and gas and to put less pressure on the climate.
Biogas in
future energy mix
Schliessmann
hopes that smaller biogas plants like this one could someday be seen in every
city and play an important role in the energy mix of the future.
"The
advantage of this kind of technology is that we can put it in the middle of a
city where people are living because there is no smell and it is a closed
system," he said.
When the
plant officially starts up at the end of April, the German car company Daimler
will fill up test cars with different mixes of methane gas to find out what
works best.
Author:
Irene Quaile and Kate Hairsine
Editor: Holly Fox
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