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The participants in this experiment are very small; in fact,
they are so tiny that they are invisible to the human eye. Jens
Hauslage taps on the glass tubes of C.R.O.P. There is nothing
to see except water trickling over the wet rocks from the Eifel
Mountains. “But inside, a war is being waged. A battle for
the best nutrients,” he says. Everything appears calm in the
lava gravel, but a look under the microscope reveals quite a
different story. Over 70 species of bacteria, fungi and other
single-celled organisms are fighting with one another on the
surface of and inside the numerous small cavities in the porous
rocks – waging a hard struggle over the waste material that
the water circuit in the C.R.O.P. system continuously flushes
over them.
“We are using this competition between organisms to
reduce the time needed for recycling.” The nutrients that are
desirable for the bacterial kingdom in the rocks are often
harmful to plants and people. Ammonia, for example, which is
too strong for soil, plants and the human nose, is one of the
more sought-after nutrients for many bacteria; what those
bacteria excrete after consuming it is an important nutrient for
plants, which would be lost without the closed circuit of the
C.R.O.P. system. This all happens without needing a lengthy
detour via a compost heap – the standard way of recycling
organic waste into fertiliser. “Could you imagine a compost
heap on the International Space Station?”
A few plants, lava rock from the Eifel Mountains, two plastic tubes, a glass container, water, fish – and organic waste.
That is all you need to create a self-contained life support system. C.R.O.P., or Combined Regenerative Organic food
Production, is designed to break down organic waste and use the resulting metabolised products to produce food.
This technique is already working, on a small scale, in the foyer of the DLR Institute of Aerospace Medicine in
Cologne, where researcher Jens Hauslage and his team regularly harvest tomatoes. The C.R.O.P. biofilter will soon
be tested in a greenhouse near Bonn to see whether it can work on a larger scale, as well to determine its suitability
for applications in harsh environments on Earth or in hostile conditions during long-duration space missions.
DLR researchers develop the C.R.O.P. biofilter
By Manuela Braun
Rock-dwellers transform waste
Once it has been primed with a spoonful of soil, life ex-
plodes inside the rocky biofilter. Here, the bacteria demonstrate
how adaptable they are in their struggle for survival – regardless
of the type of waste material in the biofilter, there are always
organisms that can use that exact material as food and break
it down. This occurs in the two one-metre-high tubes of the
C.R.O.P. test unit. “Through the microscope, the bacteria world
in the rocks looks like a real chamber of horrors,” the biologist
says. “Mites, worms – they all feel comfortable in the various
micro-climates in the gravel.” The numerous pores in the rocks
have a total surface area roughly the size of two football fields.
Plenty of habitats for a vast range of single-celled organisms
with a variety of diets – regardless of whether they prefer living
with oxygen on the surface of the rocks or without it, inside the
porous Eifel rocks. And in the event that the filter should ever
dry out, it would still not be the end of the dynamic biofilter –
the bacteria would simply go into hibernation and spring back
to life once the water returns.
In the beginning there was a murky soup
Jens Hauslage carefully plucks the old leaves from the
tomato plants, opens the tube cover and dumps the leaves on
the wet rocks. “It’s a kind of plant cannibalism – we feed tomato
leaves to the tomato plants,” he says, laughing. “The nutrients in
a tomato leaf are exactly the ones that a tomato needs – so we
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