The Economist
Apr 20th 2011
| From the print edition | Science and Technology
Bioremediation
Bottom feeders
A novel way of dealing with an unpleasant problem
For your delight and delectation
DESPITE their name, disposable nappies are notoriously difficult to
dispose of. Studies of landfills suggest they may take centuries to
rot away. But Alethia Vázquez-Morillas of the Autonomous
Metropolitan University in Mexico
City thinks she has found a
method of speeding the process up.
As she and her colleagues describe in Waste Management,
cultivating the right type of
mushroom on soiled nappies can break
down 90% of the material they are made of within two months.
Within four, they are degraded completely. What is more, she
says, despite their unsavoury diet the fungi in question, Pleurotus
ostreatus (better known as oyster mushrooms), are safe to eat.
To prove the point she has, indeed, eaten them.
The culinary use of oyster mushrooms was one reason why she
picked them for the experiment. The species is frequently used in
stir-fries and is often added to soups. The other reason was that
Pleurotus ostreatus is widely used in what is known as
mycoremediation—the deployment of fungi to clean up waste. It is,
for example, already grown on agricultural materials such as heat
and barley
straw, and industrial waste like
coffee grounds and the
leftovers from making tequila. Dr Vázquez-Morillas and her
colleagues were trying to extend the oyster mushroom’s own
culinary range.
The reason nappies are difficult to break down has nothing to do
with their use. Even a clean nappy would hang around for a long
time in a dump. The main ingredient of a nappy is cellulose, an
annoyingly persistent material. Pleurotus, however, grows on dead
or dying
trees in the wild and is thus well provided with enzymes
that break cellulose down. And, since Mexicans alone throw away 5
billion nappies every year, there is plenty of material from this
source for them to get their mycelia into.
The idea that the result might be sold and eaten may be
controversial but it is not absurd. The nappies the researchers
used were contaminated only with
urine, not faeces. A healthy
person’s urine is sterile and Dr Vázquez-Morillas also treated the
nappies with steam, to make sure. Such treatment would kill the
nasty bugs in faeces, too, though, so mushrooms grown on treated
nappies
should, in theory, be safe to eat.
In practice, overcoming the yuck factor might be an insuperable
barrier to marketing nappy-grown fungi, and the cost of the steam
treatment could make the exercise futile. Mycoremediation of this
sort does not, however, depend for its success on selling the
results. Merely getting rid of what would otherwise hang around
indefinitely is worthwhile. And of the fungi themselves, Dr
Vázquez-Morillas observes, “they are cleaner than most of the
vegetables you can find in the market, at least in Mexico.”
2
it's my little Xmas present to myself. I have all kinds of stuff that I can't wait to train my oysters to eat...
