CHARCOAL HAS BEEN A part of water treatment for at least 4000 years, but can it remove modern synthetic pesticides from drinking water? Farmers in northern in Thailand, concerned about agricultural
runoff, put the question to Josh Kearns, an
environmental engineering doctoral candidate
at the University of Colorado in Boulder and
the science director at Aqueous Solutions,
a non-profit water, sanitation and hygiene
“I didn't know the answer, and searching
the scientific literature revealed that, in fact,
no one knows the answer,” Kearns told E4C.
The answer, Kearns discovered through
his own tests, is that it can. But a lot depends on how you make the char.
GASIFIERS AND CHAR
The Thai communities make their charcoal in
traditional kilns that, when burning well, heat
the material to 350 to 500 C. In contrast,
simple gasifiers burn at 900 C. At that tem-
perature, the wood and agricultural waste
that they burn converts more completely into
char. The biomass releases gases as it heats,
opening up pockets in the material. The
result is highly porous char that is suitable
for water filtration.
One problem with introducing new technology is that people might not use it if it
doesn't feel comfortable to them.
"Don't fight culture; if people cook by stirring their stews, they're not going to use a
solar oven, no matter what you do to market
it," says Ethan Zuckerman, founder of Global
Voices. Zuckerman's advice and the maxim
An ancient filtration material removes pesticides
“consider context” is the second of E4C's
Design Principles, found in our Learning Lab.
Gasifiers seem like a match. They operate in
How to treat water with four
containers in a series. Image
courtesy of Josh Kearns
from drinking water
UPFLOW GRAVEL ROUGHING FIBER
CHARCOAL (BIO-SAND) FILTER
TREATED WATER STORAGE
a way that is similar enough to kilns, and after
a demonstration, they proved to be superior.
WATER TREATMENT WITH
Working with the farmers, Kearnes built gasifiers and a char-based water treatment system.
It's hard to overstate the importance of using
locally available materials, and the water treatment systems Kearns and the farmers are developing are entirely local. Kearns' system links four
containers in a series, the first three filled with
filtering materials such as sand, char and stone,
and the final container holds the pure water. •
“One problem with
technology is that
people might not use
it if it doesn't feel
comfortable to them.”