Figure 1: Bottom ash before (left) and after coating with ferric oxide
Ashok Gadgil, a scientist in
the Environmental Energy
Technologies Division at
Lawrence Berkeley National
Laboratory (Berkeley Lab), is developing
a cheap and effective way to provide
safe drinking water to 60 million
Bangladeshis who live with the threat
of arsenic poisoning. Gadgil’s idea is to
create arsenic filters from coal ash, the
fine gray powder that piles up, waiting
to be discarded, at the bottom of furnaces
at all coal-fired power stations.
Arsenic poisoning in Bangladesh
has been called one of the largest mass
poisonings in human history, expected
to cause 10 percent of all future adult
deaths in the impoverished nation of
130 million. For reasons not entirely
understood, the shallow tube-wells that
Bangladeshis depend on for water contain
dangerous concentrations of the
toxic substance; if ingested at these
concentrations over long periods of
time, arsenic leads to debilitating
lesions, cancer, and death.
Although still in the investigational
stage, Gadgil’s technique would
involve coating the ash with a compound
that attracts arsenic, filling tea
bag-sized pouches with the powder,
and distributing the filters throughout
the countryside, one per family per
day. Water drawn from any one of the
millions of contaminated wells that dot
Bangladesh could then be poured
through the filter and safely consumed.
After receiving $5,000 in seed
funding from the Berkeley Lab
Technology Transfer Department in
2003, Gadgil set out to develop a filter
that is affordable and effective. His
options quickly narrowed; he needed a
material that has a high surface-to-volume
ratio, is pathogen free, and is
available in large quantities at low cost.
Reflecting on carbon as a commonly
used filtration medium, Gadgil
thought about left-over coal ash, the
large piles that collect at all coal-fired
power stations, waiting to be sent to
landfills. An additional $20,000 in
seed funding from the Blue Planet Run Foundation helped him explore this
option.
Coal ash is composed of particles
that measure between one and 10
microns in diameter, much smaller
than a 100-micron-diameter human
hair. This means that even a small volume
of the powder has a lot of surface
area, maximizing the opportunity for
surface reactions to snare arsenic. The
ash is also heated to 800 degrees
Celsius during the coal burning
process, so it’s sterile and free of
volatile compounds. And it’s plentiful.
Coal-fired power plants provide most
of neighboring India’s electricity, and
the locally mined coal used is uniquely
suited for Gadgil’s purposes: it’s only
60 percent carbon, meaning 40 percent
becomes ash.
After obtaining some ash from
India, he assembled Team Arsenic,
which includes Lara Gundel, Yanbo
Pang, Christie Galitsky, Duo Wang,
and Anna Blumstein. Together, they
developed a way to coat each ash particle
with ferric hydroxide, a chemical
that reacts with arsenic and forces the
element to precipitate onto the particle
(see Figure 1). Initial tests indicate this
specially treated coal ash makes a very
powerful filter. After spiking lab water
with so much arsenic that its concentration
soared to an extremely toxic
2,400 parts per billion (ppb), the team
found that the filter lowered the water’s
arsenic concentration to 10 ppb. The
Bangladeshi standard for safe drinking
water is 50 ppb.
Gadgil estimates that five grams of
filter material could render about three
gallons of Bangladeshi well water—
with an average arsenic concentration of
400 ppb—safe to drink. Put another
way, a filter the size of a tea bag could
provide drinking water for a family of
six for one day. He also estimates the
technique will cost about thirty cents per
person per year. The next-best option is
a filter developed by a Bangladeshi
engineer, backed by the non-profit
organization IDE-International, that
uses pulverized brick instead of ash. It
would cost $9.70 per person per year.
Closer to home, the California
Energy Commission’s Public Interest
Energy Research program recently
awarded Gadgil $250,000 to explore
whether a variation of this technique
can help the state comply with a U.S.
Environmental Protection Agency
rule, effective in 2006, that tightens the
U.S. arsenic drinking water standard
from 50 ppb to 10 ppb. Currently,
600,000 California residents consume
water with concentrations above 10
ppb. Gadgil will determine whether
ash derived from U.S. coal can be
developed into a filtration system and
whether such a system can work at
small municipal water treatment facilities.
Initial results appear promising.
Currently, the cost of arsenic removal
at small municipal water systems
ranges from $58 to $327 per household
per year. Gadgil estimates that his
method would cost less than $1 per
household per year, not including the
one-time cost of coating the ash with
ferric hydroxide. In addition to this
research close to home, Gadgil will
also intensify his efforts to help
Bangladesh—if he secures more funding.
Dan Krotz is a writer in Berkeley
Lab’s Public Information Office.
Contact: DAKrotz@lbl.gov
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