A typical drinking water treatment plant sends
water through a series of steps. First, coagulants are added to the water. These chemicals
clump together sediments, which
can cloud water or make it taste
funny, so they are bigger and easier to remove. A gentle shaking
or spinning of the water, called
flocculation, helps those clumps
form ( 1). Next, the water flows into
big tanks to sit for a while so the
sediments can fall to the bottom
( 2). The cleaner water then moves through membranes that filter out smaller contaminants ( 3).
Disinfection, via chemicals or ultraviolet light,
kills harmful bacteria and viruses ( 4). Then the
water is ready for distribution ( 5).
There’s a lot of room for variation within that
basic water treatment process. Chemicals added
at different stages can trigger reactions that break
down chunky, toxic organic molecules into less
harmful bits. Ion-exchange systems that separate
contaminants by their electric charge can remove
ions like magnesium or calcium that make water
“hard,” as well as heavy metals, such as lead and
arsenic, and nitrates from fertilizer runoff. Cities
mix and match these strategies, adjusting chemicals and prioritizing treatment components,
based on the precise chemical qualities of the local
Some water utilities are streamlining the
treatment process by installing technologies like
reverse osmosis, which removes nearly everything
from the water by forcing the water molecules
through a selectively permeable membrane with
extremely tiny holes. Reverse osmosis can replace
a number of steps in the water treatment process
or reduce the number of chemicals added to water.
But it’s expensive to install and operate, keeping
it out of reach for many cities.
Well owners are on their own
Fourteen percent of U.S. residents get water
from wells and other private sources that aren’t
regulated by the Safe Drinking Water Act. These
people face the same contamination challenges
as municipal water systems, but without the regulatory oversight, community support or funding.
“When it comes to lead in private wells … you’re
Ferrate to cover many bases
on your own. Nobody is going to help you,” says
Marc Edwards, the Virginia Tech engineer who
These three new water-cleaning approaches
wouldn’t require costly infrastructure overhauls.
Reckhow’s team at UMass Amherst is testing
ferrate, an ion of iron, as a replacement for several
water treatment steps. First, ferrate kills bacteria
in the water. Next, it breaks down carbon-based
chemical contaminants into smaller, less harmful
molecules. Finally, it makes ions like manganese
less soluble in water so they are easier to filter
out, Reckhow and colleagues reported in 2016
in Journal–American Water Association. With
its multifaceted effects, ferrate could potentially
streamline the drinking water treatment process
or reduce the use of chemicals, such as chlorine,
that can yield dangerous by-products, says Joseph
Goodwill, an environmental engineer at the
University of Rhode Island in Kingston.
Ferrate could be a useful disinfectant for
smaller drinking water systems that don’t have the
infrastructure, expertise or money to implement
something like ozone treatment, an approach
that uses ozone gas to break down contaminants,
Reckhow says. Early next year, in the maiden
voyage of his mobile water treatment lab,
Reckhow plans to test the ferrate approach in the
small Massachusetts town of Gloucester.
Filtering membranes tend to get clogged with
small particles. “That’s been the Achilles’ heel
helped uncover the Flint water crisis. Edwards
and Virginia Tech colleague Kelsey Pieper collected water-quality data from over 2,000 wells
across Virginia in 2012 and 2013. Some were
fine, but others had lead levels of more than
100 parts per billion. When levels are higher
than its 15 ppb threshold, the EPA
mandates that cities take steps to
control corrosion and notify the
public about the contamination.
The researchers reported those
findings in 2015 in the Journal of
Water and Health.
To remove lead and other contaminants, well users often rely
on point-of-use treatments. A filter on the tap
removes most, but not all, contaminants. Some
people spring for costly reverse osmosis systems.
How is your water treated?
New tech solutions
“When it comes
to lead in private
wells … you’re on
your own. Nobody
is going to help you.”