Remediated Water Expands Irrigation Options
McGinnis January 12, 2009
Irrigating with recycled water is one potential solution to water
scarcity, according to research conducted by Agricultural Research Service (ARS)
Williams. The scientists are examining the effects of irrigating with
"reclaimed" watersewage water that has been treated to remove
Preliminary results suggest that reclaimed water is both safe and
effective for irrigation of public land in arid regions like Maricopa, Ariz.,
home of the
Arid-Land Agricultural Research Center, where McLain and Williams are
Since September 2006, the two researchers have collected soil and
water samples from a municipal park that is being irrigated with reclaimed
water. They have tested the samples for dangerous Escherichia coli
pathogens. To date, the team has not found a single pathogenic strain of E.
coli. The scientists did note a small increase in soil salinity, but not
enough to harm plant growth.
Williams has also tested samples for carbamazepine, an epilepsy drug
that has been detected in trace amounts in drinking water. His research has
shown that natural organic matter found in soil can prevent carbamazepine from
leaching beyond the root zone.
McLain and Williams have also addressed the accuracy of the tests used
to confirm remediated water's safety, an important step towards gaining the
In one study, the researchers established that the quality of
reclaimed water is harder to assess in winter, when
Environmental Protection Agency-approved
assessment methods return more false positives for E. coli. Over several
months, they drew samples from a wetland fed with reclaimed water, and tested
them for E. coli. The scientists placed the samples on culture media
that change color when E. coli colonies develop on them.
In December and January, they observed a surprising increase in
positive tests. However, genetic assays revealed that about 90 percent of these
were false positives. So why was the accepted culture method delivering such
Chemical analysis revealed that the water's salt content increased in
the winter months, suggesting that the false results may be related to salt
chemistry. The ARS researchers are currently collaborating with scientists at
the University of Arizona to confirm this
hypothesis, which would further support the conclusion that reclaimed water is
safe for irrigation.
about this research in the January 2009 issue of Agricultural Research
ARS is a scientific research agency of the U.S. Department of Agriculture.