Reusing graywater in dry areas may require
treatment for more efficient irrigation in arid, sandy soils, according to a
new study published in Chemosphere by researchers at the BGU's Zuckerberg Institute for Water Research (ZIWR)
Graywater includes
any wastewater generated in households or office buildings except from the
toilet.
Graywater use has been proven
safe for agriculture irrigation. "Most of the scientific research and
legislation efforts have focused on graywater's health risks, while less
attention has been given to its environmental outcomes, including its effect on
soil properties," says Prof. Amit Gross, head of the Department of Environmental Hydrology and Microbiology (EHM) in
the Zuckerberg Institute.
Prof. Gross and his
team found that graywater does not infiltrate through the soil as easily as
fresh water and is slower to reach plant roots. It can also cause water runoff
leading to erosion.
"This condition,
called ‘graywater-induced hydrophobicity,’ is likely temporary and disappears
quickly following rainwater or freshwater irrigation events,” says Prof. Gross.
“However, it is a more significant concern in arid lands with negligible
rainfall as compared with wetter regions.”
According to the
researchers, treating the graywater using biofiltration to degrade the
hydrophobic organic compounds will eliminate the problem.
In the study, the researchers examined how graywater
induces soil hydrophobicity, as well as its degree and persistence. They created three graywater models using raw, treated and highly treated
graywater to irrigate fine-grained sand compared to a freshwater control. The
result was that only the raw graywater irrigated soil showed hydrophobicity,
which could be mitigated with both moderately and highly treated solutions.
“Onsite reuse of
graywater for irrigation is perceived as a low risk and economical way of
reducing freshwater use and, as such, it is gaining in popularity in both
developing and developed countries," says Prof. Gross. “As many government
authorities are establishing new guidelines, the results of this study
reinforce the recommendations to treat graywater before reusing for irrigation,
particularly in arid regions.”
Other researchers who collaborated on the
study were Ph.D. candidate Adi Maimon of the Department of Environmental
Hydrology and Microbiology and Dr. Arye Gilboa of the French Associates Institute for Agriculture and Biotechnology of Drylands.
Together with the Swiss Institute for Dryland Environmental and Energy Research, the institutes comprise BGU’s Jacob Blaustein Institutes for Desert Research (BIDR) on its Sede Boqer Campus.
