Recharging aquifers with treated wastewater is the only hope to meet the water needs of a growing urban population
RECYCLED wastewater is no longer the
anathema it used to be. Several countries have begun using recycled waste-water for crop irrigation and landscape
gardening. Now, researchers are studying the possibility of using treated
sewage water for both drinking and
ceplenishing fast-depleting aquifers - a
water-bearing layer of permeable rock
- to satisfy the needs of ever-expanding
towns and cities (EtIvironmental Science
& Technology, Vol 29, No 4).
The primary concern of scientists is
to know whether treated wastewater is
safe enough to drink. Some researchers
believe that the disinfection process is
unable to remove all viruses from the
wastewater, while others disagree.
There are 2 ways to replenish the
aquifers with treated wastewater: the
first process, known as the soil infiltration system, involves spreading the
chemically treated sewer water on the
ground surface and then allowing it to
percolate down. Says David K Powelson
of the University of Arizona in Tucson,
"The soil can strip the remaining viruses
from the treated wastewater as the water
infiltrates an aquifer but virus removal
is dependant on virus type and environmental conditions." The second process
involves direct injection of the treated
wastewater into the aquifer.
Earle Hartling, water recycling coordinator for the Los Angeles County
Sanitation District, says the soil infiltration system reduces total organic carbon by as much as 90 per cent and 50 per
cent of all nitrogen in the water. "Soil
infiltration can also remove parasites
that tend to be resistant to the chemical
disinfection process", he adds.
Another important issue is how
benign is the chemical treatment of
wastewater to disinfect it, Chlorine
treatment is the most common way. But
chlorine disinfection byproducts are
believed to be harmful to humans. Studies on animals have shown that several
of these compounds are carcinogenic.
But with depleting aquifers, recharge may be the only economically
feasible option left. Says Henry Vaux, Jr.,
professor - IF resource economics at the
University of California-Riverside,
"Costs of artificiad recharge are variable,
but reclaimed water can be less expensive than imported water."
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