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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