Aug. 11, 2005 EL PASO – As water becomes ever more scarce, quenching thirsty crops with wastewater may be OK if done right, researchers here say.
"Managing reclaimed water by pretreating before using it to irrigate, monitoring for viruses, choosing correct crops and periodically leaching the soils should be successful and safe," said Dr. George Di Giovanni, Texas Agricultural Experiment Station environmental microbiologist.
Di Giovanni and his colleagues studied the movement of viruses carried in water through sandy and clay soils on which spinach was planted. They were interested in how long viruses in the water remain in the soil, how they move through the soil and whether they could harm humans or livestock. Their findings have been accepted for an article in Agriculture Ecosystems and Environment journal.
"No bacteriophage (virus) was found on the spinach leaves, regardless of the type of soil they grew in," Di Giovanni said.
The tests were done in a greenhouse in soil collected from the region. Two types of water were tested – a blend of reclaimed water and filtered wastewater laced with bacteriophage, which is a type of virus that infects only bacteria. A bacteriophage is often used in studies as a substitute for human viruses, Di Giovanni said. The water was dripped under the soil surface in plastic columns built for the test.
The research found that bacteriophage could be found on the crusty surfaces of both soil types and remained in the clay soil for about a month after irrigation ended.
"That suggests that human viruses could also linger in the soil," Di Giovanni said. "Reclaimed water must be effectively treated to remove or kill pathogens before use, regardless of irrigation method."
Finding such uses for reclaimed water is vital, said Experiment Station wastewater researcher Dr. Naomi Assadian.
"Wastewater reuse for agriculture and managed landscapes will be necessary to meet growing water demands and conserve current drinking supplies in arid regions such as the upper Rio Grande River area," Assadian said. "But alternative supplies, such as treated municipal wastewater, often contain microbial and chemical elements that may affect public health and/or the environment."
Assadian and Di Giovanni collaborated on the project with Dr. Jaime Iglesias, Texas Cooperative Extension agent in El Paso County; Dr. Juan Enciso, Experiment Station agriculture engineer in Weslaco; and Dr. William Lindemann, New Mexico State University agronomist.
The researchers said a "closed system," as in their method of using underground pipes to apply water to the crop, limited exposure to the soil surface and edible parts of the crop, a positive finding as scientists continue to explore how to reuse water.
While their study showed a feasible use of wastewater, the researchers said similar trials would need to be conducted at each site where such a system is considered. That's because variations in soil might yield different results, they said.
The study was funded by the Texas Department of Agriculture, U.S. Department of Agriculture and the Experiment Station.
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