Wastewater: Resource or Plague?

(version en Español)

It’s one thing to watch a scientific presentation about untreated wastewater from Mexico City, which is used to irrigate crops in a 400-square-mile valley north of the city.

It’s another to stand beside a canal in that valley and inhale the stench of thousands of gallons of untreated wastewater as they gush past, on their way to farms throughout the region.

Think: raw sewage backing up into your basement, or clogging your toilet.

On average, Mexico City emits 50 cubic meters of wastewater per second, and much of it goes to Mezquital Valley. And yet the thick gray water that courses through the valley’s intricate irrigation system, turning fields a bright spring green, helps produce tons of corn and alfalfa yearly—and a livelihood for thousands of Mexican farmers. And as clean water becomes an increasingly scarce resource, the value of wastewater cannot be ignored.

It’s one reason many in this area are opposed to the launch of a major wastewater treatment plant in the valley in the near future, which will likely remove a large portion of the crop nutrients that are found in wastewater. There’s even an opposition group that calls itself the Frente de la Defensa del Agua Residual Pura, or “Front in Defense of Pure Wastewater.”

Common sense suggests that the presence of so much untreated wastewater in and around dozens of Mézquital Valley communities would be harmful to both human health and the environment.

But common sense isn’t science.

And science is what drives public health researchers like SPH’s Joseph Eisenberg and Rafael Meza, who are collaborating on a year-long study of the health and environmental impacts of Mezquital Valley’s new wastewater treatment plant, and the use of wastewater for irrigation.

For Meza, an assistant professor of epidemiology, the project is personal. He grew up in Mexico City, an hour south of Mezquital by car. Although he works on studies in places as far-flung as Guatemala and Thailand, he has always wanted his work to benefit his own country as well. Last year, Meza conducted mathematical modeling studies to gauge the probable impact on diabetes of a nationwide tax on sugary beverages in Mexico. Initial data indicate that the tax is indeed helping to lower beverage consumption, and that can in turn help lower both obesity and diabetes rates.

Findings from the Mezquital study can have an impact on Mexican farming communities throughout Mezquital Valley—and play a major role in both current and future wastewater reuse policies and guidelines.

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