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Mexican scientists scale up solar-powered water treatment tech
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Mexican scientists scale up solar-powered water treatment tech

  • Researchers outfit a model tourist boat with a solar powered aeration pump in a canal covered with invasive water hyacinths.
    Cody Copeland/Courthouse NewsResearchers outfit a model tourist boat with a solar powered aeration pump in a canal covered with invasive water hyacinths.

MEXICO CITY — Rowers in Mexico City’s Lake Xochimilco will soon equip their boats with solar powered “nanobubble” aeration pumps in order to clean the heavily polluted lake as they guide tourists through its network of pre-Hispanic canals. 

Researchers at Mexico’s Center for Research and Advanced Studies (Cinvestav) designed the devices to oxygenate the water via dissolved nanobubbles. The process (in Spanish) eliminates harmful greenhouse gases such as methane, carbon dioxide, and hydrogen sulfide. The treatment also mitigates conditions that lead to harmful algal blooms and invasive aquatic plant species, such as the common water hyacinth. 

“These nanobubbles oxygenate the water, make it clearer, and reduce pathogens and organic contaminants,” said lead investigator Dr. Refugio Rodríguez Vázquez. She and her team of researchers have applied for the necessary patents and permits and expect to have more than 20 of the brightly colored tourist boats outfitted and aerating the water in Xochimilco by mid-October.

A UNESCO World Heritage Site, the Xochimilco Ecological Park still retains vestiges of its Aztec past. The unique agricultural system of chinampas — “floating” gardens that are in reality small manmade islands — dates back to the 13th century, when the Aztecs built the islands to meet the alimentary demands of a thriving society. 

Improved water quality has led the Cinvestav team to observe increased fish populations in areas of Xochimilco’s canals already oxygenated with the device. And more fish mean more food for the predators that feed on them, resulting in more visits to the lake by herons, ducks and other migratory birds.

Rodríguez is not alone in researching how nanobubbles can be used to clean up our increasingly filthy waterways. Dr. Wen Zhang of the New Jersey Institute of Technology is also working on getting permits for a floating water treatment apparatus that, among other methods, uses nanobubbles to aerate and clean up polluted water. He said he could use solar energy to power his multifunctional boat if it used only nanobubble aeration, but the use of other more sophisticated instruments require gasoline to get the job done. 

Revolutionary as it sounds, nanobubble oxygenation has actually been used to treat water for decades. “The downside is that the energy consumption is huge,” Zhang said, rendering the process environmentally unsustainable. Clean water is a necessity, but treatment by oxygenation currently emits more greenhouse gases than it eliminates. But he sees a ray of hope in the technology the Cinvestav team is working on in Mexico.

“With the solar panel as a source of energy, there could be a marginal benefit, because over time it can offset the hidden cost of carbon dioxide,” he said. “It could offset the balance enough to where we could truly obtain the environmental benefits while minimizing the impact of the systems we’re using.”

Rodríguez has seen these benefits firsthand and has made moves to scale her technology up and make even bigger impacts. A home rainwater collection and purification system she designed is already being sold by Rotoplas, a company whose logo can be spotted on water tanks on rooftops all across Mexico. Her advanced oxidation system can purify just under 18,000 gallons of wastewater per day, providing clean water for the kitchens and bathrooms of up to 1,000 apartment residents.

Private companies and organizations have contacted her to design solutions to a wide range of environmental concerns. The Mexico City-based sustainable development organization Siinan wants her to feature her work in a series of educational videos focusing on the United Nation’s Sustainable Development Goals

Fish and shrimp farmers in Yucatán see her technology as a solution to issues of sustainability and cost. Water in fish farms must be oxygenated, but the gas-powered aeration machines that members of the Yucatán Association of Fish Farmers currently use must be run 24 hours a day.

Turning broad paddles on the surface of the pools to aerate the water, the machines create “macrobubbles” that do what bubbles do: float to the top and join the other gases in the air. The solar power-produced nanobubbles remain dissolved in water for up to six months, thus eliminating the problem of having to aerate through the night, as well as the financial and environmental costs of doing so.

“The dissolved oxygen is the best way to increase the biomass in the fish farm pools,” said Dr. Enrique Lozano, a marine biologist at Mexico’s National Autonomous University. 

Rodríguez has plans elsewhere in Mexico as well. She is currently negotiating with fishermen in Lake Pátzcuaro, a popular Day of the Dead tourist destination in Michoacán, to outfit their boats with her solar pump. “It’s a revolution,” she said, and urged her counterparts in the United States and Europe to hop on the bandwagon.

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