The line between the two properties looks as if someone drew it with a fat, green crayon. On one side, the eroding Tijuana hillside is brown, dry and denuded. On the other side, trees and plants weave the hillside into a thriving ecosystem, a shelter for birds and pollinators. The difference between the two sites? Sewage.
This green oasis is called Ecoparque — or “Eco Park” in English. It’s a neighborhood-sized ecological wastewater treatment system plus an education center. EcoParque is a project of COLEF, El Colegio de la Frontera Norte (College of the Northern Border).
For over 30 years, wastewater from a nearby sewer line has flowed into Ecoparque, where it’s cleaned and then used for irrigation. The recycled water has helped to reforest the site, stabilize the hillside and grow over seven acres of greenery. EcoParque is Tijuana’s fourth-largest green space.
Gabriela Muñoz Meléndez attributes the long-term success of the project to the work of “lots and lots people!” from COLEF and the larger community. Meléndez, an engineer from COLEF, oversees Ecoparque’s wastewater system and designed its most recent update.
Most water flowing through Tijuana is managed in a nonsensical way, explains Meléndez. Water originates from the Colorado River, travels through aqueducts and is pumped up over a thousand meters — a process that is both expensive and energy-intensive. Then, the water is used once, dumped into overloaded wastewater treatment systems and ends up polluting beaches on both sides of the US-Mexican border, just south of San Diego, California. “We can do better,” she says.
Ecoparque is a living example of what doing better can look like. Shady paths lined with jacarandas and mesquite trees wind up the hill, past agave cactus and purple penstemon flowers. Stone-lined terraces create productive plots of land and hold the soil in place. Benches, shaded by grape arbors, overlook the city. Kids visit on field trips to learn about water reuse and composting, renewable energy and recycling, native plants and urban agriculture. This is all possible thanks to sewage.
This wastewater treatment at EcoParque is decentralized, meaning it’s small and designed to manage a fraction of the city’s total wastewater. It also uses very little energy, since the wastewater flows by gravity and is used on the same site. In contrast, water and wastewater in the rest of Tijuana are pumped multiple times.
Wastewater in the Ecoparque system is treated in three steps. First, it flows through screens to remove trash and large debris. Next, the dirty water enters a biofilter — essentially a big box filled with plastic bits that are colonized by bacteria, which eat contaminates in the wastewater and aerate it. Then, the effluent flows into a tank called a clarifier, where leftover solid bits sink to the bottom of the tank and are removed. After that, the water travels through a wetland, passing over stones and gravel, where microbes remove nutrients and bacteria. The wetland is planted with canna lilies: not only pretty, with red, yellow and orange blooms, but they also capture coliform bacteria. The last stage is a large, open-water pond, added in 2020, to improve the water quality coming out of the system.
The climate in Tijuana is hot and dry, which makes recycling water an attractive option. One treatment plant, called San Antonio de los Buenos, was designed to recycle water. But for the past 10 years it’s been inoperable, discharging untreated wastewater into the ocean. Too much sediment in the water damaged the plant, and repair costs were too high, explains Meléndez. This plant had to be rebuilt and is set to come online this year.
This highlights another lesson from Ecoparque: the benefits of integrated planning. Restoring green space, like at Ecoparque, reduces erosion, which, in turn, reduces sediment runoff that mucks-up the centralized wastewater treatment plants. Plus, being around green spaces is good for people.
Even without the sediment, managing all the wastewater in Tijuana is an enormous challenge. The agencies responsible for providing drinking water and treating sewage are unable to keep up with the rapid and unplanned urbanization in the city. And another part of the problem, points out Meléndez, is that American companies come to Tijuana expecting water and someone else to treat their prolific wastewater. Similarly, Americans move to Tijuana — to save money or retire — and also expect clean water, but they don’t pay Mexican taxes. “To solve the water pollution problem it will take resources and cooperation,” she says. Mexico has ideas and solutions, but can’t do it alone.
Some of the needed resources and solutions are coming to the region. In December, the US government unlocked 250 million dollars to fix Tijuana’s ailing South Bay International Wastewater Treatment Plant. This is one of three major projects designed to prevent most of the summer beach closures currently happening in the region due to sewage pollution.
.jpeg)
With over half the world’s waterways polluted by wastewater, sewage solutions of all sizes are needed. The centralized treatment plants can clean millions of gallons of water a day, but the high cost to build and operate limits their reach. Neighborhood-sized systems, however, with lower costs and lower-energy consuming technology, are more flexible.
A photographer once brought a drone to Ecoparque. When Meléndez saw the images — of lagoons and trees standing in a sea of houses and traffic — it was moving, she said, “to see this green space very bravely standing there… an example of how cities could be different.”
Laura Allen is a writer and educator based in Oregon. She co-founded Greywater Action, where she teaches people how to transform their homes to reuse water. She authored the books, The Water Wise Home: How to Conserve, Capture and Reuse Water in Your Home and Landscape, and Greywater, Green Landscape. Her article, For a better brick, just add poop, won the Gold Award in Children’s Science News from the AAAS Kavli Science Journalism Awards (2023). Her favorite pastimes include gardening, hiking, reading and visiting eco-toilets.
