This artificial wetland is repurposing wastewater to revive lost ecosystems

In drought South of Mexico Island, pale deserts dominate the landscape, and the Las Arena wetland feels like the Rays Rage Building. But it is true, an oasis of endemic and migratory birds that travel through the Colorado River Delta. Here, in the southern part of the US-Mexico border, the water from Mexico City was used to gain a second life. Half of them headed towards the nearby Hardy River, trying to restore an ecosystem that was considered unrecoverable.

Historically, the waterways here are filled with sewage, especially the new river that extends northward from the Colorado River, crosses the United States from Mexico into the United States, ending in the Salton Sea in California. Over the years, the water course received untreated sewage from Mexico Island (Mexicali), making it one of the worst-sized rivers in the United States. In the 1990s, U.S. and Mexican authorities no longer ignored the severity of the problem and began to work on infrastructure to mitigate pollution. Therefore, in 2007, the Las Arenitas treatment plant was operating south of Mexicoli.

Mexicali, sitting on the border, generates more than 80 million cubic meters of sewage every year. Of these, 90% were collected, and 46% were used in the Las Arena.

In a sewage treatment plant, solids and deposits are first removed from the wastewater. Next, using a lagoon on the surface, air is injected into water to stimulate the growth of aerobic bacteria, which decompose organic matter in the presence of oxygen. The water is then transferred to the facultative lagoon, where aerobic and anaerobic bacteria complement each other, the latter degrading organic matter, the former cannot. Finally, the water reaches the mature lagoon, where the rest of the solid settles.

When booted, this new system works. “Initially, the plant was underperforming,” said Edith Santiago, deputy director of the Colorado River Delta program at Sonoran Institute, a conservation nonprofit organization. To address this, some organizations have suggested to water management agencies that they should use the land surrounding the lakes that were placed decades ago to create a man-made wetland to make the water cleaner.

Such plans, as well as helping solve the city’s sewage problem, will also help restore the local landscape part to its former state. Before the Colorado River was overdeveloped, its delta crossed Baja and Sonora, California until it encountered the waters of the Bay of California, resulting in 400,000 hectares of wetlands. Although the river’s route has become a ghost, about 15% of wetlands survive, with priceless flora and fauna biodiversity. To mimic this power, the Las Arena artificial wetlands paused the destruction of local landscapes.