For utilities oriented around sustainability and efficiency, using natural systems in infrastructure has growing appeal.
Dos Rios Water Recycling Center run by the San Antonio Water System (SAWS) is one example of this trend. Twenty years ago, SAWs committed to building the largest recycled water delivery system in the nation. Dos Rios, a conventional activated sludge facility that has won awards for efficiency, is part of that system.
“The Dos Rios Water Recycling Center was the first foray into SAWS' water source diversification efforts and today, people travel from all over the world to visit it,” the San Antonio Current reported.
According to Greg Eckhardt, senior analyst at SAWS, everything that happens at the plant is natural. He described the foundation of the plant's 40-food aeration basins in an interview with Texas Public Radio.
"At the bottom there are about 5,000 of these diffusers. They look just like a stoned-in aquarium. They make fine bubbles. And the reason we’re pumping all this air into these basins is to keep organisms alive so they can consume the organic material that’s in the water. That’s basically how the treatment process works. It’s biologic. We’re using bacteria and organisms to consume the organic material that you flushed," Eckhardt said, per the report.
The plant is proud of its rigorous composting practices.
“Instead of using pesticides, SAWS employees built more than 500 purple martin houses that are hot real estate for the birds who feed on the massive amount of flies that congregate during summer. Those flies are there because SAWS is selling the leftover sludge and sediment from recycled wastewater to a contractor that turns it into compost,” the Current reported.
Lilliana Gonzalez, a communications specialist with SAWS, described the utility's focus on composting.
"It’s a very earthy smell. I always describe it as right before it rains, or a wet earth smell. That just means that it’s gone through the right biological process," Gonzalez said, per the report.
Sometimes using natural processes, and nixing pesticides, comes with a drawback: insects. But the utility has found natural ways to control pests.
"This is where [plant manager Tad Eaton] helped us design an integrated pest management system so we wouldn’t have to use — really we wouldn’t have to depend on chemical fumigation, and so that would instead use sort of more natural processes to keep the pest population under control," Gonzalez said.
"We have parasitic wasps and those help control the flies. So the birds are eating the adults, and the parasitic wasps are injecting their larvae into fly pupae, so that when they are born basically what comes out is the wasp, but not the fly," Gonzalez continued.
"We literally get visitors here from all over the world," Eckhardt said, per the San Antonio Current. "South Korea, Japan, Mongolia."