From the Toilet to the Tap


Cloacina was the ancient Roman goddess of sewers. Think about that for a minute. To the Romans, the ability to take vile, disgusting wastewater and just get it the heck out of Rome was such a miraculous feat that they created a whole deity to watch over and protect the pipeline.

Now, how much more impressive would Cloacina have been if she could turn the sludge into usable water again?

Today, cities around the world are shifting away from the historical focus of wastewater management (i.e. the miracle of making the wastewater go away somewhere where we can't see it) and adopting a new paradigm of re-use. David Sedlak, professor of civil and environmental engineering at UC Berkeley, studies wastewater and spoke about water recycling at the 2009 Nobel Conference on water conservation issues at Minnesota's Gustavus Adolphus University. He said that people are often turned off by the idea of cycling water from the toilet to the tap and back again, but water recycling is very different from simply filling a glass out of the John.

In fact, you could be drinking recycled water and not even know it.

The idea of reusing wastewater isn't really anything new. Back around the turn of the 20th century, U.S. farmers used to set up shop at the end of sewage pipes, flooding their fields with wastewater fertilizer. Sewage farms grew massive, prize produce. Unfortunately, they were also breeding grounds for parasitic worms and other nasty gastrointestinal diseases.

It wasn't until the 1970s and 80s that people began to take a second look at watewater reuse. Orange County, Cali. began purifying sewer water in 1976, injecting it back into local aquifers to protect them against infiltration by salty seawater. Just about two years ago, the county launched a massive expansion of this program, opening the world's largest wastewater recycling plant. About 10 percent of the water people drink in Orange County comes from highly purified wastewater, Sedlak said.

"The system basically starts with effluent, the output from conventional sewage treatment, and subjects that first to micro-filtration, and then to reverse osmosis, and then to advanced oxidation and disinfectant and then out in the environment," Sedlak said. "Most of the advanced treatment plants built in the US use something called UV peroxide process, which treats water with ultraviolet light in the presence of hydrogen peroxide. The UV splits the hydrogen peroxide and forms hydroxl radicals, strong oxidants that break down organic contaminants and destroy microbes. Usually, the water isn't reused straight, but after these treatments it gets injected into a groundwater aquifer and recaptured later on."

And it's not just happening in the Southwest. Over the past decade, Sedlak said, cities in Texas, Georgia and Florida have picked up on water re-use as well.

The really interesting thing here, though, according to Sedlak, is that water recycling forces us to think about all wastewater in a different way. In reality, no matter where you live, effluent makes up a large part of the free-flowing rivers and lakes. That effluent is treated and cleaned, but nowhere near as extensively as the stuff coming out of Orange County's recycling plant. And, ultimately, it's recycled, too. Effluent-laced water is used by farms, it becomes a place where fish and other animals live, and it's part of the hydrologic cycle–eventually ending up back in the tap.

But most of us don't think of wastewater as something that's reused and we don't pay attention to what goes into our sewers. Sedlak hopes intentional community wastewater recycling will change that. We need to think about our sewers less like they're a fast train out of town, he says, and more like they're a part of our ecosystem.

Recognizing that water goes down the drain ends up in surface waters or drinking water supplies might decrease the unnecessary use of toxic household products, like socks that are coated with silver nanoparticles or shirts and hats that are coated with insecticides," he said. "These products are leached from clothing in the wash and end up in sewage. They'd be filtered out by a water recyling system like Orange County's. But the toxic compounds can pass through standard treatment processes, and they have the potential to harm aquatic organisms in rivers."

Watch David Sedlak's Nobel Conference Lecture

Image courtesy Flickr user glenjdiamond, via CC