How Dow Chemical Is Turning Sewage Into a Refreshing Drink
Inside the technology that cuts the crap from water.
Amanda Little
“This is step one of the filtration process,” says Snehal Desai, struggling to suppress his gag reflex. “We call it the big-tooth comb.” There’s a torrent of raw sewage streaming through a channel below us at an Orange County Sanitation District facility that treats waste from the toilets, showers, and sinks of 1.5 million Californians. An enormous rake descends into the depths of the sludge and brings up a load of detritus—cardboard, wet wipes, tampons, marbles, toys, tennis balls, sneakers—that can’t fit through the screen covering the plant’s intake.
The flow that passes through has now begun its journey in an advanced purification process, and that’s what Desai and I have come to see. This plant is right next to the county’s water treatment facility, and together they perform a kind of alchemy, converting human sewage into purified water so clean it can go right back into residential faucets. The plants pump out 100 million gallons of drinking water daily, enough to supply 850,000 Orange County residents, which makes this the largest “toilet-to-tap” facility on the planet.
For decades, sewage has been treated and used for irrigating crops, parks, and golf courses, but making it fit for human consumption requires a much more rigorous filtration technology using polymer membranes. No thicker than a human hair, the membranes are at once delicate and durable. Using pores smaller than one-millionth of a millimeter, they’re capable of wiping out microscopic contaminants.