From Yuck to Yay: The Case for Reusing Black Water

Codiga Resource Recovery Center at Stanford University / KALW.org

“There is no new water. We can’t make more. We have to recycle and manage it better,” said Josiah Cain, with Sherwood Design Engineers at the 2017 Greenbuild in Boston. The Earth’s water is 97.5 percent saltwater and just 2.5 percent freshwater. A very small amount of freshwater is actually available, given most of it is frozen or found in clouds. As the population heads towards 10 billion and agriculture demands only increase, every drop of water counts. We need to stop doing wasteful things like washing streets and irrigating plants with potable water.

As water becomes more precious, we can soon expect there will be different qualities of recycled water, used for different purposes. Black water, another term for toilet water, may soon be another type of reused water more widely used. As Clark Brockman with SERA Architects said, “we can go from ‘yuck to yay’ and reuse black water in a safe, feasible way to save water and energy and reduce costs.”

Cain sees a future in a highly-urbanized world where water is managed via “decentralized, adaptable infrastructure platforms.” Blending tanks will take in black water. After solid waste has been removed, the tanks will cleanse and dilute the black water with rainwater, so it can be reused as grey water for commercial, industrial, and agricultural uses.

According to Ronen Barkan with Fluence, it makes sense for large countries like the U.S. and Canada to use decentralized water recycling systems. The most effective use of recycled black water is agricultural irrigation. “That water doesn’t need to be the best quality.” With higher levels of purity, which also adds to the cost, recycled black water can also be used in “building cooling towers and toilets.” The technology for these systems is already there, but it’s the cost that’s the most important factor. If treating black water costs much more than using potable water, then it won’t happen.

Beyond getting the cost right, there also needs to be trust that recycled black water is safe to use. Regulators want assurances that water recycling systems will function as engineers claim they will. At the Codiga Resource Recovery Center at Stanford University, Sebastien Stilmans said, firms, developers, and regulators can test systems and gain confidence that they work. He helps manage the facility, which pushes 1,000 gallons of black water from Stanford’s campus through test beds every day. “We then analyze the results and give objective feedback.” Already, there is a network of testing facilities that are helping regulators accept and approve decentralized waste water treatment systems.

Google is already looking into black water recycling for its California headquarters, as it assesses the amount of every type of water that comes into contact with its site. To reduce potable water use in its landscape, Google remade it with native plants. Drew Wenzel with Google said “the goal was to recreate the natural habitat of the region.” In evaluating the creation of a blending system for rainwater and blackwater in order to further reduce campus demand for potable water, they are uncovering the regulatory landscape is complex. To achieve scale with these water recycling systems, “lots of rethinking is required.”

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