Second Life for Phosphorus

Soil science professor and students turn a sometime pollutant into a valuable product

Phosphorus, a nutrient required for growing crops, finds its way from farm fields to our food and eventually to our wastewater treatment plants. At the plants, the nutrient causes major problems, building up in pipes or going on to pollute surface waters.

Brushite bounty: Phil Barak displays brushite produced during trials at the Nine Springs Wastewater Treatment Plant of the Madison Metropolitan Sewerage District. Each jar contains brushite harvested from 30 gallons of anaerobic digest. Photo courtesy of Phil Barak

Brushite bounty: Phil Barak displays brushite produced during trials at the Nine Springs Wastewater Treatment Plant of the Madison Metropolitan Sewerage District. Each jar contains brushite harvested from 30 gallons of anaerobic digest.
Photo by Rick Wayne

But soil science professor Phil Barak has an idea about how to retrieve the nutrient from wastewater in a valuable form—and it started from a basic lab experiment. “I was doing some work on crystallizing phosphorus, just out of pure academic interest,” explains Barak. “That led me to crystallize a mineral called struvite. Then I realized it was forming in wastewater treatment plants as a nuisance.”

If he could form crystals in the lab, he reasoned, why couldn’t it be done in the wastewater treatment plants in a controlled way? It could. And, even better, if he collected the phosphorus early on in the treatment process in the form of a mineral called brushite, he could harvest even more of it.

Beyond removing phosphorus from wastewater, brushite can serve as a nutrient source for growers. While Barak will do further testing to prove its utility, brushite is a phosphate mineral that’s actually been found in agricultural fields for years.

“When conventional phosphorus fertilizers are added to soil, brushite forms. I maintain that we’ve been fertilizing with brushite for decades, but nobody’s been paying attention to it,” says Barak.

Being able to remove phosphorus from wastewater and supply it back to growers is a win-win situation, Barak notes. “We’re collecting phosphorus where it’s localized, at really high concentrations, which is the most economical place to collect it,” says Barak. “This works out in just about every dimension you can consider, from the treatment plants to the cost of recycling phosphorus as opposed to mining it new.”

Graduate students in Barak’s lab suggested that he commercialize the technology and start a company. After the Wisconsin Alumni Research Foundation (WARF) passed on the patent, Barak and his students sought help from the UW Law and Entrepreneurship Clinic. They received two federal Small Business Innovative Research grants, and, with some additional funds from the state, including the Wisconsin Economic Development Corporation, their efforts have turned into a spinoff company: Nutrient Recovery & Upcycling, LLC (NRU).

The company’s next step was a big one. This summer, a phosphorus recovery pilot plant is being implemented in a wastewater treatment plant in Illinois. The pilot project will test the research ideas on a larger scale.

Additionally, the NRU team will participate in the Milwaukee Metropolitan Sewerage District’s granting system to determine if a pilot project would be a good fit in Milwaukee. They hope to start collecting and analyzing data from Illinois by September, using that pilot system to lay the groundwork for others in Milwaukee and beyond.