A technology test in Milwaukee aims to reduce the harm done when combined sewer overflows are released into Lake Michigan and local rivers.
Two to three times a year, on average, rain — or snowmelt — overwhelms the treatment system at the Milwaukee Metropolitan Sewerage District, or MMSD. When that happens, officials release untreated or partially treated wastewater into local surface waters. That's to reduce or eliminate sewage backup into basements.
Paige Peters says Milwaukee is not alone in releasing polluted water.
"Every year in the U.S., 850 billion gallons of untreated sewage are discharged into lakes and rivers, due to sewer overflows during intense storms. That's equivalent to 170,000 Mississippi Rivers filled with poop water. I know that doesn't sound appealing but I hope it bring gravity to the reality of the situation," Peters says.
Peters says MMSD and other wastewater treatment agencies around the U.S. have been taking steps to reduce the sewage overflows. But her startup company, Rapid Radicals, has started a pilot program aiming to clean more of the sewage before its released.
The company's work takes place in pipes and a series of metal tanks inside a large blue shipping container on MMSD property at about Hawley Rd. and State St. in Milwaukee.
Will Schanen of Rapid Radicals begins a tour of the container by describing how wastewater is pumped in from a nearby underground sewer. "It pulls from there into a filter. The filter takes out the solids in larger chunks. It goes to here where sensors have the influent data. Then it gets bumped up here to each separate tank. Injection tanks where we are injecting ozone. It's diffused in. And there's a reaction tank. Another injection tank, reaction tank. Injection tank, reaction tank," Schanen explains.
Peters says the ozone process is faster than what typically happens at a wastewater plant during what is called secondary treatment. That's after heavy solids are removed and a slurry, or sludge, remains to be cleaned by so-called good bacteria.
"Activated sludge is your conventional wastewater treatment technology, and it has been done for decades — if not centuries, and it's very good at treating wastewater. Unfortunately, because it's biological, it takes at least six hours to do what it needs to do. However, with chemical treatment, you can do what biological treatment does in 10 to 30 minutes," Peters says.
Peters clarifies that ozone in this case is not a harmful chemical. "What we like about ozone is it's generated on site. So, we take oxygen, split the molecules, we make ozone. It is very reactive to the organics in wastewater. So, there's no residual in it, in the water when it leaves, because it's quickly reactive with the wastewater. And, we're always monitoring to make sure we don't have any ozone in the off-gas, so that we're not adding more than we need to," she tells WUWM.
Peters says research she's done already shows the ozone treatment can be cost-effective.
The MMSD's Matt Magruder says preliminary figures from Rapid Radicals show the sewage can be cleaned to meet the standards of the district's wastewater permit. The question, he says, is can the ozone treatment scale up, without sacrificing performance. Magruder says he's optimistic that it will help with heavy rainfalls.
"You know, you're never going to out-engineer Mother Nature. But we can give it our best shot. At the end of the day, we have a pretty aggressive vision to end overflows. We're excited about the progress we've made to date. But there's always still room to improve, and this is one tool that could potentially help us get to that zero overflow goal," Magruder says.
Marquette University already has enough confidence in Rapid Radicals that the school has filed patent applications on the technology, and has completed an intellectual property license agreement with the firm.
Peters has three academic degrees from Marquette. The National Science Foundation has also supported her research.
