Effluent from sewage treatment plants is just one way that cities contribute phosphorus to waterways.
Wastewater treatment upgrades and legislation banning phosphates in consumer detergents have helped cities greatly reduce the amount of phosphorus they discharge into the Great Lakes. Still, billions of gallons of wastewater are released into the lakes each year through outdated sewage systems that use combined sewers. These sewers transport raw sewage and stormwater in a single pipe, and when heavy rains occur they can overflow directly into rivers and lakes without passing through a treatment plant. The overflows prompt beach closings and health advisories, and are also big contributors to the phosphorus pollution that drives harmful algal blooms. Many of the recent efforts to get cities to comply with the Clean Water Act have therefore focused on eliminating combined sewer overflows (CSOs).
In Toledo, the 2002 settlement of an 11-year-old lawsuit between the city and the U.S. and Ohio Environmental Protection Agencies resulted in the Toledo Waterways Initiative, a 20-year plan to reduce the city’s discharges of untreated sewage. The first phase, completed in 2007, included construction of a wet weather treatment facility and retention basin at Toledo’s Bay View Wastewater Treatment Plant, which discharged an annual average of 143 million gallons of untreated sewage into the Maumee River during heavy rain events. The wet weather facility doubled the plant’s capacity to 400 million gallons of sewage a day. Since it began functioning there have been no sewage discharges at the plant.
Toledo is now tackling the second and third phases of the project, which include eliminating sanitary sewer overflows, the separation of some sewers, and the construction of several multi-million gallon storage basins that will hold the overflow from the city’s combined sewers until it can be pumped to the wastewater treatment plant.
Before the project began, Toledo was averaging 650 million gallons of combined sewer overflows each year. That torrent should be reduced by more than 80 percent by 2020, according to Julie Cousino, a lead engineer for the initiative. The estimated total cost of the project is $US 521 million.
Efforts are even further along in Grand Rapids, Mich., where all but five of the city’s combined sewer outfalls (CSO) have been completely bricked off and all of the sanitary and storm water sewers in the western half of the city have been separated. This means that the system physically cannot release any CSOs into the Grand River. Even during record flooding this spring that covered some roads with four feet of water, no sewer overflows occurred.
However, approximately 435 million gallons of sewage did overflow from the city’s Market Avenue retention basin, according to Mike Lunn, the city’s environmental services manager. Lunn said it is difficult for cities to plan and build for events like the spring floods that occur rarely. But Grand Rapids is trying to reduce the amount of water flowing into its sewers by incorporating green infrastructure into its CSO projects to keep more rain where it falls and out of the sewers.
“The two things we’re focused on in green infrastructure and in these later phases [of the CSO project] are water quality and water quantity,” he said. “We want to reduce the quantity and improve the quality. The big paradigm shift is that now we look at all our projects up front and say, what can we do to improve water quality and reduce water quantity? What can we do with low impact development? What can we do with green infrastructure? What can we do to infiltrate and keep that water there?”
It is an idea that is gaining traction in other Great Lakes cities as well. From Buffalo, N.Y., to Chicago, Ill., and Milwaukee, Wis., municipal water managers are putting out rain barrels, building bioswales and installing water-absorbing permeable pavement to reduce the amount of water running into sewers and treatment plants.
“This new technology of green infrastructure couldn’t be more timely,” David St. Pierre, executive director of the Metropolitan Water Reclamation District of Greater Chicago (MWRD), told Circle of Blue. “Anything you keep out of the system and combined system also improves your combined sewer overflows.”
St. Pierre said the MWRD is working with its municipal partners—including the city of Chicago, which recently pledged to spend $US 50 million on green infrastructure over the next 5 years—to use green infrastructure to manage storm water and further reduce CSOs.
The District has already cut CSOs by 50 percent, and it is working on updates to its wastewater treatment system that will remove enough phosphorus to produce10,000 to 15,000 tons of fertilizer each year. CSOs and wastewater discharges from this system generally flow into the Mississippi River Basin, but during very strong storms wastewater control structures can be reversed to release untreated overflows into Lake Michigan. This has occurred approximately once a year for the past 10 years, according to St. Pierre.