“It doesn’t smell all that bad,” says Mike, a friend from work. We’re on a tour of the Madison Metropolitan Sewerage District (MMSD) Nine Springs plant on Moorland Road in Madison. We’re standing next to the settling tanks, the first stage of treatment for raw sewage – called wastewater or influent – where solids are separated from liquids. Mike adds, “It helps that we’re outside.”
Our tour guide, Catherine, explains the treatment steps. First, the settling tanks, then the aeration tanks where microbes break down organic matter and nutrients, then the clarification ponds where the microbes settle out, and finally, UV disinfection. The cleaned wastewater – called effluent – is pumped south to an outfall on Badfish Creek, between Oregon and Stoughton. MMSD produces river water, not drinking water. It pumps 40 million gallons of effluent per day into Badfish Creek – about 80 gallons per day for each of MMSD’s half million customers. Another, smaller, outfall sits on Badger Mill Creek close to Verona.
MMSD chemists test the effluent that leaves the Nine Springs facility to ensure it complies with all state and federal standards. MMSD scientists also do monthly checks on the creeks. Meanwhile, the solid waste from the bottom of the settling tanks – called biosolids – are turned into Metrogro, a fertilizer used in agriculture. Other products from wastewater include struvite (a phosphorus-based fertilizer), biogas (used to power the Nine Springs plant) and reused effluent (for plant cleaning and cooling).
The tour takes us on only a small part of the Nine Springs facility, which has been expanded eleven times since it was built in 1928. Catherine explains that at one time, the location was an airstrip. Paul Nehm, a former MMSD employee, now blogs about the history of sewage treatment in Madison on MMSD’s website.
According to Nehm, wastewater became a problem in Madison when flushable toilets became popular after the city developed a centralized waterworks system in the 1880s. Initially, private sewer lines simply discharged raw sewage into Lakes Mendota and Monona. The marshy area along East Washington Avenue west of the Yahara River was also a dumping ground for sewers and private cesspools.
It was not until 1885 that the legislature provided the city with the authority to operate a sewer system. Initially, this didn’t really help, as efforts to build a sewage treatment plant were considered too costly. Instead, the city’s sewer districts continued to discharge into the lakes. A historic plaque on the grounds of Olbrich Gardens on Madison’s east side states that sewage was pumped into Starkweather Creek in the late 1800s. This creek – still one of the most polluted in the state – empties into Lake Monona.
Madison’s first treatment plant was authorized in 1895, but it wasn’t until 1914 that the Burke Plant was built on Madison’s north side. Superseded by Nine Springs (built in 1928) the Burke plant was shut down in 1936. MMSD itself was created in 1930 to provide a more unified approach to wastewater treatment. Effluent from Nine Springs was discharged into the Madison lakes until the 1950s, when a new state law banned this activity.
Back on the tour, we descend into tunnels that cross under the aeration tanks. “I hope there isn’t a blowout,” Mike whispers to me. The tunnels are modern, clean and spacious. The fluorescent lights turn on and off automatically as we walk. Catherine explains this is to conserve energy, but admits it has a small impact on the facility’s massive monthly electrical bill. It takes a lot of energy to process human waste.
I’m interested in the color-coded pipes that run the length of the tunnel. Gray, orange, green, blue. They have unusual labels. Return Sludge. Mixed Liquor. Scum. Underground rooms hold banks of massive pumps that throb like tugboats. The wastewater plant is a huge engineering effort spread over dozens of buildings serving different functions.
Catherine is MMSD’s Pollution Prevention Specialist. She’s also an educator, leading tours for the public and first graders. She explains that a lot of things show up in sewage that shouldn’t be there. Wipes. Dental floss. Expired medications. Chloride from water softeners. Chemicals and pollutants. Catherine is passionate about wastewater and improving its quality. “It’s a group effort,” she says.
Another problem is oil and grease. Catherine mentions the Whitechapel Fatberg, a 143-ton congealed mass of oil and wet wipes found in the London sewers in 2017. The fatberg was so hard, workers had to use high-pressure jets of water to clear the blockage. A piece of the fatberg is now on permanent display in the London Museum.
“Wow!” Mike says. “Who knew fat could turn into a giant sewer-blocking rock?”