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Flush and forget – that’s the normal approach to the unwelcome waste we humans produce. But that stuff doesn’t just go away when we send it out of our homes. It’s the Milwaukee Metropolitan Sewerage District’s job to make sure it’s dealt with safely. Here’s how they make that happen:
1. It starts with a flush or a circling drain or water gurgling down a curb. About a quarter of all toilets, sinks, baths, storm drains, etc. across Milwaukee connect to a combined sewer going as far as 50-60 feet below the earth – one system of pipes that collects all that mess. During heavy storms, the Deep Tunnel stores the extra runoff so the treatment plants (hopefully) aren’t overwhelmed, causing an overflow.
⇒ Most of MMSD’s 423 miles of territory is served by separate sewer systems, with rainwater being sent directly to lakes and rivers, while septic waste takes a separate pipe to treatment facilities.
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2. Roughly 300 miles of sewer pipes send the strange sauce flowing underneath Milwaukee toward one of two destinations: South Shore Water Reclamation Facility in Oak Creek or Jones Island Water Reclamation Facility in Milwaukee’s harbor, which are operated by Veolia Water, under MMSD contract. “Reclaiming water” is a righteous way of saying removing the feces (and other toxic contaminants).
⇒ South Shore boasts a digester that captures methane gas from the waste to help power the facility. Jones Island receives renewable energy from methane gas produced in a landfill in Muskego.
3. You ever wonder why Walker’s Point stinks sometimes? Yeah, that’s the fresh and funky whiff of Jones Island. When all that wastewater enters the facility, it first goes through a screening for solid materials. Tight concrete bars strain out any debris larger than a quarter-inch – that often means towels thoughtlessly flushed, tennis balls washed down storm drains, etc. The trash is sent to a landfill.
4. The wastewater enters settling tanks, also known as primary clarification tanks (a funny word, since this water is most certainly not clear). You can see these giant circular vats out in the sun if you visit Jones Island. As the wastewater sits there, often with seagulls above, oils and grease within float to the top – a slowly-rotating arm scrapes it away and disposes of it. At the same time, remaining solids (or sludge) settles at the bottom of the tank, where it’s removed from the water.
5. When all that mess is gone, the remaining wastewater is pumped into aeration basins – long, rectangular, open-air tanks. These basins are filled with microbes, or little bacteria, that eat the … we’re running out of polite ways to say poop, and break down its nutrients. The microbes need oxygen to get that done, so MMSD pumps air into the water throughout the process, creating a bubbly witches’ brew. Pumping all that air into the waste is one of the most energy-consuming parts of the entire cleaning process. The bacteria fatten up, clump together, and then die and sink to the bottom of the basin after they’ve consumed their fill, forming what is called biomass.
⇒ The biomass is removed from the aeration basins and put into belt presses, which squeeze out the last of the water. The semi-solid remains are placed in dryers and absolutely scorched (as hot as 1,200 degrees) to kill any remaining pathogens. Simultaneously, they rotate, turning the biomass into small pellets that – once tested for safety – are bagged and sold across the nation as Milorganite fertilizer. “There’s a little bit of you in every bag,” says Bill Graffin, MMSD’s public information manager.
6. The remaining water – now free of waste and biomass – is moved to a disinfection area, where it’s pumped with chlorine. The chemical kills any pathogens that might still linger. The water is then de-chlorinated and released back to Lake Michigan. In total, the entire cleaning process usually takes 6-8 hours when it’s raining, and can take up to a full day when it’s dry.
7. After Milwaukee Water Works treats the Lake Michigan water, it goes out to sinks across the metro area, and then right back into the stomachs of Milwaukeeans (Maybe after a pass through a Brita filter.) And the cycle continues.
