Milwaukee has been turning wastewater-treatment microbes into lawn fertilizer since 1926, drying the microbes that ate the city’s waste in dryers at up to 1,200 degrees Fahrenheit and pelletizing them. 10.5 billion pounds have gone out that way rather than into landfill.

Here is a number that sits oddly in the mind: over ten billion pounds of what would otherwise have gone to landfill has instead left Milwaukee in bags of lawn fertilizer.

The bag on the hardware-store shelf, sold to people who want a greener yard, began as the stuff a city flushes away. The thing doing the work in the middle is a colony of microbes that ate the waste and then died.

The product is called Milorganite, and it has been made for a century.

So how does sewage become something you willingly spread on the grass your kids play on, and why has a city sewer district kept doing it since the 1920s?

What Milorganite actually is

The name is a mash-up: Milwaukee Organic Nitrogen. It is a slow-release fertilizer made by the Milwaukee Metropolitan Sewerage District, and it comes out of the process of cleaning the city’s wastewater rather than being made from scratch. Production started in 1926, with the first railcar shipping on February 10 that year. That makes it one of the oldest recycling programs in the country.

The plant behind it was ahead of its time. Construction on the Jones Island facility began in 1923, and Milorganite calls it the world’s first large-scale plant of its kind. Nearly a hundred years later, the district serves over 1 million customers in 29 communities. 

How the microbes do the eating

The engine of the whole thing is biology, not machinery. Naturally occurring microbes are added to the incoming wastewater, where they feed on the nutrients dissolved in it. As they eat, they clean the water.

Peter Coffaro, the district’s director of public engagement, puts it plainly: “They are eating the material. It’s a short and happy life. They are eating a lot and they are reproducing.”

Once the microbes run out of food, they die off. The cleaned water is disinfected and returned to Lake Michigan, and what is left behind is a mass of dead microbes. That leftover is the raw material. Most of what happens next is about getting the water out of it and turning it into something dry, stable, and safe to bag.

Coffaro frames the difference from a typical plant as the whole point. As he describes it, “Most treatment plant processes, it’s always about needing to remove that water and get that waste off and generally it goes to landfill, and we are able to recycle that product.”

Why 1,200 degrees matters

The obvious worry with anything made from sewage is what might still be living in it. The answer is heat, and a lot of it.

According to the maker, the dead microbes are dried in high-temperature rotating kilns “heated to 900–1200 ⁰F to kill pathogens and form pellets.” That temperature is the safety step. It turns a wet, biologically active sludge into a dry pellet that can sit in a garage.

What comes out is a slow-release nitrogen product that the maker says feeds plants over about 8-10 weeks, which is the selling point for gardeners who don’t want a fast green burst followed by a crash.

We’re not soil scientists or public-health researchers, and these process details come mostly from the producer rather than an independent audit, so read them as the manufacturer’s description of its own method. The heat-kill step is standard for this type of heat-dried product, but the specifics are the district’s account of its own plant.

The ten-billion-pound question

So what does nearly a century of this keep out of landfill? Milorganite’s own history page puts the running total over 10.5 billion pounds. The National Association of Clean Water Agencies, which gave the district an award, similarly credited it with having “diverted over ten billion pounds of nutrient-rich fertilizer pellets to residential, professional, and agricultural markets.”

What strikes us is how the whole thing rearranges the idea of “waste.” A landfill treats the leftover solids as an endpoint, something to be buried and forgotten. Milwaukee treats the same material as inventory. The microbes that cleaned the water become the product, the product goes onto lawns and farms, and the thing a city would normally pay to throw away instead ships out by the railcar.

The staying power of the idea is the part that lingers. Plenty of clever environmental schemes launch, win an award, and fade. This one started a century ago is still running on the same premise. Maybe it was never really about being clever. It was about noticing that a pile of dead microbes and a bag of fertilizer were, on closer inspection, the same thing.