Downers Grove Sanitary District turns sewage into 'Class A' fertilizer

DOWNERS GROVE – The last time most residents see or think about waste leaving the bathroom is when they flush the toilet.

But after the toilet’s “whoosh,” the waste is just beginning a three-year process at the Downers Grove Sanitary District that ends in a safe byproduct available for free to residents as a fertilizer.

The district produces about 4,000 cubic yards of the byproduct, called biosolid fertilizer, each year. And it manages to give away every ounce of the nutrient-rich material to residents, contractors and governmental bodies to fertilize landscaping projects. None of it ends up in landfills.

“It has a lot of micronutrients that you don’t typically get in your standard fertilizer that are really important for things like root growth and plant health,” Downers Grove Sanitary District General Manager Nick Menninga said. “So it gives you stuff other than common fertilizer does. It makes it a slightly different product than if you got a bag of stuff at the store.”

Producing biosolid fertilizer is a fairly unique ability for a sanitary district,

Menninga said. Downers Grove has the large amount of space required for the process, unlike some more constricted suburbs.

In Downers Grove, raw sewage enters the plant and first goes through a grit removal system, before heading through a series of concrete channels during what’s called the primary clarification stage. The primary clarifiers separate water from the sludge, which is basically dissolved toilet paper and everything else flushed or washed down the drain.

At that point, the water goes on its own journey through a separate set of cleaning processes before eventual discharge into the DuPage River.

The sludge removed by the clarifiers is diverted to anaerobic tanks, where bacteria that thrives in low-oxygen environments feed on it, removing pathogens and other nasties.

After that, the sludge, which at this point resembles crude oil, is sent through a press that squeezes moisture out of the product, and adds a coagulant. When it exits the press, the material is thicker and looks like heavy, wet mud, known affectionately as “freshly de-watered sludge.”

“This stuff that just comes off the belt press, this would be a Class B product,” Menninga said during an interview and tour of the expansive plant. “This would be suitable for putting on a corn or soybean field. But this is not a material you would give away for public distribution. A lot of waste water plants in the Chicago area, in particular, stop at this stage and then they have it trucked out to farms, which is a pretty long haul.”

Most of the biosolid fertilizer produced by the Downers Grove Sanitary District goes to local recipients in the Downers Grove, Woodridge and Westmont area, he said. But if a large landscape contractor further out, say in Minooka, is willing to take a large amount, they’ll drive it there.

After the belt press, the mud-like substance is piled across several fields by sanitary district employees. The piles of Class B material are rotated from stack to stack over three years as it slowly dries.

“Once it’s gone through the freeze-thaw cycle for two or three winters, it’s very stable,” he said.

Now there are only two steps left. Employees use large auger tractors to spread the stuff 4-inches-thick across an asphalt pad about half the size of a football field. This is the last step of the drying process before employees feed what is now biosolid fertilizer through a trommel screen. It removes any rocks or other debris and pulverizes the large chunks of fertilizer into something that visually resembles dirt.

At this point, the fertilizer is kept under cover to stay dry as it awaits order requests from the community.

“After we’re done with it, it’s a Class A material, the highest standard the EPA has for biosolids,” Menninga said.

One of the sanitary district’s biggest biosolids customers is the Glen Ellyn Park District.

“We think it works really well,” said Glen Ellyn Park District horticulturalist Alice Murray. “We use it a lot for reseeding and sodding.”

She said the park district has used about 30 truckloads worth of the byproduct each of the last two years. Park district employees rake it onto athletic fields, especially, to help grow the turf.

“I consider it a superior product,” she said.