Firm seeks to add sewage sludge to composting mix

  • Article by: LAURIE BLAKE , Star Tribune
  • Updated: May 10, 2012 - 12:46 PM

For the first time in Minnesota, treated "bio-solids" would be blended with yard and food waste to create nutrient-rich black dirt.

For the first time in Minnesota, treated sewage sludge will be permitted to go into a mix of grass, leaves and food waste for composting into black dirt.

SKB Environmental Inc. of St. Paul is close to getting a permit from the city of Rosemount, the Minnesota Pollution Control Agency and Dakota County to include sludge in the materials it will compost at a landfill off Hwy. 55 in Rosemount.

Known by the sanitized term "bio-solids," the sludge is what remains of household sewage after contaminants have been removed at wastewater treatment plants. Although some states compost sludge, in Minnesota it's incinerated in the metro area and spread on land to improve soils in rural areas.

"This is going to be the first project in the state of Minnesota that will do this," said Ginny Black, organics recycling expert for the Minnesota Pollution Control Agency (MPCA). If things turn out well in this trial, it could open the door to broad use of sludge to create a beneficial product, Black said.

SKB has discussed the proposal with Rosemount for more than a year. The company has had extensive experience with composting and has promised the city that odor and rats will not become a problem.

The city wants to prevent contaminants from coming into the landfill with sludge, said City Planner Eric Zweber.

"The landfill is licensed as an industrial-demolition landfill. We want to be sure that what is brought in is material the landfill is licensed for."

To get that assurance, the city will count on Dakota County and the MPCA to test all sludge before it is composted to be sure it has the right chemistry and is free of excessive contaminants, Zweber said. That will ensure the sludge can be used to produce Class I composted dirt -- the kind clean enough for any use.

The compost operation will not accept small loads of yard waste from homeowners. It will be looking to make money by charging waste haulers tipping fees for large loads of grass clippings, food waste from schools and restaurants, and vegetable and fruit waste from food producers, said Geoff Strack, engineer for the company.

One sub-contract for yard waste from the city of Minneapolis has already been secured for the composting, Strack said. "Once we get all our approvals in we will have our sales people out trying to secure those kinds of materials."

That goes for sludge as well -- the company does not have a contract to receive it yet, he said. June is the earliest composting would begin.

Strack said there are more than 200 places around the country that have a permit to compost bio-solids. "We would be the first ones to have it permitted in Minnesota."

The composting will be done on the surface of the landfill -- which is considered a plus because any organic material washed into the ground by rain would be caught by the liner under the landfill before it reaches groundwater.

To create a pad for composting, SKB plans to level an area of the landfill, cover that with several inches of dirt and cover that with 6 inches of gravel. On the gravel, below the composting materials, perforated pipes will blow air into the composting mix to promote its decomposition without odor, Strack said.

The compost will be formed into three long rows and turned and worked. It takes about 90 days for microorganisms that eat through the waste to produce compost, he said.

The compost will not be sold to the public. SKB plans to use the dirt to cover its landfills when they are closed. The composted dirt will also be used for landscaping purposes by the Carl Bolander & Sons construction firm, which owns SKB.

Laurie Blake • 952-746-3287

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