SIOUX FALLS, S.D. - One of the Dakotas' largest metro areas since 1995 has been turning a byproduct of their wastewater treatment - sludge from city water waste - into farm fertilizer.

Officials there say most city residents and even neighbors don't know how their "beneficial re-use" of nutrients is saving on their landfill.

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Phil Greenwood, the residue coordinator for the city of Sioux Falls and southeast South Dakota, says the process is highly touted among farmers in the immediate area, who receive enough material to fertilize 2,500 acres of land a year, at no cost to the farmer.

It's not correct to call the product manure, but instead a byproduct of bacteria that feed on those wastes. The process has been used in large metropolitan areas around the country for decades.

Greenwood loves to tell the story of sludge fertilizer as a win-win for farmers and the environment. He says he comes by his interest in the process two ways: his grandparents farmed in Minnesota and used fertilizer, and his father was in wastewater treatment. He holds an animal science degree from Missouri State University where he and worked on a Platte, S.D., farm before hiring on with Sioux Falls in 2009.

Regional center

The Sioux Falls facility is a truly regional wastewater treatment center, serving the city of Sioux Falls, Harrisburg, Brandon, and soon the city of Tea. Sioux Falls takes in 18 million to 20 million gallons of wastewater daily. Of that, 99 percent is water - from things like dishwater, sinks and laundry. Only about 0.4 percent of the wastewater solid material - suspended or dissolved solids, and only part of that is human.

The wastewater comes to the plant through pipes. The city screens out plastics, paper and other materials. The bacteria thrive on the waste in aeration basins, each provided with blowers to add oxygen and mix the food and bacteria.

The bacteria die and end up in the city's sludge holding lagoons. The material settles to the bottom where it further decomposes. About twice a year, the ponds are cleaned out and the material is taken to farm fields.

The liquid has the look and texture of chocolate milk. It goes out in gallons but the solids are measured as 3,200 "dry ton" equivalent.

Farm cooperators

The farm fertilizer value is calculated like other fertilizers, according to active ingredients, based on agronomic rates and yield goals for such crops as corn. The city provides soil testing when they are planning to go to the field of a cooperating farmer.

The city has an approved list of nine farmers, controlling 4,000 eligible acres from 3 miles to 20 miles from the treatment plant.

Greenwood coordinates the application of the material on three to four farms per year, totaling about 2,500 acres a year - an area roughly the size of one typical farm. For simplicity's sake, they don't deliver into nearby Minnesota or Iowa.

Farmers who initially signed up did so on all of the acres they could.

Typically, about 75 percent of the sludge is applied from late September to ground freeze-up around Veteran's Day. Most field sizes must be more than 20 acres.

The material has a stable fertilizer analysis of 5-5-0, referring to its percentage concentrations of nitrogen, phosphorus and potassium, respectively.

They run the material to the field with three bulk liquid tankers filled to 6,200 gallons each.

Trucks empty directly into an applicator in the field that handles 6,800 gallons. They use a Challenger tractor, pulling a Balzer Magnum plow system that runs mostly from 6 to 10 inches deep.


'Jump on it'

Two happy users are farmers Tom Brown and his son Joey Brown of Brandon, S.D., who also sell Pioneer seed through their Brown Seed and Crop Protection, LLC.

"It helps the city and it helps us grow our crops," Tom says.

The Browns farm about 6 miles from the facility on about 400 acres, mostly in demonstration plots, with half each in corn and soybeans. They get fertilizer covering 120 acres per year. They've been using the city sludge product for about five years.

"It's all natural, all recycled," Joey says. "The fertilizer has everything we need to grow a full crop of corn and a full crop of beans without having to add anything to it. There really isn't a downside."

There are discussions about a similar operation being considered in Fargo, although officials said the concept is preliminary.

If the product should become available in the Fargo area, Joey Brown advises farmers to "jump on board and take it because it is very, very good stuff."

Environmental Protection Agency rules are strictly followed. At Sioux Falls, they must observe limits on how much liquid can be incorporated, and carefully watch 10 heavy metal levels, which are affected by industrial influences.

If the material exceeds standards on any one of 10 "heavy metals," (typically from metal-related city industries) the material must go to a landfill or other approved method.

EPA rules include preventing application on frozen or snow-covered ground. The product must be set-back 50 feet from roadways and waterways, and 300 feet from any inhabited dwelling or drinking water wells.

The city steers clear of housing, floodplains, and certain areas around the Big Sioux River, which is an EPA Source Water Protection District.

Sterilized product

Early in the spring, the city gives farmers about a month's notice that the material will be available. That timing depends on frost, ground-drying and other schedules. Soybean stubble typically dries out the fastest in the spring. The machine knives sometimes can become plugged when applying into high-residue corn stubble.

Sometimes it's a question of whether the farmer will wait. "Farmers today can plant 200 acres a day and I'm lucky if I can (fertilize) 20 acres," Greenwood says.

Besides providing value to farmers, the farm field use saves the $36 per ton the city would pay if they had to take it to the landfill. That's a savings of about $400,000 a year.

Sioux Falls is preparing for a system that in 2019 will allow sterilized material to go on lawns, gardens and tree farms.

Fargo is considering a similar system which could be a small part of a $140 million wastewater system expansion. Compared to the Sioux Falls facility, which takes up to 20 million gallons in wastewater per day, Fargo brings in 13 million gallons and will expand to a 30 million gallon capacity. Across the river in Minnesota, Moorhead brings in 4 million gallons per day of wastewater and has been field-applying byproducts for more than 20 years.

Jim Hausauer, wastewater utility director for the city of Fargo, says the city is considering a pilot program for field application for 2019, initially working with one farmer who already leases land from the city on a pilot program.

"It's in the talking stage right now, but we are considering it," Hausauer says, noting he'd budgeted for some leased equipment for 2019.

Karla Olson, a wastewater engineer with Apex Engineering of Fargo and consulting on the expansion Fargo project, said it may involve a product that is 20 percent solid, as compared to the Sioux Falls program, which deals with 5 percent solid - essentially a liquid.