WLSSD sludge program spreads to Douglas County fieldsJim Soyring looks at the black stuff spread on his field and sees better hay growing, fatter beef cows down the road and a better bottom line for his Douglas County farm.
By: John Myers, Duluth News Tribune
MAPLE — Jim Soyring looks at the black stuff spread on his field and sees better hay growing, fatter beef cows down the road and a better bottom line for his Douglas County farm.
The stuff — Field Green fertilizer from Western Lake Superior Sanitary District — is packed with nitrogen, phosphorus and organic matter that will jumpstart his fields.
Soyring pays $19 an acre for Field Green, less than half the $58 he’d have to pay for commercial urea to get the same nitrogen benefit.
“It wouldn’t make sense for us to do this any other way. The numbers
wouldn’t work for me to fertilize,” said Soyring, who farms about 800 acres with about 300 cows and calves grazing before they are sold into the beef market.
For the first time, treated Duluth-area sewage sludge is crossing the state line to be spread on Wisconsin farm fields like Soyring’s. It’s part of an effort by WLSSD to expand its service area for Field Green.
The district tries to keep its delivery area for the sludge, called biosolids, within a 40-mile radius of Duluth to keep transportation costs down. But, until now, nearly half that potential territory was off-limits in Wisconsin.
WLSSD staff worked with the Wisconsin Department of Natural Resources, county extension and township officials to open up the Wisconsin market. And, while each individual field must be approved by the DNR, Wisconsin has approved the overall WLSSD system as safe. That’s opened up potentially dozens of new farms for Field Green.
“The closer we can stay to the plant, the less fuel we use. And that keeps costs down for our customers,” said Craig Lincoln, environmental programs coordinator for WLSSD. Those customers are both businesses and homeowners who pay to have their sewage treated and the farmers who buy Field Green.
Better hay, less stink
Troy Salzer, Carlton County extension agent, ran the numbers on Field Green and found impressive results. WLSSD biosolids double the amount of usable grass that grows on hayfields — from about a ton per acre to
more than two tons. And the grass itself has more protein; it’s better stuff to help cows grow.
“This is really a big benefit to the farmers in our area that they couldn’t get anywhere else,” Salzer said. “The fact that the nitrogen comes with this organic matter really helps hold the nutrients in place until the plants can take it up.”
WLSSD has been treating sewage sludge through a process called anaerobic digestion since 2001. The end product, about 30,000 tons per year, is then dried and spread on hayfields and other cropland used for livestock in Carlton and St. Louis counties. Field Green is not yet approved for use on crops that humans eat directly.
Over that decade, WLSSD scientists, with the help of national experts, have worked to improve the Field Green product — namely by making it less odiferous. But it also appears drier, more organic, almost like compost rather than sludge.
On a recent hot, sunny day on Soyring’s farm, as WLSSD tractor driver Bob Graves let his load fly, there was barely a whiff of the ammonia-like smell often associated with treated sewage sludge and that was common with the WLSSD product a decade ago.
Kathy Hamel, WLSSD operations and maintenance supervisor for clean water, credits the change to tweaking how the sludge is processed to kill pathogens — germs, viruses and other nasties. By running the sludge through a series of three separate vats called digesters, rather than just two vats, the stuff “cooks” longer and at varied temperatures. The temperatures were tweaked as well, and the natural breakdown of organisms seems to be more complete.
“The number of volatiles we’re removing has gone from 47 percent to 53 percent,” she said. “That may not sound like a big jump, but it’s made a huge difference.”
From flush to field
Input to WLSSD, untreated wastewater, comes from homes and industry in Duluth, the near North Shore, Hermantown, Proctor, Oliver and into Carlton County as far as Cloquet. Paper mills are a huge share of that wastewater load.
The WLSSD’s output is treated water, released into the harbor; methane gas (used to help heat the WLSSD plant); and Field Green.
Field Green is now spread on dozens of farms across about 2,000 acres in St. Louis and Carlton counties in Minnesota, about 80 percent on farm land and 20 percent on taconite tailings basins. The organic material is perfect for the sterile, rocky slopes of mine dumps because it helps hold the nitrogen in place while giving tree roots something to dig into, Salzer noted.
Farmers in Blackhoof, Twin Lakes, Mahtowa, Barnum, Clear Creek and Holyoke are the district’s biggest customers, with increasing interest in the Cromwell-Wright area. Thomson Township around Esko, where concerned residents had spurred a ban on WLSSD spreading a decade ago, recently rescinded the ban and WLSSD will start spreading there this fall.
Not everyone is ready to welcome Field Green. Automba Township near Kettle River, after a protest by residents, continues to ban Field Green, as do Split Rock, Silver Brook and Wrenshall townships in Carlton County. Culver, Stoney Brook, Duluth and Lakewood townships ban biosolids in St. Louis County.
Most concerns in the past centered on odors. But critics of biosolids on farm fields also say there are too many new substances, including man-made chemicals and diseases, flowing through the sewage stream for anyone to claim all biosolids are safe. While the treatment process removes most disease-causing germs, for example, it can’t remove some chemicals or problem elements like lead or mercury.
And there are still concerns in some regions as the quality and content of biosolids varies widely across the U.S. Some sludge seems to have more problem materials to start; other systems apparently aren’t as good at removing them. In some areas of the U.S., animals have died and people become sick after biosolids were spread on fields.
Because WLSSD and regulators have worked with Duluth-area industry to remove problem materials from the process before they get into the wastewater stream, WLSSD sludge is lower in most all potential problem materials than many nationwide, agency officials say.
Trace amounts of heavy metals are found in sludge as well. But soil scientists found it would take 391 years of annual Field Green applications to reach unsafe levels of copper, 682 years for arsenic and 1,875 years for nickel.
Other concerns have risen over excess nitrogen and phosphorus running off farm fields and into waterways, where it can spur algae growth and overfertilize streams and lakes. But WLSSD officials say they have that under control. They limit the amount of Field Green they put on each field by what the nitrogen needs are for one year.
WLSSD tractor operators use GPS navigation to precisely mark where to turn the spreader on and off, shutting the spreader off near waterways, steep slopes and even dry ditches that might funnel phosphorus into nearby waters during heavy rains.
“The question then becomes, if not this (fertilizer), then what do you do with it?” Salzer said.
Better than burning, burying?
WLSSD could simply truck its sludge to the Superior landfill and bury it. That’s what the city of Superior does with its sludge. But that costs more than field spreading and would mean higher sewage rates for Duluth homeowners and businesses.
Another option is to burn sludge. That’s what the WLSSD did for years before the Field Green program. But that process created air pollution and ash and was prone to mechanical troubles.
Nationally, at least some biosolids in all 50 states are used as fertilizer — more than 3 million dry tons per year. About half of all U.S. sewage sludge now becomes fertilizer.
One popular brand of fertilizer that gardeners purchase at Menards and other stores, called Milorganite, is in fact treated sewage sludge from Milwaukee and has been making gardens green since 1925.
Supporters of the Field Green program say the fact that it’s cheaper is secondary to the idea of using a waste product that everyone creates into a recycled, useful product for farmers.
“We know that it’s safe, it’s highly regulated, so why waste something that’s beneficial? Why would we want to concentrate this into a landfill when we can spread it out?” Salzer said. “This is the ultimate recycling effort, from waste back to the land to food.”