Sludge's odor in crosshairs

At some point soon, officials at the Western Lake Superior Sanitary District want to be able to hold their noses in the air and proudly proclaim that their sludge don't stink.

At some point soon, officials at the Western Lake Superior Sanitary District want to be able to hold their noses in the air and proudly proclaim that their sludge don't stink.

Kathy Hamel will know when that can happen. It's when her phone stops ringing.

Hamel, operations supervisor for WLSSD, is in charge of the district's biosolids, or sewage sludge treatment system. She gets the calls from rural residents when a whiff of WLSSD sludge on Northland farm fields wafts into open windows of nearby homes. She's also leading efforts, including a new $67,000 research project, to reduce those odors.

Scientists at Virginia Technical University and Bucknell University in Pennsylvania will analyze WLSSD's sludge in coming months to see if tweaking the processing system can cut odors.

This month, samples of WLSSD sludge are being shipped via overnight courier to the researchers specializing in sewage science. Results should be available late in 2007.


"We're trying to determine if we can operate the process a little differently and really reduce odors,'' Hamel said. "I think we're going to come up with some changes that will make a difference.''

Matt Higgins, lead sludge researcher at Bucknell, said past efforts have used additives, and even cover scents, to resolve smelly sludge problems.

"We had one where they used a big industrial aerator that sprayed a lemon scent in the field,'' Higgins said. "That didn't work very well.''

Higgins said most success has come by adjusting the sludge cooking recipe. Scientists also look at what comes into the treatment plant -- everything from the iron and calcium content in city water to the types of industries in town and what they send down the drain.

"I don't know if we can ever eliminate odor from biosolids, but that's the goal,'' Higgins said. "We're getting close.''

Farm field fertilizer

Raw sewage that comes into the WLSSD from homes, businesses and industry is treated at the West End/Lincoln Park plant. Water is separated and cleaned before flowing back into the harbor, while solids are cooked to remove pathogens.

That cooked sludge, called biosolids, is then trucked to Northland fields and spread as fertilizer, about 34,000 tons each year, spread across 2,400 acres at 130 sites. Neighbors of those farms and mineland reclamation sites sometimes complain that the stench is unbearable. The callers usually describe an ammonia-like odor, also compared to rotting animal flesh.


Complaints average fewer than a dozen each year. But WLSSD officials are sensitive to the fact that they need to be a good citizen in rural areas. And they are considering expanding their markets beyond just farms.

As more homes and cabins are developed near the few remaining active farms in Carlton and southern St. Louis County, WLSSD could face mounting opposition to its on-land spreading of biosolids.

Some townships in the region already have banned WLSSD sludge based on odor and health issues. Concerns over bacteria, viruses, heavy metals and other contaminants still spur health complaints, while other opponents cite increased nutrients, like phosphorus, that could pollute local waterways.

Heidi Carlson of Mahtowa is one of those neighbors who has called to complain. A nearby farmer's field that gets regular doses of WLSSD biosolids is just behind her back yard. Now, she's one of more than a dozen people WLSSD calls before biosolids are spread nearby -- so they know in advance and not just when the wind blows.

"It's better now, especially when they disked it into the ground and didn't just leave it on top,'' Carlson said. "The worst was when it was sitting out there and it would freeze and thaw and freeze and thaw. The smell got worse each time it thawed out or got wet.''

Carlson said there's no mistaking the odor of WLSSD biosolids.

"It has its own distinct smell, and it's not good. It's kind of [like] ammonia,'' she said. "To me, it's worse than manure.''

The smell thing


WLSSD has been dealing with odors since its inception 30 years ago. Complaints about the treatment plant have diminished greatly in recent years as processing systems have changed. And there were only two complaints in 2006 from the fields, Hamel said.

A 2003 effort to reduce odors spurred changes in the sludge centrifuge process. By reducing the amount of protein in the sludge, odors have been reduced, confirmed both by analyses of gases and independent laboratory testing with real human noses.

"Bacteria breaking down protein are the biggest source of odor,'' Higgins said.

Now, engineers and scientists are looking at how long and at what temperatures WLSSD is processing sludge. It's that system, inside anaerobic digesters, where microorganisms break down pathogens, the nasty stuff in sewage sludge.

Currently, all WLSSD sludge goes into a giant,million-gallon tank and is cooked for a week at 132 degrees Fahrenheit. It then moves to one of three secondary tanks, where it's held for three more weeks at 107 degrees.

Vancouver, British Columbia, sewage experts found they got fewer odors in their biosolid fertilizer if they kept temperatures hot for a longer period and moved sludge through multiple tanks. Tacoma, Wash., steps down its temperatures as the material moves through a series of tanks, rather than the two-tank system WLSSD uses.

It worked so well in Tacoma that the sewer plant markets products -- biosolid mixed with mulch, fertilizer and potting soil -- for homeowners' gardens and even indoor plants. Judging by sales, up 57 percent in one year, odor no longer is a problem.

Higgins said WLSSD will be run through setups similar to what Tacoma and other plants are using to find what works best.

While WLSSD likely won't market its product to consumers anytime soon, it may someday want to offer it to golf courses, nurseries and other commercial growers. Before that happens, WLSSD needs a product that's consistently easy on the olfactory.

"We think it's in the temperature and (tank configuration) where we'll find the difference,'' Hamel said. "But [each treatment plant's sludge] reacts a little differently. We'll have to see what works for us.''

John Myers can be reached at (218) 723-5344 or by e-mail at .

John Myers reports on the outdoors, natural resources and the environment for the Duluth News Tribune. You can reach him at
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