Think of it as a big kidney.
Columbia Heights’ new membrane filtration plant at Reservoir Boulevard near 45th Avenue NE will soon be using polymer filters to sift out impurities and organisms in the city’s water supply. The plant cost $58 million to build and is part of the Minneapolis Water Works’ ultrafiltration program begun in 2000. The 95,000 square-foot plant isn’t on line yet, but according to Minneapolis Water Works project engineer Dale Folen, it should be running any day now.
Minneapolis set up shop in Columbia Heights in 1910, building its first water filtration plant on a site determined to be at the highest elevation in the Twin Cities. The plant was built on 80 acres of land; construction took three years. It was expanded in 1914, 1917 and 1918, according to Water Works information. The old filtration process involved several steps, including filtering the water by passing it through sand 30 inches deep and adding chlorine.
The new membrane filtration plant is just west of the old plant. Its ultrafilters look like long, thin cocktail straws (with corrugated innards), and are bunched together inside long tubes. When the water is pumped through the tubes, the filters trap things like bacteria, viruses, algae, giardia and Cryptosporidium—a microorganism that can cause illness or even death. Both giardia and Cryptosporidium are microscopic parasites that live in the small intestine of the host.
Cryptosporidium, Folen said, is so small that it can pass through the plant’s old sand filtration system. It is also resistant to chlorine. “Chlorine kills most pathogens, but Cryptosporidium has a shell that closes up in a hostile environment.”
Cryptosporidium, in fact, might be credited for recent advances in water filtration technology. The pathogen made headlines in Milwaukee, Wisc., in 1993, after it caused more than 400,000 people to fall ill and killed somewhere between 30 and 100 people. Milwaukee was slapped with 25 lawsuits, even though the city’s water works plant had not violated any drinking water standards.
After the Milwaukee incident, Minneapolis spent the next six years on a technical evaluation study to upgrade its water filtration system. The ultrafiltration technology the city decided on is being used in some smaller plants near London and one in North Holland, Folen said, adding, “This is the largest plant of its kind in North America.”
Once it’s running, the plant will be able to filter 70 million gallons of drinking water a day.
The plant also “backwashes” the membranes (cleans out the filters) every 25 minutes. In addition to chlorine and fluoride—which is good for teeth—a chemical called polyphosphate is added to the water to stop the lead and copper corrosion in residential plumbing pipes.
The new building has an operations floor (where the 36 ultrafiltration units are), a pump room, a mechanical room, and an air compressor room. Staff tests every ultrafiltration unit daily to check its integrity. “If we see half a gallon per minute [of water going through], it means we have a solid membrane. The pore structure is so small that air doesn’t pass through easily. If there’s defect, however, air can pass through. That’s how we catch the defect.”
Trees, asbestos, deer
The exterior of the plant was designed to blend in with the early 1900s buildings already on the site. The building has a Spanish tile roof, which Folen said will likely last up to 75 years. A small stone wall in front of the plant was built from pieces of Minneapolis’ original cobblestone streets. The cobblestones and large pieces of granite and limestone were “dumped in our back 40” years ago, Folen said, so Water Works officials decided to make use of them.
Although the building looks nice and its purpose is a good one—to improve the quality of the city’s drinking water—the project got off to a rocky start in 2003, with a series of bad public relations incidents.
Some Columbia Heights residents who lived west of the plant on 45th objected to a landscaping/holding pond plan that included cutting down mature trees. The cottonwood, poplar and oaks shaded their back yards; some were more than 40 feet high. They organized quickly, starting a petition and calling on State Representative Barbara Goodwin for help.
After several meetings, Minneapolis officials agreed to stop cutting down trees. They eliminated the holding pond to the west and enlarged one to the north.
But then residents learned about the asbestos removal that was to take place after construction started. (Apparently, construction crews uncovered fill material, which included floor tile and roofing products with asbestos, when they began excavation for the new building.) Residents expressed concerns for their own safety if it became airborne, but officials assured them risks were minimal.
The deer herd at the site, which had lived there for years, was another concern. Clearing the land to make way for the new building took away much of the undergrowth and woods that the deer had depended on for food and shelter.
After an organized bow hunt on Water Works property that left many people enraged—and also didn’t kill all the deer—some residents found a private animal sanctuary, Minnesota Wildlife Connection, near Sandstone, Minnesota, that agreed to relocate the remaining deer and take care of them. That sparked a struggle with the state’s Department of Natural Resources (DNR). The DNR claimed ownership of the deer, saying they were wild animals, and the sanctuary couldn’t have them. Eventually the residents prevailed, however, and 16 deer were rounded up and shipped to the sanctuary.
When the Northeaster toured the membrane filtration plant last week, Folen pointed out the trees that remain at the original holding pond site. He assured the reporter that all the deer are gone. He also pointed out a sloped driveway next to the building, where tanks that deliver liquid chemicals park. The sloped road, he said, makes sure that if there is any kind of a spill, the chemicals will run toward the plant and not toward neighboring houses.
For information on the new membrane filtration plant (which is not open to the public), call 612-661-4904.