Wastewater plant about six weeks from 100% capacity

I first started at the Bemidji (Minn.) Pioneer as an intern in the summer of 1996. That would begin six years as a news reporter, sports reporter and copy editor for a small, six-day-per-week daily newspaper in northern Minnesota. I wrote a large range of stories from multiple beats, to features to sports, my favorite being the coverage of the Red Lake Reservation High School basketball team named the Warriors. Here is a collection of my stories from my time at the Pioneer.

Oct. 20, 1997

By Devlyn Brooks

Staff Writer

The Bemidji wastewater treatment plant is about six weeks away from 100 percent capacity, according to plant Superintendent Tim Whiting, who said Friday that preliminary work replacing a failed cover on the plant's secondary digester began last week.

Problems first arose with the digester early last year when plant employees noticed the tank cover periodically sticking to the walls of the tank. Normally, the tank is heated to 85 or 90 degrees, full of millions of anaerobic bacteria that "eat" solid waste in the tank. However, since February, when the tank's cover slipped a final time, the tank has been lifeless and half full of sludge.

The disabled floating cover, which sat at a slant in the tank for months, was designed to contain methane gas, which is harnessed to help fuel the plant. The cover was supposed to rise and fall to adjust to the tank's gas pressure.

Motorists cruising past the plant on Old Midway Drive last week witnessed the beginning of the repairs on the cover, as Krause-Anderson Construction Co. of Bemidji removed insulation that was atop the old cover and began to remove the cover itself with torches and a crane.

This week, according to Whiting, the construction company will remove some 1,200 cubic yards of sand that was placed in the tank as a safety precaution. It was designed to "catch" the 144-ton tank cover had it slipped farther.

The Bemidji City Council awarded the removal of the tank cover project to Krause-Anderson for about $36,500 earlier this summer, and another $37,000 was approved by the council to pay for the sand because the cover's stability was in question. In all, the project to repair the tank's cover will exceed $425,000. The money for the repairs came from the city's utility fund, which is large enough to cover the cost, City Manager Phil Shealy said at a council meeting this summer.

When Krause-Anderson is finished removing the old cover sometime this week, work will begin to replace it with a membrane-style cover that will make the tank look like a mini-Metrodome. The flexible cover, named Dystor, is made by U.S. Filter/Envirex and consists of two durable membranes. First, an outer one is restrained by cables in a fixed position, and the second, inner one is free to expand and contract as it stores or releases gas for use within the wastewater treatment plant.

Compressed air is used to exert a constant pressure between the two membranes, which keeps the outer one inflated and creates the necessary force on the inner membrane for gas pressure. The new cover will more than double existing sludge capacity in the digester and will also provide 400 percent more gas storage.

The "dome" will also offer nearly complete odor containment since the membrane covers the entire top of the tank, and there is no potential for freezing up as there was with the original steel cover.

Since the failure of the secondary tank's cover in February, the wastewater treatment plant has been relying on a secondary digester to keep operating, according to Whiting. However, the plant has continued to operate effectively and within environmental safety standards throughout the year.

The new cover should be in place by the end of November, he added.

"Things seem to be on schedule, and contingent on what happens," he said. "We should be able to begin on the new cover in the next two weeks."