Simple valve keeps odors away

Four options for relief

We considered requiring the agricultural processing plants to expand pre-treatment operations, but that would have increased their costs. We were reluctant to take this step because of the potentially negative impact on local employment. During the Great Recession, we didn’t want to take any action that might make Decatur less attractive to business.

We considered chemical deodorization with hydrogen peroxide or chlorine injection, but it would have required building a plant that cost at least $1 million and tens of thousands in annual operational expenses.

We considered building a pump station to bypass downtown in a sealed force main. Because we’re dealing with a combined sewer, this turned out to be more expensive than the deodorizing system.

One day our sanitary sewer engineer, Paul Caswell, was doing research on the Internet. He came across an animation of an inline check valve made by Tideflex Technologies of Carnegie, Pa., a division of Red Valve Co. Inc.

“When I saw it, I knew the CheckMate was a strong potential solution that we should research further,” he says.

The valve is a single piece of elastomer fabric — basically, rubber — which means it’s flexible and doesn’t have a mechanical flapgate that will warp or rust. It can be installed from the upstream or downstream end of any type of pipe, even corrugated steel, ranging in diameter from 4 inches to 72 inches.

Like most backflow valves, the CheckMate operates on differential pressure. However, unlike most backflow valves, it’s activated with less than 1 inch of head and seals much tighter. In addition to combined sewers, the design also works on sanitary and storm sewer outfalls and manholes.

City Engineer Matthew Newell, PE; Paul; and I called in Tideflex representative Hydro-Kinetics Corp. of St. Louis to discuss how the valve could resolve downtown’s odor issue and how much it would cost. Initial estimates ranged from $40,000 to $60,000.

We devised the following plan: Insert the valve into a new, closed-lid manhole near the library about halfway down the hill where the old brick arch sewer feeds into the 36-inch, reinforced concrete interceptor (see map in slideshow). There’s a manhole with an open grate lid a few feet upstream where we could easily perform sniff-tests to see if the valve was working.

The contractor, Decatur-based Entler Excavating, originally ordered a 36-inch valve for the 8-foot-diameter manhole. But the interceptor pipe was out of round, so Tideflex replaced it with one about an inch smaller.

Total cost of the valve and manhole construction was about $55,000. Budgets are tight and taxpayers are strapped, so this was a fantastic value compared to the alternatives.

Next page: Cuts off odors at the source