TRAVERSE CITY — City commissioners agreed to a recommended $825,000 membrane filter replacement at the city’s sewage treatment plant, but aren’t yet sold on a rate hike to pay for it.
Commissioners debated the economics of replacing an existing bank of filter membranes with a newer, more expensive model during a Monday meeting. Commissioner Jim Carruthers opposed the plan. Commissioners Tim Werner and Ross Richardson also questioned the need to upgrade from C model membranes to newer D models, but said in the end the price difference of $50,000 didn’t justify going against the experts’ recommendation.
“I’m not sure exactly why we are being pushed into the Ds, but for the small variance of money I’m not going to argue the point,” Richardson said.
The treatment plant is equipped with eight tanks that hold multiple cartridges of filtering membranes that are close to the projected end of their useful life, but could last another four or five years. Occasionally, the filters clog with a bacteria unique to the plant. Officials from plant operator CH2M Hill suspect the problem stems from the plant’s unique biology, but don’t know if membrane age is a contributing factor.
Operators are concerned that if the bacteria clogging occurs during a time of peak flows, sewage will back up and overflow into the surrounding area that includes Boardman Lake and Boardman River.
Plant operators want to replace the membranes in one tank with the newer membranes that have both operational efficiencies and a longer lifespan. The existing membranes would be installed in open slots in the remaining tanks, creating a larger filtering area and reducing the likelihood of an overflow.
The membrane manufacturing company also put the city on notice it plans to discontinue production of the C model within three years, so the city will have no choice but to install the newer models in the remaining tanks.