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December 11, 2013

Sewer plant fix could prevent a disaster

TRAVERSE CITY — An environmental disaster could result if local officials fail to replace at least one of eight filtering membranes at Traverse City’s waste water treatment plant.

So said a consultant who this week urged city and township officials to spend $825,000 to replace membranes in one of eight tanks or face a possible sewage overflow at the treatment plant on the bank of the Boardman River. The plant sits at the end of the sewer line and there is no place for backed-up sewer water to go but onto the ground and possibly the river if membranes clog, said Scott Levesque, Principal Technologist with the engineering firm CH2M HILL.

“I don’t want to sound alarmist ... but there would be catastrophic results,” Levesque said. “Do you want to risk it?”

The membranes are made of hollow fibers so small they filter out bacteria. They have an expected eight- to 10-year life span and were installed in 2004. Despite their age they have not shown any reduction in the ability to filter water, known as permeability.

The membranes could last another two to four years before they start to degrade, Levesque said, possibly because the plant operates at about 50 percent of its design capacity.

But every so often the plant experiences growth of a unique bacteria that clogs all membranes, significantly reducing permeability. Should the bacterial bloom occur at the same time the plant experiences a peak flow, the sewage could overflow.

The bacteria problem began about three years ago and officials for CH2M HILL, which operates the plant, have not been able to diagnose the cause. They’ve also discovered the bacteria is unique. No other similarly designed treatment plants have the same bacteria.

Levesque proposes the city put all new membranes in one tank and spread the old membranes into extra slots in the other seven tanks. Increasing membrane area would increase the system’s ability to handle a peak flow and bacteria bloom simultaneously. It also would allow plant officials to study the impact new membranes have on the bacterial problem.

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