Cote Crane and Rigging workers insert a bearing Tuesday within one of five new rotating biological contacts installed at the Gardiner Wastewater Treatment. Andy Molloy/Kennebec Journal

GARDINER — The $3.5 million project to upgrade Gardiner’s waste water treatment plant that has been several years in the making is now underway and is expected to be substantially complete by the end of the year.

Once they are online, Doug Clark, the city’s director of wastewater treatment, said the new equipment will be more energy efficient and bring about savings on the city’s energy bill.

“The scary stuff is done,” Clark said earlier this week in an update to the Gardiner City Council.

As part of the project to replace the treatment plant’s rotating biological contacts, contractors had to remove the outer wall at the north end of the plant to take out the old trains of RBCs with the help of a gantry crane and install the new ones.

The first train, made up of five units of discs on which microorganisms grow that help break down the solids collected at the treatment plant, has been installed and is expected to be up-and-running next month, growing microorganisms to treat the sewage.

Once that’s done, Clark said, the second train will be installed.


“They are 12 feet in diameter and they weigh 20,000 pounds each,” said Dan Marks, an environmental engineer with the Hoyle, Tanner and Associates, the city’s consultant on wastewater projects.

Marks said city officials bought the RBCs directly, rather than relying on a contractor to procure them and as they were being fabricated, the details of the exchange were completed.

“They don’t just come off the shelf,” he said. “They take about six to eight months to complete.”

The RBCs being replaced were powered with compressed air that blew up from underneath to catch air to rotate them. They would lose efficiency when the air cups broke off.

The new RBCs are an improved design, using a mechanical drive and are better supported. Because they are more energy efficient, Clark said the treatment plant’s electric bill, currently around $100,000, is expected to drop.

City officials started working on the project after some RBCs stopped spinning during the winter season, prompting attention from the state Department of Environmental Design.

The project is funded through a $3 million loan and a $500,000 grant from the U.S. Department of Agriculture Rural Development. They are anticipated to last for 20 to 25 years.

Clark said that one of the trains being replaced was installed in 1998, and the other was replaced in the early 2000s. When that was done, contractors used a rolling door in the wall to remove the old RBCs and bring in the new ones in parts. That process, he said, was time-consuming.

Once the installation is complete, a new wall will be built out of wood to enclose the plant.

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