LEWISTON — A methane-burning electricity generator is not guaranteed to be part of a proposed sewage treatment plant, according to officials.

Members of the Lewiston-Auburn Water Pollution Control Authority are scheduled to vote next week on designs for an anaerobic digester plant that would be built alongside the current treatment facility.

The proposed plant’s most important job would be to reduce the amount of sewage solids by digesting them slowly, Superintendent Mac Richardson said.

The authority currently makes compost out of half of the bio-solid waste it treats, and distributes about one-quarter to Maine farms. The rest must be trucked to landfills, where the authority pays tipping fees to dispose of it.

“So reducing the amount of solids is the most important thing,” Richardson said. “It’s the part that’s going to save us the most money.”

The digestion process also creates methane, and the new facility could be designed to include a methane-fueled electricity-generator. If built, that generator could create enough electricity to power the rest of the plant.

“Generating electricity is the most popular part,” Richardson said. “It’s what people hear when we talk about this, but it’s not the biggest cost saver. That remains reducing the biosolids. “

The authority’s board is scheduled to vote on whether to proceed with bids at a special 7 p.m. meeting at Lewiston City Hall. Richardson said he’s recommending the board design the entire system, with the digester and the methane-burner included.

“But when we go out to bid, we would do the co-generator as an alternate,” he said. Contractors could submit a bid for building the entire facility, then a second bid with the methane-burner removed.

“It all depends on how the bid price comes in,”  said Phil Nadeau, chairman of the authority’s board. The current estimate calls for spending $16.6 million to build the plant.

“But the bids would really determine what we’d be able to do,” Nadeau said. “We’ve been surprised in the past at bids coming in lower than we expected and we don’t know if that can be replicated now. Then again, we’ve been surprised at bids coming higher than expected, too. We’ll have to see.”

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