LEWISTON — Bids for a new solid waste treatment system at the Lincoln Street headquarters of the Lewiston-Auburn Water Pollution Control Authority were lower than expected.

Superintendent Mac Richardson said the authority’s board of directors must decide whether it wants to include a methane-burning electricity generator in the project now, or wait.

“We have the money to do it now,” he said. “But, we might qualify for grants if we wait. That’s the question the board will have to grapple with next.”

Methuen Construction of Salem, N.H., submitted the low bid, saying it would build the solid waste digester and methane-burning electricity generator for $11.96 million.

Richardson said the most recent estimates placed the work at $13.3 million.

The new facility’s job will be to reduce the amount of solids the water treatment plant has to deal with. It does that by using anaerobic micro-organisms and heat to digest the solid materials left behind by sewage treatment, reducing that solid waste volume by 40 percent. Right now, those materials are composted, used to fertilize farms and sent to landfills.

The process creates methane gas as a byproduct. That methane can be burned to generate up to 150 kilowatts of electricity per month, enough to save about $15,000 to $20,000 per month.

The project is being paid with a 1 percent loan from a state Revolving Loan Fund that includes a bonus 5.96 percent forgiveness on the principal. That translates into a $900,000 savings for the project on the financing alone.

Delaying the methane-burning generators would reduce the overall cost of the project by another $817,000.

“The way the bid was set up, we can put that part aside for 120 days and still come back and get the same price,” Richardson said.

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