The facility manages non-hazardous waste from households and businesses
A council has admitted it is losing up to £1m a year by paying a private company to burn and recycle waste.
Kent County Council (KCC) signed a 25-year contract with Kent Enviropower 10 years ago to provide 320,000 tonnes of waste for the Allington incinerator.
However, the value of recyclable waste has more than doubled in a decade.
A council spokesperson said they were advised at the time that the deal, which has just come into effect, would save them "a lot of money".
Councillor Keith Ferrin, the council's environment spokesperson, said: "At the time it seemed entirely the right thing to do.
"People said it was going to save us a lot of money when the incinerator was built.
"Ten years later it doesn't look like that sort of deal at all."
He said the contractors needed the assurance there would be enough money to build the incinerator and "one thing led to another".
Kent Enviropower manages non-hazardous waste from households and businesses for recycling and incinerating at its site at Allington Quarry, on the outskirts of Maidstone.
Under the terms of the contract, KCC cannot benefit from the additional resale profit for the waste that is recycled.
The estimated £1m a year in lost revenue could have been invested in any of their services, such as education or elderly care, a council spokesperson confirmed.
Enviropower said in a statement: "The facility at Allington is key to reducing Kent's reliance on landfill and is part of an integrated, sustainable and environmentally friendly solution to managing local people's waste."
The price of some recycled materials has doubled, but the council can't benefit from the additional resale profit.
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