WANTAGH - Nassau is looking to cut costs by selling off three sewage treatment plants to private companies, but critics of the plan say it could end up backfiring on county residents.County Executive Ed Mangano (R-Nassau) says the privatization would raise millions in needed revenue. However, Legislator Dave Dennenberg (D-Merrick) is calling the proposal a one-shot deal that would sell off a valuable county asset. Dennenberg says taxpayers have invested millions in the plants, and selling them off isn't a good deal for residents since it is likely to result in higher sewer rates. Mangano insists there will be safeguards in the contract to address rate increases and protect taxpayers. He says four companies have expressed interest in taking over the county's sewage treatment plants.As with any financial plan in Nassau County, the watchdog agency NIFA will have to approve the privatization plan, and the state Legislature may have to weigh in as well. A decision on whether to go forward with the plan will be made next year.