Mayor Michael Bloomberg wants to turn trash into energy — at least a little bit. The city collects more than three million tons of waste a year from residences and institutions, and the administration has proposed a pilot project to convert some of that into electricity.

But both the location and the technology are "To Be Determined." The city is currently soliciting proposals, and if a project gets off the ground, it could take years to develop.

Last week, City Hall altered one attention-grabbing part of its Request for Proposals: it’s no longer offering Fresh Kills as a possible site for a “Waste-to-Energy” plant, following an outcry by residents of Staten Island, elected officials and environmentalists.

City Council Speaker Christine Quinn praised the withdrawal, saying a plant would “a step backwards towards the bad old days of Fresh Kills Landfill.”  Her rival candidate to succeed Mayor Bloomberg, Public Advocate Bill DeBlasio, said “It is a tremendous relief that Staten Islanders no longer face the prospect of an experimental waste-to-energy plant at Fresh Kills.”

But Nickolas Themelis, director of Columbia University’s Earth Engineering Center, said politicians and environmentalists are using an out-of-date caricature of waste-to-energy technology.

“They’re describing the plants in the 1980s,” Themelis said. He explained tighter standards by the U.S. Environmental Protection Agency and improved technology have greatly reduced toxic emissions — for instance, from 80 tons of mercury a year nationwide to one ton.

The request for proposals specifically excludes "conventional incineration" or "mass burn" methods.

Themelis said “combustion is combustion,” but there are significant ways of mitigating what gets into the air. One technique in widespread use is to inject activated carbon dust to capture heavy metals.

Nick Dmytryszyn, an environmental engineer for Staten Island Borough President James Molinaro, said the city needs to consider all options technologically — but not geographically.

“We’re in favor of the concept. What is there to fear, if it's a modest pilot project that meets environmental clean air criteria and is made with private money?” Dmytryszyn said. “But why single out Fresh Kills, instead of just saying ‘any properly zoned public or private land?’ With Fresh Kills, they’re just opening old wounds, and it’s totally unnecessary.”