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Sandy has formally abandoned its controversial four-year partnership with a technology startup that boldly promised to turn the Utah city's trash into low-emission, low-cost power.

Navitus Sustainable Industries' proposed $100 million South Valley Recycling and Renewable Power Facility has been on the ropes for months, but city officials had granted the company reprieves in the hopes that it could eventually deliver.

Those hopes were buried this month, and the city is now looking to conventional landfilling to solve its municipal-waste challenges.

"Their technology was not coming together and working for us, so we amicably parted ways," said Sandy spokeswoman Nicole Martin.

While the project was billed as the ultimate in green technology, Salt Lake City-area environmentalists feared that the plan would add to Utah's air-quality problems. Navitus' promises seemed "too good to be true," according to Matt Pacenza, HEAL Utah's executive director.

"Sandy residents who were skeptical this startup company with no track record could cleanly turn trash into cheap electricity should feel vindicated," Pacenza said. "Sandy residents should breathe easy today. They no longer need to fear that their backyard will be the testing ground for an unproven technology."

Four years ago, Navitus CEO Heidi Thorn convinced city officials her firm could achieve a dream that would-be innovators have long tried and failed to accomplish. She executed a 20-year contract with the city to build and operate a plant on a 5.5-acre lot that houses Sandy's public works complex at 8775 S. 700 West. The site had been slated to house a solid-waste transfer station.

Navitus planned to use a proprietary technology known as "Tucker Advanced Pyrolysis," which heats waste to between 1,600 and 1,800 degrees and combusts it in the absence of oxygen, producing methane. The gas would fire an on-site electrical generator, whose output would create a back-end revenue stream for the company. The arrangement would save Sandy millions of dollars each year in reduced waste-disposal costs, executives said.

Now the city has returned to the idea of a transfer station and is joining with other cities to dump trash at a landfill under development in neighboring Utah County, Martin said.

Thorn said the length of time required to obtain permits prevented her firm from meeting Sandy's time frame, which hinges on the anticipated closure of the landfill currently accepting its waste. Utah environmental regulators had no experience drafting permits for the proposed new use of pyrolysis.

"We enjoyed our relationship with the city. It's a matter of timing and getting everything to work," Thorn said. "Honestly, the process took quite a bit longer than any of us anticipated."

Based in Salt Lake City, Navitus remains a viable company, but it is looking to developing nations for future business and expects to make some announcements soon, according to Thorn.

"In emerging countries with large populations in concentrated areas, garbage is a matter of life and death. It is appalling to see what is being done to humanity and the environment in these places," she continued. "Being a Utah company, we always had the idea of having a model project here locally, but Sandy needed to be able to take advantage for an opportunity for a long-term solution."

Twitter: @brianmaffly