The Denver Zoo has halted plans for an innovative biomass gasification system that would have turned animal waste into energy — at least for now.

Zoo officials attributed the decision largely to a question of resources and money. They and prominent supporters acknowledged Friday that the system still faced a significant hurdle: getting the thing to work.

The zoo’s announcement left room for an outside partner to revive the plans by helping with costs and know-how. But officials made clear that the gasification system would not operate on the zoo’s campus, as had been planned.

The decision on the much-heralded green energy system — with the equipment already installed, but not yet tested — came at a curious moment for the zoo.

Its leaders have defended the privately funded plans heartily for months while a small group of vocal, passionate neighbors and activists raised questions about its safety and impact of what they portrayed as an incinerator in the middle of City Park.

The timing of the decision left some suggesting political considerations played a role. Some supporters expressed disappointment.

“I hope the zoo does not give up on the patent or the idea or the technology,” City Councilman Paul Lopez said. “It’s a step in the right direction. It’s a step into the future.”

The zoo’s engineers working on the system had run into concerns about mounting costs and the difficulty of adapting new, untested technology for the zoo’s needs.

“Converting waste into fuel pellets was the most innovative portion of the system and the area we were most complete in finishing,” spokeswoman Tiffany Barnhart told The Denver Post. But turning those pellets into power on site, through gasification, raised technical difficulties that “would take significant effort and financial resources to finalize.”

But the prospect of costly campus changes called for in a recently unveiled master plan raised the main consideration that led zoo officials to make what president and CEO Shannon Block called the difficult decision to pull the plug. She was hired early last year.

The master plan has ambitions of making the zoo the best in the country over the next 15 to 20 years, and she said that will require the zoo to muster all resources available.

Block made the announcement during a news conference Friday morning in front of the equipment near the Toyota Elephant Passage exhibit. Zoo officials did not detail cost estimates to finish the system, other than saying the zoo had invested $3.7 million so far.

Block said her decision came down to focusing on core zoo operations, not any opposition to the plan.

But the zoo spokeswoman’s decisive comment about potential future plans for the gasification system — “It will not operate here at the Denver Zoo,” Barnhart said — certainly put some opponents at ease.

“I’m congratulating them for making the right decision,” said Bridget Walsh, a member of the Citizen’s Exploratory Committee for Health and Safety, and the lead activist. “It takes big people to admit (that) maybe this wasn’t the best thing for the city. There were health concerns for people in Denver and safety issues for the animals.”

Block, though, reaffirmed the zoo’s interest in the technology and said the zoo would look for a partner to “pick up the ball” from the 10-yard line.

“We will take a timeout in order to find the right strategic partner to score the touchdown,” Block said. “We can share what we’ve learned with other industry leaders who can advance the green energy research necessary to respond to the unique challenges that this system presents.”

As for reviving the plan in another form, George Pond, the zoo’s senior vice president of design and campus management, says he has talked preliminarily with potential partners.

Before making the decision, Barnhart said, zoo officials contacted major donors to the project, which was part of the recently improved elephant exhibit. She didn’t identify the donors.

The gasification project had received green lights from the Denver City Council as well as city, state and federal regulators.

Zoo crews have been installing equipment in a building at the back of the zoo near City Park lakes, paths and the boathouse jazz pavilion.

The plant was designed to reduce reliance on coal-fired grid electricity by using waste to light buildings, melt snow on walkways and warm a pool where elephants soak.

In the past, zoo officials said their goal was to make the facility the greenest zoo in the world.

In the “gasifier” system, which the zoo had developed for years, machines installed behind the elephant house would break down dung, wood, plastics and some other waste, turning it to pellets. The system would convert those pellets into a gas that could power a generator, producing electricity and heat.

The zoo planned to stop hauling 1.5 million pounds of waste a year to landfills, saving $8,000 on trucking, and cut grid electricity use by 20 percent.

“It was bold, audacious and probably just didn’t consider the finances and resources that would be extended to this program,” said Councilman Albus Brooks, whose district includes the zoo. “So that’s why they ultimately made the decision. I’m sure some of the political pressure from neighborhoods outside the district had something to do with that.”

But he said he trusted the judgment of zoo leaders.

Larry Ambrose, president of Denver’s Inter-Neighborhood Cooperation coalition, said the zoo’s plan deserved more scrutiny.

“People didn’t understand all the ramifications of this policy,” Ambrose said, though zoo officials cite a series of public meetings. “This is not a zero-waste practice,” Ambrose added. “It still puts tons of pollutants into the atmosphere.”

He signed a letter last month asking Mayor Michael Hancock and the council to conduct hearings on the plan, which has not occurred.

A spokeswoman said Hancock did not weigh in before zoo officials made their latest decision on the energy project.

Staff writer Bruce Finley contributed to this story.