If Palo Alto is willing to risk building and operating a composting facility on future parkland, it could save millions of dollars that otherwise would be spent hauling food scraps and yard trimmings elsewhere, according to a newly updated study.

An anaerobic digestion facility could cost as low as $58.6 million over a 20-year period if operated by the city, says the study by Alternative Resources Inc., a Concord, Mass.-based consultant. In contrast, trucking organic waste to composting facilities in San Jose and Gilroy would cost between $77.5 million and $139.5 million over the same period.

But the consultant recommends that the city take a less-risky approach — albeit a more expensive one — by enlisting a private company to finance, build and operate the facility.

Former mayor Peter Drekmeier, an outspoken advocate of building the composting facility in Palo Alto, said the consultant’s cost estimates support his contention that a home-based operation is the way to go.

“It’s an issue of risk and reward,” Drekmeier said.

Former council member Emily Renzel immediately questioned the accuracy of the study’s cost estimates.

“They’re putting out their most optimistic figures,” said Renzel, who opposes using the city’s current landfill for anything but a park. “In the end it’ll be much more costly than whatever is shown.”

In November, city residents will vote on a ballot measure that seeks to set aside 10 acres of the 126-acre Palo Alto landfill for an anaerobic digestion composting facility, which would use microorganisms to break down yard trimmings, food waste and sewage sludge in a closed container.

The landfill is scheduled to close July 1 and open in phases as parkland added to Byxbee Park over the next two years.

Drekmeier and a group called the Palo Alto Green Energy and Compost Initiative collected 5,128 certified signatures to qualify the ballot measure in March — 772 more than needed.

After two years of debate about what to do with the city’s compost when the landfill closes, the council voted in April 2010 to hire consultants to conduct a $250,000 feasibility study comparing alternatives. On Monday, the council is scheduled to discuss the latest version of that study, after some initial findings were discussed by the council in March.

Alternative Resources Inc. analyzed a wide variety of scenarios and concluded an anaerobic digestion facility built at the landfill next to the water treatment plant could range from about $58.6 million to $294.3 million over 20 years. The estimates vary according to whether grants and loans are used and whether the composting facility would be built by the city or by a private company.

Drekmeier said his group will push for the lowest-cost, $58.6 million option for an anaerobic digestion facility owned and financed by the city.

In recommending that the city instead consider selecting a private company to finance, build and operate the facility, the consultant explains: “To put on and train staff to operate and maintain a complex waste management facility, such as an (anaerobic digestion facility), may not be an easy undertaking.”

Former council member Enid Pearson, who along with Renzel opposes a local composting project, said the technology is experimental and “there are all kinds of things that can go wrong and undoubtedly will go wrong.”

She and Renzel said a huge amount of garbage would have to be excavated from the landfill to make space for the compost facility. The area has been designated to become parkland since the adoption of the city’s Baylands Master Plan in 1978.

“It’s really horrendous,” Renzel said. “It’s just total disrespect for the park and the long history of trying to get that designed and built.”

Email Diana Samuels at dsamuels@dailynewsgroup.com.