Urban decay, redefined

City hopes to turn yard clippings and food scraps into heat, electricity

By Andrew Ryan

Globe Staff / February 26, 2008

Fall comes to Boston in fleeting bursts of color, when crimsons and ambers briefly illuminate trees before leaves drop to the ground, turn brown, and decay.

City officials hope to harness some of that ephemeral energy at a novel composting facility that would generate electricity and heat from decomposing yard clippings and food scraps. The process would curtail emissions of a destructive greenhouse gas, produce enough electricity to power up to 1,500 homes, and support a rooftop greenhouse for trees, shrubs, and flowers.

"I think we are looking to do something unique here that's appropriately scaled for an urban environment," said James Hunt, Boston's environmental and energy services chief. "We think it's the first of its kind."

The project, which is still in the early conceptual stage, would take the city's 6,000-ton composting program indoors. For more than a decade, leaves and yard clippings have been collected each spring and fall and trucked to a muddy clearing off American Legion Highway in Roslindale. The undulating mound is almost two stories tall, loaded with tan, brown, and black leaves in various states of decay. On a recent afternoon, white steam gushed from the pile, evidence that microorganisms were hard at work, generating heat that pushes the internal temperature near 130 degrees, said Nora Goldstein, executive editor of BioCycle magazine.

In an enclosed facility, officials would recycle heat and biogas released when leaves, grass clippings, and other organic material decay. Biogas includes methane, which would fuel a turbine, generating up to 1.5 megawatts of power, and carbon dioxide, which would nurture plants in the greenhouse.

"There have been pieces of this that have been done other places, so there isn't as much of a worry that it would fail," said Tom L. Richard, director of the Institutes of Energy and the Environment at Penn State University. "But it is new enough and innovative enough that it would hopefully be an example that other places in the country could follow."

The plan is part of Mayor Thomas M. Menino's vision to transform "Beantown into Greentown" by making the city an urban environmental leader.

Solar panels have been installed on the roofs of three schools and two other city buildings, and $500,000 has been awarded to install photovoltaic panels atop the Franklin Hill housing project in Dorchester.

Six other schools are being studied as locations for wind turbines.

Administration officials caution that this latest green idea is preliminary, and they hope it fares better than Menino's short-lived plan to erect a 150-foot turbine in City Hall Plaza. (A microturbine will be installed this spring on the roof of City Hall as a demonstration project to power a half-dozen computers and desk lamps.)

For the indoor compost facility, the city intends to reach out to green companies in late March to evaluate existing technology and gauge potential. They have not begun to seriously discuss possible locations or estimated how much it will cost.

"The first step for us is looking at the market place, what's out there," Hunt said. "We are going to do a full cost-benefit analysis on this to see whether this makes sense from an environmental perspective, an energy perspective, and from a bottom-line perspective."

Recently at the compost site in Roslindale, a massive yellow front-end loader with a scoop the size of a car took a bite out of the pile, dumping its load into a grinder that spit out cocoa-colored mulch. After a year, it will be black and ready for use in city flowerbeds and community gardens. It is also sold to private gardeners for $22 a yard, Hunt said.

The city's vision is an indoor facility that would accommodate up to 15 trucks a day and nearly quadruple current capacity. The leaves and wood chips would be separated, pulverized, and added to a compost pile that would be tilled and rotated by machines.

The grass and other nitrogen-rich organic waste, which may include food scraps from supermarkets or hotels, would be processed in an anaerobic digester, a machine that decomposes without using oxygen.

It is there that biogas would be captured to create electricity, up to one-third of which would power the greenhouse, grinders, and other machines. The leftover sludge would be used to enrich the leaf and wood chip mix to form an ultrafertile compost in just 90 days.

"There is a savvy to running an integrated system like that," said Richard. "They are more efficient in concept, but they have to be well managed."

The facility could potentially employ up to 25 people, a work force that officials hope would boost the city's image as a destination for environmental leaders.

"This is the ultimate type of green-collar job," said Goldstein, the BioCycle magazine editor.

•graphic Trash that gives back