PORTLAND — U.S. companies build some of the best-operating waste-to-energy plants in the world, an expert in the industry said Monday, but they will have to cut construction costs drastically to rival the growth that’s happening in other countries.

That’s especially true as low natural-gas prices make electricity cheaper and erode the revenue that waste plants count on to limit disposal fees, said Mark Weidman, president of Wheelabrator Technologies Inc.

If energy prices stay low, he said, “we’re not going to build a lot more plants in the United States than we are building today.”

Weidman’s comments came during the 20th annual North American Waste-to-Energy Conference, which began Monday at the Holiday Inn by the Bay. The three-day event drew more than 300 people, some of whom will tour ecomaine’s waste-to-energy plant in Portland on Wednesday.

In opening comments by Kevin Roche, ecomaine’s general manager, the plant was held up as an example of how to integrate aggressive recycling into the waste-to-energy process. In addition to the plant, ecomaine operates a large recycling program and an ash landfill.

The U.S. has 87 waste-to-energy plants, most of which were built in the 1980s and 1990s. After years of losing out to lower-priced disposal at landfills, the American waste-to-energy industry is growing again, especially overseas.

But, Weidman said, a giant plant in China that can burn 3,000 tons of trash a day is being built by Wheelabrator for roughly one-quarter the cost of a similar, $700 million plant that’s going up in Palm Beach County, Fla.

The cost and operation of waste-to-energy plants is of special interest in Maine, where four plants burned 856,941 tons in 2010, disposing of 35 percent of the trash from the state’s cities and towns.

Maine ranks second in the country, behind Connecticut, in the percentage of trash handled by waste-to-energy plants. But a plant in southern Maine has generated years of negative headlines about truck traffic, noise and odor. Biddeford is trying to close the downtown Maine Energy Recovery Co. plant and direct trash elsewhere.

Waste-to-energy has broad-based opposition, as well. The Sierra Club, for instance, which has a chapter in Maine, generally opposes using the technology for municipal waste.

Local opposition can be a challenge, Weidman said, but well-run plants make good neighbors. In Europe, where the technology was born, green-leaning cities like Vienna, Austria, and Zurich, Switzerland, send two-thirds of their trash to waste-to-energy plants.

Recycling and waste-to-energy co-exist in Europe through a waste management priority list similar to Maine’s. It favors reducing and recycling waste over burning for energy. Landfills come last.

In China, migration to the cities is driving the need for 302 new waste-to-energy plants by 2015. Working through a joint venture, Wheelabrator has three plants running in China and five being built.

Wheelabrator is based in Hampton, N.H. It’s a subsidiary of Waste Management Inc., which operates a commercial landfill in Norridgewock but has a goal of doubling trash-based power output by 2020.

In the U.S., stable diesel fuel prices make it economical for large cities to truck and rail their trash hundreds of miles to remote landfills. The waste-to-energy industry is hoping that today’s high fuel prices will endure, and make that option less attractive. Five waste plants have expanded in recent years, and four new ones are being built.

To grow at a faster pace, Weidman said, the industry should consider modular designs that lower construction costs, and scaled-down facilities for smaller communities. Another way to improve economics while gaining public support, he said, is through “eco-energy parks,” which combine recycling, composting and energy production with industrial customers that can use the heat and power.

Ecomaine is trying to recycle more materials from the 44 communities it serves. That frees up capacity to solicit burnable waste from other sources, Roche said. In the past decade, waste from ecomaine’s 21 owner communities has gone down by 28 percent, but overall tons are up 14 percent. That’s important, because with electricity revenue down by half over the past three years, the plant needs to keep up waste volumes to run at full capacity.

Ecomaine is considering a composting program for food waste, which doesn’t burn well.

Staff Writer Tux Turkel can be contacted at 791-6462 or at: [email protected]