Still, the Portland metropolitan area generates more than a million tons of garbage per year. That garbage has to go somewhere, and it is Metro’s responsibility to manage it in a way that protects the environment, protects people’s health, and gets good value for the public’s money.
As the Metro Council considers where to send the region’s garbage starting in 2020, landfills remain the most readily available, and likely the least expensive, option for getting rid of trash. But there will be other methods on the table. One method the Metro Council may consider is anaerobic digestion of organic waste.
Anaerobic digestion is already being used in the Portland area for food waste from businesses, like restaurants and grocery stores, and industrial sources, such as food packaging plants. Food waste that's anaerobically digested is processed in a contained, oxygen-free environment.
The breakdown of the food produces a methane-rich gas (biogas) that can be converted to electricity. The material remaining after processing can be used as fertilizer or further processed into compost.
As of the most recent study in 2009, 18.1 percent of Portland metro's solid waste sent to landfills is food waste. If the Metro Council opted to employ anaerobic digestion as part of the plan for handling garbage, it is that 18.1 percent that would be addressed.
“What is critical to know is that AD would never be the solution to all the problems,” said Jacques Franco, science and policy fellow for the University of California at Davis Policy Institute for Energy, Environment and the Economy. “Anaerobic digestion would be a piece of the solution.”
Like Franco, Joerg Blischke, director of project engineering for Zero Waste Energy, said he views anaerobic digestion as part of the bigger picture.
Zero Waste Energy runs an anaerobic digestion facility in San Jose.
Blischke said the facility accepts trash from businesses, which is then sorted and the part that is organic or likely organic is put into large garage-type rooms that are sealed off for 18 to 21 days. During that time, all the gas emitted is captured and the volume is reduced by about 30 percent. Afterward, the remaining material in the digester is goes through a composting process.
"The overall intent is to reduce the amount of reuseables in a landfill site," Blishke said. "But also to make sure what is put into the landfill is very stable so the landfill won't produce methane gas. "
Blischke, who grew up in Germany, said there was a very elaborate system in place in his home country.
"I think the overall goal should be to dispose of as little as possible," he said. "In order to get to that point, there will be multiple approaches and anaerobic digestion is one tool in the toolbox."
Franco said it will be interesting to see what Metro Council and Portland voters will choose to do about solid waste.
“It definitely would cost more to use anaerobic digestion than it would to send the trash straight to a landfill." Franco said. "The question is what is the willingness of the public to pay a bit more to have a more environmental collection system.”