“We have to handle this waste somehow.”
Meltem Urgun Demirtas
For companies interested in anaerobic digestion, however, producing methane is the goal. Since these facilities are closed, the mixture of methane and carbon dioxide produced by microbes, called biogas, can be captured and purified into biomethane, which can be used as a substitute for natural gas.
Some producers use this biomethane (also called renewable natural gas) or the unrefined biogas on-site, burning it to power their facilities. Some sell it to utilities, so it is injected into existing natural-gas pipelines and used to generate electricity in power plants, or used in homes for heating or cooking.
Overall, anaerobic digestion can benefit the climate, but how much the process reduces emissions will depend heavily on the details, said Troy Hawkins, a researcher at Argonne National Laboratory who studies the environmental impact of energy systems.
Divert works with more than 5,000 retail stores across the US to collect food waste and process it using anaerobic digestion. The company now operates 10 digester sites in the US and uses tracking systems to help understand why some food ends up going to waste in the first place, Begin added.
Anaerobic digester deployment is not cheap: a full-scale facility can cost tens or hundreds of millions of dollars. Designing new facilities can also take time, as most are customized for particular processing tasks. An on-site facility for an ice cream factory can look different from one that receives everything from grocery waste like expired frozen pizza and old apples to used oils in cooking from restaurants, McKiernan said.
More than 11,000 additional sites in the US are ripe for the deployment of anaerobic digesters, from wastewater facilities to food waste sites, according to a 2014 report from US federal agencies. If all the facilities are built, they could generate enough energy to power 3 million homes. The American Biogas Council, an industry trade group, puts the figure at 15,000 sites, which would require about $45 billion to build them all.
It’s not cheap and it’s not easy, but anaerobic digesters will be an important food waste destination in the future, helping to turn one person’s table scraps into another person’s energy.