As the Metro Council considers where to send the region’s garbage starting in 2020, refuse-derived fuel, or RDF, is one method that may be considered.
"Refuse derived fuel is a method of sorting and processing the garbage," said Marco Castaldi, associate professor in the chemical engineering department at The City College of New York / City University of New York.
"RDF is nothing really special in the sense that there is some magical process," Castaldi said. "There are two targets: One, let's process waste to produce a specific quality of refuse derived fuel, or two, let's process the waste to pull out as many reusables as we can."
Castaldi explained that refuse-derived fuel is usually a more consistent and homogenous fuel because the trash is so well sorted and then chopped and shredded to make a fluff or pellets. The more homogeneous the fuel, the better it can work for thermal processes like gasification, he said.
Bruce Howie, practice director for energy from waste consulting and vice president at HDR, Inc., said there are approximately 12 existing refuse-derived fuel facilities in the United States. Most were built in the 1980s when there was a big effort to come up with coal substitutes.
"There is a lot of interest right now in mixed waste processing and that's what RDF is," Howie said. "There is a big benefit for communities not yet doing curbside recycling because you can just dump everything in the trash and it will get sorted. There is also a benefit for cities like Portland that are already separating the waste because mixed waste processing captures even more of those other recyclables that are not finding their way into the recycling bin."
Howie said that since the sorting and shredding of trash has to happen to create the refuse-derived fuel and the pellets or fluff then have to go through another process before becoming energy, making a facility to create refuse-derived fuel is often cost prohibitive.
"The struggle with RDF is always economic," he said. "It costs quite a bit of money to put the equipment in place and to maintain it."
Castaldi said he agrees that the price of refuse-derived fuel is the real barrier.
Castaldi explained that while pulling more recyclables out of the waste stream before combustion may have a positive environmental impact, including them in the trash that is combusted is easier and less expensive. The same goes for other processes like gasification.
"The combustion places I have spoken with are very reluctant to work with RDF sorting and shredding equipment because of the high cost," he said.