Plastics make up only 9.5 to 17 percent of each state's municipal solid wastes, yet many plastics are more energy dense than coal. So the more than 85 percent of already used material that goes to the landfill means a lot of energy isn't being harvested. Converting these nonrecycled plastics (NRP) into energy with current technologies could reduce US coal consumption and boost domestic energy reserves, a study by Columbia University's Earth Engineering Center (EEC) says. (You can download a pdf copy here). An added benefit is reducing the carbon footprint of waste management efforts.
Sponsored by the Plastics Division of the American Chemistry Council (ACC), the study quantifies the amount of plastics discarded by each state and how much gets diverted to landfills, materials recovery facilities, or waste-to-energy plants. It also estimates the potential energy value of recovering this material.
The EEC estimates that 28.8 million tons of post-consumer NRP ended up in landfills in 2008. The chemical energy contained in that material is 807 trillion British thermal units, which would require 36.7 million tons of coal to produce. Some conventional thermal treatment technologies for converting plastics to energy are mass burn, refuse-derived fuel (RDF), solid recovered fuel (SRF), gasification, and pyrolysis.
Nonrecycled plastics can be source-separated and converted to crude oil or other types of fuel oil via pyrolysis. Doing this to 28.8 million tons of NRP could create enough fuel oil for 6 million cars in a year. Alternately, the diverted and converted plastics could produce enough electrical power each year for over 5 million homes when used as fuel in specially designed power plants.
"Capturing the energy value of nonrecycled plastics -- and municipal solid waste in general -- makes good sense because it provides a good domestic form of energy while minimizing impacts on the environment," Marco J. Castaldi, a professor at Columbia and associate director of the EEC, said in a press release.
The study's authors conclude that some states already do a pretty good job of diverting plastics from landfills by combining recycling with energy recovery. Those states include Connecticut, Massachusetts, Hawaii, Maine, Virginia, and Minnesota. Their diversion rates range from 65 percent in Connecticut to 32 percent in Minnesota.
Waste management facilities in Asia, Canada, and Europe use several different technologies on a commercial scale to convert nonrecycled plastics into crude oil, as well as into other fuels and electricity. In the US, the study's authors report, processes are being developed to use pyrolysis to turn NRP into synthetic oils. When fully industrialized, these processes may be capable of converting one ton of NRP into three barrels of oil.