Take plastic waste and burn it at super-heated temperatures without any oxygen. Then take the resulting gas and burn it with oxidants to generate heat and steam. The steam can be used to generate electric power.
That's basically the idea behind a setup devised by students at Northeastern University. Their waste combustor breaks down non-biodegradable plastics to create an alternative source of fuel.
Their prototype was featured at the fifth annual MIT Energy Conference this past March. The team worked for nine months on the research, which, for the undergraduates, was their senior capstone project.
Northeastern recently put out a press release describing the effort in a bit more detail: