Generating Energy out of Waste Plastic
Anaerobic Digestion Process
More than one million tonnes of contaminated plastic deemed unfit for recycling is sent to landfill in Australia each year. In the United States the figure is almost 10 million tonnes. The first systems to use anaerobic digestion technology to turn waste plastics into energy and fertiliser are being developed in South Australia.
Inventor David Thompson of Poet Systems, Adelaide, Australia, has developed a plastic-to-energy technology prepares waste plastic in a way that microbial digestion can take place quickly. The anaerobic digestion process varies upon disposal feedstock and depends also upon temperature and system set up. Thompson says his technology has so far successfully been applied to polyethylene, polypropylene, polystyrene and expanded polystyrene.
Poet Systems expects to have its first two machines – each capable of processing 20 tonnes of plastic a week – operating commercially in about 12 months. They will be installed at wastewater treatment plants in regional areas of the Australian state of Victoria. The same microbes will treat the plastic and the water simultaneously. The microbes then die and leave behind liquid and solid biomass, which can be used as fertilizer, and biogas, which can be separated into methane and carbon dioxide. Thompson says the methane could be used to create heat and energy, possibly to power the wastewater plant, while there was also potential for the carbon dioxide to be captured and reused. “So basically the plastics go into an anaerobic situation in wastewater where the microbes digest the plastic and create energy,” he says.
Thompson plans to lodge provisional patent documents for the technology in the coming weeks. He says the system does not impact on existing recycling practices as it targets plastics destined for landfill and would add a new revenue stream for companies in the waste industry.