Anaerobic digestion technology under development for plastic-to-energy systems

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Photo by Sustainable Initiatives Fund Trust A system using anaerobic digestion to turn plastic into energy is being developed

The first systems to use anaerobic digestion technology to turn waste plastics into energy and fertiliser are being developed in South Australia.

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. POET is an acronym for Polymer - Organic - Energy – Treatment. The technology has been developed by David Thompson, who, after years of research and testing, is now at the point of scaling the process up to, as he put it, “where it becomes a positive business model”.

He claims his plastic-to-energy technology has so far successfully been applied to polyethylene, polypropylene, polystyrene and expanded polystyrene.

The anaerobic digestion process varied upon disposal feedstock and depended also upon temperature and system set up, Thompson said. He was careful to add that he had the ability to control the degradation of the plastics - and that the bacteria completely digest the polymers with no toxins or heavy metals.

“The POET system prepares waste plastic in a way that microbial digestion can take place quickly and I think that’s really the key to making it a commercial opportunity,” explained Thompson, who is based in the South Australian capital Adelaide.

“I have already got inquiries from overseas including a large consortium in South America that is really quite interested to get involved and take the technology over there,” he said.

However, the first two POET machines will be built 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 fertiliser, and biogas, which can be separated into methane and carbon dioxide. The methane could then 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 said.

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.

Thompson said his system did not impact on existing recycling practices as it targeted plastics destined for landfill and would add a new revenue stream for companies in the waste industry.

He plans to lodge provisional patent documents for the technology in the coming weeks.

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