Biotechnological upcycling of plastic waste and other non-conventional feedstocks in a circular economy

[Display omitted] •Non-conventional feedstocks can contribute to a circular chemical industry.•Non-conventional feedstocks open stoichiometric opportunities for niche applications.•Plastic waste as feedstock allows integration of production with end-of-life management.•CO2 as feedstock: challenges remain, opportunities emerge. The envisaged circular economy requires absolute carbon efficiency and in the long run abstinence from fossil feedstocks, and integration of industrial production with end-of-life waste management. Non-conventional feedstocks arising from industrial production and societal consumption such as CO2 and plastic waste may soon enable manufacture of multiple products from simple bulk chemicals to pharmaceuticals using biotechnology. The change to these feedstocks could be faster than expected by many, especially if the true cost, including the carbon footprint of products, is considered. The efficiency of biotechnological processes can be improved through metabolic engineering, which can help fulfill the promises of the Paris agreement.