Enhancing biodegradation of polyolefins and real mixed plastic waste by combination of pretreatment and mixed microbial consortia

Polyolefins (PO)1 are the most common consumer plastics, constituting about half of plastic waste. This work investigated the process combining physicochemical pretreatment and PO-enriched mixed microbial consortia (MMCs) on biodegrading European real mixed plastic waste. The MMCs, acclimatized on PO powders, were enriched with strains that could use PO, primarily dominated by the genus Rhodanobacter. Several pretreatment methods were investigated on pure polyethylene (PE) and polypropylene (PP). UVC combined with Fenton's reagent was found to be the best pretreatment process for pure PO, increasing the total oxidative indices of PE and PP by 135 and 21 times, respectively, and decrease the total crystallinity of PP by 2.3 times (but not PE), compared to the untreated ones. Maximum 7.7% and 16.3% weight reductions were achieved after MMCs biodegradation of UVC-Fenton-treated PE and PP powders (80 μm), with a 4.3- and 27.2-times improvement from the untreated ones. Selected pretreatments and MMCs were then applied to real mixed plastic waste and post-consumer multilayers from 10 different streams. The highest weight reductions after 30-days biodegradation were obtained using mixed plastic reject from a biogas plant (MW2) followed by the unrecyclable mixed plastic waste from a Danish municipality (MW1), with a reduction of 36.8% and 30.0% using radio frequency (RF) oxygen plasma pretreatment, respectively. Integration of ultrasonic irradiation with atmospheric pressure plasma treatment increased the biodegradation of MW1 to 39.4%. This study addressed the bottleneck of slow biodegradation of recalcitrant plastics, laying down the basis for future development of biotechnological recycling of unrecyclable plastic fractions.