Polyethylene plastics are a major source of industrial and household wastes, the majority of which end up in the environment or in landfills. These wastes pose challenges for microbial biodegradation due to their polymeric structure. There is a critical need for a process that aids in the breakdown and reuse of plastic compounds. Pyrolysis of high-density polyethylene (HDPE) has previously been used to induce chemical changes in plastic compounds, resulting in more structurally simplistic compounds. Here, we demonstrate the ability of pyrolysis to produce microbially biodegradable intermediate compounds. Biodegradation of pyrolysis-treated plastics has not previously been demonstrated. We found that enrichment cultures derived from six different environmental inocula were able to achieve extensive biodegradation of polyethylene pyrolysis products over the course of 5 days. We verified the biodegradation by quantifying residual compound concentrations of alkenes using gas chromatography/mass spectrometry (GC/MS). 16S rRNA gene amplicon sequencing results demonstrated that the most dominant taxa in the microbial community belonged to the phylum Proteobacteria. Many organisms in this phylum have previously been shown to metabolize hydrocarbons. Our results indicate that the coupling of chemical and biological processes can speed up the breakdown and conversion of polyethylene to bacterial biomass by microbial consortia.

Plastic pollution is one of the biggest environmental problems that the world is currently facing. Pyrolysis is a frontier technique aimed at converting plastic waste back into virgin-quality resin. However, the transfer of the waste plastic feed into the pyrolysis reactor must be optimized before the process can be upscaled to a continuous process. In this study, a new solvent that reduces the viscosity of molten plastic was introduced and characterized. The results revealed that the polymers are soluble in the ratio of up to 75 wt % plastic and 25 wt % solvent at 240 °C. The viscosity of pure low-density polyethylene (LDPE), high-density polyethylene (HDPE), and polypropylene (PP) in the solvent was measured in different weight percentages of polymer in solvent (30–80 wt %) and at 160, 180, 200, 220, 240, and 260 °C. The viscosity decreased with the decreasing polymer-weight percentage and with increasing temperature. The viscosity of LDPE/solvent and PP_s(isotactic)/solvent is much lower than for HDPE/solvent and PP_p(polypropylene impact copolymer)/solvent. Differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) were applied to characterize the thermal behavior of LDPE, HDPE, and PP in the solvent in three different weight percentages (25, 50, and 75 wt %). The DSC results indicate that in the mixture of PP_s/solvent and LDPE/solvent the melting point of PP and LDPE decreases as the amount of solvent increases. Overall, these results indicate that the selected solvent is an effective agent to prepare waste plastics for pyrolysis.