Pyrolysis-Aided Microbial Biodegradation of High-Density Polyethylene Plastic by Environmental Inocula Enrichment Cultures

Abstract

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.