Accelerating biodegradation efficiency of low-density polyethylene and its hazardous dissolved organic matter using unexplored polyolefin-respiring bacteria: New insights on degradation characterization, biomolecule influence and biotransformation pathways

Abstract

The COVID-19 outbreak has significantly increased low-density polyethylene (LDPE) waste in landfills, posing new environmental risks due to the release of hazardous dissolved organic matter (DOM). Current LDPE degradation technologies are inadequate and are restricted by a limited understanding of the biotransformation pathway. This study aims to accelerate the biodegradability of LDPE and DOM using Morganella morganii PQ533186 isolated from LDPE-laden municipal landfill. The in-vitro LDPE biodegradation demonstrated a 42.18% weight loss within 120 days. The accelerated biodegradability of LDPE by M. morganii is attributed to the concurrent production of biocatalysts and bio-amphiphiles, coupled with effective bacterial colonization on LDPE surfaces. The FT-IR analysis reveals oxidation with enhancement in O-H (11.29-folds), C=O (17.65-folds), C=C (6.70-folds), C-O (8.51-folds), and C-O-C (6.37-folds) indices. The DSC and XRD analyses divulge reduced crystallinity (33.57%) and increased interplanar d-spacing of (110) and (200) reflections from 4.09 and 3.71 Å to 4.17 and 3.80 Å, respectively. The Raman, XPS, TG-DTG, and Contact-angle measurements demonstrate reduced density, carbon content, thermal stability, and hydrophobicity. The degradation was confirmed using ¹H NMR, GC-MS, and Py/GC-MS analyses. Furthermore, DOM released from LDPE biodegradation, comprising monomers and additives was biodegraded with an 84.61% COD reduction within 6 days. The mechanistic investigation elucidated a two-stage oxidoreductase and hydrolase-mediated LDPE biotransformation pathway involving biocatalytic oxidation and DOM release. Subsequently, the released DOM undergoes terminal biocatalytic oxidation, yielding simpler non-toxic end products. The present study is the first report to present novel insights into the degradation characterization, pivotal contribution of biomolecules, and in-depth biotransformation pathways which are responsible for the accelerated degradation of both LDPE and hazardous DOM.