Laccase driven biocatalytic oxidation to reduce polymeric surface hydrophobicity: An effective pre-treatment strategy to enhance biofilm mediated degradation of polyethylene and polycarbonate plastics

Abstract

Plastic pollution is a major global environmental issue due to its structural complexity and poor biodegradability. Biological approaches are appropriate due to cost effectiveness and environmental friendliness, however effective polymer degradation is still in its infancy. As biological treatments are slower than physical and chemical approaches, they could be applied in conjunction with pre-treatment techniques such as photo-oxidation, heat treatment, and chemical treatments. But these processes lead to high energy consumption and hazardous secondary pollution. To address these concerns, an enzymatic pre-treatment strategy has been proposed in this study, with an aim of promoting surface oxidation on the plastics leading to improved hydrophilicity. This in turn, facilitates the surface attachment of microbes, ultimately, accelerating biodegradation. Scanning Electron Microscopy (SEM) and Fourier Transform Infrared (FT-IR) spectroscopy analyses confirmed the surface oxidation of the polyethylene (PE) and polycarbonate (PC) plastics mediated by the action of laccase enzyme. Contact angle measurement witnessed the increased hydrophilicity of the treated plastics. Following, a potential biofilm forming microbial consortium has been employed for the biodegradation of enzyme treated plastics. SEM analysis indicated the increased formation of corrosive pits and surface aberrations on the enzymatically pre-treated plastics and Confocal Laser Scanning microscopy (CLSM) analysis exhibited the enhanced biofilm formation and exopolysaccharide deposition on the pre-treated PE and PC. In addition, X-ray photoelectron spectroscopy (XPS) revealed the reduction in the elemental composition of carbon with an increment in the oxygen composition of plastics. Gel permeation chromatography (GPC) further confirmed the greater reduction in the molecular weights of the plastics subjected to integrated enzymatic and biofilm treatment than only biofilm treated plastics. This is the first report on the integration of enzymatic pre-treatment with the biofilm mediated microbial degradation to achieve enhanced treatment of plastics which demonstrated to be a promising technology for the effective mitigation of plastic pollution.