Thermochemical and Chemo-biological Molecular Recycling of Plastic Waste and Plastic-Biomass Waste Mixtures: An Updated Revision

Abstract

Massive amounts of plastic and biomass waste is mismanaged worldwide, causing detrimental consequences to the human health and the environment. In fact, the disposal of residues through landfill without further processing and burning for household heating and cooking are common practices. Thermochemical processing such as pyrolysis, chemical depolymerization and bioprocessing, prove feasible for recovering valuable building block molecules from plastic residues. The main goal of pyrolysis is to obtain aliphatic hydrocarbons useful as fuel, while chemical processing conducts to constitutive molecules of the plastic (i.e., monomers and polyols) able to be repolymerized and reinserted in the market. On the other hand, the bioprocessing of plastic waste requires prior chemical depolymerization in order to unleash the building blocks. Chemo-enzymatic treatment of waste plastic-biomass mixtures is an open challenge due to the diverse composition of the residues, along with the presence of additives and contaminants. The few reports found in the literature regarding the bioprocessing of plastic residues with lignocellulosic biomass and paper, indicate that a chemical pretreatment cannot be avoided and that some substances present in the residues can act as fermentation inhibitors that affect waste bioprocessing.