Coupled Biological and Thermochemical Process for Plastic Waste Conversion Into Biopolymers

Abstract

The aqueous phase produced from the hydrothermal liquefaction (HTL) of three matrices (Plasmix treated with different operative conditions and polystyrene) was subjected to acidogenic fermentation (AF) batch tests to obtain organic acids, which are the ideal substrates for biopolymers (e.g., polyhydroxyalkanoates, PHA) production from mixed microbial cultures (MMC). Parallel tests in the presence of only HTL water fractions or only glucose (an easily biodegradable compound), or in presence of both, were conducted and compared to assess any possible recalcitrant or inhibitory effect of plastic waste from the HTL treatment during the AF process. These tests resulted, within approximately 30 days of operation, in a conversion of 96 ± 21% (COD/COD) of the Plasmix by-products after a 2h thermochemical treatment into organic acids, a 54 ± 7% (COD/COD) of conversion for Plasmix by-products treated 4h, and 29 ± 1% (COD/COD) of conversion in the presence of polystyrene residual water.