Converting multiple hydrophobic aromatic plastic monomers into a single water-soluble substrate to increase bioavailability for the synthesis of polyhydroxyalkanoates by bacteria using batch, fed batch and continuous cultivation

Abstract

We demonstrate the proof of concept of increasing the bioavailability of carbon substrates, derived from plastic waste, for their conversion to the biodegradable polymer polyhydroxyalkanoate [PHA] by bacteria and test various approaches to PHA accumulation through batch, fed batch and continuous culture. Styrene, ethylbenzene, and toluene are produced from the pyrolysis of mixed plastic waste (Kaminsky, 2021; Miandad et al., 2017), but they are volatile and poorly soluble in water making them difficult to work with in aqueous fermentation systems. By chemically converting these aromatic compounds to benzoic acid, and subsequently to its sodium salt, we increased the solubility and reduced the volatility of the substrate supplied to Pseudomonas putida CA-3 to accumulate polyhydroxyalkanoates. 1 L scale batch, fed batch, and continuous fermentations were carried out; the fed batch fermentation resulted in the maximum volumetric PHA productivity of 61.67 ± 7.34 mg L^-1 h^-1; while batch and continuous, at a dilution rate, d = 0.2 h^-1, fermentations resulted in 13.30 ± 0.01 and 4.06 ± 0.01 mg L^-1 h^-1 of PHA respectively.

Keywords: Benzoate; Bioplastics; Bioreactors; Fermentation; Mixed plastics waste upcycling; Polyhydroxyalkanoates; Pseudomonas.