A novel sustainable PHA downstream method

Abstract

The pernicious impact of plastic originating from petroleum-based sources has been an increasing threat to our environment. Amongst several strategies tested and implied to manage these plastic wastes, one promising alternative is switching to biodegradable polymers. Polyhydroxyalkanoates (PHAs) are a class of microbial polyesters that are biodegradable, biocompatible and an attractive alternative for future packaging applications. They offer an approach to carbon neutrality and support a more sustainable industrialization. However, as these microbial polymers are stored intracellularly, development of downstream processes for extraction and purification are essential and are the most cost-intensive steps. A major drawback in most of the existing state-of-the-art is the use of harsh organic solvents which contributes to the non-eco-friendliness of the processes. This work proposes an alternative, sustainable PHA downstream process comprising the use of a green solvent. Biomass with an intracellular PHA content of ca. 49% (gPHA/gVSS) produced by mixed cultures was used in this study. A new hydrophobic natural deep eutectic solvent (hydrophobic NADES), Thymol : Vanillin (8 : 2 molar ratio) was synthesised and used as the extraction solvent while 1-heptanol was used as the purification solvent. Also, different intensities of sonication were applied to assist the cell wall rupture for the efficient release of PHAs. The optimised process yielded ∼99% polymer purity and recovery of ∼42% and did not alter the polymer composition. Furthermore, after successful extraction and purification of PHA, the organic solvents (hydrophobic NADES and 1-heptanol) used can be recycled or reused as per end-user requirements.