Isolation of Biopolymer Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) via Aqueous Two-Phase Systems (ATPS): Towards Optimisation of Green Purification Procedures

The development of bioplastics, such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), as sustainable alternatives to petroleum-based plastics, requires efforts to reduce their economic and environmental impacts. Aqueous Two-Phase System (ATPS) represents a sustainable alternative to isolate PHBV, as it is water-based. A polyethylene glycol (PEG8000)/phosphate salts-based ATPS was employed as a sustainable approach to isolate and purify PHBV produced by the haloarchaeon Haloferax mediterranei. The Taguchi design method was used to optimise an ATPS, integrating variables such as the concentration of commercial PEG8000 and phosphate salts, extraction temperature, system pH, and biomass-to-system volume ratio. Results revealed a maximum PHBV recovery of 80% with a purity of 93% under the following conditions: 20% of PEG8000, 20% of phosphate salts, pH of 7, 50 °C, and a 1:100 ratio. Furthermore, the potential recycling of ATPS components was studied to reduce the overall cost of the biopolymer isolation procedure. However, a significant decrease in the PHBV recovery was observed (52% when using recycled components). Finally, the use of PEG8000 from ethylene glycol (EG) polymerisation, aimed at the valorisation of EG obtained from other industrial processes, yielded comparable recovery and purity of PHBV (78% and 89%, respectively).