Recovery of Polyhydroxyalkanoates From Single and Mixed Microbial Cultures: A Review.

Giorgia Pagliano,Cristian Torri,Paola Galletti,Chiara Samorì,Agnese Zaghini

doi:10.3389/fbioe.2021.624021

Abstract

An overview of the main polyhydroxyalkanoates (PHA) recovery methods is here reported, by considering the kind of PHA-producing bacteria (single bacterial strains or mixed microbial cultures) and the chemico-physical characteristics of the extracted polymer (molecular weight and polydispersity index). Several recovery approaches are presented and categorized in two main strategies: PHA recovery with solvents (halogenated solvents, alkanes, alcohols, esters, carbonates and ketones) and PHA recovery by cellular lysis (with oxidants, acid and alkaline compounds, surfactants and enzymes). Comparative evaluations based on the recovery, purity and molecular weight of the recovered polymers as well as on the potential sustainability of the different approaches are here presented.

Highlights

Polyhydroxyalkanoates are a family of bio-polyesters constituted by 3-hydroxy acid monomers and produced by bacterial fermentation as intracellular carbon and energy storage
The application of recoverable and recyclable surfactants can bring an overall improvement of the process, both in terms of economics and environmental footprint; for example, Switchable Anionic Surfactants (SAS) are compounds whose water solubility can be tuned by the addition and removal of CO2 (Samorì et al, 2015b): cellular lysis is accomplished by using the water-soluble form of the surfactant, whereas the recovery of the surfactant in its non-ionic form is achievable by changing the pH of the aqueous solution using CO2
This variegate scenario strictly reflects the variability of bacteria, PHA initial content, PHA type, and recovery methods

Summary

Introduction

Polyhydroxyalkanoates are a family of bio-polyesters constituted by 3-hydroxy acid monomers (e.g., mainly 3-hydroxybutyric acid copolymerized with longer monomers as 3-hydroxyvaleric acid) and produced by bacterial fermentation as intracellular carbon and energy storage. Despite their potential in the scenario of fossil plastic replacement due to thermo-physical properties like petrochemically-derived plastics, PHAs are currently more costly than standard petrochemical plastics (1.18–6.12 €/kg vs.

Objectives

Findings

Conclusion