An environmentally sustainable extraction protocol for polyhydroxyalkanoates from mixed culture biomass

Polyhydroxyalkanoates (PHA) have recently been established as one of the main biopolymer alternatives to conventional petroleum-based plastic materials. Still, despite being easily produced, PHA extraction from sewage sludge has yet to be improved. The lack of an environmentally friendly and efficient extraction protocol is one of the main challenges hampering the spread of the process. In this context, this study presents promising results for a new extraction procedure of PHA using bio-based organic solvents for non-PHA cell mass (NPCM). PHA-rich sewage biomass was produced by adopting aerobic dynamic feeding as an enrichment strategy and controlled pulsate-feeding, automatically performed by homemade software adopting synthetic wastewater and real fermented sludge liquid. Extraction results highlighted the high efficiency of the bio-based solvents such as 2-methyl tetrahydrofuran (2-MeTHF), glycerol, glycerol formal and ethyl lactate. Especially, the adoption of 2-MeTHF resulted in higher PHA recovery yield (78.3 ± 11.9%) and similar purity (93.2 ± 2.4%) than chloroform (71.6 ± 14.5% and 96.1 ± 1.3%, respectively), known to be one of the best solvents to extract PHA. Furthermore, contrary to all the other solvents tested, 2-MeTHF showed good efficiency even without pre-treating the biomass sample with NaClO, allowing a one-step extraction process that reduces the process cost. Around 96% of 2-MeTHF was successfully recovered at the end of the extraction, showing similar purity compared to the commercial one. PHA thermal analysis showed that the polymer obtained had properties in line with commercial polymers. The overall protocol indicates a promising and consistent environmentally friendly procedure to recover PHA from sewage sludge biomass. • Bio-based solvents were successfully tested to recover PHA from sewage sludge • 2-methyl tetrahydrofuran showed higher efficiencies than chloroform • 2-methyl tetrahydrofuran extraction did not require biomass pretreatments • 2-methyl tetrahydrofuran achieved around 78% recovery and 93% purity on average • 96% of 2-methyl tetrahydrofuran used was successfully recovered after extraction