Comparative evaluation of polyhydroxyalkanoates recovery methods for a mixed microbial culture derived from waste activated sludge

The production of polyhydroxyalkanoates (PHAs) using a mixed microbial culture (MMC) derived from waste activated sludge (WAS) is a promising strategy for converting wastewater treatment plants into biorefinery facilities. Despite many studies on PHA production, the recovery of PHA stored in WAS-derived MMC has received less attention. In this study, we comparatively evaluated three solvent extraction, three cellular digestion, and two mechanical disruption methods to determine their effectiveness in the recovery of PHA from WAS-derived MMC. Chloroform extraction, sodium hydroxide digestion, and ultrasonic disruption were selected as effective candidates in initial screenings, and their processing conditions were optimized. While PHA recovery by the optimized chloroform extraction was 74%, the recovered polymers contained ignorable impurities and had superior molecular properties. In contrast, sodium hydroxide digestion and ultrasonic disruption enabled PHA recovery without loss, but the purity (> 73% and ≥ 80%, respectively) and molecular properties of the recovered polymers required some improvement. Our findings suggest that these PHA recovery methods would be applicable in PHA production using WAS-derived MMC with pre- or post-processing as necessary, though they did not necessarily satisfy all the requirements in PHA production systems.