Activated Sludge for Aerobic Polyhydroxyalkanoate (PHA) Production with Acetate Supplement
Polyhydroxyalkanoates (PHAs) are promising biodegradable alternatives to conventional plastics due to their biodegradability and biocompatibility. This study aimed to determine the optimal operational mode for high-content PHA production using acetate-enriched activated sludge and to identify the key microbial populations responsible for efficient PHA synthesis, addressing the feasibility of scaling up sludge-based PHA production. Activated sludge collected from a local full-scale wastewater treatment plant was acclimated under fully aerobic conditions to enrich PHA-accumulating microorganisms. Acetate was supplied as a low-cost carbon source. Laboratory-scale fermentation experiments (n = 5) were conducted to compare fully aerobic operation with conventional feast and famine strategies. PHA accumulation was quantified, and microbial community composition was analyzed using shotgun metagenomic sequencing. Fully aerobic conditions with acetate supplementation achieved the highest content of PHA in biomass, reaching 243.2 mg 3HB g −1 dry weight (367.8 mg 3HB g −1 VS) after 64 days of fermentation. Unlike conventional feast-and-famine selection strategies, this study demonstrates that high PHA contents can be attained under stable aerobic conditions. The produced PHA consisted primarily of the monomer 3-hydroxybutyrate (3HB) due to the use of acetic acid as an even-carbon acid. Shotgun metagenomic sequencing revealed that the microbial communities were dominated by the phyla Pseudomonadota and Actinomycetota, while the most abundant genus presented during the accumulation of PHA was Xanthobacter , known as a PHA producer. This integrated process–microbial insight provides new understanding for optimizing and scaling sludge-based PHA production systems. The study demonstrates that fully aerobic condition is an effective strategy for enhancing PHA production in acetate-fed activated sludge systems. These findings offer practical insights for scaling up sludge-based PHA production fermentation, contributing to the development of circular bioeconomy approaches in wastewater treatment.