Potential of activated sludge-derived mixed microbial culture enriched on acetate to produce polyhydroxyalkanoates from various substrates

The use of waste activated sludge (WAS) as a biocatalyst to produce polyhydroxyalkanoates (PHA) from waste streams may help promote the beneficial use of WAS for low-carbon, sustainable wastewater treatment. However, it remains unclear which types of substrates can be used for efficient PHA production, and how the PHA production can be maximized. This study aimed to assess the substrate versatility of mixed microbial cultures (MMCs) constructed from WAS by enriching PHA-accumulating bacteria using an aerobic dynamic discharge (ADD) process fed with acetate. Twelve different substrates, including organic acids, saccharides, and alcohols, were selected as the test substrates. In single-batch assays, the highest PHA production (583-680 mg/L) was achieved using butyrate, acetate, and pyruvate. In fed-batch assays, > 30 wt% PHA content was achieved using acetate, butyrate, propionate, lactate, and ethanol, with the highest content (60.3 wt%) using acetate. These results indicate that acetate-fed MMC by the ADD process could efficiently produce PHA from volatile fatty acids, lactate, pyruvate, and ethanol. Polyhydroxybutyrate was preferentially produced from acetate, butyrate, pyruvate, lactate, and ethanol, whereas polyhydroxyvalerate was notably produced from propionate. The results suggest that PHA can be efficiently produced from a wide range of substrates using MMCs enriched on a single substrate.