Synthesis of Short-Chain-Length and Medium-Chain-Length Polyhydroxyalkanoate Blends from Activated Sludge by Manipulating Octanoic Acid and Nonanoic Acid as Carbon Sources.

The effects of octanoic acid/nonanoic acid and acclimation time on the synthesis of short-chain-length and medium-chain-length PHA blends from activated sludge were investigated. An increased concentration (847-1366 mg/L) of PHAs resulted from 4-month acclimation compared with the concentration derived from 2-month acclimation (450-1126 mg/L). The content of octanoic acid had a positive linear relationship with the content of even-numbered carbon monomers among the PHAs. The blending products were identified mainly with scl-PHAs during the 2-month acclimation period and were thereafter dominated by mcl-PHAs until 4 months of acclimation. Thermal properties analysis demonstrated that the products derived from 4-month acclimation were a mixture of scl-PHAs and mcl-PHAs rather than a copolymer of scl-PHAs and mcl-PHAs. High-throughput sequencing results indicated that Pseudofulvimonas, Paracoccus, and Blastocatella were the dominant genera that might be responsible for scl-PHAs production during the 2-month acclimation period, whereas Comamonas and Pseudomonas that were responsible for mcl-PHAs production then became the dominant genera after 4-months acclimation.

Production of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) from excess activated sludge as a promising substitute of pure culture.

This study aimed to investigate the feasibility and technology to harvest poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) by mixed culture. Copolymer PHBHHx, usually fermented by pure strains, was reported to be synthesized from activated sludge for the first time. Sodium laurate was used as the sole carbon substrate for sludge acclimation and PHBHHx accumulation. Batch experiments were designed to look into the impact of the carbon, nitrogen, phosphorus and oxygen supply on PHBHHx production. The results showed that the acclimated excess sludge was able to produce PHBHHx, and the maximum output (505.6 mg/L PHBHHx containing 6.34 mol% HHx) was achieved with conditions of the continuous aeration, nitrogen and phosphorus limitation, and adequate carbon source implemented by pulse feeding 0.5 g/L sodium laurate every 4h. Moreover, composition and structure of the PHBHHx from sludge were found similar to that from pure culture, according to literature, FTIR and NMR spectra. Finally, high-throughput sequencing technique characterized that phylum Chlorobi and genus Leadbetterella should be critical groups for PHBHHx synthesis in the sludge community.