Sequential recovery of extracellular alginate and intracellular polyhydroxyalkanoate (PHA) from mixed microbial culture PHA production system

Polyhydroxyalkanoate (PHA) is a biodegradable plastic that exhibits properties similar to petroleum-based plastics. The mixed microbial culture (MMC) process utilized a waste carbon source to produce PHA, reducing the raw material costs associated with pure bacterial technology. However, the high cost of PHA recovery and environmental pollution are significant challenges to the sustainable development of MMC technology. In this study, a sequential recovery strategy was proposed. This strategy involved the use of Na2CO3 to break down the structural extracellular polymeric substances and rhamnolipid to digest non-PHA cell material (NPCM). The recovery rate of PHA in this strategy achieved 61.29 +/- 5.92% and a purity of 97.55 +/- 0.92%. Additionally, the strategy allowed the sequential recovery of the by-product alginate-like extracellular polymers. FT-IR analysis confirmed that the recovered biopolymer was PHA material, possessing mechanical and thermal properties similar to those obtained through CHCl3 extraction. However, it was important to note that this method had the potential to alter the distribution structure of the PHA polymer, although it successfully avoids the issue of reducing the molecular weight of PHA during NPCM digestion. A comprehensive evaluation demonstrates that the cost of PHA production using this method was only 14.61 CNY/kg, with a more positive environmental impact in terms of global warming potential and carbon emission reduction. Therefore, the sequential recovery strategy presents a feasible alternative for the downstream recovery process and overall economy of the MMC PHA process.