Coagulation–Flocculation\nfor\nPolyhydroxyalkanoate Downstream Processing

Polyhydroxyalkanoates (PHA), a family of natural microbial\nbiobased\nand biodegradable polyesters, are considered potential substitutes\nfor traditional fossil fuel-based polymers. However, high operating\ncosts during production and processing hinder commercial competitiveness.\nSeparation of PHA-containing cells from the fermentation broth via\ncentrifugation is both capital- and energy-intensive, especially at\nthe industrial scale. In this study, an alternative method for bioseparation\nof the PHA-containing cells via coagulation is demonstrated for the\nfirst time. At a 15 mL scale screening, the best candidates for coagulating\nagents were found to be cationic polymer (at 2.67 mg/mL) and cationic\npolymer combined with aluminum sulfate (at 1 mg/mL). A novel dilution\nmethod was also developed to improve bioseparation in fermentation\nbroth at higher cell concentrations (optical density above 30). Mechanical\nand chemical characterization of polymer derived from the coagulation-based\nprocess was also demonstrated to be similar to commercial polyhydroxybutyrate\n(PHB), a member of the PHA family. Therefore, the proof-of-concept\nof coagulation-based processing as a low-energy alternative was demonstrated,\nthus paving the way for future development for improved cost-competitiveness\nof large-scale PHA downstream processing. The LCA evaluation reveals\nthat using only cationic polymer results in higher global warming\npotential and nonrenewable energy use compared to centrifugation.\nHowever, combining a cationic polymer with aluminum sulfate shows\na 25% lower global warming potential. The chemical cost analysis indicates\nthat this combination is more cost-effective.