Separation of Alcaligenes eutrophus cells containing poly(3-hydroxybutyrate) from fermentation broth with pretreatment using Al- and Fe-based coagulants

Alcaligenes eutrophus containing intracellular poly(3-hydroxybutyrate) was recovered from fermentation broth by centrifugation and filtration after pretreatment with Al-and Fe-based coagulants. Coagulation efficiency was largely affected by pH, and the optimum pH's for cell recovery were about 4.6-5.6 for the Al-based coagulants and about 5-8 for the Fe-based coagulants. Ammonium ions that combined with metals to form complex compounds increased the coagulant requirement, and the additional requirement of coagulant was found to be proportional to the ammonium concentration. In addition, various ligands in addition to ammonium ions contained in the culture medium interfered with the coagulation reaction and increased the coagulant requirement also. The coagulant requirement increased with the cell concentration regardless of coagulant type. The polymeric coagulants such as PACS, Hi-PAX, and Ferix-3 were more effective than nonpolymeric coagulants of aluminum sulfate and ferrous sulfate. The optimum dosages of the coagulants tested were determined over a broad range of cell concentration of 20.5-210 g/L. It was observed that the energy requirement for centrifugation could be greatly reduced with cell coagulation.