Ultrafiltration of Coagulation-Pretreated Serratia marcescens Fermentation Broth: Flux Characteristics and Prodigiosin Recovery

The dead-end ultrafiltration (UF) of coagulation-pretreated fermentation broth of Serratia marcescens SMΔR for prodigiosin recovery was studied. Experiments were performed using different types (regenerated cellulose, YM; polyethersulfone, PES) and molecular weight cut-offs (MWCOs, 1-10 kDa) of the membranes, feed concentrations of prodigiosin (300-1000 mg/L), applied pressures (68.9-206.8 kPa), and stirring speeds (200-400 rpm). With the same MWCO, the YM membrane had a higher retention of prodigiosin and a lower flux than the PES membrane. A two-fold concentration of prodigiosin was observed in the retentate using a 1-kDa YM membrane compared to the concentration in the permeate using a 10-kDa YM membrane. In addition, the extent of membrane fouling was quantitatively analyzed in terms of the modified fouling index. Flux decline in the present batch UF process was mainly due to cake layer formation and partly due to pore blocking. A two-stage UF process was proposed for this purpose, with 81% recovery yield and four-fold concentration.