Flux decline and membrane cleaning in cross-flow ultrafiltration of treated fermentation broths for surfactin recovery

Recovery of surfactin from the fermentation broths with culture of Bacillus subtilis ATCC (American Type Culture Collection) 21332 by cross-flow ultrafiltration (UF) process was experimentally examined, in which the broth was pretreated by acid precipitation and the precipitate was then dissolved in NaOH. Two types of membranes, polyethersulfone (PES) and cellulose ester (CE), with a molecular weight cut-off (MWCO) of 100 kDa were compared, and the effect of the presence of micelle-destabilizing solvent ethanol on the performance was studied. Experiments were performed at different initial concentrations of surfactin (1.13-4.57 g/L), transmembrane pressures (TMP, 20-100 kPa), and cross-flow velocities (0.16-0.48 m/s). Under the conditions investigated, the flux increased with increasing cross-flow velocity, but decreased with increasing the initial surfactin concentration and TMP. Finally, four cleaning agents and two cleaning ways (flushing and back-flushing) were screened to recover the flux. From the viewpoint of maximizing surfactin recovery, flushing with NaOH solution at pH 11 was suggested to clean the fouled PES membrane in this cross-flow UF process.