[Membrane fouling based on change of membrane characteristic parameters during ultrafiltration of protein]

In order to further understand membrane fouling mechanism of various protein systems during ultrafiltration, polyethersulfone (PES) ultrafiltration membrane with relative molecular weight cut off of 50 x 10(3) was used, the ultrafiltration processes of three kinds of protein solution were investigated: lysozyme ( LYS), bovine serum albumin ( BSA), and LYS + BSA. Contact angle meter, field emission scanning electron microscope (FESEM) and atomic force microscope (AFM) were adopted to determine the change of membrane characteristic parameters at different fouling stages. The results indicated that the changes of ultrafiltration membrane flux obviously exhibited three stages: sharp flux decline in the initial stage (approximately between 0-5 min), slow flux decline during the transition stage (approximately between 5-60 min), and stable flux in the late stage (approximately between 60-120 min). During the whole ultrafiltration process, the LYS-fouled membrane had the largest flux decline, followed by the LYS + BSA-fouled membrane, and the BSA-fouled membrane had the least decline. The changes of membrane characteristic parameters clearly indicated that the initial filtration stage of LYS was controlled by pore constriction, while pore blocking and pore constriction were the main fouling mechanism at the transition stage. Pore blocking was the main fouling mechanism of BSA in the initial fouling stage, while the transition stage was controlled by pore constriction. Cake filtration was the main fouling mechanism of LYS and BSA in the late stage. The membrane fouling of binary mixtures LYS + BSA appeared to be dominated by LYS.