FOULING OF MICROFILTRATION MEMBRANES BY BROTH-FREE ANTIFOAM AGENTS

The fouling tendencies of seven commercial antifoam agents used with m icrofiltration membranes were investigated in a stirred cell. Paramete rs such as viscosity, oil droplet size distribution, contact angle, wo rk of adhesion (W-a), membrane type, operating pressure, and feed conc entration were examined. The results show that a silicone-based antifo am, G832, gave a significantly lower flux (less than or equal to 100 L h(-1) m(-2)) than the polypropylene glycol antifoam PPG2000 (1500-250 0 L h(-1) m(-2)) over the concentrations from 0.5 to 4.0 mt L-1 at.50 kPa, 700 rpm, and 25 degrees C. The significantly lower flux attained by the antifoam G832 was attributed to a number of factors, such as it s greater viscosity (1.25 x 10(-3) kg m(-1) s(-1) compared with 1.05 x 10(-3) kg m(-1) s(-1) for PPG2000), a smaller average oil droplet siz e (0.28 vs. 0.65 Cim) comparable to the membrane pore size distributio n (0.26-0.62 Crm), a higher contact angle (98 vs. 51 degrees); and a s ignificantly larger value of work of adhesion (26.0 vs, 0.81 mN m(-1)) . The different magnitudes of membrane adsorption by these antifoam ag ents, as reflected by their values of work of adhesion, were also obse rved in the field emission scanning electronic microscopy photographs. In terms of membrane type, the inorganic Anopore alumina membrane was found to offer a higher PPG flux than the organic Millipore polyvinyl difluoride (PVDF) membranes (both hydrophilic and hydrophobic). Furth ermore, the mixed-type antifoams (B5600, B426, and G832) were found to give an increased hydraulic resistance and fouling percentage with an increase in pressure or feed concentration. Conversely for PPG2000, a reduction of the hydraulic resistance and fouling percentage was obse rved with increases of these two parameters. (C) 1997 John Wiley & Son s, Inc.