Surface modification of polypropylene microporous membrane to improve its antifouling characteristics in an SMBR: Air plasma treatment

Polypropylene hollow fiber microporous membranes (PPHFMMs) were surface-modified by air plasma treatment. Morphological changes on the membrane surface were characterized by field emission scanning electron microscopy (FE-SEM). The change of surface wettability was monitored by contact angle measurements. The static water contact angle of the modified membrane reduced obviously with the increase of plasma treatment time. The relative pure water flux for the modified membranes increased with plasma treatment time up to 2 min, and then it decreased with further increase of plasma treatment time. Decreases in the tensile strength and the rate of tensile elongation at break of the modified membranes were also observed. The antifouling characteristics of the membranes in a submerged membrane-bioreactor (SMBR) for wastewater treatment were investigated. After continuous operation in the SMBR for about 110 h, flux recoveries after water and caustic cleaning are 11.66 and 34.99% higher for the 4 and 2 min air plasma treated membrane than those of the unmodified membrane. Result indicated that reversible fouling was only weakly dependent on membrane surface chemistry; in contrast, irreversible fouling exhibited a marked dependence on surface chemistry.