Chemically enhanced pretreatment (CEPT) to reduce irreversible fouling during the clean-in-place process for membranes operating under constant flux and constant pressure filtration

Abstract

The goal of this study was to evaluate membrane degradation after 10 clean-in-place (CIP) cycles for polyvinylidene fluoride (PVDF) membranes exposed to chemically enhanced pretreated (CEPT) feed water under constant flux (CF) and constant pressure (CP) filtration modes. Cycles of filtration (20 min) and backwashing (3 min) were employed for both filtration modes for a period of 10 h, followed by the CIP process. The changes in the membrane pore size distribution, membrane symmetry, and bond structure were analyzed using the Brunauer-Emmett-Teller method, scanning electron microscopy, and Fourier-transform infrared radiation, respectively. Severe damage to the membrane pores and significant structural variation were observed with the use of untreated feed water, particularly under CF mode, due to the defluorination and oxidation of the membrane arising from the action of the residual inorganic foulants and cleaning chemicals. Membranes exposed to CEPT feed water exhibited a recovery of 79 % and 83 % of the initial membrane flux under CF and CP modes, respectively at end of study. Interestingly, a decrease in irreversible fouling of 16.7 % was observed for CEPT feed water, with fewer inorganic foulants (Al and Mn) on the membrane surface. The fouling propensity was 14.54 % and 14.78 % lower when using CEPT feed water under CP and CF modes.