CALCIUM-SULFATE FOULING OF REVERSE-OSMOSIS MEMBRANES - FLUX DECLINE MECHANISM

The cake filtration fouling model for reverse osmosis (RO) was examined and found to be physically unrealistic for flux decline due to calcium sulfate precipitation fouling. Continuous flow RO experiments on a saturated solution of calcium sulfate were performed to elucidate the flux decline mechanism. The calcium sulfate deposit on the membrane was characterized by SEM and computer-aided image analysis. It is shown that flux decline is due to blockage of the membrane surface by lateral growth of the deposit rather than the hydraulic resistance of a cake building up at the membrane surface. The importance of deposit characterization for the verification of fouling mechanisms is emphasized.