Mechanism of CaCO3 chemical fouling formation in water reclamation process using reverse osmosis membrane

Mechanism of CaCO3 chemical fouling formation in water reclamation process using reverse osmosis membrane
Water Reuse; Reverse osmosis membrane; chemical fouling; CaCO3
Issue Date
2012 International Conference on Environment and Waste Management
VOL 66, 1692-1692
Reuse of wastewater is important to removal of contaminants such as microorganisms and inorganic salts. Thus, wastewater reclamation processes using reverse osmosis (RO) membrane have been increasingly applied around world. Membrane fouling is the main cause of permeate flux decline and loss of product quality in RO system. Recently, an understanding of the mechanism involved in both organic fouling and bio-fouling has been focused in many recent research projects. However, researches on chemical fouling (inorganic fouling or scaling) in RO process are insufficient. The most common chemical fouling found in RO process is CaCO3 because it precipitates quickly once concentrated beyond its solubility limit. CaCO3 precipitates have been the most probable foulants for seawater and wastewater reclamation application. In this study, the formation of CaCO3 deposits on RO membranes was investigated in connection with permeate flux decline. Experiments were carried out in a cross-flow RO membrane test cell when the initial concentrations of calcium and carbonate in the feed solution were 100 mg/L. CaCO3 was quickly formed approximately 50% of the total formation within 10 min, then it was slowly deposited on the membrane surface. Based on the observed CaCO3 scale formation pattern and morphology on the membrane surface by AFM and SEM analysis, the CaCO3 precipitation could be divided in two steps of CaCO3 nuclei formation and growing nuclei to agglomerate up to 235μm(d50). Furthermore, the SEM observation on fouled membrane samples revealed that small size CaCO3 particles formed early resulted in initial membrane fouling and then secondary membrane fouling occurred by the transformation of vaterite to calcite or the growth of CaCO3 nuclei into agglomerate.
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