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This paper illustrates the effects of coagulant residuals from conventional pretreatment(rapid mix, flocculation, sedimentation, and dual-media filtration) on polyamide reverseosmosis (RO) membrane performance. Testing included experiments with aluminumsulfate (alum), aluminum chlorohydrate (ACH), and ferric chloride coagulants, variouscoagulant aids (cationic, anionic, and nonionic organic polymers), free and total chlorine,and phosphonate- and polycarboxylic acid-based antiscalants. Results indicate thataluminum residuals, most notably from alum coagulation, caused colloidal fouling of ROmembranes through interactions with ambient silica to form aluminum silicates, andantiscalant components. Furthermore, elevated aluminum hindered antiscalantefficacy used to mitigate sulfate-based precipitates. While ferric chloride coagulationgreatly reduced colloidal fouling propensity, the corrosive nature of Fe (III) may attackuncathodically protected metals, leading to enhanced polyamide membrane oxidation inthe presence of chloramines by liberated Fe (II) ions. Similar to ferric chloride, ACHminimized colloidal fouling and potentially minimized aluminum-antiscalant interactions.However, membrane performance data suggested that ACH-pretreatment conditions mayalso facilitate enhanced oxidation reactions on the polyamide membrane surface. Includes 30 references, tables, figures.

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Edition: Vol. - No. Published: 06/17/2004 Number of Pages: 15File Size: 1 file , 920 KB