AWWA WQTC57012

Soluble aluminum (Al3+) reacts with both ambient silica and antiscalant components to form colloidal foulants during reverse osmosis (RO) treatment. Aluminum sulfate (alum) and polyaluminum chloride (PACl) were evaluated at various coagulant dose and influent water pH conditions to lower the total aluminum to below 50 ug/L, a level previously observed to cause RO membrane fouling. Results from pilot-scale testing demonstrated that PACl consistently met the 50 ug/L aluminum goal regardless of pH (pH 6.0-8.3), whereas alum could only meet the goal for soluble aluminum below pH 6.5. For total aluminum, alum coagulation at pH 6.0-8.3 failed to meet the 50 ug/L goal, which may result in colloidal fouling of any downstream membrane. Further testing using RO fed with optimized alum or PACl coagulated water are needed to confirm that reduced membrane fouling may result by controlling the conventional treatment plant residual aluminum concentration. Includes 24 references, table, figures.