Ultrafiltration organic fouling control: Comparison of air-sparging and coagulation

摘要

Air sparging and coagulation/flocculation were compared as fouling-control strategies during ultrafiltration (UF) of surface waters. Fouling was assessed following coagulation [0.5 and 15 mg/L alum as Al_2(SO_4)_3-14H_2O] and surface shear stress representative of different air-sparging conditions: continuous coarse bubble, intermittent coarse bubble, and large pulse bubble. Results indicated that 0.5 mg/L of alum reduced membrane fouling, especially for waters with higher concentrations of organic matter (＞ 4 mg/L dissolved organic carbon [DOC]). A 15-mg/L alum dose did not significantly improve membrane performance relative to the low dose. Air-sparging reduced fouling, but the benefits were not additive in combination with coagulation. Potential cost savings were calculated based on longer permeation times made possible by reduced fouling, and the value associated with water produced relative to energy costs (air-sparging) and chemical costs (coagulant). For the waters investigated, 0.5 mg/L of alum or the application of large-pulse bubble air-sparging were shown to be optimal for membrane fouling control.