Cleaning strategies for flux recovery of an ultrafiltration membrane fouled by natural organic matter

Abstract

One of the most common problems encountered in water treatment applications of membranes is fouling. Natural organic matter (NOM) represents a particularly problematic foulant. Membranes may be fouled by relatively hydrophilic and/or hydrophobic NOM components, depending on NOM characteristics, membrane properties, and operating conditions. To maximize flux recovery for an NOM-fouled ultrafiltration membrane (NTR 7410), chemical cleaning and hydraulic rinsing with a relatively high cross-flow velocity were investigated as cleaning strategies. The modification of the membrane surface with either an anionic or a cationic surfactant was also evaluated to minimize membrane fouling and to enhance NOM rejection. Foulants from a hydrophobic NOM source (Orange County ground water (OC-GW)) were cleaned more effectively in terms of permeate flux by acid and caustic cleanings than foulants from a relatively hydrophilic NOM source (Horsetooth surface water (HT-SW)). An anionic surfactant (sodium dodecyl sulfate (SDS)) was not effective as a cleaning agent for foulants from either hydrophobic or hydrophilic NOM sources. High ionic strength cleaning with 0.1 M NaCl was comparatively effective in providing flux recovery for NOM-fouled membranes compared to other chemical cleaning agents. Increased cross-flow velocity and longer cleaning time influenced the efficiency of caustic cleaning, but not high ionic strength cleaning. The membrane was successfully modified only with the cationic surfactant; however, enhanced NOM rejection was accompanied by a significant flux reduction.