How to recognize membrane foulants: Pretreating feedwater can lengthen the life of membrane elements, improve the quality of the water produced and reduce the amount of maintenance and cleaning a system requires. Membrane fouling occurs when materials from the feed stream collect on or near the membrane surface and restrict water permeation. Fouling may occur as layers of deposition on the surface of the membrane (cake fouling), a hardened layer on the membrane surface (scale), particle insertion into the pore channel or entrance (pore blockage), or chemical attachment of particles to the membrane (adsorption). Foulant Effects Action Inorganic Salts Reduced permeate flow Remove hardness via pretreatment and softening Scale formation on membrane surface Add antiscalant or dispersant Increased salt passage Decrease feed pH Increased differential pressure Clean with an acid cleaner Organics (oils, grease) Decreased permeate flow Optimize pretreatment Increased salt passage Install an activated carbon filter Clean with suitable detergent Iron Stains membrane surface Remove iron with pretreatment Rapid reduction in permeate flow Clean with chelating agent Silica Decreased permeate flow Evaluate recovery and pH Slight increase in salt passage Optimize pretreatment for colloidal removal Biological Foul odor or taste Perform routine sanitizing Slime Reduced permeate flow Employ continuous operation Slime formation Increased differential pressure