Polyelectrolyte-grafted microfiltration membranes to control fouling by natural organic matter in drinking water

Membrane fouling by natural organic matter (NOM) adsorption is a major factor limiting the use of microfiltration for drinking water treatment. Charged and non-charged hydrophilic polymers were grafted as a flexible layer onto a polypropylene hollow fibre to alter the surface properties and the electrostatic interactions between the feed components and the membrane surface. The hydrophilic polymers were polyacrylic acid, 2-(N,N-dimethylamino)ethyl methacrylate and poly(ethylene glycol)900 monomethyl ether monoacrylate. The flux of the graft-modified membranes depends on electrostatic properties of the feed stream, such as pH and multi-valent counterions. Non-ionic and cationic hydrophilic grafts have rates of flux decline by NOM fouling up to 50% lower than ungrafted polypropylene. Anionic hydrophilic grafts have initial flux increases up to 140% at high graft yields due to multi-valent ions in the natural water, although the pure-water flux is substantially lower than for the ungrafted membrane. These membranes can filter an NOM-containing surface water for extended periods without any flux decline due to fouling or without compromising permeate quality. These tailor-made modified membranes function by increasing permeability to counteracting fouling. Rejection is not compromised as the original membrane is fully intact. Performance may be controlled to suit a particular feed source by matching graft polymer and graft yield to source pH and counterion concentration (e.g. hardness).