Development of fouling control strategies pertinent to nanofiltration membranes

Nanofiltration schemes are being increasingly applied in the treatment of surface water. The application of this membranes separation techniques offers numerous advantages as compared to conventional techniques. Elimination of chemical disinfection, removal of soluble organic compounds, softening capacity and elimination of biological pollutants are advantages manifested by nanofiltration schemes. The performance of nanofiltration systems is controlled by feed water characteristics specially the ionic strength, concentrations and types of divalent cations and natural organic matter. Under specific conditions, the concentration of these fouling materials may lead to complex interactions causing rapid and sometimes irreversible flux decline due to the fouling layer. Successful implementation of a nanofiltration-based water treatment system requires careful selection of the water source, tailored pretreatment (if necessary), establishing of specific operating conditions and cleaning cycles to maintain membrane integrity and required production levels. This paper presents a performance analysis of some commercial NF membranes via reported flux decline data. Empirical equations have been developed to predict the impact of some water contaminants on flux decline of the NF membranes. These formulae enable decision making concerning the suitable pretreatment for NF schemes and also selection of the most appropriate cleaning cycle. The paper is concluded with guidelines for appropriate design of NF-based systems for the treatment of moderately polluted surface water.