A novel method for investigating the influence of feed water recovery on colloidal and NOM fouling of RO and NF membranes

Abstract

A systematic investigation on the role of feed water recovery (or concentration factor) in colloidal and natural organic matter (NOM) fouling of reverse osmosis (RO) and nanofiltration (NF) membranes is reported. Fouling experiments were conducted using a laboratory-scale crossflow test unit with continuous permeate disposal to simulate concentration factor (CF) and feed water recovery as commonly observed in full-scale RO/NF systems. With this novel method, the deterioration in membrane performance due to fouling and recovery-related osmotic pressure buildup can be distinguished. For colloidal fouling of RO membranes, the so-called "cake enhanced osmotic pressure" is a key fouling mechanism resulting in severe decline in permeate flux and significant decrease in salt rejection with increasing CF. On the other hand, NOM-calcium complexation rather than enhanced osmotic pressure is the key mechanism for NOM fouling of NF membranes. The decline in permeate flux and decrease in solute rejection with increasing CF were significant under favorable conditions for fouling, namely at higher initial permeate flux, ionic strength, and calcium ion concentration