Natural organic colloid fouling of low pressure membranes under unfavorable interaction conditions.

In this study, the deposition of natural and effluent organic colloid (OC) on low-pressure membrane materials were investigated, together with the resulting effects on membrane permeability-selectivity relationships. It was found that OC had different breakthrough characteristics when passing through the filter beds packed with resin beads made of similar materials as the studied membranes. The deposition coefficient (α) of OC was consistently greater for a secondary wastewater effluent (0.0050 and 0.010) than a natural surface water (0.0040 and 0.0086), for polyvinylidene fluoride and polyvinyl chloride resins, respectively. The low α values suggested the occurrence of colloidal attachment under unfavorable interaction conditions. Further experimental and modeling results revealed that OC characteristics (size and zeta potentials) strongly affected their deposition on the resin and inside the membrane pores. Inner-pore OC deposition caused evolution of the selectivity-permeability relationships for the studied membranes, by increasing selectivity while decreasing permeability, to the extents depending upon membrane properties. Under unfavorable attachment conditions, OC deposition formed monolayer in the narrow pores of the ultrafiltration membrane, but multilayer in the large pores of the microfiltration membrane. The weak deposition was also reversible by altering the hydrodynamics or adhesion interactions, as manifested in membrane cleaning studies. Overall, this study provided important insights into the colloidal fouling mechanisms of porous membranes, which are instructive to sustainable operation of membrane-based, full-scale water and wastewater treatment facilities.