| The fouling behavior of natural organic matter (NOM) and particles was assessed for spiral-wound nanofiltration membrane elements using a membrane pilot-plant. Experiments involved circulating experimental waters spiked with varying concentrations of collected NOM and different particle size ranges through elements for a period of 28 days. Twelve experiments were conducted, each using a new membrane element. At the end of each experiment, elements were dissected and examined visually and microscopically for deposited matter.; Data showed NOM adsorption following a Freundlich Isotherm. Adsorption was non-linear, adsorbing quickly in the first 48 hours, slowly decreasing over a period of two weeks to a steady-state (i.e., up to 13 percent of the total available mass of NOM). Adsorbing NOM was characterized primarily by lower and higher molecular weight molecules <5k da and >30k da, respectively. Particles were shown to interfere with NOM adsorption resulting in reduced levels.; Particles deposited continuously and at a constant rate. NOM increased the rate of deposition for 0.5–1.0 μm size particles while decreasing the rates for >1.0 μm size particles.; Although high concentrations of both NOM and particles were used in some experiments, neither was sufficient to cause membrane fouling. Hydraulic conductivities remained constant throughout the 28 day duration of each experiment.; Inspections of dissected elements showed both NOM and particle deposits on membrane surfaces. Patterns were influenced by the hydraulic flow conditions through the element and the feed water spacer. Deposits were heaviest in regions where velocities were relatively low or near stagnant such as those occurring at the periphery of the element and in front of feed water spacer fibers.; The feed water spacer was central to the deposition of both NOM and particles. A modified spacer design that provides a uniform flow across the surface of the membrane at an adequate cross-flow velocity to improve scouring, may reduce surface deposits, which in turn, should reduce membrane fouling. |
