Characterization of Fouling Potential for Pressure-Driven Membrane Processes: A New Simulated Flow Cell

Abstract

Membrane systems are unit processes that are becoming widely accepted for the demineralization of saline and other waste waters. Dissolved and particulate material, specifically colloidal matter, present in the feed stream to membrane systems are considered the principal causes of membrane fouling and reduced efficiency. Conventional water analysis do not yield the information needed to determine the amount of fouling that will occur. Therefore, some rapid indication of the water quality and its potential to foul is needed. Presently there are five tests available to evaluate feed-water quality for membrane processes. However, in each of these tests the apparatuses used do not model tangential (shear) flow across the membrane surface. Therefore, a new apparatus was designed and constructed to predict how the feed water foulants would behave in a flow field. A new apparatus, named the Simulated Flow Cell (SFC), was developed and tested in the laboratory with feed waters containing polystyrene latex spheres (PSL) as foulants and in the field with well-water and precholorinated secondary effluent. The SFC reproduced essentially the same results as the standard non-flow cell when operated under the same conditions. However, the SFC was also able to model flow regimes to membrane systems. The Simulated Flow Cell was tested using irradiated polycarbonate membranes with pore diameters ranging from 0.1 µm to 1.0 µm. The feed water turbidity was varied during the testing by the addition of PSL spheres. Varying these parameters permitted data collection under a wide range of conditions. For laboratory feed water with the addition of PSL spheres, a theoretically expected threshold velocity was observed with the SFC using 0.1 µm pore diameter membranes. The threshold axial velocity was directly proportional to the square root of the initial flux through the 0.1 µm Nuclepore membranes, which is in agreement with data collected from actual hyperfiltration plant operations. The Simulated Flow Cell is a low cost apparatus for the rapid characterization of permeator feed waters. The Simulated Flow Cell promises to become an important tool in the ever widening use of membrane processes in water and wastewater applications.