(381z) In Situ Measurement of Concentration Polarization in Pressure Driven Membrane Systems Using Laser-Based Spectrophotometric Method

Performance of membrane based separation process can be greatly influenced by scaling and fouling of membranes concentration polarization (i.e., increase in solute concentration near the membrane surface) is a phenomenon that has significant impact on mass transfer and formation of solids on the membrane surface. Previous studies focused on characterization of the concentration polarization layer in pressure driven system using semi-empirical models to estimate the extent of solute concentration increase compared to that in the bulk solution. However, actual concentration of solute near the membrane surface has not yet been experimentally characterized with requisite spatial resolution to allow comparison with semi-empirical models commonly used in practice.

This study presents a details of the spectrophotometric method specifically developed to measure the solute concentration profile near the membrane surface. To achieve this objective, a visible spectrophotometer using collimated laser beam as a light source and a CCD line camera as a detector were combined with specially designed membrane filtration cell to probe the solute concentration near the membrane surface. This experimental system was capable of probing the concentration polarization layer with spatial resolution of 4.5 µm. This system that was used to study concentration polarization layer in membrane distillation will be applied to UF and MF membranes using Direct Red 80 (dye) to study the effect of dye concentration, inlet pressure, feed flow rate and membrane characteristics on concentration profile. Results of these studies will be used to develop theoretical models for prediction of concentration polarization coefficient and boundary layer thickness that will be discussed in the presentation.