Non-destructive Characterization of Nano- Filtration and Reverse Osmosis Membrane Module Fouling Using Magnetic Resonance Imaging

Magnetic Resonance Imaging (MRI) has been applied to non-invasively elucidate several aspects of bio-fouling of nano-filtration and reverse osmosis membranes (ROMs) modules as a function of fouling time. These include the spatial distribution of biomass accumulation and its effect on system hydrodynamics, the effect on these parameters of ROM cleaning protocols and the detailed validation of 3D simulations of ROM biofouling. These developments are summarised and preliminary work using the earth’s magnetic field for MRI detection purposes of biofouling outlined. INTRODUCTION Membrane filtration technologies, such as reverse osmosis (RO) and nanofiltration (NF) membranes, are increasingly being used for desalination purposes in a wide range of industries. Such membrane filtration however suffers from susceptibility to biofouling: the accumulation of attached microorganisms to surfaces in the membrane unit. The negative consequences of biofouling are several-fold and well documented [e.g. Patching et al., 2003], including reduced permeate, increased feed channel pressure drop, increased cleaning costs and earlier membrane replacement. Biofouling of these modules is conventionally studied and monitored by macroscopic parameters such as pressure drop or by membrane “autopsy”, which is destructive opening and inspection. There is a substantial need for novel measurement techniques that enable non-invasive, real-time and spatially resolved observation. Here we present a range of Magnetic Resonance Imaging (MRI) measurement capabilities as one non-invasive option for such studies. MATERIALS AND METHODS Two types of membrane modules were considered: (i) an industrial scale spiral wound membrane (Hydranautics ESPA1-2540) with an o.d. of 55 mm and a length of 1200 mm and (ii) a 2D analogue flow cell, hereafter referred to as the Spacer Membrane Fouling Simulator (S-MFS) [e.g. Vrouwenvelder et al., 2009], which was used for more fundamental studies. Figure 1(a) shows the spiral-wound membrane module whilst figure 1(b) shows the S-MFS. M.L. Johns, H.S. Vrouwenvelder 2 (a) F ibreglas s press ure ves sel Desalinated water S alty concentrate Mesh spacer F abric-backed semi-permeable membrane P orous layer Membrane sandwiches