Design and test of a reverse osmosis pressure cell for in-situ small-angle neutron scattering studies

We introduce a new method for real-time studies of membrane scaling and biofouling on thin film composite membranes (TFC) in reverse osmosis and nanofiltration water treatment using in-situ small-angle neutron scattering (SANS). SANS delivers information on nano and microscopic structures that support the interpretation of relevant engineering parameters such as membrane permeability and water flux. A flow cell high pressure SANS is described, followed by SANS characterization of TFC membranes finding ~0.5μm large cavities and ~300Å diameter large rod-like cavities inside the non-woven polyester and micro-porous polysulfone layer, respectively. In-situ desalination experiments in cross-flow mode at an applied pressure of 6bars and feed flow velocity of 0.2cm/s are followed. The scattering cross-section times sample thickness (μt=Σt×DS) derived from the transmission coefficient shows an overall enhancement due to newly formed scattering centers which is accompanied by a reduced membrane permeability measured simultaneously. This observation is supported by enhanced scattering of the membrane due to μm large domains of mass fractal structure. The addition of the protein BSA to the feed after desalination of 30h effectuates strong enhancement of the permeability accompanied by a about a 50% decline of μm large scattering centers.