Modelling and Experimental Investigation of Geometric Solutions to Scaling on Reverse Osmosis Membranes through innovative Feed Spacer Design

The demand for clean, safe drinking water continues to grow at near-exponential rates as a function of both the burgeoning world population and depletion of easily accessible water sources. As a result, research into improvements into desalination capabilities is swiftly increasing as the ocean represents an infinite supply of water conveniently located to the most densely populated portions of the world, providing a simple answer to growing municipal water demands. One method to improve desalinization processes involves reducing scaling within reverse osmosis (RO) membranes. With reduced scaling, membrane permeability remains higher reducing the energy bill required per volume of water treated. Associated impacts also include reduction in cost to replace RO filters impacting traditional water treatment plants as well as Reverse Osmosis Water Purification Unit (ROWPU) used in austere environments. Two different centers (the Center for Environmental and Geographic Sciences at the United States Military Academy and the U.S. Army Tank Automotive Research, Development and Engineering Center in Warren, MI) are conducting research in this area that enables enrichment of the undergraduate experience. The partnership between the two centers provides a link between industry need and undergraduate research. The research provides an additional capstone-type experiential learning opportunity for students which incorporates a three-week summer internship and a one or two-semester long independent study experience for environmental engineering students. The purpose of this study is to examine the impact of different feed spacer geometries that separates membranes within RO filters in order to increase filtration efficiency and requires students to develop innovating solutions in a group project work setting. A model was developed in SolidWorks using Flow Simulation to replicate the hydrodynamic conditions within a cell (Sterlitech SEPA Crossflow Cell, 316SS) to match an experimental configuration set up. The initial model evaluated changes in flow velocity and pressure. Subsequent model refinement enabled the evaluation of the impact of three different geometries on flow regimes with significant parameters investigated that included pressure drop within the cell, flow velocities, flux, and dead zones. Selection of the three different geometries evaluated was based upon the ability to reduce dead zones and streamline flow velocities thus minimizing the conditions necessary for scale to form. Experiments were conducted to validate the response of designed and 3D printed feed spacers placed in identical cell compared to modelled results. A feed solution of 0.0304 M CaCl2 and 0.0304 M Na2SO4 was used to evaluate scaling within a 24-hour period for each of the different geometries. Detailed data of the different spacer geometries was obtained through physical testing and computer modeling. Preliminary experimental results indicate a correlation between changes in designed feed spacers and scaling associated with decreased flow velocities and increased dead zones. Experiments and modeling efforts over the coming months are designed to enable further validation of the model and in so doing enable improved efficiencies toward the redesign of feed spacer geometry.