Project Goals and Approach Experimental Sequence Predicting RO Removal of Toxicologically Relevant Unique Organics Lauren Breitner, Dr. Kerry J. Howe, Dr. Andrea F. Corral Background Water reuse, specifically direct potable reuse (DPR), is continuing to be seen as a viable option for communities with extreme water scarcity. The need for investigating the removal of CECs has become crucial for further DPR considerations. Reverse osmosis (RO) has been demonstrated to remove many CECs. However, RO removal efficiency can be affected by many factors, including the physical-chemical properties of the CEC, membrane properties, process operating conditions, and feedwater characteristics. A useful relationship between these variables can be achieved by using a quantitative structure activity relationship (QSAR) model. This study aims to conduct laboratory-scale experiments of trace organic rejection to develop an integrated process and QSAR model to predict the rejection rates of a wide range of compounds via RO treatment. Model Development Process Model Rejection: Permeate Concentration: Mass Transfer Coefficients: Using a numeral integration across the length of a RO element, then across multiple elements in a stage for overall plant performance, the above can be calculated. This approach also takes concentration polarization into account via a boundary layer model. Membranes Selected Process Model (kW and kS for salts) QSAR Model Combined Model Organic Removal Efficiency Operating Conditions (Pf, Cf, T, v, , , , etc.) Membrane Properties (Permeate flow, salt rejection) Literature Removal Data kS for organics Experimental Data Membrane Chemistry Intrinsic Interactions between Organics and Membrane, ΔGintr Selection of Organics Manufacturer Product Type 1 Permeate Flow 2 (m3/d) NaCl Rejection (%) Dow Filmtec SW30XHR SW 23.0 99.82 Toray TM800M 26.5 99.8 Hydranautics ESPA2-LD BW 37.9 99.6 GE AG LF 39.7 99.5 TMG(D) 45.8 99.7 BW30HR 48.0 AP ULP 47.2 95.0 NF 270 47.0 97.0 3 Project Goals and Approach Develop a model to predict the removal efficiency of organic compounds of potential health concern (PPCPs, EDCs, etc.) by reverse osmosis for potable reuse applications. The model will account for organic compound characteristics, membrane properties, and operating conditions. Experimental Methods Experimental Conditions and Variables Experimental Sequence Bulk Average kw and ks Values Variable Notes Organic compound 25 to 30 compounds Membrane product 8 membranes Feed pressure 7.5, 15, and 22.5 bar (109, 218, and 326 psi). Feed flowrate Cross-flow velocity = 0.18 m/s Temperature 20 C Permeate pressure 0 bar TDS concentration 2,000 mg/L NaCl Spacer thickness 28 mil pH Depends on final compound selection Solution composition DI water, NaCl, H3BO3, NaHCO3 (buffer), organics, acid or base for pH adjustment Experimental Setup Measured Parameters Preliminary tests are being completed currently to understand any variations in experimental data that can be attributed to the experimental setup or sampling procedures. Experiments have been performed with ethanol and sodium chloride to gain an understanding of these variations. Rejection based on the following test conditions: Feed pressure: 100 psi Ethanol feed concentration: 8 mg/L Sodium Chloride feed concentration: 2,000 mg/L Note: Rejection is measured as conductivity rather than concentration of NaCl. This may lead to a slightly higher rejection of ions than shown above. Preliminary Results Parameter Feed Permeate Concentrate Flow rate  Pressure Temperature Conductivity Organic concentrations H3BO3 concentration pH Step Notes Cleaning and compaction Insert new membranes, operate for 24 hours, recycle permeate and concentrate, change water periodically, measure baseline water flux. NaCl rejection Operate 24 hours, recycle permeate and concentrate, measure permeate flux and conductivity for NaCl rejection. Organic equilibration Operate 72 hours, recycle permeate and concentrate, allow organic concentrations to equilibrate (allows for adsorption). Sampling Each permeate measured individually, starting with membrane 1. Change operating conditions (e.g. pressure), wait 1 – 2 hours, repeat sampling. Bench-scale Experimental Setup 5-Chamber RO Test System The University of New Mexico gratefully acknowledges the WateReuse Research Foundation’s financial, technical, and administrative assistance in funding and managing the project through which this information was discovered, developed, and presented. The comments and views detailed herein do not necessarily reflect the views of the WateReuse Research Foundation, its officers, directors, employees, affiliates, or agents.