Comparative assessment and multivariate optimization of commercially available small scale reverse osmosis membranes

Abstract

Requirement of reverse osmosis (RO) process at places facing energy and water quality problem makes its assessment and optimization vital while considering recovery, rejection as well as specific energy consumption. In the present paper, three thin film composite (TFC) RO membranes (make: CSM, Dow and Vontron) in spiral wound (SW) configuration have been chosen to study their relative performance. Comparative study of RO membranes was conducted using experimental observations supported by membrane characterization. Optimization experiments were performed using central composite design (CCD) of response surface methodology (RSM). Four input variables viz. feed water pH, temperature, pressure and concentration were optimized and interaction between them was observed, while, recovery, rejection and specific energy consumption (SEC) were taken as response attributes. The experiments conducted employing the optimized input values validated the developed RSM model. Predictive model using multiple response optimization revealed the optimal efficiency of CSM RO membrane at 6.53 pH, 1500 mg/L concentration, 0.78 MPa pressure and 31.94°C temperature producing 19.25% water recovery, 89.21% salt rejection and 17.60 kWh/m3 SEC, respectively. Membrane surface characterization was carried out by FE-SEM, AFM, contact angle measurement and FTIR. The lesser contact angle and smoother surface apparently contributed to the better performance of CSM RO membrane. This paper may demonstrate a simple method for optimizing the commercially available small scale RO membranes.