Optimization and economic analysis of small scale nanofiltration and reverse osmosis brackish water system powered by photovoltaics

Integration of renewable energy with desalination technologies is a strongly emerging field in many regions of the world having drinking water and energy crisis. This study presents the results of a techno-economical investigation of a small scale, photovoltaic (PV) powered hybrid nanofiltration (NF) and reverse osmosis (RO) membrane system for the brackish water treatment. Optimization experiments of six commercially available small scale RO and NF membranes were carried out using central composite design (CCD) of response surface methodology (RSM). Experiments employing optimized input conditions validate the developed RSM model. Predictive model, using multiple response optimizations, revealed that CSM RO and NF250 membranes showed the optimal efficiency with 20.24% and 18.98% water recovery, 90.22% and 70.64% salt rejection and 17.87 and 9.35 kWh/m3 of SEC respectively. Comparison of membranes was also carried out by membrane characterization duly supported by experimental observations. Membrane surface was characterized by AFM, contact angle measurement and FTIR. Hybrid experiments were performed with NF and RO membranes in concentrate and permeate staging configurations. Results also suggested that techno-economic performance of the hybrid PV-NF/RO system was affected by factors like mode of integration of NF and RO membranes, recovery ratio, daily average operating hours and government subsidy.