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. © 2014 Elsevier B.V. All rights reserved.

The combination of photovoltaic system with NF–RO is one of the most promising solutions, especially in remote and arid regions. A techno-economic study was conducted on small scale hybrid NF and RO water desalination system powered by PV system. The following conclusions could be drawn from the present study: (1) CSM RO membrane showed the best performance among all RO membranes with 20.24% water recovery, 90.22% salt rejection and 17.87 kWh/m3 of SEC. Also, NF250 showed the best performance among NF membranes with 18.98% water recovery, 70.64% salt rejection and 9.35 kWh/m3 of SEC. (2) NF-C-RO hybrid configuration showed an optimum performance with 35.79% water recovery, 78.51% salt rejection and 5.02 kWh/m3 SEC. (3) Amount of AC current generated by 1.5 kWh PV system during the PSSH was found enough to operate the NF-C-RO hybrid membrane unit. (4) The water production cost of NF–RO hybrid system (Rs.99.81/m3) was about 1.6 times lesser than NF (Rs.158.46/m3) and 4 times lesser than RO (Rs.400.49/m3) system in isolation. Moreover, this cost could be further reduced on increasing the capacity of the membrane system and by providing more subsidy on solar system as an incentive to its users. (5) The water production cost of Rs.146.5/m3, Rs.370.26/m3 and Rs.92.87/m3 for the PV–NF, PV–RO and PV–NF/RO hybrid [1] UNEP, 21 Issues for the 21st Century: Result of the UNEP Foresight Process on Emerging Environmental Issues, Kenya, Nairobi, 2012. 56. [2] REN21, Renewables Global Futures Report, REN21, Paris, 2013. [3] M.A. Hanjra, M.E. Qureshi, Global water crisis and future food security in an era of climate change, Food Policy 35 (2010) 365–377. [4] A.K. Misra, A. Mishra, Study of quaternary aquifers in Ganga Plain, India: focus on groundwater salinity, fluoride and fluorosis, J. Hazard. Mater. 144 (2007) 438–448. [5] J.K. Nayak, J.A. Prajapati, Handbook on Energy Conscious Buildings Indian Institute of Technology, Bombay and Solar Energy Centre, Ministry of Non-conventional Energy Sources, Government of India2006. [6] K.M. Sassi, I.M. Mujtaba, Simulation and optimization of full scale reverse osmosis desalination plant, in: S. Pierucci, G.B. Ferraris (Eds.), Computer Aided Chemical Engineering, Elsevier, 2010, pp. 895–900. [7] O.K. Buros, The ABCs of Desalting, 2nd ed. International Desalination Association, Topsfield, Massachusetts, USA, 2000. [8] H.J. Krishna, Introduction to Desalination Technologies, Texas Water Development, 2 (2004). [9] F.H. Fahmy, N.M. Ahmed, H.M. Farghally, Optimization of Renewable Energy Power System for Small Scale Brackish Reverse Osmosis Desalination Unit and a Tourism Motel in Egypt, Smart Grid and Renewable Energy, 3 (2012) 43–50. [10] D.P. Clarke, Y.M. Al-Abdeli, G. Kothapalli, The effects of including intricacies in the modelling of a small-scale solar-PV reverse osmosis desalination system, [11] A. Soric, R. Cesaro, P. Perez, E. Guiol, P. Moulin, Eausmose project desalination by reverse osmosis and batteryless solar energy: design for a 1 m3 per day delivery, [12] F. Banat, H. Qiblawey, Q. Al-Nasser, Design and Operation of Small-Scale Photovoltaic-Driven Reverse Osmosis (PV–RO) Desalination Plant for Water Supply in Rural Areas Computational Water, Energy, and Environmental Engineering, 1 (2012) 31–36. [13] L.A. Richards, B.S. Richards, A.I. Schäfer, Renewable energy powered membrane technology: salt and inorganic contaminant removal by nanofiltration/reverse osmosis, J. Membr. Sci. 369 (2011) 188–195. [14] H. Qiblawey, F. Banat, Q. Al-Nasser, Performance of reverse osmosis pilot plant powered by Photovoltaic in Jordan, Renew. Energy 36 (2011) 3452–3460.