Brackish groundwater treatment by nanofiltration, reverse osmosis and electrodialysis in Tunisia: performance and cost comparison

The possibility of producing drinking water from brackish groundwater using nanofiltration (NF), reverse osmosis (RO) and electrodialysis (ED) processes was studied. Brackish groundwater samples were taken from the south of Tunisia (Gabes and Zarzis cities), and characterized in terms of pH, conductivity, hardness and inorganic matters. The results obtained in this work show that nanofiltration permits to reduce the concentrations of Ca2+, Mg2+ and SO42−, which are responsible for elevated sulfate hardness. The total dissolved salts of the produced water is equal to 1890 mg.l−1. This is higher than the maximum value for drinking water fixed by the WHO at 500 mg.l−1. Desalination of brackish groundwater by RO or ED might be technically and economically viable to cope with water scarcity and overcome the water deficit in Tunisia. The results showed that RO and ED were actually efficient since they highly reduced the content of inorganic matters present in raw waters. The treatment by RO or ED shows that the concentrations of ions in the obtained permeate (or the diluate) did not exceed the permissible WHO standards. ED seems to be the economical desalination process for Gabes water due to its low energy consumption whereas Zarzis water should be treated with the RO process.