Nano-porous Membrane Process for Brackish Groundwater Treatment: Efficiency Analysis Using Response Surface Methodology

Excessively high concentration of inorganic salts in the groundwater is the main threat for residents to drink directly in the remote areas of northwestern China. In this paper, nano-porous membrane process was proposed to removal of diverse ions in such raw water. Through the response surface methodology (RSM), the effects of multiple factors on permeate flux and ion rejection rates were analysed, and the application scope of nanofiltration for various water resource was evaluated. It was found that the factors affecting permeate flux, chloride removal and nitrate removal (response value) followed some typical sequences, and the operating pressure was always the most influential factor. Besides, nanoporous membrane process showed predominant performance in the removal of sulphate, chloride and fluoride; the rejection rates were over 99%, 97% and 95%, respectively, and the produced water could completely satisfy the relevant national standards for drinking water. However, nitrate removal rate was seldom over 80%, and it reduced obviously with the increasing initial concentration of nitrate, thus the nitrate content of raw water should be controlled within 40 mg.L-1.