Analysis of nanofiltration membrane performance during softening process of simulated brackish groundwater

In this paper, one brackish water quality, which typically represented the water quality in the Huanghuai region of China, was simulated and used as feedwater to run an ultrafiltration (UF)-nanofiltration (NF) integrated membrane system. Laboratory-scale experiments were carried out to evaluate NF softening performance. The influences of transmembrane pressure (0.6-2.2 MPa), inlet tangential flow velocity (0.087-0.384 m·s− 1) and feedwater temperature (7-35 °C) on the softening efficiencies of two NF membranes denoted as DK (termed as NF1) and DL (termed as NF2) were investigated. The experimental results revealed that the calculated total hardness and the bivalent ion (SO42 −, CO32 −, Mg2 + and Ca2 +) concentrations in NF2 product water on the same operation were all slightly lower than those in NF1 permeate in two schemes. Additionally, pH value of NF permeate decreased prominently than those in feedwater with increasing of transmembrane pressure, inlet tangential flow velocity or decreasing of feedwater temperature within the testing scope.