Effect of feed water characteristics on nanofiltration separating performance for brackish water treatment in the Huanghuai region of China

In this paper, one brackish groundwater quality, which represented typically the water quality in the Huanghuai region of China, was simulated and used to run a bench-scale ultrafiltration (UF)-nanofiltration (NF) system. The influences of feed pH (3.0-10.0), feed total dissolved solids (TDS) (1182-5319 mg L−1) and feed dissolved organic carbon (DOC) (0.54-2.43 mg L−1) on the separating efficiencies of two different NF membranes (Thin-Film Composite (DL) and Polyamide (DK)) were investigated. In addition, long-term operation for 580 h was also conducted by the superior NF membrane to evaluate the performance stability and fouling potential after a number of subsequent cleaning cycles. Within the scope of the test, NF separating performance in terms of salt rejection showed different changing tendencies: V-shaped curve for pH, inverted V-shaped curve for TDS and linear curve for DOC. While in general, specific permeate flux was reduced in different degrees except for DK membrane with feed pH variation. The observed separating performance decline with operating time was mainly due to the scale formation on the NF membrane surface, which was rinsed effectively (FR1 = 97.80% and RR1 = 61.63%; FR2 = 95.40% and RR2 = 49.35%) by chemical cleaning, as certified by FESEM−EDX and AFM images.