Laboratory-scale experiments were conducted with two different commercial types of the nanofiltration (NF) membranes (DL and DK) to soften one brackish water in the Huanghuai region of China. The influences of feed pH (3-10)

feed total dissolved solids (1317-5926 mg·L-1) and total organic carbon (2.72-12.24 mg·L-1) on both selected NF membranes separating efficiencies were evaluated. The experimental results indicated that with the increase of feed pH

both DL and DK nanofiltration membrane specific fluxes firstly increased

then decreased

and finally slowly declined. But it decreased all the time with the increase of feed TOC and TDS. The divalent ions (Mg2+ and Ca2+) rejection rates for candidate NF membranes were on the rise during the testing scope. DL nanofiltration membrane was selected to continue to carry out the long-term stability test. When the operating time was running to 267 h

the membrane specific flux decreased by more than 10%

and chemical cleaning was adopted immediately. After chemical acid cleaning

the membrane specific flux recovery rate reached 85.05%; and after the coupling acid cleaning and alkali cleaning

the value is as high as 97.2%. Combined with scanning electron microscope and atomic force microscope characterization images

it was clearly showed that the chemical cleaning has good removal effect for membrane fouling.