In the process when inlet bulk solution with low or medium concentration was involved

the scaling was apt to appeared on the nanofiltration (NF) membrane surface in the retentate side. Therefore

the study of surface electrokinetic phenomena of NF membrane termed as DK membrane under threshold concentration condition is very important. In this paper

the surface charge properties of DK nanofiltration membrane were studied using streaming potential method

and a series of two-component ternary electrolyte solutions (K2SO4+CaCl2) with the molar ratio of 1:1 were involved as the study objects. Using the home-made tangential streaming potential test device

DK membrane was characterized with streaming potential (Es)

Zeta (ζ) potential and other measurements encountering with a wider scale-prone ionic concentration (0.5-18 mol·m-3)

operating pressure (25-200 kPa) and feed pH (3.0-10.0). The results showed that at operating pressure of 180 kPa

with the scale-prone ionic concentration of feed solution ranged from 0.5 to 18 mol·m-3

it turned out Es and ζ -potential values increased from -87.37 and -59.13 mV to -3.41 and -36.34 mV

respectively. It becomes less negative and tends to be neutral due to electrostatic charge shielding and compression of the diffuse layer. But the calculated surface charge density (σ) value always increased from 13.94 to 34.86 mC·m-2 under the same operating conditions. It could be inferred that under the condition of non-alkaline sparingly soluble salt CaSO4 occurring in brine side

there are still some surface electrokinetic phenomena with low or medium level on NF membrane surface.