Oil/water separation using nanofiltration membrane technology

Traditionally, ultrafiltration has been used to separate relatively clean water from oil/water emulsions. This water was once suitable for discharge to all sewer lines, but in general, it was inadequate for reuse. Recent changes in sewer discharge limits have created a need to generate cleaner water. A different type of membrane filtration, nanofiltration, may offer an effective means of recycling water from oil solutions or for generating clean enough water for discharge. Results of ultrafiltration and nanofiltration batch concentration tests indicate that nanofiltration can effectively treat industrial machining coolant. The mass transfer model fit the flux behavior. At lower pressures, nanofiltration flux was slightly lower, mostly due to the higher membrane resistance of the nanofilter. However, at higher operating pressures, the nanofiltration mass transfer coefficient increased while the ultrafiltration transfer coefficient decreased. Except at very high percent recovery levels, lower levels of COD and conductivity were observed in the nanofilter permeate as compared to the ultrafilter permeate: the quality of nanofiltration permeate resembled that of ultrafiltration permeate near the end of the concentration cycle.