Mechanistic Model for CaSO4 Fouling on Nanofiltration Membrane

One of the major limitations of nanofiltration (NF) in drinking water treatment is inorganic scaling. In this study, a mechanistic model has been proposed to describe the permeate flux decline process during CaSO4 scaling in NF. It has been observed that the permeate flux decline follows four distinct stages. At first stage, 22-30% flux is reduced due to concentration polarization. At the second stage, flux is not reduced, instead, nucleation of CaSO4 occurs. The major permeate flux decline (60-70%) occurred at the third stage due to CaSO4 cake formation. At the final stage, the system reached the steady state, where rate of CaSO4 deposition on the membrane is balanced by shearing caused by the increase of concentrate flow rate. Beyond this stage, the flux does not decrease significantly. At each stage, the concentration of the salt at the membrane surface was estimated. The maximum salt concentration was found at the initial stage of permeate flux reduction, which gradually decreases as the filtration proceeds.