Flux decline due to gypsum precipitation on RO membranes

Abstract This paper extends our initial study [3] of flux decline caused by precipitation fouling of RO membranes. A systematic series of experiments covering the Reynolds number range of 4,700–11,600 was carried out with a saturated solution of CaSO4 fed to a parallel plate osmotic cell. Flux decline data were found to be well correlated on the basis of a simulation model describing surface blockage of the membrane by radial spread of crystals from nucleation sites. The model is based on a single adjustable parameter km(N) 1 2 embodying a crystal growth rate coefficient (km) and a nucleation sites density magnitude (N). The data obtained indicated that gypsum crystal growth followed first-order kinetics. Salinity measurements showed a clear trend for permeate salt concentration to increase with the decrease in permeate flux. The salinity data were successfully correlated by the simulation model. A few experiments were also carried out measuring flux decline due to CaCO3 precipitation on the membrane surface at the Reynolds number range of 4,900–9,100. Permeate flow decline data were again successfully correlated by the simulation model using a well-known kinetic expression for CaCO3 precipitation.