Modeling pore blocking of nanofiltration and reverse osmosis membranes during NaCl removal

摘要

Moroccan surface water and groundwater mark an increase of salt concentrations in the authorized drinking water levels. Membrane processes are a helpful technology to minimize these concentrations and to achieve high water quality in the distribution systems. However, the performance of a given membrane is found to be degraded due to membrane fouling and hence it results into a significant decline in the permeate flux. Membrane fouling is mainly associated with the deposition of solute molecules on the membrane surface. Therefore, it is necessary to interpret the fouling mechanism in order to predict the permeate flux evolution. In this paper, the permeate flux decline with time through two nanofiltration (NF) membranes (NF90, NF270) and one reverse osmosis (RO) membrane (BW30LE4040) was studied at a laboratory pilot scale using synthetic water doped with NaCl. Then, the mechanism of membrane fouling was studied through describing four pore-blocking models such as Complete Pore Blocking, Standard Pore Blocking, Intermediate Pore Blocking and Cake Formation. Parameters of these models were evaluated using a mathematical optimization procedure. The accuracy of the fitted model was judged using thestatistical parameters: regression coefficient, root mean square error (RMSE), normalized root mean square error (NRMSE) and Nash-Sutcliffe efficiency (NSE). Results show that the Complete Pore Blocking Model was the best representation of pore blocking and permeate flux decline of RO and NF membranes in filtration operations.