Parameters affecting backwash variables of RO membranes

The optimal setup of backwash (BW) cleaning methods was determined by analyzing the parameters affecting BW flux: accumulated volume during the process, and permeate salinity. An investigation was carried out on the parameters affecting BW flux and accumulated volume based on existing data and the 2D time-dependent FEM model developed in a previous study. According to this model, the absence or presence of feed velocity and applied pressure relates to Case 1 or Case 2 of BW cleaning methods, respectively. The main parameters affecting BW flux and accumulated volume are BW time tBW and feed concentration Cf. Effects of membrane thickness, salt and water diffusivities, and feed velocity on BW flux are negligible within ± 10% change. Results show that BW flux based on Case 1 is higher than fluxes of Case 2. This result provides a clear advantage of BW cleaning methods to Case 1 over Case 2 methods. Permeate salinity increases with Cf and tBW and decreases with desalination time tRO and feed pressure Pf. A preferable BW cleaning method resulting from this study is a cleaning method based on Case 1 for tRO > 20 min, at a tBW as short as possible and Cf around 31 kg/m3.