Modeling of backwash cleaning methods for RO membranes

A new comprehensive and time-dependent 2D model using finite element method (FEM) was developed to account for different versions of the backwash (BW) cleaning method for RO membranes. Two distinct cases of backwash were identified: Case 1, which has no applied pressures and velocities; and Case 2, where inlet velocity and pressure are applied in the feed channel, and in some cases pressure is also applied in the permeate channel. The model was verified by comparing it to existing BW data from both cases. The current 2D model is accurate enough to describe the actual 3D time-dependent BW process. Case 1 reduces to a 1D model agrees with the existing 1D analytical model and was found to be fully predictive. Case 2 deals with reported studies in a 2D format, and is suited to an industrial interest of keeping desalination setup unchanged while activating BW membrane cleaning. Water and salt diffusion coefficients were determined and found to be dependent on feed concentration and applied pressures. Dynamic change of concentration profiles of feed and permeate channels were illustrated. The resulting profiles reveal that in Case 2, changes in feed concentration profiles are negligible, while all other profiles of both cases change substantially with time.