Simulations of BWRO systems under different feedwater characteristics. Analysis of operation windows and optimal operating points

Reverse osmosis (RO) is the leading technology for desalinating seawater and brackish water (BW). In general, the desalination efficiency of BW is higher than that of seawater due to its lower total dissolved solids content. In addition to membrane fouling, fluctuations in the feedwater source are one of the main problems that affect desalination systems. These variations can have a significant impact on the operating parameters and efficiency of BWRO systems. In this work, hydrochemical fluctuations in well groundwater were used to evaluate the different operation windows of two BWRO system configurations, as well as their optimal operating points in terms of minimum specific energy consumption (SEC) and maximum flow recovery (R). Both configurations comprised two stages and 6 BWRO spiral wound membrane elements per pressure vessel (PV). One configuration had 2 and 1 PVs in the first and second stages respectively, and the other 3 and 2 PVs. Both systems were simulated using a range of feed flow and feed pressure values in addition to the inorganic compositions of 24 feedwater samples taken over a 10-year period. The results showed wider operation windows for the 3:2 than the 2:1 configuration. A common operation window (able to operate with all 24 feedwater samples) with wide operating margins was obtained for each configuration. For the 2:1 configuration, the 24-sample average SEC, average maximum SEC and average minimum SEC of this common operation window were 0.760, 1.198 and 0.339 kWh m−3, respectively, while the corresponding R values were 33.47, 67.66 and 19.86%. •Impact of feedwater concentration (1.2–5.8 g L−1) on BWRO systems (2:1 and 3:2 configuration)•Notable reductions in operation windows were obtained.•Maximum flux recovery (avoiding scaling) of between 70.8 and 89.1%•SEC variations of −55.4 to +57.6% in common operation window for 2:1 configuration•SEC variations of −56 to +60.1% in common operation window for 3:2 configuration