Parameters influencing semi-batch reverse osmosis - Model based analysis

Semi-batch closed loop reverse osmosis (CLRO) provides an alternative to overcome the challenges associated with the recovery rate, brine volume and specific energy consumption (SEC) in conventional RO. A flexible modelling tool is developed to size a CLRO system and predict its performance under various operating conditions. This tool was used for designing a pilot scale CLRO system, which was experimentally validated for brackish water treatment in Qatar. The predictions were within 5 % accuracy when compared to experimental results. The influence of system parameters, such as the feed ratio (F R ), the concentrate recirculation (Q̇ C_RCL ) and the recovery rates of the RO membrane in plug flow (PF) mode (R PF ) and closed loop (CL) mode (R CL ) on performance are analysed to deepen process understanding. A system with a 4-inch LG SW 4040 R treating 25 g/l of artificial NaCl solution is considered for the examining the impact of these key parameters. Assuming an ideal plug flow without any mixing, the results show that the F R has little impact on system performance. An increase in Q̇ C_RCL and in R CL results in significant increase in flux and permeate quality with a slight increase in SEC. R PF has a little impact on overall SEC of the system. To reach a high overall recovery rate with low SEC, low R PF , R CL and low Q̇ C_RCL are necessary. If permeate quality is a concern, low R PF , high R CL , and high Q̇ C_RCL are required. • A flexible dimensioning and projection tool is developed for semi-batch RO. • The tool is validated on a pilot plant for BWRO application. • A parameter variation study is conducted using the tool. • Concentrate recirculation and CL recovery rate are the key influencing parameters.