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 (FR), the concentrate recirculation (Q˙ C_RCL) and the recovery rates of the RO membrane in plug flow (PF) mode (RPF) and closed loop (CL) mode (RCL) 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 FR has little impact on system performance. An increase in Q˙C_RCL and in RCL results in significant increase in flux and permeate quality with a slight increase in SEC. RPF has a little impact on overall SEC of the system. To reach a high overall recovery rate with low SEC, low RPF, RCL and low Q˙C_RCL are necessary. If permeate quality is a concern, low RPF, high RCL, and high Q˙C_RCL are required.