A diafiltration-nanofiltration-reverse osmosis (DiaNF-RO) process for brine management in seawater reverse osmosis (SWRO) desalination

• Main Authors: Truong, Vinh Hien, Chong, Tzyy Haur
• Other Authors: Interdisciplinary Graduate School (IGS)
• Format: Conference or Workshop Item
• Language: English
• Published: 2023
• Subjects: Engineering::Environmental engineering::Water treatment; Desalination; Brine Management
• Online Access: https://hdl.handle.net/10356/167913; https://icom2023.jp/
• Institution: Nanyang Technological University

In recent years, brine management in seawater reverse osmosis (SWRO) desalination has been more emphasized to reduce environmental hazards and recover valuable resources. However, current brine treatment methods are often hindered by the high brine concentration and energy consumption. To mitigate these challenges, this work applies a diafiltration-nanofiltration-reverse osmosis (DiaNF-RO) process, which aims to achieve divalent-monovalent ion separation in the pre-treatment step prior to RO. The diafiltration process is to enhance the separation performance of NF stage, while the RO stage is to produce the desalinated water and the diluent required by the diafiltration process. This study would justify the benefits of pre-treatment method (i.e., DiaNF-RO) over post-treatment method (i.e., RO-DiaNF), Fig. 1, in brine management by comparing the processes in 3 aspects (i.e., performance, operation, economic) via practical simulations, including pressure drop within module and concentration polarization (CP) effect, at the same number of stages and system water recovery, under similar input conditions such as NF/RO pressures and NF recovery rates. As shown in Table 1, compared to RO-DiaNF, the DiaNF-RO has better Mg-Na ion separation factor (SF) in both NF and RO brines; higher Na dilution in NF brine; lower RO area requirement; larger potential to operate at higher pressure and recovery due to lower osmotic pressure difference at membrane stages; less total operating cost especially with more stages due to more RO area saving. Overall, the pre-treatment DiaNF-RO achieves better results in performance, operation, and economic than the conventional post-treatment RO-DiaNF.