Abstract: Reverse osmosis (RO) technology is one of the effective methods to address the inherent secondary waste volume issue in supercritical water oxidation (SCWO) treatment of radioactive organic liquid waste from nuclear power plants. To improve the metal ion rejection rate of the RO unit and further reduce waste generation, this study takes the simulated SCWO process effluent containing ions such as Li⁺, Cs⁺, Mn²⁺, Co²⁺ and Ni²⁺ as the research object, uses BW30 as the reverse osmosis membrane material, and investigates the effects of operating pressure, feed pH and feed flow rate on the metal ion rejection performance, membrane flux and volume reduction factor of the RO unit through orthogonal experiments, and analyzes the influence of residual acetic acid on the ion rejection rate. The results show that operating pressure is the dominant factor affecting the rejection of metal ions from the simulated wastewater by reverse osmosis. Under the operating conditions of feed pH 6, operating pressure 1.3 MPa and feed flow rate 1.4 L/min, excellent ion rejection and volume reduction performance can be achieved. The membrane has a rejection rate of over 98% for divalent metal ions, while the rejection effect for monovalent ions is relatively poor. Acetic acid has little effect on metal ion rejection, but its own rejection rate increases significantly with the rise of concentration. Scanning electron microscopy and atomic force microscopy characterization confirm that fouling phenomenon exists on the surface of the BW30 membrane, and attention should be paid to its long-term operation stability.

Key words: membrane separation, reverse osmosis, liquid radioactive waste, volume reduction