A Study on the Performance of Vacuum Membrane Distillation in Treating Acidic, Simulated, Low-Level Radioactive Liquid Waste

This study systematically explored the performance of a vacuum membrane distillation (VMD) system equipped with polytetrafluoroethylene (PTFE) hollow fiber membranes for treating simulated, acidic, low-level radioactive liquid waste. By focusing on key operational parameters, including feed temperature, vacuum pressure, and flow velocity, an orthogonal experiment was designed to obtain the optimal parameters. Considering the potential application scenarios, the following two factors were also studied: the initial nuclide concentrations (0.5, 5, and 50 mg·L−1) and tributyl phosphate (TBP) concentrations (0, 20, and 100 mg·L−1) in the feed solution. The results indicated that the optimal operational parameters for VMD were as follows: a feed temperature of 70 °C, a vacuum pressure of 90 kPa, and a flow rate of 500 L·h−1. Under these parameters, the VMD system demonstrated a maximum permeate flux of 0.9 L·m−2·h−1, achieving a nuclide rejection rate exceeding 99.9%, as well as a nitric acid rejection rate of 99.4%. A significant negative correlation was observed between permeate flux and nuclide concentrations at levels above 50 mg·L−1. The presence of TBP in the feed solution produced membrane fouling, leading to flux decline and a reduced separation efficiency, with severity increasing with TBP concentration. The VMD process simultaneously achieved nuclide rejection and nitric acid concentration in acidic radioactive wastewater, demonstrating strong potential for nuclear wastewater treatment.