Abstract
Membrane filtration has been applied to the treatment of liquid low-level radioactive wastes (LLRW) worldwide. In this study, removal of dissolved salts and transition metal species from simulated nuclear wastewater was investigated with NF270 and several RO membranes at different pH conditions. Rejection rates of various species are highly dependent on the solution pH. Generally, rejection rates of transition metals increased with elevated pH levels while the opposite trend occurred in those of alkali and alkaline earth metal species due to cake-enhanced concentration polarization. Other operating parameters such as pressure and feed concentration were also discussed. To investigate membrane fouling mechanism, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) combined with α-step profilometer was first applied in fouled membrane analysis. The results of foulants spatial distribution and depth profile are quite consistent with the two-phase fouling mechanisms based on Hermia model. Besides, ultrasonic imaging system was used to observe the morphology of membrane surface in micro-scale. It provides a quick and convenient way to evaluate the severity of membrane fouling.