BACKGROUND Reverse osmosis (RO), which is widely utilized in wastewater treatment, has been proven to be an effective tool for ion separation with high salts rejection. However, owing to the extremely low concentration of nuclides in boron-containing low-level radioactive wastewaters (LRWs), there is a significant reduction in rejection of nuclides by using commercial RO membranes. In this study, in order to obtain higher nuclides rejection under trace-level condition, novel polyamide RO membranes were fabricated by grafting polyethylenimine (PEI) with different molecular weights on commercial RO membrane surfaces. RESULTS The properties of PEI-modified membranes were analyzed, such as surface charge, morphology and hydrophilicity. The results showed that zeta potential at pH 7 increased from -22.89 mV to 20.19 mV, which indicated that surface charge altered from negative to positive. Meanwhile, hydrophilicity of membranes was improved since the contact angle decreased from 65 degrees to 36 degrees. The decontamination factor (DF) of cesium(I) increased from 11.69 to 114.23 and the DF of cobalt(II) increased from 28.62 to 3306.88. CONCLUSION The laboratory-scale experiments with cross-flow demonstrated the effective rejection of nuclides without obvious membrane flux loss of PEI-modified membranes. In addition, PEI-modified membranes offered a stable nuclides removal under high-level background boron and various pH conditions, which demonstrated a possible application in boron-containing LRW treatment. (c) 2019 Society of Chemical Industry