Comparison of low-pressure reverse osmosis filtration and polyelectrolyte-enhanced ultrafiltration for the removal of Co and Sr from nuclear plant wastewater

• Simulated low-level radioactive wastewater was treated by membrane systems.
• Reverse osmosis (RO) did not improve with chelating polymer, and lost permeability.
• Addition of polyacrylic acid to ultrafiltration enhanced metal removal significantly.
• Polyacrylic acid effects were pH-dependent, while polyethylenimine was metal-specific.
• Polymer-enhanced ultrafiltration performances were comparable to those by RO.

Volume reduction and the concentration of long-lived radioactive species are critical issues for the management of liquid low-level radioactive waste. This study investigated and compared the performances of low-pressure reverse osmosis (LPRO) and polyelectrolyte-enhanced ultrafiltration (PEUF) for the removal of target metals (Co and Sr) from simulated low-level radioactive waste. The effects of dosage and types of chelating polymers, such as polyacrylic acid (PAA) and polyethylenimine (PEI), were evaluated at acidic and neutral pH levels. The metal removal efficiencies by precipitation at acidic pH (4.5) and neutral pH (6.5) were marginal. The addition of PAA to LPRO had no effect on metal removal, but had a negative impact on membrane permeability, particularly at acidic pH levels. The LPRO itself already achieved sufficient metal rejection; therefore, the addition of PAA only caused fouling. In contrast, the PAA dosage and solution pH governed the metal rejection in PEUF. Deprotonated PAA molecules bound to metal ions, but the distribution of PAA species had no significant impact on flux decline. The PEUF with PEI exhibited almost no pH dependency in metal removal, but showed metal-specific removal behaviors. The PEUF with PAA achieved metal removal as high as LPRO, with relatively high water permeability.

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