Effect of surfactants on the treatment of radioactive laundry wastewater by direct contact membrane distillation

BACKGROUND Direct contact membrane distillation (DCMD) was applied to treat the radioactive laundry wastewater produced from nuclear power plants (NPPs), with surfactants. RESULTS The experimental results show that when 0.08 mmol L‐1 surfactants was added into feed solution, the permeate flux reduced sharply by 3–30% in 1 h, and the largest reduction was found in the case with non‐ionic surfactant. The decontamination factors (DF) of Sr(II), Co(II), and Cs(I) were correspondingly decreased 10–100 times within 4–8 h. Compared with the no salt‐added case, the addition of high concentration salt (100–300 g L‐1) slowed down the reduction rate of the permeate flux caused by sodium dodecyl benzene sulfonate (SDBS). The wetting of membranes by surfactants mainly results from the spontaneous adsorption of surfactant molecules onto the membrane surface and the reduction of solution surface tension. However, the high concentration of NaNO3 in SDBS solution decreases the critical micelle concentration (CMC) of SDBS to less than 0.06 mmol L‐1, and thus SDBS micelles formed, which were hard for the membrane surface to absorb. CONCLUSION The study shows that surfactants could cause serious reduction in permeate flux and rejection of nuclides, and thus they should be removed from the feed solution of DCMD process. © 2018 Society of Chemical Industry