Treatment of radioactive wastewater solutions by direct contact membrane distillation using surface modified membranes

Abstract

Direct contact membrane distillation (DCMD) is proposed for processing low and intermediate level radioactive liquid wastes by means of surface modified flat sheet membranes to produce distilled water and to reduce the volume of the radioactive wastes for further safe storage and disposal. Different membranes were prepared by the phase inversion method using different fluorinated surface modifying macromolecules (SMMs). The host polymers are polysulfone and polyethersulfone. The structural characteristics of the membranes were studied. During membrane formation, SMMs migrate to the top membrane surface changing its characteristics. The DCMD experiments were performed with non-active and radioactive model solutions containing the most common radioisotopes present in liquid radioactive wastes, cobalt-60, Co-60, caesium-137, Cs-137 and strontium-85, Sr-85. The surface modified membranes removed completely radioactive species in one stage. The obtained permeate has activity on the level of natural background. The performance of the surface modified membranes was compared to that of the commercial membrane TF200 (Gelman). Higher values of the liquid entry pressure of water, lower permeate fluxes, higher rejection factors and lower radioactive adsorption to the membrane surface were observed for the surface modified membranes. The obtained results indicate that fluorinated surface modifying macromolecules have potential for application in nuclear technology.