Efficient Separation\nof Tritiated Water from Light\nWater Based on Membrane Distillation by Gas–Liquid Exchange

The\nremoval of tritiated water (HTO) from “ALPS-treated\nwater” originating from the disabled Fukushima Daiichi Nuclear\nPower Plant (FDNPP) is an important environmental issue. In this paper,\nwe report a new method of separating HTO from light water (H<sub>2</sub>O) based on membrane distillation by gas–liquid exchange.\nHTO-containing water loaded on a hydrophobic membrane modified with\na photothermal black dye was exposed to artificial sunlight. The heat\ngenerated from the dye upon sunlight exposure vaporized the water,\nwith the HTO-containing water vapor penetrating through the membrane.\nThe permeated HTO-containing water vapor was mixed with H<sub>2</sub>O added to hydrophilic filters under the membrane. Gas–liquid\nexchange occurred in these filters and significantly decreased the\npercentage of HTO in the water collected under all filters. The increases\nin both the filter number and H<sub>2</sub>O content in the hydrophilic\nfilters increased the efficiency of HTO separation. When four hydrophilic\nfilters containing H<sub>2</sub>O and four hydrophobic filters were\nset alternately, the ratio of HTO collected under these filters decreased\nto 12 ± 0.3%. This process was also effective for the removal\nof <sup>137</sup>Cs from <sup>137</sup>Cs-containing water.