| 摘要 |
Method and apparatus are described for removing dissolved radon gas from water for the purpose of reducing the exposure of household occupants to elevated airborne Rn levels, using a radon-permeable membrane at the interface between gaseous and liquid process streams. The membranes are permeable to the passage of radon gas but substantially impermeable to the passage of the bulk phases. Water is passed along one surface of a membrane in a high-surface-area membrane module, while stripping air is passed along the second surface of the membrane. Radon diffuses from the water stream into the stripping air. The membranes allow rapid and efficient mass transfer in compact devices. The stripping air stream is preferably maintained at a pressure substantially below that of the water undergoing treatment and is supplied to the membrane stripping module by a low-pressure fan or by a blower. Hollow-fiber and other high-surface-area (e.g., tubular, flat-sheet, and spiral-wound) membrane modules are suited to the practice of the invention; hollow fibers provide significant advantages in terms of low cost and high packaging density. The water undergoing treatment may be recirculated between the membrane module and a storage tank or accumulator. Membranes suitable for the practice of the present invention may be (i) dense, polymeric membranes of silicone rubber and various of its copolymers (e.g., the block copolymer formed from polydimethylsiloxane and polycarbonate) and (ii) hydrophobic, microporous membranes prepared from such non-wetting polymers as polytetrafluoroethylene (PTFE) and polypropylene (PP). Porous membranes may be either isotropic or asymmetric. Non-porous or "dense" membranes may either be self-supporting or supported. Preferred are "composite" membranes consisting of a dense film residing atop or within a porous support membrane.
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