PURPOSE: To decompose and remove a volatile organohalogen compd. by the charging of a reduced amount of energy without generating a side reaction product and environmental pollution by diffusing diffusion gas from water containing a volatile organohalogen compd. to bring the same into contact with an adsorbent and regenerating the saturated adsorbent by nitrogen gas while bringing the waste regeneration gas into contact with a reducing agent.

CONSTITUTION: Water containing a volatile organohalogen compd. is guided to a diffusion tower 3 to be sprinkled from above and countercurrently brought into contact with air sent from below. The exhaust air from the tower 3 is guided to an adsorbing tower 6 packed with an adsorbent such as active carbon to adsorb the volatile organohalogen compd. Thereafter, heated nitrogen gas is passed through the adsorbing tower 6 for the sake of regeneration to separate the organohalogen compd. from active carbon. The separated gas is brought into contact with a reducing agent such as hydrogen gas in the presence of a Pd-alumina catalyst.