Abstract: An on-demand portable chlorine dioxide generator has a reagent bound medium in a first enclosed volume; a complementary reagent solution in a second enclosed volume, and a structure for selecting between a first position where the complementary reagent solution is forced through the reagent bound medium and a second position where said complementary reagent solution remains isolated from the reagent bound ion exchange medium, where a ClO2 solution is generated only during periods when the structure for forcing is actuated. The ClO2 solution can be discharged for use as a portable sprayer that can be used to treat surfaces infected by anthrax or other biological contaminants. When the bound reagent is chlorite, the complementary reagent is an acid or an oxidant. When the bound reagent is an acid or an oxidant, the complementary reagent solution is a chlorite solution.