In one embodiment, a treatment system for removing dissolved contaminants (e.g., arsenic) from a contaminated fluid (e.g., water) utilizes in-situ generation of adsorption filtration media or reactive components. Corrosion materials (e.g., iron oxide complexes) that serve as the adsorption filtration media or reactive components are generated by supplying a flow of contaminated fluid, and injecting air, into a generator vessel containing pieces of an oxidizable source (e.g., zero-valent iron spheres). The pieces of the oxidizable source are agitated to release particulates of corrosion materials from their surface into solution with the contaminated fluid. Simultaneous to the ongoing generation of corrosion materials, dissolved contaminants in the contaminated fluid are adsorbed on the corrosion materials. New particulate compounds generated by adsorption of the dissolved contaminants on the corrosion materials precipitate from the solution, and are filtered out, thereby removing the contaminants, and yieldin
