A process for killing microorganisms and controlling biofouling in high chlorine demand waters comprises mixing two components, one of which is an oxidant and the other an ammonium salt, and adding the mixture immediately to the aqueous system to be treated. A key tree is formed so as to include a plurality of subtrees serving as category trees categorized in accordance with categories and managed by category entities. The output signal, the switch signal, the adapted input signal, and the first controller are referenced to a first ground potential.