An efficient cyclic process and related compositions for the in-situ generation of oxyhalogens from anions of chloride, bromide and chlorite in an aqueous system using in-situ generated sulfate free radicals. The cyclic process and compositions enhance the rate of inactivation of microbiological organisms especially those resistant to inactivation from free halogen based sanitizers, and oxidation of oxidation resistant organic based compounds in aqueous solution. Aquatic facilities susceptible to accumulation of organic N-chloramines and other oxidation resistant compounds, as well as oxidation resistant parasitic organisms such as cryptosporidium and Giardia, obtain dramatic improvements in the rate of oxidation and subsequent inactivation of these undesirable contaminants.