The present description relates to a method and a system for generating a Fenton reagent. Particularly, the description relates to a method and a system for oxidizing contaminants from wastewater. The Fenton reagent can react with various organic compounds and metallic elements. The method of producing an in-situ Fenton reagent comprises: providing an aqueous solution comprising at least one contaminant; providing at least one column comprising i) an inlet and an outlet separated by a flow chamber, and ii) a mass of iron fibre in the flow chamber between the inlet and the outlet; providing at least one dispenser retaining a hydrogen peroxide generating solid and permitting passage of the aqueous solution through the dispenser; optionally acidifying the solution upstream of the at least one column, and passing the aqueous solution through the at least one column.