The invention provides methods and compositions for reducing the malodorous sulfide gas released by a wastewater treatment system. The method preserves the vitality of waste consuming organisms within the system. The method comprises the steps of: determining the SRP PAA demand of the system, determining the aerobic PAA demand of the system, and adding a composition in an amount such that it is in excess of the SRP PAA demand but is below the aerobic PAA demand. Even though the composition increases the amount of sulfates within the wastewater it reduces the amount of SRP which prevents the malodorous sulfite gas release. The composition comprises at least one percarboxyacid.