GT 9900 is applied to the wastewater containing remaining long-acting oxidants. For example, the wastewater discharged from pulp and paper plant often contains trace of toxic substances such as Isothiazolinone, which is easy to inhibit the biological system of the wastewater treatment plant and affect the quality of the discharged water. Using GT9900 can effectively remove this kind of oxidizing agent. Reduce the impact on the biological system in the closing stages and the wastewater treatment plant can operate stably.