Desulfurization issue

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The coke oven gas purification process consists of cold drumming, desulfurization, ammonium sulfide production, and benzene extraction. The desulfurization process employs a wet desulfurization method, which falls under pre-desulfurization. The hydrogen sulfide concentration at the outlet of the desulfurization section (at the exit of the desulfurization tower) is no more than 10 milligrams per cubic meter; at the inlet of the ammonium sulfate production section, it is 20 milligrams per cubic meter, while it is 100 milligrams per cubic meter after the ammonium sulfate production section and after the benzene washing section. Why is there a difference of 10 times between the hydrogen sulfide levels analyzed after the desulfurization section and those analyzed after the benzene washing section? What is the reason for this? How to solve this problem? I would appreciate it if experts could provide some insights