ho can i doud in farst plan

Answer 1

ho? doud? farst? What are those words?
H2S is a poison. I doubt if it would be used for wather treastment. Have you tried Googling the subject?
Use the words
<<water treatment hydrogen sulfide>>

Answer 2

Hydrogen sufide is a water contaminant that needs to be removed to below 1 ppm levels. Chlorine addition can do this. See
http://ohioline.osu.edu/aex-fact/0319.html