The best way to remove H2S is by scrubbing at about _______ by bubbling CO2 through the water before aeration to reduce the pH

The best way to remove H2S is by scrubbing at about _______ by bubbling CO2 through the water before aeration to reduce the pH

• A. pH 4.5
• B. pH 5.5
• C. pH 6.0
• D. pH 6.5

Answer: (A)

Lowering the pH makes hydrogen sulfide (H2S) the dominant form of sulfide in water. H2S is a neutral, highly volatile molecule that readily transfers into the air, so stripping it from water works best when most sulfide is in this molecular form. Bubbling CO2 through the water before aeration adds carbonic acid, driving the pH down to about 4.5. At this low pH, the equilibrium shifts toward H2S rather than HS− or S2−, so aeration afterward removes H2S much more effectively. If the pH were higher (like 5.5, 6.0, or 6.5), a larger fraction of sulfide would be present as HS− or S2−, which are not as volatile and thus not as readily removed by aeration. By targeting roughly pH 4.5, you maximize H2S removal before the aeration step. After treatment, the water can be adjusted back toward acceptable distribution pH as needed.

Lowering the pH makes hydrogen sulfide (H2S) the dominant form of sulfide in water. H2S is a neutral, highly volatile molecule that readily transfers into the air, so stripping it from water works best when most sulfide is in this molecular form. Bubbling CO2 through the water before aeration adds carbonic acid, driving the pH down to about 4.5. At this low pH, the equilibrium shifts toward H2S rather than HS− or S2−, so aeration afterward removes H2S much more effectively.

If the pH were higher (like 5.5, 6.0, or 6.5), a larger fraction of sulfide would be present as HS− or S2−, which are not as volatile and thus not as readily removed by aeration. By targeting roughly pH 4.5, you maximize H2S removal before the aeration step. After treatment, the water can be adjusted back toward acceptable distribution pH as needed.