Which parameter most affects hydrogen sulfide generation in sewer systems?

Which parameter most affects hydrogen sulfide generation in sewer systems?

• A. BOD concentration
• B. DO concentration
• C. pH
• D. SS concentration

Answer: (C)

The main factor here is how sulfide species exist in water, which is controlled by pH. In sewers under anaerobic conditions, bacteria can produce sulfide from sulfate using available organic matter. What matters for whether that sulfide ends up as hydrogen sulfide gas versus staying dissolved as bisulfide (HS-) or sulfide (S2-) is the pH of the wastewater. At lower pH, hydrogen sulfide (H2S) is the dominant form and readily escapes as a gas, leading to stronger odor and corrosion potential. As the pH increases, the equilibrium shifts toward HS- and S2-, which stay dissolved in water and are less likely to volatilize as gas. So pH directly controls how much hydrogen sulfide is released from the sewer system. While factors like BOD provide the substrate for sulfide production and DO influences whether sulfide is oxidized back to sulfate, the proportion that becomes gaseous hydrogen sulfide is most strongly governed by pH.

The main factor here is how sulfide species exist in water, which is controlled by pH. In sewers under anaerobic conditions, bacteria can produce sulfide from sulfate using available organic matter. What matters for whether that sulfide ends up as hydrogen sulfide gas versus staying dissolved as bisulfide (HS-) or sulfide (S2-) is the pH of the wastewater.

At lower pH, hydrogen sulfide (H2S) is the dominant form and readily escapes as a gas, leading to stronger odor and corrosion potential. As the pH increases, the equilibrium shifts toward HS- and S2-, which stay dissolved in water and are less likely to volatilize as gas. So pH directly controls how much hydrogen sulfide is released from the sewer system.

While factors like BOD provide the substrate for sulfide production and DO influences whether sulfide is oxidized back to sulfate, the proportion that becomes gaseous hydrogen sulfide is most strongly governed by pH.