Which item is not listed as contributing to chlorine demand?

Which item is not listed as contributing to chlorine demand?

• A. Nitrate
• B. Ammonia
• C. Cyanide
• D. Hydrogen sulfide

Answer: (A)

Chlorine demand is the amount of chlorine that gets consumed by substances in water as they react with chlorine during disinfection. Nitrate sits in a highly oxidized state and doesn’t readily react with free chlorine under typical disinfection conditions, so it doesn’t consume chlorine. In contrast, ammonia reacts with chlorine to form chloramines, hydrogen sulfide is readily oxidized to sulfate or other sulfur compounds, and cyanide is oxidized to cyanate or related products. These reactions pull chlorine away from the desired disinfectant, contributing to chlorine demand. So nitrate is the item that does not contribute.

Chlorine demand is the amount of chlorine that gets consumed by substances in water as they react with chlorine during disinfection. Nitrate sits in a highly oxidized state and doesn’t readily react with free chlorine under typical disinfection conditions, so it doesn’t consume chlorine. In contrast, ammonia reacts with chlorine to form chloramines, hydrogen sulfide is readily oxidized to sulfate or other sulfur compounds, and cyanide is oxidized to cyanate or related products. These reactions pull chlorine away from the desired disinfectant, contributing to chlorine demand. So nitrate is the item that does not contribute.