Sulfur ___ produce sulfates and sulfur ___ produce hydrogen sulfide.

• A. Oxidizers - reducers
• B. Reducers - oxidizers
• C. Oxidizers - oxidizers
• D. Reducers - reducers

Answer: (A)

This question hinges on redox changes of sulfur. Sulfates are the oxidized form of sulfur (sulfur in a high oxidation state), so they form under oxidizing conditions when sulfur is pushed to a higher oxidation state. Hydrogen sulfide is the reduced form of sulfur (sulfur in a low oxidation state), forming under reducing conditions where sulfur is kept in or pushed to a lower state, often by sulfate-reducing bacteria in anaerobic environments.

So, sulfur in oxidizing environments tends to become sulfates, while sulfur in reducing environments tends to become hydrogen sulfide. In wastewater terms, aerated (oxidizing) conditions promote sulfate formation, and anaerobic (reducing) conditions promote hydrogen sulfide production. That’s why the correct pairing is oxidizers producing sulfates and reducers producing hydrogen sulfide.