Failure to frequently remove solids from a manually cleaned bar screen is most likely to cause an increase in:

• A. pH
• B. Hydrogen sulfide
• C. Influent grit
• D. DO

Answer: (B)

Bar screens remove large solids from incoming wastewater. If they aren’t cleaned frequently, solids build up in the screen area and create stagnant, oxygen-poor pockets. In those conditions, microbes decompose organic matter without enough oxygen, producing hydrogen sulfide—a rotten-egg smelling gas that can cause odors and corrosion. That direct outcome makes hydrogen sulfide the most likely change. Changes in pH or dissolved oxygen aren’t as directly tied to this buildup, and while grit can accumulate, the immediate effect of neglecting cleaning is the production of hydrogen sulfide.