Florida Wastewater Practice Test

What is the likely cause of black and odorous wastewater leaving a primary clarifier?

1. Poor aeration

2. Improper sludge removal

3. Excessive chemical dosing

4. Inadequate screening

The correct answer is: Improper sludge removal

The presence of black and odorous wastewater leaving a primary clarifier is often indicative of improper sludge removal. When sludge is not adequately removed, it can lead to anaerobic conditions in the clarifier. This anaerobic environment can cause the breakdown of organic material in ways that produce foul odors and dark coloration in the effluent. In a properly functioning wastewater treatment system, the primary clarifier is responsible for settling out solids and reducing the organic load before the water moves to secondary treatment processes. If sludge accumulates and is not effectively removed, it can not only compromise the quality of the effluent but also lead to the release of gases like hydrogen sulfide, which contribute to the characteristic unpleasant smell. Other options, while they can affect overall treatment effectiveness, do not directly relate to the specific problem of black and odorous wastewater in the same immediate and critical manner as improper sludge removal does.