Wastewater Treatment Operator Certification Practice Test

What causes primary effluent to become black and odorous?

1. Excessive sludge pumping

2. Oil leak from the sludge pump

3. Crack in the launder

4. Improper sludge removal from the clarifier

The correct answer is: Improper sludge removal from the clarifier

Primary effluent becomes black and odorous primarily due to the accumulation of organic matter and the lack of proper treatment, particularly during the sludge removal process in the clarifier. When sludge is not adequately removed, it begins to decompose anaerobically, producing foul-smelling gases and creating a black coloration due to the presence of hydrogen sulfide and other organic compounds. The breakdown of organic materials in the effluent leads to the formation of a thick layer of sludge that contributes to the blackness, while the anaerobic conditions generate unpleasant odors. Proper sludge management is crucial in wastewater treatment processes, as it directly impacts the quality of the effluent and the overall efficiency of the treatment system. By ensuring timely and effective sludge removal, operators can prevent these undesirable characteristics in the primary effluent.