Tennessee Wastewater Operator Practice Exam

What happens to the BOD load when primary sludge is successfully reduced in the primary clarifier?

1. It remains constant

2. It increases

3. It decreases

4. It fluctuates

The correct answer is: It decreases

When primary sludge is successfully reduced in the primary clarifier, the biochemical oxygen demand (BOD) load decreases. This reduction occurs because primary sludge consists largely of organic material that can contribute to the BOD levels. By effectively removing a significant portion of the suspended solids and organic materials during the primary treatment phase, the overall concentration of biodegradable material entering the subsequent treatment stages is lowered. A decreased BOD load indicates that there are fewer organic pollutants in the wastewater needing treatment, which can lead to more efficient processing in secondary treatment systems. This reduction can improve the biotreatment process's efficiency and effectiveness, as lower BOD levels mean that the microbial population in the treatment system will have less organic matter to break down, potentially leading to improved treatment performance and lower energy requirements.