Typically, primary treatment has a BOD removal efficiency in the range of what?

Typically, primary treatment has a BOD removal efficiency in the range of what?

• A. 5-15%
• B. 20-50%
• C. 50-70%
• D. 70-90%

Answer: (B)

Primary treatment relies on physical processes to settle solids and skim fats and oils, removing the BOD that’s attached to those solids. Because most of the BOD in wastewater is tied to particulate matter, settling and scum removal reduce the organic load only by a portion, not the entire load. In typical municipal systems, primary treatment achieves about 20–50% BOD removal, which is why this stage is followed by biological treatment to tackle the remaining dissolved organics. Higher removals (50–90%) are characteristics of secondary or advanced treatment, while very low removals (5–15%) aren’t practical for a well-operated primary clarifier.

Primary treatment relies on physical processes to settle solids and skim fats and oils, removing the BOD that’s attached to those solids. Because most of the BOD in wastewater is tied to particulate matter, settling and scum removal reduce the organic load only by a portion, not the entire load. In typical municipal systems, primary treatment achieves about 20–50% BOD removal, which is why this stage is followed by biological treatment to tackle the remaining dissolved organics. Higher removals (50–90%) are characteristics of secondary or advanced treatment, while very low removals (5–15%) aren’t practical for a well-operated primary clarifier.