Basic Wastewater Operator Practice Exam

What is a typical range of BOD for untreated sewage?

1. 10-30 mg/L

2. 100-300 mg/L

3. 300-600 mg/L

4. 600-900 mg/L

The correct answer is: 100-300 mg/L

The typical range of Biochemical Oxygen Demand (BOD) for untreated sewage is generally around 100-300 mg/L. BOD is a crucial parameter that indicates the amount of organic matter present in wastewater. It measures the oxygen required by microorganisms to decompose organic matter over a specified period, usually five days at 20°C. Untreated sewage often contains substantial amounts of organic material, leading to higher BOD values. While some lower figures exist for certain types of wastewater, untreated sewage typically reflects values that fall within the 100-300 mg/L range. This range is significant because it highlights the potential environmental impact if such wastewater is discharged without treatment, as high BOD can result in oxygen depletion in receiving water bodies, adversely affecting aquatic life. Values below this range could reflect treated or less polluted waters, while those above may indicate extremely high pollution levels that require more intensive treatment to ensure environmental compliance and protection. Understanding this range is critical for wastewater operators, as it informs necessary treatment processes and regulatory compliance.