Question

Biochemical Oxygen Demand (BOD) in a river water:

• A. Increases when sewage gets mixed with river water
• B. Remains unchanged when an algal bloom occurs.
• C. has no relationship with the concentration of oxygen in the water
• D. gives a measure of Salmonella in the water

Answer 1

The correct option is A Increases when sewage gets mixed with river water

Biochemical Oxygen Demand (BOD) in a river water increases when sewage gets mixed with river water. When BOD levels are high, dissolved oxygen (DO) levels decrease because the oxygen that is available in the water is being consumed by the bacteria in the sewage.
BOD increases in the presence of the algal blooms also because they also use oxygen.