Water Resources and Environmental Engineering

Biochemical Oxygen Demand (BOD)

The oxygen microorganisms consume while breaking down the organic matter in water, usually measured over five days.

BOD measures how much organic pollution water carries by the oxygen bacteria use to decompose it. The standard test incubates a diluted sample for five days at 20°C; BOD₅ = (D₁ − D₂)/P, the drop in dissolved oxygen divided by the decimal fraction of sample in the bottle.

The oxygen exerted by time t follows BOD_t = L₀(1 − e^(−kt)), with L₀ the ultimate BOD. Discharging high-BOD waste into a stream draws down its dissolved oxygen, which is why treatment plants are permitted on effluent BOD and why loadings are tracked in pounds per day.

How much of the FE Civil exam is Water Resources and Environmental Engineering?