5 days-biochemical oxygen demand (BOD5) is taken at a temperature of

In waste water engineering, the 5-day biochemical oxygen demand (BOD₅) test is typically conducted at a temperature of 20°C. This specific temperature is considered standard for measuring the amount of dissolved oxygen consumed by microorganisms during a 5-day incubation period.

Therefore, the correct completion is: "5 days-Biochemical Oxygen Demand (BOD₅) is taken at a temperature of 20°C."