GATE 2016 CE (CE2) – Question 62

Water and Waste Water Quality and Treatment · Primary, secondary and tertiary treatment, effluent standards · 2 marks · Numerical answer

For a wastewater sample, the three-day biochemical oxygen demand at incubation temperature of 20°C (BOD3day, 20°C) is estimated as 200 mg/L. Taking the value of the first order BOD reaction rate constant as 0.22 day-1, the five-day BOD (expressed in mg/L) of the wastewater at incubation temperature of 20°C (BOD5day, 20°c) would be _________

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Correct answer: 275 to 278

Explanation

First-order BOD exertion is BODt=L0(1−exp(−kt)). Eliminating L0 gives BOD5=200(1−exp(−0.22·5))/(1−exp(−0.22·3)). Evaluation gives **276.159mg/L**. The common temperature is20°C, so no temperature adjustment of k is needed.