1) Differentiate between BOD and COD in wastewater

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1) Differentiate between BOD and COD in wastewater. 20 mL of sewage sample was added directly into a 300 mL BOD incubation bottle. The initial DO of the diluted sample was 7.8 mg/L and the final BOD after 5 day was 1.3 mg/L. The corresponding initial and final do of the seeded dilution water were 8.1 and 6.9 respectively. What is the BOD, of the sewage sample?

2.A town on the bank of river Ganga discharges 18000 m³day of treated wastewater into the river. The treated wastewater has a BOD, of 20 mg L-1 and a BOD decay constant of 0.12 day at 20°C. The river has a flow rate of 0.43 m³sec1 and an ultimate BOD of 5.0 mgL-1. The DO of the river is 6.0 mgL 1 and the DO of the wastewater is 0.4 mg L- Compute the DO and initial ultimate BOD in the river, immediately after mixing.

3.A treatment plant disposes 50 MLD of treated effluent into a river. The river flow rate is 20 m²/s and its DO is 8 mg/L before the mixing point. If the BOD of the effluent is 50 mg/L, find the BOD and DC of the river water at the d/s of mixing point. Assume BOD of river water as 0 and DO in WW effluent as 0.

4.A circular sewer of 45 cm diameter was designed for a town of population 30,000. The sewer wa designed to carry 3.5 times of the dry weather flow. What slope should be provided to the sewer whe running full? Value of n= 0.012 in Manning's equation. Assume other relevant data suitably.

5.Design a sewer to serve a population of 36,000; the daily per capita water supply allowance being 135 litres, of which 80% finds its way into the sewer. The slope available for the sewer to be laid is 1 in 625 and the sewer should be designed to carry four times the dry weather flow when running full. What would be the velocity of flow in the sewer when running full? Assume n = 0.012 in Manning's formula.