a) A city discharges 1.5 m3/sec of wastewater into a river whose flow rate is 10m3/sec. The velocity of the river is 1.0 km/hr. The temperature of the wastewater is 20oC, while that of the river is 15 oC. The 20oC BOD5 of the i) wastewater is 200 mg/L, while that of the river is 1.0mg/L. The wastewater contains no dissolved oxygen (DO), but the river’s DO is 90% saturated upstream of the discharge. At 20oC, BOD decay coefficient is estimated to be 0.3/day, while re-aeration rate coefficient is 0.7/day. Using temperature coefficients of 1.135for BOD decay coefficient and 1.024 for re-aeration, answer the following questions i. Determine the DO of the river before discharging the wastewater (saturation concentration of DO at 15oC is 10.1 mg/L) ii. Determine the temperature, DO and BOD of the mixture. iii. Determine the ultimate BOD5 of the mixture b) In a water treatment plant the responsible sanitary engineer designed a cone aerator for aeration of the water. According to the manufacturer’s specification the cone has an oxygenation capacity of 40 g oxygen per second. Determine the level of oxygen that could be transferred by the cone under working conditions at 24o C given that the level of dissolved oxygen to be established is 1.6 mg/l.
a) A city discharges 1.5 m3/sec of wastewater into a river whose flow rate is 10m3/sec. The velocity of the river is 1.0 km/hr. The temperature of the wastewater is 20oC, while that of the river is 15 oC. The 20oC BOD5 of the i) wastewater is 200 mg/L, while that of the river is 1.0mg/L. The wastewater contains no dissolved oxygen (DO), but the river’s DO is 90% saturated upstream of the discharge. At 20oC, BOD decay coefficient is estimated to be 0.3/day, while re-aeration rate coefficient is 0.7/day. Using temperature coefficients of 1.135for BOD decay coefficient and 1.024 for re-aeration, answer the following questions
i. Determine the DO of the river before discharging the wastewater (saturation concentration of DO at 15oC is 10.1 mg/L)
ii. Determine the temperature, DO and BOD of the mixture.
iii. Determine the ultimate BOD5 of the mixture
b) In a water treatment plant the responsible sanitary engineer designed a cone aerator for aeration of the water. According to the manufacturer’s specification the cone has an oxygenation capacity of 40 g oxygen per second. Determine the level of oxygen that could be transferred by the cone under working conditions at 24o C given that the level of dissolved oxygen to be established is 1.6 mg/l.
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