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9.27 The influent of 10,000 m /day to a secondary reactor has a BOD5 of 150 mg/L. It is desired to have an effluent BOD5 of 5 mg/L, an MLVSS (mixed liquor volatile suspended solids) of 3000 mg/L, and an underflow concentration of 10,000 mg/L. The effluent suspended solids concentration is 7 mgL at 71% volatile suspended solids content. The sludge is wasted at the rate of 43.3 m /day. Assume the aerator to be of the fine-bubble diffuser type with an a = 0.55; depth of submergence equals 2.44 m. Assume ¡3 of liquor is 0.90. The influent TKN is 25 mg/L and the desired effluent NH3 - N concentration is 5.0 mg/L • f = 1.47. The average temperature of the reactor is 25°C and is operated at an average of 1.0 mg/L of dissolved oxygen. The AOR is calculated to be 3.36 kg/d • m . Calculate the volume of the reactor.

9.28 The volume of a secondary reactor is 1611 m . It receives a primary-treated wastewater containing a BOD5 of 150 mg/L. It is desired to have an effluent BOD5 of 5 mg/L, an MLVSS (mixed liquor volatile suspended solids) of 3000 mg/L, and an underflow concentration of 10,000 mg/L. The effluent suspended solids concentration is 7 mgL at 71% volatile suspended solids content. The sludge is wasted at the rate of 43.3.m /day. Assume the aerator to be of the fine-bubble diffuser type with an a = 0.55; depth of submergence equals 2.44 m. Assume ¡ of liquor is 0.90. The influent TKN is 25 mg/L and the desired effluent NH3 - N concentration is 5.0 mg/L • f = 1.47. The average temperature of the reactor is 25°C and is operated at an average of 1.0 mg/L of dissolved oxygen. The AOR is calculated to be 3.36 kg/d • m . Determine the volume of inflow to the reactor.

9.29 The volume of a secondary reactor is 1611 m . It receives an inflow of 10,000 m /day from primary-treated wastewater. It is desired to have an effluent BOD5 of 5 mg/L, an MLVSS (mixed liquor volatile suspended solids) of 3000 mg/L, and an underflow concentration of 10,000 mg/L. The effluent suspended solids concentration is 7 mg/L at 71% volatile suspended solids content. The sludge is wasted at the rate of 43.3 m /day. Assume the aerator to be of the fine-bubble diffuser type with an a = 0.55; depth of submergence equals 2.44 m. Assume ¡ of liquor is 0.90. The influent TKN is 25 mg/L and the desired effluent NH3 - N concentration is 5.0 mg/L. f = 1.47. The average temperature of the reactor is 25°C and is operated at an average of 1.0 mg/L of dissolved oxygen. The AOR is calculated to be 3.36 kg/d • m . What is the influent BOD5?

9.30 Using the data in Problem 9.29, calculate the effluent BOD5 from the secondary reactor if the influent BOD5 is 150 mg/L.

9.31 Using the data in Problem 9.29, calculate the rate of sludge wasting from the process if the influent BOD5 is 150 mg/L.

9.32 Using the data in Problem 9.29, calculate the underflow concentration from the secondary clarifier if the influent BOD5 is 150 mg/L.

9.33 An experiment was performed on a trickling filter for the purpose of determining the overall mass transfer coefficient. Raw sewage with zero dissolved oxygen was introduced at the top of the filter and allowed to flow down the bed. A tracer was also introduced at the top to determine how long it takes for the sewage to trickle down the bed. At the bottom, the resulting DO was then measured. From this experiment, the overall mass transfer coefficient (KLa)w was found to be 2.53 per hour. This information is then used to design another trickling filter. The j of the waste = 0.9 and the respiration rate r = 1.0 mg/L • hr. Assume the average temperature in the filter is 25°C and the effluent should have a DO = 1.0 mg/L. What void volume should be provided in the interstices of the bed to effect this detention time? The inflow rate is 10,000 m /d. The detention time of the sewage in the proposed filter to effect this DO at the effluent of 1.0 mg/L is calculated to be 0.06 hour. Calculate the overall mass transfer coefficient of the wastewater.

9.34 Using the data in Problem 9.33, calculate j if the overall mass transfer of the wastewater is 2.53 per hour.

9.35 Using the data in Problem 9.33, calculate the saturation dissolved oxygen concentration at the dissolution pressure if the overall mass transfer of the wastewater is 2.53 per hour.

9.36 Using the data in Problem 9.33, calculate the effluent DO if the overall mass transfer of the wastewater is 2.53 per hour.

9.37 Using the data in Problem 9.33, calculate the respiration rate if the overall mass transfer of the wastewater is 2.53 per hour.

9.38 An aerator in an activated sludge reactor is located below the surface. The temperature inside the reactor is 29°C. The rise velocity of the bubbles is determined to be 0.26 m/s at a time of rise of 13.46 sec. The approximate average diameter of the bubbles at mid-depth is 0.25 cm. Calculate the depth of submergence.

9.39 An aerator in an activated sludge reactor is located 3.5 m below the surface. The temperature inside the reactor is 29°C. The time of rise of the bubbles to the surface is 13.46 sec. The approximate average diameter of the bubbles at mid-depth is 0.25 cm. Calculate the rise velocity.

9.40 A packed absorption tower is designed to removed SO2 from a coke oven stack. The water flow rate L = 16.64 kgmols/s and the gas flow rate G = 0.39 kgmols/s. The mole fraction of SO2 in the air at the bottom of the tower is 0.03 and its mole fraction in the absorption water at the bottom of the tower is 0.0007. If the mole fraction of SO2 in the air at a point in the tower 7 meters from the bottom is 0.016, what is the corresponding mole fraction of the SO2 in the downward flowing scrubbing water.

9.41 Using the data in Problem 9.40, calculate the corresponding mole fraction of SO2 in air if its mole fraction in water at the 7-m point is 0.0004.

9.42 Using the data in Problem 9.40, calculate the gas flow rate G if the mole fraction of SO2 in water at the 7-m point is 0.0004.

9.43 Using the data in Problem 9.40, calculate the water flow rate L if the mole fraction of SO2 in water at the 7-m point is 0.0004.

9.44 Using the data in Problem 9.40, calculate the mole fraction of SO2 in the air at the bottom of the tower if the mole fraction of SO2 in water at the 7-m point is 0.0004.

9.45 Using the data in Problem 9.40, calculate the mole fraction of SO2 in the water at the bottom of the tower if the mole fraction of SO2 in water at the 7-m point is 0.0004.

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