Activated sludge tank

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1) (20 points) A municipal wastewater of 5000 gpd flows in an activated sludge tank with the volume 85 m3. The biomass (VSS) and the substrate concentration in this tank are 2500 mg VSS/L and 40 mg BOD5/L, respectively. Assume 25% of the flowrate is disposed from this tank as sludge waste. Use the default values from Table 6.7: a. What is the rate of substrate consumption (4,.) and rate of biomass growth (rs)? b. What is the net microbial growth rate (r’s)? c. If the concentration of biomass in the effluent is negligible, and the solid retention time of this tank is fixed at 7 days, what would be the concentration of biomass in the sludge in mg VSS/L?

2) (25 points) The analysis of a sample of water with a pH ■•7.2 has produced the following concentrations:

Ca”: 34 mg/I. Mg’: 36.5 mg/t. Fe’ : 28 mg/L Na’: 23 mg/1. HC0i: 122 my„/I. SIN’: 144 mg/I. Cr: 56.8 mg/L

a. Determine the meq/L of each ion and compare cations and anions. b. Draw the mcq/L bar chart. c. Determine the Total Hardness & Non-carbonate Hardness as CaCO3. d. Determine the Alkalinity as CaCO3 in mg/L. e. Determine the concentration of FeSO4 as mg/L CaCO3.

3) (25 points) A volume of 25 L of Benzene (C61I6) has been spilled into a 3.375 m3 cube of sand aquifer. The amount of C6H6 dissolved in the aquifer is 25% of its aqueous solubility. Pump and Treat was used to remove all the C6H6. a. How much C6H6 is formed as LNAPL mass (in kilograms)? b. The hydraulic gradient of the sand aquifer is 0.01 when pumping the aquifer using the Pump and Treat. Using Tables 5.11 & 5.12, what is the linear average velocity of the aquifer (in m/day)? c. How long will it take to remove all the C6H6 (in years) if the retardation factor of C6H6 is 2.5?

4) (20 points) A chemical with particle size of 0.02 mm and density of 1.35 kg/L flows into a circular primary clarifier at 20°C. The flowrate of wastewater in this tank is 30 m3/min. The density and viscosity of water at 20°C are 998.2 kg/m3 and 1.0x le kg/m.s, respectively. a. Determine the terminal velocity of settling for this particle. b. What is the surface area (Ab) of the clarifier? c. What is the diameter of the clarifier? d. Assume detention time of the clarifier is 5 hours, what would be the minimum depth of the tank?

5) (10 points) A fuel efficiency test shows that an automobile travels with 26 mpg in cities and 32 mpg in highways. a. What is the CAFE fuel efficiency for this automobile? b. Assume we substitute a flex-fuel vehicle for this automobile and it uses 70% of its miles on gasoline and 30% on ethanol. This vehicle gets 27 mpg while running on gasoline and 18 mpg while on ethanol. Assume one gallon of ethanol equals 0.20 gallon of gasoline. Determine the CAFE fuel efficiency of this vehicle.