7-25. A short distance downstream from the tannery in Problem 7-23, a glue factory and a municipal wastewater treatment plant also discharge into Cattaraugus Creek. The wastewater flows and ultimate BODs for these dis- charges are listed below. Determine the initial ultimate BOD after mixing of the creek and the three wastewater discharges. Source Glue factory Municipal WWTP Flow, m³/s Ultimate BOD, mg/L Temperature, °C 20 20 0.13 0.02 255 75

You’re working on a preliminary design for a water treatment plant expansion for Fell City.  The required capacity is 12 MGD (million gallons per day).  The TSS of the sedimentation basin effluent is 16 mg/L of TSS.  Assume the effluent TSS is 0 mg/L. (a)  Based on a filtration rate of 2 gpm/ft2, how big (area) must the filters be? (b)  If 3% of the treated water is used for backwashing, what would the backwash TSS be?  (Set up a mass balance analysis.) (c)  How many tons of sludge (dry solids) would be generated in 30 days?  Answers:  4170 ft2, 533 mg/L, 24 ton

The lowest flow in the Ozama River in July is about 48 m3/s. The dissolved oxygen concentration of the river just upstream of the discharge point is 4 mg/l and the ultimate BOD of the river is 10 mg/l. A farm discharges 2m3/s of untreated wastewater with a dissolved oxygen concentration of 0.5 mg/l and an ultimate BOD of 300 mg/l. Both the river and the discharge are at 25°C. what is the initial oxygen deficiency after mixing (i.e., as soon as the wastewater and the river have mixed)? What is the ultimate initial BOD after mixing? Can the farm be allowed to continue discharging raw water? Justify your answer.

A primary circular clarifier for a municipal wastewater treatment plant is to be designed for an average flow rate of 3570 m³/d. Given the surface loading rate is 35 m³/day.m² and assume that the peak flow factor is 2.5. Calculate: 1) Peak Flow Rate 2) Surface Area of the Clarifier 3) Diameter of the clarifier