Q4: A wastewater treatment plant as shown: The surface area of each unit 800 m². Depth of each unit 2 m. and %BOD removal in Primary and Secondary sedimentation tanks = 25%. Find: 1- Total % BOD removal in the plant. 2- BOD removal in the Trickling filter. 3- The flow rate (m³/d) in the plant. r-150% BOD, 180 mg/l Pri. sed. tank River BOD,-20 mg/1 Trickling filter Sec. sed. tank (25 marks)

Q2: A wastewater containing 300 mg/l SS and 250 mg/l BOD passes through a primary sedimentation tank of surface area 600 m². The flow is 15*103 m³/d. Estimate the effluent SS and BOD. (Use Figure 1)

9-2. A flow of 20,000 maay which contains 100 mg/L of suspended solids is coagulated with 50 mg/L of alum. If 90 percent of the solids and chemical precipitates is removed in sedimentation estimate: (a) Total dry mass of sludge produced per day. (b) Total wet mass produced per day, assuming the sludge is 5 percent solids by weight. (c) Total volume produced per day, assuming the specific gravity of the wet sludge is 1.05.

Design a sedimentation basin for a water treatment plant with the following specifications assuming it is required to supply a city with a population of 50,000 people: Rectangular or square basin • Depth: 7-18 ft ● . • Width: 10-50 ft Detention time: 4-8 hours Flow through velocity: <0.55 ft/min Overflow rate: 400-1,100 gal/day-ft² Draw a figure to show calculated dimensions. You may consider to use SI units in calculations. ● ● Hint: Overflow rate is Flow/Surface Area; Detention time is Volume of tank/Flow rate; and Depth= Volume/Surface area