Problem 2.13 Assuming that each person contributes a BOD load of 0.06kg/d, and a suspended solids load of 0.08kg/d, find the daily domestic pollutional load of a town of 20000 inhabitants. If the DWF is 120l/ capita.d, compute the concentration of BOD and suspended solids in the sewage. Problem 2.16 The treated sewage of 20000 people is discharged to a nearby stream which is flowing at a rate of 0.15m//s with a BOD of 2mg/l. The water consumption by the inhabitants' amount to 150l/ capita.d and the BOD contribution is 0.065kg/ capita.d. If the BOD in the stream below the outfall is not to surpass 4mg/l, find the required efficiency of the treatment plant needed to cope with this condition. Problem 3.4 Calculate the settling velocity of an organic suspension with a relative density of 1.001 and a diameter of 0.5mm in water, given that the dynamic viscosity is 1.1103Ns/m2. Assume that the particles are spherical in shape. Example 3.5 An activated sludge plant has been selected for treating a settled sewage at a daily flow rate of 3000m. The 5-day BOD of the waste is 200mg/l. The plant consists of two aeration tanks each of 4m depth, 5m width and 25m length. The MLVSS concentration is 2100mg/l. Compute: a) Detention time. b) Volumetric organic loading rate. c) Sludge loading ratio. Example 3.6 Estimate the sludge age for a conventional activated sludge plant from the relationship: c1=1Ukd Where: c= mean cell residence time (d) Y= sludge yield coefficient U= specific utilization rate (per day = (mass BOD removed) / (mass volatile solids in basin) ( kg BOD/ kg MLVSS.d) Given: Y=0.8,kd=0.05/d, MLVSS =3000mg/, retention time =0.2 days, and incoming BOD5 of 180mg/l. Example 3.6 In a conventional activated sludge plant the aeration volume is 60l/ capita, while the MLSS is 2400mg/l and sludge wasting amounted to 0.025kg/ capita.d. Compute the mean cell residence time. Example 3.7 The concentration of the mixed liquor suspended solids, MLSS, in the basin of a step aeration system is 2300mg/L, and the volume of settled sludge after 30 minutes in a 11