A sample of 1 litre is drawn from the aeration tank and is then allowed to settle for 30 min. The settled sludge occupies 300 ml at the bottom. This sludge, when dried, is found to have a mass of 3.2 g. The Sludge Density Index is mg/ml (round off to two decimal places).

1. The following information is provided for an activated sludge system design: Parameter Symbol Value Units Flow rate Q 10000 m³/d Influent BOD So 150 mg/L Effluent BOD S 2 mg/L Hydraulic residence time Ꮎ 4 hr Mean cell residence time Oc 6 d Maximum specific growth rate μm 3 1/d Half saturation constant Ks 40 mg/L Yield coefficient Y 0.5 Endogenous decay coefficient b 0.08 1/d Death rate coefficient γ 0.04 1/d Determine: a) The aeration tank biomass concentration (X) in mg/L b) The aeration tank oxygen requirement in kg/d c) The rate of biomass wasting in kg/d

A complete-mixed activated sludge process (CMAS) is to be designed to treat 6.0 MGD of primary effluent having a BOD5 of 190 mg/L. The requirement is that the effluent BOD5 and TSS concentrations be 20 mg/L or less on an annual average basis. The following biokinetic coefficient obtained at 15°C: Y = 0.6 mg VSS/mg BOD5, k = 2.85 d-1, Ks = 70 mg/L BOD5, and kd = 0.041 d-1. Assume that the MLVSS concentration in the aeration basin is maintained at 2,500 mg/L. Determine: a. The minimum MCRT (d) b. The MCRT necessary to meet the requirement (d) c. The volume of the aeration basin (ft3)

A rectangular settling basin has a depth of 3 m, a length of 40 m and a width of 6 m. The water treated in the basin has a flow rate of 500 L/s and contains 50 mg/L of type a particles, 100 mg/L of type b particles and 180 mg/L of type c particles (particle type letters refer to the particles listed in problem 1). What is the suspended solids concentration in the effluent from the settling basin? Determine the overall percent removal of suspended solids from the water achieved by the settling basin.

9-2 (15 pts) Determine the alkalinity, total hardness, carbonate hardness, and non-carbonate hardness (in mg/L CaCO3) for the water (pH 7.4) with the following chemical concentrations. Calculate the doses of lime and soda ash to soften this water. Constituent Concentration, mg/L Ca2+ 95 Mg2+ 13.5 Na 25.8 HCO3 244 SO 2- 73 CI 67.8 H2CO3 7.7