How to determine the needed surface area of the secondary clarifier tank given that the flow is 40,000 m3 per day and the recycling ratio is 0.5 . The necessary solids concentration in the underflow is 13,000 mg/L, while the Mixed liquor suspended solids concentration in the activated sludge is 4,500 mg/L. The table below shows the settling properties of sludge: Mixed liquor suspended solids Mg/l Settling velocity m/hr 2000 6 4000 3 6000 1 8000 0.2 10000 0.1 13000 0.1

Given a settling tank operating at 80% TSS removal efficiency, an inflow of 0.5 m3/s, and an influent concentration of 100 mg/L.  Assuming steady state operations, at what flow would operators have to remove sludge in order to achieve a TSS concentration of 1500 mg/L in the sludge?  Answer:  0.027 m3/s

The 750-bed Associated Center of Medical Excellence (ACME) Hospital has a small activated sludge plant to treat its wastewater. The average daily Medical Center discharge is 1,250 L per day per bed, and the average soluble BOD5 after primary settling is 450 mg/L. The aeration tank has effective liquid dimensions of 10.0 m wide by 25.0 m long by 3.5 m deep. The plant operating parameters are as follows: MLVSS = 2,750 mg/L MLSS = 1.25 (MLVSS) Settled sludge volume after 30 min = 250 mL/LDetermine the following: aeration period, F/M ratio, SVI, solids concentration in return sludge.

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)