Question

1. A circular secondary clarifier (a.k.a. a final clarifier) is to be designed for an activated sludge treatment plant serving a municipality. The state regulatory agency criteria for final clarifiers used for activated sludge are: Peak SOR = 1,200 gal/day-ft2 Average SOR = 500 gal/day-ft2 Peak solids loading 50 lb/day-ft Peak weir loading-30,000 gal/day.ft The average flow to the aeration basin prior to junction with the recycle line is 3.5 MGD ·The recycled sludge flow is 30 percent of the average influent flow rate and is constant throughout the day. 0.3 The mixed liquor suspended solids (MLSS) 2,500 mg/L. The ratio of the peak hourly influent flow to the average hourly flow is 2.0 Qpsayo..g = 2.0 Determine a. The clarifier diameter b. The peak weir loading if peripheral effluent weirs are used.

Answer 1

Find the peak flow of clarifier Q 1200x2x1 -2400 ga/dayxft Find the surface area. 2400 500 -4.8 lb Find the diameter of the clarifier 4.8- 03 4.8 x4 D-3.10 1 Take depth of clarifier is 3.5 MGID Find the volume of the clarifier -π 2.25x 3.5 24.72

Find the weir length. 10.99 Find the design weir loading Weir loading = 2400 10.99 -21838 gal/day/ft1 The design weir loading is less than the peak weir loading. Therefore it is acceptable for the Criteria design.