Question

Problem 3 (20 pts) Your firm is doing a wastewater treatment plant upgrade for a plant using activated sludge with an influent BODs concentration of 300 mg/L. Recently, the steady state inflow increased to 50.0 mᵒ/d. To maintain proper performance, a VSS concentration of 150 mg/L in the bioreactor and 2500 mg/L in the WAS line needs to be maintained. a) Draw a diagram of this scenario. b) Design the aeration tank for a cell retention time of 7 days. What should the aeration tank volume be? c) What should the flowrate of the WAS line be?

Answer 1

Given that BODG concentration - 300 mg ili VSS concentration - cell retention time = 7 days (Biological react81) (a). - Aeration Basin secondary O₂ A e Clarifier (setting tank) 4 V (wartewaters) Q aroto dute d ..(0) Influent (Walte water) Qe ye → Effluent so zuen (Raw wate yi mixed Suspended flganismos Liquor x MLVSS sludge cwaste activate Qu ,xu bwaw: tu R. AS [Qr5,Xr5] 10) Cell retention time ,o= I days (given) let Asume F/M = 0.adt f/m = Q lyi-ye) 1. v*x Hiere, Q+ inflow => 50 mold. Yi+ in fluent BUD -> 300 mg/l yet effllient BOD = omgic (let assume) V volume of reactoy (m3) X+ MLVSS in the reactos => 150my in =4 ve 50 mm x (300 – 0) mg 0.20-.X 150 mg

. volume of the aeration tank (u) = 500 m3 © D = V x x 1 . Qwx Xu => Hd = 500 m 3 x 150 mgle O Qw X 2500 mg/l .: Qw = 4.285 m3/d]