Question

An activated sludge system has three square reactor tanks in series (CFSTRs) that are each 60 ft wide, 60 ft long, and 18 ft deep. The engineers have decided to add a new reactor in parallel. It will be a plug flow reactor (PFR) with a depth of 18 feet and a width of 18 feet. The length is to be calculated. The flowrate of wastewater is 2 MGD and the BOD is 165 mg/L. This will be split in half so that each side (3 square tanks in series and the new PFR) will treat one half the flow. The reaction rate is first order and the constant (k) = 4.0 d^-1.

What is the steady-state effluent BOD concentration from the last of the three existing tanks at flow = 1.0 MGD (mg/L)?

What is the required length of the new PFR so that is will have the same steady-state effluent concentration as the existing CFST reactors (ft)?

What is the BOD concentration at the middle length of the PFR (mg/L)?

Answer 1