A two-stage high-rate trickling filter with 200% recycle will be used to treat 5.0 million gallons per day (MGD). The influent BOD to the primary clarifier is 225 mg/L and the primary removes 30% of the incoming BOD. The effluent BOD should be 20 mg/L or less. Assume that the design BOD loading to the trickling filter system is 40 lb BOD/(d⋅1,000 ft3) and a depth of 6 ft will be used. Use the NRC equations for designing the trickling filter system, and assume that there are two treatment trains operating in parallel. Determine:
a. The diameter (ft) of the high-rate trickling filter system.
b. The effluent BOD concentration (mg/L).
