Design of Constructed Wetland
1. Design a subsurface flow constructed wetland system to treat 1.0 mld of septic tank effluent having a BOD of 130 mg/L and 25 mg/L of ammonia nitrogen. The effluent BOD must be 10 mg/L and ammonia nitrogen concentration 8 mg/L. Assume the overall first order BOD removal rate is 1.1 d-1, rate constant for nitrification 0.107 d-1 at 200C and average wastewater temperature during coldest month is 100C.
2. A FWS constructed wetland system is to be provided to treat 0.60 mld of septic tank effluent with BOD5 of 300 mg/L and 20 mg/L ammonia nitrogen. Design a FWS wetland to produce an effluent BOD5 30 mg/L (or less) and ammonia nitrogen 6 mg/L. The first order rate constants for BOD5 and ammonia nitrogen removal are 1.2 d-1 and 0.22 d-1 at 200C respectively. Assume average wastewater temperature during coldest month to be 120C.
3. A FWS constructed wetland has an aspect ratio of 3:1 and a wastewater hydraulic loading rate of 75 mm/d. For a flow of 2 mld and a depth of 350 mm, calculate the area, dimensions, and flow velocity. Calculate Manning’s, the hydraulic gradient and headloss in the system. Assume the value of the resistance factor is 1.95. Also determine the detention time for 90% BOD removal using apparent rate constant at 150C.
