Biological Nitrogen Removal- Wastewater contains 40 mg/l of nitrate nitrogen and has a flowrate of 10,000 m3/d, Singapore

Assignment 1

Biological Nitrogen Removal

1. Wastewater contains 40 mg/l of nitrate nitrogen (177 mg/l as Nitrate) and has a flowrate of 10,000 m³/d. Effluent requirements have been set at 2 mg/l total nitrogen. Using a mean cell-residence time of 15 d and a mixed-liquor concentration of 1500 mg/l, determine the volume of a complete-mix reactor that will be required to provide the necessary treatment. Also determine the rate of cell production and the methanol utilization rate, assuming that the influent DO is equal to 5 mg/l. Assume that the final clarifier will produce an effluent with 10 mg/l suspended solids.

Kinetic coefficients:

m_m=0.3 d^-1

Ks=0.1 NO₃^–-N mg/l

Y=0.8 NO₃^–-N, mgVSS/mg

K_d=0.04 d^-1

2. Design an aerobic-anoxic process for nitrification/denitrification of wastewater. After preliminary treatment, 20,000 m³/d of wastewater containing 150 mg/l of BOD₅ and 30 mg/l of ammonia nitrogen is to be treated. The following conditions are to be used in the design:

Denitrification rate = 0.1 mgNO₃^–-N/mgVSS.d at 20°C

MLVSS = 3,500 mg/l

Calculate the anoxic volume requirement for denitrifcation and the BOD removal in the anoxic and aerobic zones.

3. A wastewater contains 10 mg/l of ammonia nitrogen and no organic carbon. If the plant flowrate is 10,000 m³/d, estimate the methanol requirement and cell production for the complete bacterial assimilation of ammonia.