Question

Question: The town of Camp Verde has been directed to upgrade its primary WWTP to a secondary plant that can meet an effluent standard of 25.0 mg/L BOD5 and 30 mg/L suspended solids. They have selected a completely mixed activated sludge system for the upgrade. The existing primary treatment plant has a flow rate of 2,506 m3/d. The effluent from the primary tank has a

The town of Camp Verde has been directed to upgrade its primary WWTP to a secondary plant that can meet an effluent standard of 25.0 mg/L BOD5 and 30 mg/L suspended solids. They have selected a completely mixed activated sludge system for the upgrade. The existing primary treatment plant has a flow rate of 2,506 m3/d. The effluent from the primary tank has a BOD5 of 240 mg/L. Using the following assumptions, estimate the required volume of the aeration tank:

BOD5 of the effluent suspended solids is 70% of the allowable suspended solids concentration.

Growth constant values are estimated to be: Ks = 100 mg/L BOD5; kd = 0.025 d–1; μm = 10 d–1; Y = 0.8 mg VSS/mg BOD5 removed.

The design MLVSS is 3,000 mg/L.

Answer 1

To estimate the required volume of the aeration tank for the upgrade of the primary WWTP to a secondary plant, calculate the BOD5 removal rate and the oxygen requirements. The BOD5 removal rate is 215 mg/L and the oxygen requirements are 14.31 kg/d. Assuming an oxygen transfer efficiency of 30% and an oxygen saturated concentration of 9 mg/L, the required volume of the aeration tank is 53.67 m3/d.

Step-by-step explanation:

In order to estimate the required volume of the aeration tank for the upgrade of the primary WWTP to a secondary plant, we will need to calculate the BOD5 removal rate and the oxygen requirements.

First, calculate the BOD5 removal rate:

BOD5_influent - BOD5_effluent = BOD5_removal_rate

240 mg/L - 25 mg/L = 215 mg/L

Next, calculate the oxygen requirements:

Oxygen_requirements = (BOD5_removal_rate * flow_rate * Y) / (MLVSS * (1 - (Ss/S0)))

Oxygen_requirements = (215 mg/L * 2506 m3/d * 0.8 mg VSS/mg BOD5 removed) / (3000 mg/L * (1 - (70/100)))

Oxygen_requirements = 14.31 kg/d

The required volume of the aeration tank can be estimated using the following equation:

Volume = Oxygen_requirements / (oxygen_transfer_efficiency * oxygen_saturated_concentration)

Assuming an oxygen transfer efficiency of 30% and an oxygen saturated concentration of 9 mg/L:

Volume = 14.31 kg/d / (0.30 * 9 mg/L)

Volume = 53.67 m3/d