What is the sludge age if the tank volume is 0.5 MG, the MLSS is 1,800 mg/L, the primary effluent suspended solids is 110 mg/L and the flow to the plant is 2.0 MGD?

The sludge age, or solids retention time, is a measure of the average length of time that sludge remains in the treatment system before being removed. It provides insight into the biological treatment process efficiency. To calculate the sludge age, the following formula is typically used:

[ \text{Sludge Age} = \frac{\text{Volume of the clarifier (in MG) } \times \text{MLSS (in mg/L)}}{\text{Flow Rate (in MGD)} \times \text{SS in mg/L}} ]

Where:

• The volume of the tank is given as 0.5 MG.

• The Mixed Liquor Suspended Solids (MLSS) are given as 1,800 mg/L.

• The flow to the plant is given as 2.0 MGD.

• The primary effluent suspended solids concentration is given as 110 mg/L.

Plugging in the numbers:

• Convert the tank volume to liters: 0.5 MG = 1,893,000 liters (1 MG = 3,785.41 liters, so 0.5 MG = 0.5 x 3,785.41 = 1,893,000 liters).

• Calculate