For a secondary clarifier that is 75 ft in diameter with a combined flow of 4.0 mgd and a MLSS concentration of 2450 mg/L, what is the solids loading rate?

To determine the solids loading rate for a secondary clarifier, the formula used is:

[

\text{Solids Loading Rate} = \frac{\text{Flow Rate} \times \text{MLSS Concentration}}{\text{Surface Area of the Clarifier}}

]

First, we need to calculate the surface area of the clarifier. The area of a circular tank can be calculated using the formula:

[

\text{Area} = \pi \times \left(\frac{\text{Diameter}}{2}\right)^2

]

With a diameter of 75 feet:

[

\text{Area} = \pi \times \left(\frac{75}{2}\right)^2 \approx 4417.86 \text{ ft}^2

]

Next, we convert the flow rate from mgd (million gallons per day) to gallons per minute (gpm) for easier calculations. Since 1 mgd equals 1,000,000 gallons per day and there are 1,440 minutes in a day:

[

4.0 \text{ mgd} = 4,000,000 \text{ gallons per day} \div 1,440