Enter the digester volume (gallons), the solids concentration (ppm), the solids concentration of the effluent, and the volume wasted each day (gallons/day) into the Solids Retention Time Calculator. The calculator will evaluate the Solids Retention Time.

## Solids Retention Time Formula

The following formula is used to calculate the Solids Retention Time.

SRT = V*Cs/(Q*Co)

Variables:

- SRT is the Solids Retention Time (days)
- V is the digester volume (gallons)
- Cs is the solids concentration (ppm)
- Q is the volume wasted each day (gallons/day)
- Co is the concentration of the effluent (ppm)

To calculate solids retention time, multiply the digester volume by the solids concentration, then divide by the product of the volume wasted each day times the concentration of the effluent.

## How to Calculate Solids Retention Time?

The following steps outline how to calculate the Solids Retention Time.

- First, determine the digester volume (gallons).
- Next, determine the solids concentration (ppm).
- Next, determine the volume wasted each day (gallons).
- Next, gather the formula from above = SRT = V*Cs/(Q*Co).
- Finally, calculate the Solids Retention Time.
- After inserting the variables and calculating the result, check your answer with the calculator above.

**Example Problem:**

Use the following variables as an example problem to test your knowledge.

digester volume (gallons) = 500

solids concentration (ppm) = 2.5

volume wasted each day (gallons) = 100

concentration of the effluent (ppm) = 3.5

SRT = V*Cs/(Q*Co) =** ** ?