Calculate solids retention time and hydraulic retention time using volume, solids concentration, daily wasting, wasted-stream concentration, and flow rate.
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Solids Retention Time Formula
This single wasting-stream approximation calculates solids retention time when other solids losses are negligible. Co must be the solids concentration in the same stream represented by Q. General SRT includes all solids leaving the system in its denominator. Select the quantity to solve above; HRT is separately calculated as reactor liquid volume divided by hydraulic flow.
Variables:
- SRT is the Solids Retention Time (days)
- V is the digester volume (gallons)
- Cs is the solids concentration (mg/L)
- Q is the volume wasted each day (gallons/day)
- Co is the wasted-stream solids concentration (mg/L)
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 solids concentration in that wasted stream.
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 (mg/L).
- Next, determine the volume wasted each day (gallons/day), then its solids concentration (mg/L).
- 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 (mg/L) = 2.5
volume wasted each day (US gallons/day) = 100
wasted-stream solids concentration (mg/L) = 3.5
SRT = V*Cs/(Q*Co) = 500 × 2.5 / (100 × 3.5) ≈ 3.5714 days.
