If you need volume of the reactor or tank (v) and hydraulic retention time (hrt) and you already have inlet flow (q), settling area (a) and side water depth (h), this calculator does the substitution for you. It suits a quick check, a homework answer you want to confirm, or any figure you need to sanity test.
What Is the Hydraulic Retention Time Calculator?
The hydraulic retention time calculator turns inlet flow (q), settling area (a) and side water depth (h) into volume of the reactor or tank (v) and hydraulic retention time (hrt).
It is a quick way to get from the numbers you have to the number you need, without setting up a spreadsheet or reaching for a formula.
How the Hydraulic Retention Time Works
Each result follows from the ones before it, and the calculator shows every step, so a surprising answer can be traced back to the input that caused it.
Round your inputs to the precision you actually know, and keep more precision than that in the intermediate steps.
Getting a Result You Can Trust
Run the calculation twice with slightly different inputs. A sensible calculator moves its output in proportion; a wild change points to a unit or a decimal point problem in what you entered.
Write the inputs down next to the answer. It takes a moment and it is the difference between a number you can explain and one you cannot.
A Worked Example
Working through an example, with inlet flow (q) set to 10, settling area (a) set to 5, side water depth (h) set to 2, the calculator returns volume of the reactor or tank (v) of 10, and hydraulic retention time (hrt) of 1. Substitute your own figures and the same steps produce the same kind of answer.
Frequently Asked Questions
What do I need to work out volume of the reactor or tank (v)?
Enter inlet flow (q), settling area (a) and side water depth (h). The calculator then works through the relationship and reports volume of the reactor or tank (v) and hydraulic retention time (hrt).
What does the hydraulic retention time actually calculate?
It takes inlet flow (q), settling area (a) and side water depth (h) and converts them into volume of the reactor or tank (v) and hydraulic retention time (hrt) using the standard relationship for this problem. Each step is applied in turn, so every output is traceable back to the numbers you typed in.
How should I enter inlet flow (q)?
Use the value you actually have, in the unit shown next to the field. Enter every value in the same unit system. The calculator assumes the figures you supply are consistent, so it cannot correct a mistake that happens before the calculation starts.
Does anything you type get stored?
No. The whole calculation runs inside your browser, and nothing you enter is uploaded, logged or sent anywhere.
Can I use this for a quick estimate as well as a precise answer?
Yes. The calculator is built for quick checks, so round your inputs to a sensible number of significant figures and the result will be just as useful. If you need more precision, keep the same method and add digits to the inputs rather than adjusting the method itself.