Watercalcs
Estimates only — verify before relying on results. Terms of Use
v3.0
How to do the testabout 30 minutes, mostly waiting
  1. Take the sample from the settling zone of the clarifier. A blanket sample tap is the easiest way if the clarifier has them; otherwise a sampling tube or a jar on a pole. Fill it in one go and take it straight to the cylinder.
  2. If the clarifier has taps at several heights, run them together. Fill a cylinder from each, start them at the same moment and read them at the same times. Three cylinders side by side tell you how the blanket is layered, which one sample never can.
  3. If you are using a tap, flush it first. Run it until what comes out matches what is in the clarifier, then fill the cylinder. Open it wide rather than cracking it: a nearly shut valve shears floc apart and you will measure the damage instead of the sludge.
  4. Fill the cylinder to the top graduation and start the timer as you set it down.
  5. Leave it still and out of the sun, at about the temperature of the clarifier. Do not stir it or tap it.
  6. Read the graduation the interface sits on — the line where cloudy sludge below meets clearer water above — at each of the times below. Write down the millilitre number.
  7. At each reading, note what the interface and the water above it look like. Those two change through the test and they tell you as much as the numbers.
  8. Read often in the first few minutes. That is the part the settling velocity comes from; the later readings show how far it compacts.
If no clear interface ever forms, that is a result, not a failed test. Record it and carry on.
Who and when
Samples
SampleDepth below the surface (m)Solids
The cylinder
mm, measured across the inside. This is what turns a millilitre reading into a settling velocity, so measure it rather than guess.
Readingsthe graduation the interface sits on, and what you can see
The sample as a wholethese do not change through the test
The clarifier optional

Enter these and the tool compares the settling velocity against the rate the water is rising through the clarifier. That comparison is what the test is really for.

m². For a plate settler use the projected plate area.
m. Leave width blank for a circular clarifier.
What the test tells you
The settling curve

This is the interface falling down the cylinder. The steeper the line, the faster the sludge is settling. The shaded stretch is the straight run the velocity was taken from; the flattening towards the end is compaction, which is a different process and is not used. Hover or tap any point for what was measured there.

Keep this test

Saving takes a dated snapshot of the results above. It does not change anything on this tab, and you can carry on editing afterwards. Saved tests are listed on the Records tab, where the trend is drawn.

One test tells you about today. A run of them tells you whether the floc is getting lighter, whether a dose change did anything, and how much margin the clarifier loses as the water cools.

Tests are saved from the bottom of the Settling Test tab. This tab lists what has been saved and draws the trend.

Save a record even when everything looks normal. A good day is what you need to compare a bad day against, and nobody ever has enough of them written down.

Saved records
Trend

Everything leaves the tool from here and nowhere else.

  • PDF prints what you tick below, with every value written out as text so nothing comes out blank.
  • CSV gives you the readings and results as a spreadsheet.
  • Save writes a file holding everything, including records and settings. Load it back later on any machine.

Nothing is uploaded anywhere. The tool runs entirely in your browser and files go to your own downloads folder.

What to include in the PDF

In the print dialogue, turn headers and footers off and leave background graphics on.

Spreadsheet and save file