On-Site Jar Testing Guide
Jar tests on construction projects help select and quantify a chemical treatment program for removal of suspended solids from stormwater run-off. As the project progresses, jar tests help confirm that the chemicals are not "over-dosed" resulting in product wastage and potentially harmful residual release or "under-dosed" resulting in non-compliant site discharges.
To perform a jar test on-site, you will need some basic tools:
- 1 L glass jar(s),
- 1 mL plastic syringe(s), or a micro-pipette (20-200 µL),
- chemical sample bottles, and
- hand-held pH meter
Complete test kits are available for purchase from Flowlink.
Jar Test Calculator
Input volume of source water added to the jar and final quantity of chemical added in the jar test to calculate the chemical dose rate in ppm. Enter your chemical price per unit and calculate the treatment cost per cubic meter using dose rate(s) from the jar test.
Volume of source water
Qty of chemical
Chemical unit price, $
Cost per m3:
*One ppm is one part by weight, or volume, of a chemical added to the water in one million parts by weight, or volume, of the final solution.
The general procedure for on-site jar testing is as follows:
1. Fill a 1 L transparent glass jar with your source water half-way.
For more accurate results, measure 500 mL with a 500 mL/1000 mL graduated cylinder if available, or use a 500 mL plastic bottle to measure the volume, after which draw a line on the jar with a waterproof marker to indicate the 500 mL file line for repeat tests.
2. Test pH using a hand-held pH meter.
Make sure your pH meter is calibrated - a step-by-step pH calibration guide can be found here.
If pH is around neutral (6.5-7.5) proceed to the next step.
If pH is too acidic (pH < 6.5), raise pH to neutral using either caustic soda, soda ash, or sodium bicarbonate (baking soda) solution, then proceed to next step.
If pH is too basic (pH > 8.0), bring it down to neutral using a 10-20% (w/w) solution of citric acid or any inorganic acid, then proceed to the next step. If chemical grade citric acid is unavailable, a food grade anhydrous citric acid can be found at most grocery stores and used to prepare an aqueous solution.
3. Add 0.05 mL (50 µL) of your coagulant using a 1 mL syringe or a micro-pipette to the jar, quickly tighten the lid, and shake vigorously for about 30 seconds.
Coagulant examples include chitosan, polyaluminum chloride (PAC), aluminum chlorohydrate (ACH), ferric chloride, starch or tannin-based coagulants.
4. Look at the jar under a bright light. Do you observe any reaction?
If coagulant is working, you will start seeing very small flocs (pin-flocs) appear. Cloudiness will begin to disappear, which should be most noticeable at the of the water level.
If water looks clear (not murky) after addition of 0.05 mL, you may want to repeat the experiment and add a smaller amount of coagulant or use a bigger jar with 1 L of source water to find out the smallest effective coagulant dose.
5. Continue adding your coagulant in small doses of 0.05 mL (50 µL) and shaking the jar (Step 3) until water looks clear while being observed under the light (Step 4).
If using two-part chemistry - coagulant and flocculent, size of the flocs does not matter much at this point; if using chitosan alone you will want to start paying attention to the floc size now.
Combined amount of coagulant is your final dose rate, e.g. 50 µL is 100 ppm, 100 µL is 200 ppm, etc.
6. If using two-part chemistry, you can now start adding your flocculent to the water treated with coagulant following the same process (Steps 3-5).
7. After settling for a period of time (typically 10-15 min.), note supernatant appearance.
If available, the latter may be quantified using a turbidimeter.
8. Verify pH.
This step is to ensure it is still within allowable discharge limits post-treatment. Depending on the chemistry used, you may also want to test for residual.
8. Once the jar test is done, repeat the process with the final dose rates added at once.
This is to confirm the process works as intended.
9. Empty the jar and thoroughly clean it for the future tests.
- When evaluating different chemistries, you will want to pay attention to not only the flow rates, but also relative floc sizes and settling rates.
- Jars with different treatment protocols or the same product at different does rates can be run for side-by-side comparison and the results can be compared to a blank (untreated source water).