Water Treatment > Quality Water Solutions > Operational Issues > Jar Test Basics

Jar testing is a versatile tool that can provide essential information on the effectiveness of an existing coagulant program, how to change dosage in an excursion, and which candidate coagulants perform best in a plant trial, among many other uses.

This relatively quick and easy bench-scale procedure should reflect a plant's operations. For instance, plants with little mixing in the rapid-mix stage should not stir vigorously during the test, while those with short retention times (where floc settling rate is crucial) should shorten settling times accordingly.

Jar tests typically take 30 to 60 minutes to complete. In performing the test:

• Clarify the goals to be met. This may involve evaluating performance with regard to turbidity, color, pH, cold water, etc. Define what products, dosage range, addition sequences, other additives and mixing protocols will be used before starting the test so reagents do not spoil and raw water does not change as these decisions are made.
• Make sure all glassware, pipets and other equipment are clean.
• Make sure all chemicals are fresh and uncontaminated. Prepare coagulant use solutions daily, if they are used.
• Use fresh raw water. If a large sample (30 to 40 liter) is taken for multiple tests, keep it stirred (not air agitated) and at the initial raw water temperature.
• Use commercial square plastic beakers, candy jars or battery jars. Employ baffles when using round beakers, if possible.
• Keep the light off as much as possible on jar testers with lighted bases so warming of the water is minimal. Use a water bath, if possible.
• The jar test "control" should match the plant. This requires careful evaluation and the scaling back of many plant processes, e.g., a 20-minute detention time in the process does not necessarily equate to 20 minutes in jar testing. Update test protocols to match plant upgrades.

Parameters typically evaluated during jar testing include coagulant and flocculant dosages, mixing times, chemical addition sequences and mixing energy. Jar testing can also be effective in predicting dosages of taste and odor control chemicals and oxidants. Jar tests are also useful in determining how a change in a coagulant program would affect the filtration process.