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Jar Test

06/10/2020

In water treatment, coagulation and flocculation are practically always applied before a physical separation. With the rising costs of chemicals, finding the best way to run a water or wastewater process can be difficult. Not to mention trying to keep up with stringent environmental regulations. The Jar Test is the best way amongst other options to identify the most adept mix of chemical compounds and concentrations for coagulation‐flocculation.  Jar testing tries to mimic, on a small scale, what could happen in your full-size setup. It allows you the freedom to try different chemicals in various amounts without changing the design of your full-scale setup. 

Jar testing involves taking some of the raw water, wastewater or surface water and mixing it with different compounds in the lab. The common chemicals are: mineral and/or organic coagulants (typically iron and aluminum salt, organic polymers), flocculation additives (activated silica, talcum, activated carbon, etc.), anionic or cationic flocculants and pH control reagents such as acids or bases. Certain heavy metal chelating agents can also be added during the coagulation step.

The coagulation‐flocculation process is a cost-effective method to remove a bulk amount of suspended solids. Through the process, the suspended solids can be changed into larger and heavier settleable solids by physical and

chemical changes brought about by adding and mixing the suitable chemicals in the raw water. These larger and heavier particles can then be removed by following sedimentation and filtration processes. The lab can control the dosing rate of each chemical and the amount of time the water is in contact with the chemical. The stirring is monitored and maintained at an optimum speed for coagulation and flocculation respectively. Agitation plays an important role in jar testing since the chemical reacts with numerous compounds present in water. Turbidity of the filtered water is measured after the test. It should be noted that a raw water sample from the plant is also tested for its turbidity. This would serve as a baseline to evaluate the effectiveness of the jar test.

 

Jar testing is used for both drinking water treatment and waste water treatment process exploration. Also, the jar test dosing chemical rate varies as the seasons change. What works well in the summer may not work as well in the winter since surface water is comparatively clean in the winter vs. in the summer. More chemical dosage may be needed in the summer but if you are adding chemicals at the same rate year-round, you may be wasting chemicals and spending more money than necessary.

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