The Jar Test
by Jlmaltais on March 21, 2017 - 3:59pm
In a water treatment facility, it can be sometimes difficult to determine what are the parameters that suit the best for the water that is treated. Polluted water have a composition that is always changing. With a different composition requires different parameters of operation. Since small changes in the parameters (pH, chemical dosage, agitation speed …) can have a huge impact on a full scale water plant, it is not recommended to try it because it could disturb the process. To avoid process disturbances, a method has been developed to simulate a full scale water treatment facility: The Jar Test. It is a simple method that has saved thousands of dollars to companies. This method can be divided into five main steps: Gathering material, scheduling tests, preparing each test, processing the tests and finally, analyze each tests.
The first step to perform a Jar Test is gathering the material. The main equipment needed is a gang stirrer. A gang stirrer is a machine that is used to agitate many (generally 4 to 6) containers at the same time. Another essential material are the Jars. They can be any type of recipient, but they must all have the same form/volume and be transparent. Transparency is a must to be able to compare each water’s clarity after the tests. Another item that must be acquired is a pH meter. This instrument is used to measure and adjust the pH (potential hydrogen, also known as acidity) of every sample of water contained in Jars. pH is adjusted with a base as sodium hydroxide or an acid as hydrochloric acid. It is also recommended to acquire a turbidity meter, which measure the clarity of a water, to make an easier comparison between each test. Finally, the last items that are needed are the water treatment chemicals that must be compared.
The second step consists of planning a schedule for each of the tests. The schedule must cover all parameters that have to be tested. For instance, test #1 to 5 would study the influence of pH and #6 to 10 would be testing chemical dosage. Only one parameter has to differ from each test.
The third step is the preparation of the ‘’batch’’ of tests. Since a gang stirrer only has 4 to 6 places, only 4 to 6 tests can be done simultaneously. During the preparation, every jars are set under the same conditions: water volume and composition, pH, temperature…Only one parameter is different. For instance, if the chemical dosage is different between each tests, the pH, temperature agitation will be the same.
The fourth step consists of the test itself. The jars are agitated at a specific speed for a specific time. There is no ‘’golden procedure’’: what is important is each batch are done in the same manner.
The fifth step is the comparison of each tests. Difference between each test are noted. This is where a turbidity meter can be helpful to compare the clarity of each treated waters. It can be possible to conclude on what were the best conditions to treat that specific composition of water. If the results are uncertain, it is always better to do the test over again or until a conclusion can be made. Once every tests are done, it is possible to determine the optimal conditions by comparing results and observations.
In conclusion, the Jar Test is a method used to simulate a full-scale water plant without disturbing its productivity. It is a must in every facility because it helps to save thousands of dollars in chemical waste. It is often known that an operator would add ‘’ a little extra ‘’ chemical just to make sure it all reacted with the water. With the Jar Tests, waste are avoided.