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Water and Wastewater

Jar Testing


by Jack Swanson Jar testing is a pilot scale test that is used by water treatment operators to simulate a full scale water treatment process. Operators use various types of treatment chemicals that mimic coagulation and flocculation processes that remove organic and inorganic matter, colloidal particles of turbidity, and microorganisms found in raw water. System operators use 1000 milliliter jars to determine which chemical works best with their system's raw water. Jar testing requires careful attention to detail. It also requires knowledge of the system's actual mixing and stirring processes and how to mimic this using a jar testing machine. There is no set requirement on how many jar tests should be conducted, but the more tests conducted the better the plant will perform. Jar testing should be done as seasons change, weather changes, raw water charteristics change, and whenever the system is shut down or when part of the system is taken out of service for maintenance. It should be every operator's goal to optimize the plant's performance and improve the plant's efficiency. Finally, a jar test should be run to save money. Chemicals are expensive. By optimizing

coagulation and flocculation, hundreds of dollars can be saved. A common problem of water treatment is overdosing, that can hurt the quality of water while costing more than when proper jar testing technique is followed. Jar Testing Procedure The following is an example of how to perform a jar test. The chemical used is alum (aluminum sulfate) commonly used in coagulation and flocculation, and a six-gang jar tester with variable speed mixer. · First: Prepare a standard solution of alum using a stock solution containing 50% alum having a specific gravity of 1.2. * 1.2 specific gravity × 0.50 = 0.6 gram equivalent weight of alum. * 1 gram ÷ 0.6 gram equivalent weight = 1.67 mils equal one gram alum. * 1.67 mils × 10 = 16.7 mils equal 10 grams alum. * Add 16.7 mils to 1000 milliliter graduated cylinder holding some distilled water and bring up to the 1000 milliliter mark, mix thoroughly. * This will provide an increase in dosage of 10 mg/L when


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adding 1 ml in 1 ml increments. * Run as many jar tests as necessary to determine the optimized dosage. (Note: Always use actual treatment chemicals used in the treatment process.) · Second: Add 1,000 milliliters of raw water to each of the jars. Record temperature, pH, turbidity, alkalinity and TOC of the raw water (See Table 1). · After dosing each jar, turn on stirrers. This part of the procedure should mimic

the actual conditions of the plant. After coagulation and flocculation are completed, turn off the stirrers and allow floc to settle. Underfeeding of coagulant will cause a cloudy appearance with little or no floc formation. Overfeeding will cause a dense fluffy floc to form and will settle very slowly. The best way to determine proper dosing is to run a turbidity test on each sample. The Texas Commission on Environmental Quality (TCEQ), recommends turbidity of 2 NTUs or less as being optimized. Proper jar testing will provide

longer filter runs, and a greater reduction of microorganisms and organic matter while using less filter water to backwash and clean the filter. It also provides for better use of coagulant chemicals. Make sure you are properly performing a jar test so that you are providing the best product available to your customers. Note: Jack Swanson is an associate training specialist in the TEEX Public Works Training Program.

For more information on TEEX's Water and Wastewater Training Program: Website: Toll Free: 800-723-3811


Texas Engineering Extension Service ©2011



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