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Jar Testing & Simulated Distribution System Testing – Removal of Disinfection Byproduct Precursors and Trihalomethane Control

Case Study - Removal of Disinfection Byproduct Precursors and Trihalomethane Control

Jar Testing & Simulated Distribution System Testing – Removal of Disinfection Byproduct Precursors and Trihalomethane Control 

 

Background and Objectives

A municipality was looking to draw water from a secondary source to supplement their current drinking water supply. Bench-testing was performed to determine both the most effective coagulant type and optimum treatment conditions.  A series of 15 jar tests were conducted evaluating alum, aluminum chlorohydrate and ferric sulfate coagulants, as well as optimization of pH, dose, pre-oxidation for manganese removal with chlorine dioxide, and dose of powdered activated carbon for the current source water, as well as the proposed new source water. Once jar testing was completed, 4 treatment conditions were selected, and freshly treated water was prepared for a simulated distribution system (SDS) test. The SDS test is intended to simulate the distribution system by dosing with the proper amount of chlorine to achieve a target disinfection residual, maintaining the temperature expected in the distribution system, and monitoring the chlorine decay and disinfection byproduct (DBP) formation.

Testing Outcome

Following the jar testing regime, the 4 selected treatment scenarios used for the SDS testing were as follows:

  • Test 1 – New source water pre-treated with 0.8 mg/L ClO2, 60 mg/L alum at pH 6 and 10 mg/L PAC
  • Test 2 – New source water pre-treated with 0.8 mg/L ClO2, 60 mg/L alum at pH 6 and 20 mg/L PAC
  • Test 3 – Current source water pre-treated with 1.0 mg/L ClO2, 60 mg/L alum at pH 6 and 10 mg/L PAC
  • Test 4 – New source water pre-treated with 0.8 mg/L ClO2, 60 mg/L ferric sulfate at pH 6 and 10 mg/L PAC

The four pre-treated water samples were dosed with the proper amount of chlorine to meet a 5-day residual of 0.5 mg/L of free chlorine. The chlorine decay was monitored to verify the residual was within a valid range for the test, and aliquots were quenched with an appropriate reducing agent and analyzed for TTHMs to develop formation kinetics curves for each treatment regime. These DBP results were used to determine which treatment was the most effective at removal of DBP precursors, as well as whether the secondary source water could meet treatment objectives and be a suitable source to supplement the facility’s drinking water supply.

  Figure 2. Chlorine decay and TTHM formation.

For additional information contact: TestAmerica Corvallis Brad Suedbeck 541-243-6131.