Improved Chlorine Residuals After Tank Cleaning with Top Ultra®

Problem

The town of Dustin, Oklahoma provides water to approximately 500 customers and produces 45,000 gallons per day (gpd) of treated surface water. Water is stored in a 60,000-gallon clearwell at the plant and a 50,000-gallon elevated tank near the town center. In 2001, chlorine loss in the distribution system triggered repeated boil-water orders. Washing out the clearwell and a regular flushing program improved the situation somewhat, but boil-water orders continued. The Oklahoma Rural Water Association suggested the use of Blue Earth Labs’ Top Ultra product for chemical tank cleaning to stabilize the chlorine residuals.

Solution

In late November of 2001, the elevated tank was flushed conventionally with pressurized water. In December 2001, the package treatment unit and clearwell were chemically cleaned using Top Ultra, and tank cleaning was completed in one day. The flushing of the elevated tank resulted in the removal of approximately 18” of sludge. However, Top Ultra’s chemical tank cleaning improved the free chlorine residual in the nearby city hall only slightly (0.54 to 0.62 ppm). The Top Ultra surface cleaning procedure was effective in removing heavy surface deposits from the clearwell and package treatment unit. Additionally the chemical cleaning resulted in significant improvement of chlorine residuals within the distribution system. Additionally the chlorine demand of the clearwell was directly determined by measuring the chlorine residual before and after an overnight, off-line period. A control water sample was kept in a clean laboratory glass beaker. The decline in the control sample represented the demand of the bulk water and the gassing off of the chlorine.

Results

Overall, the severe chlorine demand of the clearwell (94%) was the main cause of poor chlorine residuals in the distribution system. After the Top Ultra chemical tank cleaning, dramatic, system-wide improvement occurred, eliminating boil orders and allowing the customer to reduce their total chlorination from ≥4.0 ppm to ≤2.2 ppm.