(800) 726-4187
December 7, 2012
Cal~Flo Case Study – Replacing Liquid Caustic

Replacing Liquid Caustic: Study of North Carolina ACTIFLO® Treatment Plant

Overview

The city of Salisbury Water Treatment Plant contacted Burnett Lime Company in January of 2000 to set up a test of the CAL~FLO System. Floyd Rusher, the Water and Treatment Superintendent, was concerned with the rising price of liquid caustic, the need for added hardness and alkalinity, and the safety of the operators working with a hazardous chemical.

The first trial of the CAL~FLO System was conducted in February of the same year. The CAL~FLO test was successful in lowering overall chemical dosing, reducing overall chemical cost, increasing hardness and alkalinity, while replacing liquid caustic with non-hazardous CAL~FLO Slurry.

Over the next three-year period, the Salisbury Water Plant expanded to meet the growing demand for water. The existing plant, a conventional flocculation-sedimentation process, was expanded by adding an ACTIFLO® System. During the expansion, another test of the CAL~FLO System was conducted. Results were comparable to the first trial performed three years earlier.

After the feasibility study, the CAL~FLO System was installed and startup occurred on August 18, 2004. The CAL~FLO System feeds chemical to both the conventional plant and the newly commissioned ACTIFLO® System.

Data and Results

Data for this case study was summarized from two separate feasibility studies and the current feed rate averages. The first set of test results were from two ACTIFLO® System tests conducted in 1996 and 1997. The second set of test results came from CAL~FLO studies in 2000 and 2002. Current plant trends, feed rates, and logs were also included and reviewed to validate the results of the earlier studies. While information included in this case study was summarized from three different feasibility reports, the raw water quality, supply, and treatment processes, are comparable between 1996 and 2007.

In 1996, the plant supervisor was concerned with limited space. The city commissioned engineers to conduct two ACTIFLO® System trials. The ACTIFLO® trials utilized liquid caustic, alum, PAC, and micro-sand. Also, the ACTIFLO® System offered faster treatment time over the existing conventional water treatment plant.

Alkalinity

Alkalinity measurements were taken from finished water of the ACTIFLO® System tests using caustic, the current ACTIFLO® System using CAL~FLO, the conventional plant using caustic, and the conventional plant using CAL~FLO. The raw water allkalinity averages were consistent for each sample of finished water measurments. As shown in Fig. 1-A, when used with the ACTIFLO® System, CAL~FLO showed a 45% increase in finished alkalinity compared with liquid caustic. The alkalinity in the conventional plant was higher than the water coming from the ACTIFLO® System. The conventional plant ran higher doses of both liquid caustic and CAL~FLO Slurry. Also, the conventional plant did not remove as much natural alkalinity in the water as the ACTIFLO® System. The addition of alkalinity was confirmed and repeated in the monthly averages of the conventional water plant.

Cost Savings

Salisbury’s liquid caustic price averaged over $500 per ton. When pound-for-pound calculations were completed, CAL~FLO Slurry reduced Salisbury’s chemical cost by 44%. When the CAL~FLO plant trial was completed, a 15% chemical feed rate reduction was gained over caustic. Therefore, the total chemical cost reduction over liquid caustic was 59% as shown in figure 1-B.

Hardness

The results on hardness in Figure 1-C shows hardness displayed over a 13-day period. Although each data set was collected on different years, the time of year and raw water characteristics were similar. Also, current plant averages matched the data in Figure 1-C.

The average hardness when feeding CAL~FLO Slurry during the test at the conventional water plant was 40 parts per million (ppm). The average liquid caustic hardness for the thirteen days prior to feeding CAL~FLO Slurry was 25 ppm.

The current ACTIFLO® System hardness averages between 26 ppm and 30 ppm depending on the time of year. During the ACTIFLO® System trial, feeding liquid caustic produced water hardness of 21 ppm. Salisbury could add additional hardness to the water by increasing the feed rate of CAL~FLO Slurry. However, they do not currently feed alum in the ACTIFLO® System and choose to feed as little CAL~FLO as possible to produce acceptable results and reduce cost.

The conventional plant feeds alum and requires higher doses of CAL~FLO for pH adjustment, which also substantially raises the hardness over caustic.
Regardless, in both the conventional water treatment plant and the ACTIFLO® System, CAL~FLO increased the hardness as much as 38% in the conventional plant train and as much as 30% in the ACTIFLO® System train. The increase in hardness demonstrated with the CAL~FLO System in the conventional treatment plant was directly related to a higher feed rate than the ACTIFLO® System. Alum dosages require more CAL~FLO Slurry to reach acceptable plant level pH. The ACTIFLO® System hardness could be raised using the CAL~FLO System to the same level, but the plant is meeting all current quality requrements and chooses to save chemical cost.

Conslusion and Follow-up

The city of Salisbury Water Plant has continued operating the CAL~FLO System since 2004. They have participated in the CAL~FLO Maintenance Program (C.M.P.) The C.M.P. provides annual maintenance and yearly system diagnostics performed by a CAL~FLO System technician.
Salisbury was North Carolina’s first ACTIFLO® System. When asked about CAL~FLO System’s performance, Floyd Rusher stated, “The performance of the CAL~FLO System has met and exceeded all our expectations.”

For more information on the Salisbury Water Plant, contact Floyd Rusher at 1-800-851-7266.

For more information on the CAL~FLO System, please call 1-800-726-4187.

Case study information was compiled by Dallas Burnett.

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Burnett, Inc.     7095 Highway 11      Campobello, SC 29322      1-800-726-4187      (864) 592-1658 tel      (864) 592-1690 fax