AWWA WQTC58971

In search of a less labor intensive and costly solution to the problem of losing disinfectantresidual, the Southern California Water Company - Southwest District (District) implemented a study to investigate the long-term effect ofpolyphosphate based corrosion inhibitors on disinfection residuals, hydraulics, and waterquality. The major objectives of this study were to:determine the relationship between the application of the polyphosphateblend and chlorine residual level;determine the effect of the addition of the polyphosphate blend on biofilmaccumulation within the distribution system;determine if customer complaints due to color were reduced after the additionof the polyphosphate blend; and,determine if customer complaints due to taste, odor and particles were reducedafter the addition of the polyphosphate blend. The addition of the polyphosphate blend started on November 6, 1998, in a small,isolated area of the distribution system less than 1 mi2 and was expanded on June17, 1999 to approximately 3.6 mi2 in size. Pipe diameters in the study area vary from 4to 12 inches in diameter and material composition is approximately 50% unlined castiron, 25% cement-lined cast iron and 25% asbestos cement pipe. The study area isapproximately 80% residential and 20% commercial and light industrial facilities and isrepresentative of the rest of the distribution system.The polyphosphate blend was initially added to one groundwater source and then expanded to five more groundwater sources and one surface waterconnection. In November of 2002, two more groundwater sources and onesurface water source were added. The addition of at least two more groundwater sources to this program isplanned for the end of this year or the beginning of next year. Currently, thepolyphosphate blend is added to five groundwater sources and two surface waterconnections. Each source is disinfected with a chloramine dose of 1.2 to 2.5 mg/L. The chloraminesare formed by combining free chlorine with natural ammonia in the well water, orby adding a 19% strength ammonium hydroxide solution at a Cl2 to NH4-N ratio of 5:1 tochlorinated water.Dosing of the polyphosphate blend is set according to the following: 1 mg/L per mg/L ofiron and manganese plus all divalent metals, 1 mg/L per 200 mg/L of hardness measuredas CaCO3, plus 0.15-0.3 mg/L for residual and corrosion control. At all sites thepolyphosphate blend solution is injected after the chlorine and/or ammonia addition at theplant effluent line.To evaluate the study objectives, water quality constituents are currently collected atseven distribution sites, which are representative of the plant sites. In addition to theseven primary locations, water quality samples are also collected from the wells and up to25 other locations within the distribution system. This paper summarizes and discusses results obtained from one specific area of thedistribution system as described before. All the water sources for this area are treatedwith the polyphosphate blend, and water quality data from this area has been collected sinceJune of 1998. Includes 16 references, tables, figures.

Product Details

Edition:

Vol. - No.

Published:

11/02/2003

Number of Pages:

12

File Size:

1 file , 700 KB