In search of a less labor intensive and costly solution to the problem of losing disinfectant
residual, the Southern California Water Company - Southwest District (District) implemented a study to investigate the long-term effect of
polyphosphate based corrosion inhibitors on disinfection residuals, hydraulics, and water
quality. The major objectives of this study were to:
determine the relationship between the application of the polyphosphate
blend and chlorine residual level;
determine the effect of the addition of the polyphosphate blend on biofilm
accumulation within the distribution system;
determine if customer complaints due to color were reduced after the addition
of the polyphosphate blend; and,
determine if customer complaints due to taste, odor and particles were reduced
after 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 June
17, 1999 to approximately 3.6 mi2 in size. Pipe diameters in the study area vary from 4
to 12 inches in diameter and material composition is approximately 50% unlined cast
iron, 25% cement-lined cast iron and 25% asbestos cement pipe. The study area is
approximately 80% residential and 20% commercial and light industrial facilities and is
representative 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 water
connection. In November of 2002, two more groundwater sources and one
surface water source were added. The addition of at least two more groundwater sources to this program is
planned for the end of this year or the beginning of next year. Currently, the
polyphosphate blend is added to five groundwater sources and two surface water
connections. Each source is disinfected with a chloramine dose of 1.2 to 2.5 mg/L. The chloramines
are formed by combining free chlorine with natural ammonia in the well water, or
by adding a 19% strength ammonium hydroxide solution at a Cl2 to NH4-N ratio of 5:1 to
chlorinated water.
Dosing of the polyphosphate blend is set according to the following: 1 mg/L per mg/L of
iron and manganese plus all divalent metals, 1 mg/L per 200 mg/L of hardness measured
as CaCO3, plus 0.15-0.3 mg/L for residual and corrosion control. At all sites the
polyphosphate blend solution is injected after the chlorine and/or ammonia addition at the
plant effluent line.
To evaluate the study objectives, water quality constituents are currently collected at
seven distribution sites, which are representative of the plant sites. In addition to the
seven primary locations, water quality samples are also collected from the wells and up to
25 other locations within the distribution system. This paper summarizes and discusses results obtained from one specific area of the
distribution system as described before. All the water sources for this area are treated
with the polyphosphate blend, and water quality data from this area has been collected since
June of 1998. Includes 16 references, tables, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 700 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 12 |
| Published : | 11/02/2003 |
