Polyphosphates. What you need to know

The District will be adding polyphosphate to the water beginning May 1, 2016. The following information is provided to you as is relates to the use of polyphosphates in drinking water.

What are phosphates?

Phosphates are water treatment chemicals used to solve specific water quality problems resulting from inorganic contaminants (iron, manganese, calcium, etc.) in ground water supplies and also to maintain water quality (inhibit corrosion, scale, biofilm, reduce lead and copper levels) in the distribution system. Orthophosphate and polyphosphate are two general types used in water treatment along with many different phosphate compounds that exist for use in the water treatment process. Ortho and polyphosphates work together, stabilizing water quality and minimizing color, scale, deposits, corrosion, and chlorine demand in drinking water systems.

What are the problems that phosphates help to solve?

Phosphates are used in municipal water systems to perform three broad functions: inhibit corrosion of water mains/plumbing (iron, steel, galvanized, asbestos/cement, lead, copper), sequester nuisance metals in the water supply (iron, manganese, calcium, magnesium). They can also improve the quality of water in the distribution system by removing scale deposits & tuberculation, discourage microbial film formation/regrowth, and stabilizing free chlorine disinfectant residuals.

How do phosphates work in a water system?

Orthophosphate based additives are classified as corrosion inhibitors and as such react with dissolved materials (e.g. Ca, Mg, Zn, etc.) in the water to form a very thin metal-phosphate coating or it reacts with metals on a pipe surface to form a microscopic film on the inner surface of the pipe that is exposed to the treated water.

Polyphosphate type chemicals react with soluble metals (iron, manganese, calcium, magnesium, etc.) by sequestering (bind-up) the metals to maintain their solubility in water. The phosphate sequestering process minimizes the risk of discoloration, staining, scaling, taste/odor and other water quality complaints.

Are phosphates safe and approved for water systems?

Various forms and purity grades of phosphates exist. Most dry powders and liquid concentrates are safe to handle and store, except for the standard precautions required for orthophosphate acids and zinc orthophosphate solutions. All Carus phosphate additives are either food quality grade or certified to ANSI/NSF Standard #60 Drinking Water Treatment Chemicals as approved for use in potable drinking water. Material Safety Data Sheets (MSDS) are available for all Carus products. Polyphosphates and Jefferson Water and Sewer District

What other benefits of phosphate treatment exist?

Phosphates easily adapt to any pre-existing water quality without changing the water chemistry. Referred to as inhibitors (ortho), sequestrants (poly), or blends (ortho/poly), phosphates have a selective function, yet wide range of performance. Primary treatment benefits include: corrosion control, lead/copper control, sequestration of iron/manganese, control of calcium carbonate scale, and water softening, etc.

Many secondary benefits develop, such as: reduced chlorine demand due to corrosion inhibition and sequestration of Fe/Mn, lower color and turbidity in the distribution system, less staining, removal of system scale deposits, control of biofilm regrowth, lower TOC, fewer system coliform violations, increased C-factors and hydraulic flow rates in system, reduced electrical demand, fewer main breaks, better valve operation, improved meter accuracy, increased revenue, reduced hydrant flushing frequency, less wasted water during flushing, less maintenance and service expenditures, fewer complain calls, and overall improved consumer satisfaction.

Scale Inhibition and Removal

The formation of scale on surfaces in potable water systems is due to the crystallization of carbonates or sulfates of magnesium or calcium from solution. Very low levels of polyphosphates (1-10 ppm) interfere with crystal growth. This type of scale inhibition is referred to as a threshold property because it occurs at a level much lower than would be required for a stoichiometric reaction.

Threshold inhibition by polyphosphates of calcium and magnesium carbonate formation is particularly effective at a pH range of 8 to 10 where carbonate scale in potable water is a major problem. Calcium sulfate scale is often a problem at lower pH ranges. The same mechanism of scale inhibition that can occur with calcium carbonate at a high pH range can also occur with calcium sulfate at a lower pH range at similar low (1-10 ppm) levels of phosphate addition.

Experience has shown that polyphosphates not only inhibit scale formation, but they can also help remove existing hard deposited carbonate or sulfate scale. Pipelines carrying potable water treated with polyphosphate for extended periods of time (several months) first show a gradual softening of the scale followed by disintegration and removal. The soft scale particles are deflocculated by the polyphosphate and carried away resulting in a clean piping system.

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