Phosphates are water treatment chemicals (dry or liquid solutions) used to correct problems resulting from inorganic groundwater contaminants (iron, manganese, calcium, etc.) 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. ‘Ortho’ and ‘Poly’ phosphates, used either alone or blended together are able to stabilize water quality and minimize color, scale, deposits, corrosion, and chlorine demand in drinking water systems.
How do phosphates work in a water system?
Orthophosphate based additives are classified as corrosion inhibitors and as such react with dissolved metals (e.g. Ca, Mg, Zn, Al etc.) in the water to form a very thin metal-phosphate coating or simply react with metals on a pipe surface acting as a barrier between the pipe and the water. Polyphosphate type chemicals react with soluble metals (Fe, Mn, Ca, Mg, etc.) by sequestering (bind-up) the metals to maintain their solubility in water. The sequestering process minimizes the risk of discoloration, staining, scaling, chlorine demand and related taste/odor and other water quality complaints. Certain types of polyphosphates also inhibit corrosion since they bind with metallic pipe surfaces or with the corrosion deposits inside water pipes. As water ages, polyphosphates loose their ability to control color and suspend iron/manganese, when they chemically revert to orthophosphate.
Are all phosphates safe or approved for water?
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 acidic solutions. Phosphates should be listed in the ANSI/NSF Standard #60 Drinking Water Treatment Chemicals, for approved use in potable water. Some phosphates vary in quality ranging from food grade to technical grade industrial chemicals. Over 20 phosphate compounds are listed in Std 60 for use in drinking water with many more proprietary phosphate blends available on the market. Understanding which ingredients are in your product and the functional chemistry, are essential for optimal water quality.
How much phosphate is required?
The most effective dosage rate is determined by running a complete water analysis to determine the total demand of the finished water and the consumption rate from the distribution system. ANSI/NSF STD 60 has limited use of inorganic phosphates at 10 mg/L as total phosphate ion. In most cases, this is not a health related or safety limitation, but a practical guideline for the maximum quantity of phosphate typically applied in drinking water. Most ground and surface water supplies contain naturally occurring phosphate at low levels, however additional phosphate chemical (0.25-10 mg/L) is added to water with a chemical metering pump. Maintaining the optimal chemical dosage rate requires special monitoring.
Working with Spon Water Consulting takes the guesswork out of your phosphate treatment program. We evaluate your water quality, treatment process, chemicals used and ingredients, identify your options, generate a cost analysis, and many times during the process, save you significant revenue.