Performance Products Group - Church & Dwight Co., Inc.

Potable Water

Corrosion Control in Municipal Water Systems

Drinking water suppliers in many parts of the United States and Canada have difficulty in meeting the standards for lead and copper in potable water effect by the EPA. The method of corrosion control chosen by a municipality can have far-reaching effects on overall operational costs beyond those for metals control. This is particularly true in comparison to the use of phosphates.

Bicarbonate alkalinity is a natural ingredient of most water supplies. Waters that are deficient in this key parameter are often corrosive. Supplementing waters deficient in alkalinity with sodium bicarbonate restore those waters to their naturally non-corrosive state. Addition of sodium bicarbonate to increase alkalinity level between 30 and 40 mg/L (as CaCO3) with an optimum pH between 7.5 and 8.5 will create thin, tenacious, carbonate coating on the interior of lead and copper pipes. This coating effectively seals the interior surface of the pipes from water and significantly reduces the leaching of metals. The town of Bennington, Vermont, achieved a 90% reduction in lead levels in the first six months of treatment. They are now safely below the EPA standard (refer to case study)

Phosphate suppliers may quote a dosage as low as 0.5 ppm of PO4 for corrosion control, and this would appear to provide favorable economics. However, you may find that the actual effective concentration for optimum corrosion control could be up to six times this amount. Metallic phosphates have a minimum solubility at a pH of 7.6 and thus require constant pH adjustments and the addition of alkalinity. These chemical costs are usually not included in the cost of the phosphate.

Other Potable Water process considerations:

Bicarbonate alkalinity is required for the optimization of other water processes such as chlorination, flocculation and coagulation. Church & Dwight has several success stories showing significant chemical cost reduction by improving the performance of the flocculent, typically alum, and eliminating the need for costly polymers (see case studies).

Phosphates are nutrients and can promote bio-film growth in the distribution system and algae growth in open water storage units. Bicarbonate alkalinity is not a nutrient and will not cause or contribute to these problems. Looking further downstream, phosphates, especially those containing zinc, will pollute the wastewater treatment plant often making them unfit for sale as soil nutrients. This is not a problem with bicarbonate alkalinity.