Phosphate inhibitor use at US utilities

Surveys of US drinking water utilities were conducted in 1994 and 2001 to investigate trends in phosphate inhibitor use. More than half of those water providers surveyed reported adding phosphate inhibitors to their water. Zinc orthophosphate and polyphosphate were commonly used inhibitors, and a shift from poly/orthophosphate blends to orthophosphate was observed from 1994 to 2001. Inhibitor doses ranged from 3 mg/L as PO 4 (although many utilities could only report dosages “as product” because of the proprietary nature of the inhibitor chemicals). Surprisingly, most utilities based their inhibitor selection on limited information, with smaller utilities relying more on nontechnical information (e.g., vendor information, success of the chemical at another utility) than on direct confirmation of the inhibitor's effectiveness. Many utilities are aware of potential drawbacks of inhibitors, especially increased biological activity and more treatment costs and residuals.