This paper describes a multi-phase systematic process in which several direct and indirect
parameters and methods were used to optimize the selection of phosphate treatment under high
pH conditions to mitigate calcium precipitation while simultaneously evaluating the impact of
such mitigation on lead solubility. The primary study objective was to find a solution that both protected the public from harmful lead
levels and prevented calcium carbonate from precipitating. Two possible methods to control CaCO<sub>3</sub>
precipitation were evaluated: lowering the pH; and, maintaining an elevated pH (9.0) with the
addition of a phosphate-based inhibitor. CaCO<sub>3</sub> deposition is inhibited by the presence of
phosphates, particularly polyphosphates, which act in essence as a crystal growth "poison."
A series of desktop and bench-scale studies were structured to answer the following questions:
what is the pH level required to eliminate (or minimize) calcium carbonate precipitation;
what effect, if any, would such a pH change have on lead solubility in the distribution system;
how effective are various sequestering agents in controlling calcium deposition; and,
does the addition of a sequestering agent affect lead solubility? The success of the recommended treatment, including post-implementation
monitoring results demonstrating reduction in both 90th percentile lead
concentration and customer complaints are also covered. Includes 8 references.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 150 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 5 |
| Published : | 11/01/2005 |
