Use of Sodium Hexametaphosphate in Manganese Stabilization

Abstract

In the Pittsburgh metropolitan area alone there are several communities using manganese‐bearing waters as a primary source of supply. Several of the smaller communities feed glassy phosphate directly to their wells at feed rates varying from 3 to 5 ppm. At least two large water supplies have also occasionally used glassy phosphate to tie up dissolved manganese that has leaked through the filters when the manganese content in the raw water was unusually high. As manganese leakage through the filter amounts to less than 1 ppm, stabilization can be achieved safely at a metaphosphate feed rate of 2 ppm. A fairly reliable indication of the effectiveness of glassy phosphate for manganese stabilization can be obtained in a relatively few weeks. In extreme cases of “black water,” improvement should be noticed almost immediately. Fewer complaints should be received, particularly after loosely adhering manganese deposits have been cleaned out. Furthermore, water utilities that conduct systematic hydrant‐flushing programs on an annual, semiannual, or even a quarterly basis will find that hydrants clear up much more quickly than formerly and, in most cases, require less frequent flushing. Although attempts have been made to measure the extent of manganese deposition in systems when the average manganese content is as low as 0.1‐0.3 ppm, a more practical method is to check manganese concentrations of the water at various points throughout the distribution system. After a system using water properly treated with glassy phosphate has been cleaned of old, loose deposits, the level of manganese should be the same at the various sampling points throughout the system. It has been shown that glassy phosphates can be utilized successfully to stabilize dissolved manganese under different operating conditions and in waters of markedly different chemical characteristics.