Effect of sodium silicate on lead release from lead service lines

The effect of sodium silicate addition on lead release from lead service lines (LSLs) was investigated using laboratory-based pipe loop experiments with LSLs harvested from a water utility that has one of the Great Lakes as its source water. The LSLs were first conditioned with a synthetic water similar to that of Buffalo Water that matched the major water chemistry that the pipes had experienced in the field; the one exception was the absence of dissolved organic carbon in the synthetic water. After conditioning, the LSLs were used in tests with the same synthetic water and with sodium silicate added to the water for half of the LSLs. In one test sodium silicate addition was performed with adjustment of the pH to maintain it at the same value (pH 7.7) as before addition. In this test sodium silicate effectively reduced the dissolved and particulate lead concentrations in the water within six weeks of treatment. Periodic assessments of the corrosion scales in the pipes found that sodium silicate accumulated throughout the scale thickness and gradually decreased the lead release. In the other test the pH was allowed to increase from 7.7 to 8.8 upon addition of 20 mg/L as SiO₂ sodium silicates, and parallel control experiments were performed with the same pH increase made using sodium hydroxide addition. In these tests the lead concentrations decreased in both the silicate-treated and control pipes, and the decreases were not significantly different between the silicate-treated and control pipes.