Wisconsin Administrative Code
Department of Natural Resources
NR 800 - Environmental Protection - Water Supply
Chapter NR 811 - Requirements For The Operation And Design Of Community Water Systems
Subchapter VII - Treatment
Section NR 811.56 - Sequestration

Universal Citation: WI Admin Code ยง NR 811.56

Current through August 26, 2024

(1) SEQUESTRATION BY POLYPHOSPHATES. Sequestration by polyphosphates is suitable when concentrations of iron, manganese, or a combination of both, are 1.0 mg/1, or less. Polyphosphate treatment may be less effective for sequestering manganese than for iron. The following requirements shall be met:

(a) Where phosphate treatment is used, chlorine residuals shall be maintained in the distribution system. In addition:

(b) Polyphosphates may not be applied ahead of iron and manganese removal treatment. The point of application shall be prior to any aeration or oxidation and as far upstream as practical from the chlorine or other oxidant application.

(c) Chemical feed installations shall conform to the requirements of subch. VI.

(d) Chemicals for new or existing installations shall meet the applicable NSF/ANSI Standard 60 requirements of s. NR 810.09 (1) (c).

(e) Stock phosphate solution shall be kept covered and disinfected by carrying an approximate 10 mg/1 free chlorine residual unless the phosphate is not able to support bacterial growth, has a pH of 2 or less, and has not been diluted.

(g) If polyphosphate sequestration is practiced, appropriate orthophosphate testing equipment shall be provided.

(h) Possible adverse affects on corrosion shall be considered and addressed if necessary when phosphate addition is proposed for iron or manganese sequestering.

(2) SEQUESTRATION BY SODIUM SILICATES. Sodium silicate sequestration of iron and manganese is appropriate only for groundwater supplies prior to air contact. Sodium silicate addition is applicable to waters containing up to 2 mg/l of iron, manganese, or a combination of both. The following requirements shall be met:

(a) On-site pilot tests are required to determine the suitability of sodium silicate for the particular water and the minimum chemical feed rate needed.

(b) Chlorine residuals shall be maintained throughout the distribution system to prevent biological breakdown of the sequestered iron.

(c) Rapid oxidation of the metal ions such as by chlorine or chlorine dioxide shall accompany or closely precede the sodium silicate addition. Injection of sodium silicate more than 15 seconds after oxidation may cause detectable loss of chemical efficiency. Dilution of feed solutions much below 5% silica as SiO 2 shall also be avoided for the same reason.

(d) The amount of silicate added shall be limited to 20 mg/l as SiO 2. The combined amount of added and naturally occurring silicate may not exceed 60 mg/l as SiO 2.

(e) Chemical feed installations shall conform to the requirements of subch. VI.

(f) Sodium silicate may not be applied ahead of iron or manganese removal treatment.

(g) Liquid sodium silicate shall meet the applicable NSF/ANSI Standard 60 requirements of s. NR 810.09 (1) (c).

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