La. Admin. Code tit. 51 § XII-187

Current through Register Vol. 50, No. 11, November 20, 2024

Section XII-187 - Iron and Manganese Control

A. Iron and manganese control, as used herein, refers solely to treatment processes designed specifically for this purpose. The treatment process used will depend upon the character of the raw water. The selection of one or more treatment processes must meet specific local conditions as determined by engineering investigations, including chemical analyses of representative samples of water to be treated, and receive the approval of the state health officer. It may be necessary to operate a pilot plant in order to gather all information applicable to the design. Consideration should be given to adjusting pH of the raw water to optimize the chemical reaction.

1. Design elements for removal by oxidation, detention and filtration are as follows.

a. Oxidation. Oxidation may be by aeration, as indicated in §185 of this Part, or by chemical oxidation with chlorine, potassium permanganate, sodium permanganate, ozone or chlorine dioxide.

b. Reaction. A detention time shall be provided following aeration to insure that the oxidation reactions are as complete as possible. The reaction tank/detention basin shall be designed to prevent short circuiting. If a reaction tank/detention basin is provided, it shall be provided with an overflow, vent and access hatch in accordance with §225 I, §225 J, and §225. K of this Part.

c. Sedimentation. Sedimentation basins shall be provided when treating water with high iron and/or manganese ([GREATER THAN EQUALS TO] 7*SMCL) content, or where chemical coagulation is used to reduce the load on the filters. Provisions for sludge removal shall be made.

d. Filtration. Filters shall be provided and shall conform to §177 of this Part.

2. For removal by the lime-soda softening process, see §181. A of this Part.

3. Removal by manganese coated media filtration. This process consists of a continuous or batch feed of potassium permanganate to the influent of a manganese coated media filter.

a. Provisions should be made to apply the permanganate as far ahead of the filter as practical and to a point immediately before the filter.

c. An anthracite media cap of at least six inches or more as required by the state health officer shall be provided over manganese coated media.

d. Normal filtration rate shall be based on the manufacturers performance studies.

e. Sample taps shall be provided:

i. for the raw water;

ii. immediately ahead of filtration; and

iii. at the filter effluent.

4. Removal by Ion Exchange. This process of iron and manganese removal should not be used for water containing more than 0.3 milligrams per liter of iron, manganese or combination thereof. This process is not acceptable where either the raw water or wash water contains dissolved oxygen or other oxidants.

5. Sequestration by Polyphosphates. The total phosphate applied shall not exceed 10 mg/L as phosphate (PO4). Possible adverse effects on corrosion must be addressed when phosphate addition is proposed for iron sequestering.

a. Feeding equipment shall conform to the requirements of Subchapter A "Chemical Application" §201-§209 of this Part.

b. Polyphosphates shall not be applied ahead of iron and manganese removal treatment.

c. The phosphate feed point shall be located at least five feet ahead of the oxidant feed point.

6. Sequestration by Sodium Silicates. Sodium silicate sequestration of iron and manganese is appropriate only for groundwater supplies prior to air contact. On-site pilot tests are required to determine the suitability of sodium silicate for the particular water and the minimum feed needed. Rapid oxidation of the metal ions such as by chlorine or chlorine dioxide must 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 five per cent silica as SiO2 should also be avoided for the same reason. Sodium silicate treatment may be less effective for sequestering manganese than for iron.

a. Sodium silicate addition is applicable to waters containing up to 2 mg/L of iron, manganese or combination thereof.

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

c. The amount of silicate added shall be limited to 20 mg/L as SiO2, but the amount of added and naturally occurring silicate shall not exceed 60 mg/L as SiO2.

d. Feeding equipment shall conform to the requirements of Subchapter A "Chemical Application" §201-§209 of this Part.

e. Sodium silicate shall not be applied ahead of iron or manganese removal treatment.

7. Sampling taps. Smooth-nosed sampling taps shall be provided for control purposes. A means of collecting samples shall be provided for each raw water source, each treatment unit influent and each treatment unit effluent.

8. Testing equipment shall be provided for all plants. Where polyphosphate sequestration is practiced, appropriate phosphate testing equipment shall be provided that meets the requirements of §137. G of this Part.

La. Admin. Code tit. 51, § XII-187

Promulgated by the Department of Health, Office of Public Health, LR 44325 (2/1/2018), effective 8/1/2018.

AUTHORITY NOTE: Promulgated in accordance with the provisions of R.S. 40:4.A.(8), 40:4.13.D.(1)(2) and 40:5.A.(2)(3)(5)(6)(7)(17).