Section 920. Iron and manganese control

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 shall 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 division.

It may be necessary to operate a pilot plant in order to gather all information pertinent to the design.

A. Removal by oxidation, detention, and filtration.

1. Oxidation may be by aeration or by chemical oxidation with chlorine or potassium permanganate.

2. A minimum detention of 30 minutes shall be provided following oxidation by aeration in order to insure that the oxidation reactions are as complete as possible. This minimum detention time shall be reduced only when a pilot plant using the water under study demonstrates a lesser detention time. The detention basin shall be designed as a holding tank with no provision for sludge collection but with sufficient baffling to prevent short circuiting. Sedimentation basins shall be provided when treating water with high iron or manganese content or where chemical coagulation is used to reduce the load on the filters. The detention time shall be in a range of one to four hours where sedimentation is necessary prior to filtration. Pilot studies should be made of the water to determine the necessary detention time.

3. Filtration - see 12VAC5-590-880.

B. Removal by lime-soda process - see 12VAC5-590-900 A.

C. Removal by units using continuous potassium permanganate regeneration.

This process consists of a continuous feed of potassium permanganate to the influent of a manganese greensand filter. Positive displacement type feeders shall be provided, and the feed rate shall be adequately controlled by using feeders which are paced by water meters or ratio type feeders (which are a combination type feeder and flow meter) to prevent an overdosage of potassium permanganate.

1. The permanganate shall be applied following pH affecting chemicals.

2. Other oxidizing agents or processes such as chlorination or aeration may be used prior to the permanganate feed to reduce the cost of the chemical.

3. The normal filtration rate is three gallons per minute per square foot. Lower filtration rates may be required or higher filtration rates may be permitted if justified by field studies and approved by the division.

4. The normal wash rate is eight to 12 gallons per minute per square foot.

5. Air washing may be provided.

6. Sample taps shall be provided.

a. Prior to application of permanganate;

b. Immediately ahead of filtration;

c. At a point between the anthracite coal media and the manganese treated greensand;

d. Halfway down the manganese treated greensand; and

e. For filter effluent.

D. Removal by ion exchange. This process of iron and manganese removal may not be acceptable for waters containing high concentrations (more than 1.0 milligrams per liter) of iron, manganese, or combination thereof. Applications may be limited based on the media used. This process may not be acceptable where either the raw water or wash water contains dissolved oxygen. (See 12VAC5-590-900 B for general cation exchange information.)

E. Sequestering - see 12VAC5-590-950 E.

F. Sampling taps shall be provided for control purposes. Taps shall be located on each raw water source, each treatment unit influent and each treatment unit effluent.

G. Testing equipment shall be provided for all plants. The equipment shall have the capacity to accurately measure the iron content to a minimum of 0.1 milligrams per liter and to indicate manganese removal.

Historical Notes

Derived from VR355-18-009.08 § 3.29, eff. August 1, 1991.

Statutory Authority

§ 32.1-12 and 32.1-170 of the Code of Virginia.