12 Va. Admin. Code § 5-590-920

Current through Register Vol. 41, No. 8, December 2, 2024

Section 12VAC5-590-920 - Iron and manganese control

A. Iron and manganese control, as used in this section, refers solely to treatment processes designed specifically for this purpose. The treatment process used will depend upon the character of the source 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 department. The department may require that pilot studies be conducted.

B. Iron and manganese removal by oxidation and filtration.

1. Oxidation shall be accomplished by aeration or by chemicals, such as chlorine, potassium permanganate, sodium permanganate, or a combination thereof.

2. The design shall consider:

a. pH adjustment to promote rapid oxidation;

b. A pre-settling tank located ahead of the filters to remove oxidized iron and increase filter run times;

c. A manganese-oxide coating on the filter media, such as manganese greensand. The total depth of media shall not be less than 30 inches. Media shall have an effective size from 0.3 to 0.35 mm and a uniformity coefficient of no more than 1.6. Following initial placement of the media, care shall be taken to remove fines by backwashing and skimming the surface; and

d. An anthracite cap layer over the manganese-oxide coated media having a depth of six to 18 inches.

3. Aeration shall be designed in accordance with 12VAC5-590-910.

4. Flow proportional chemical feeders shall be provided, and the feed rate shall be adequately controlled by using feeders that are paced by water meters to prevent an over-dosage of chemical. A flow switch in place of a flow proportional feeder may be permissible.

5. Sample taps shall be provided before the application of the oxidant, immediately ahead of filtration, and at the filter effluent.

6. Pressure filters shall include provisions for:

a. Pressure gauges on the inlet and outlet pipes of each filter or a differential pressure gauge on each filter;

b. An easily readable meter or flow indicator on each battery of filters. A flow indicator is recommended for each filtering unit;

c. Filtration, backwashing, and filter-to-waste of each filter individually:

(1) Backwash water shall be evenly distributed in an adequate quantity to achieve at least a 30% media bed expansion during backwashing. The backwash rate shall be based on the media;

(2) The top of the backwash water collection trough shall be at least 18 inches above the media surface;

(3) An underdrain system to efficiently collect the filtered water and to distribute an adequate quantity of backwash water to achieve at least a 30% media bed expansion during backwashing;

d. Flow indicators and controls are located so that they are easily readable while operating the control valves;

e. An air release valve on the highest point of each filter;

f. An accessible manhole to facilitate inspections and repairs for filters greater than 36 inches in diameter;

g. A means to observe the wastewater during backwashing; and

h. Construction to prevent cross-connection.

C. Iron and manganese removal by ion exchange shall only be approved for removing low concentrations (less than 0.5 mg/L) of combined iron and manganese. The department may require pilot studies be conducted to determine post-exchange pH/alkalinity adjustment. See 12VAC5-590-900 for general ion exchange design requirements.

D. Sequestering iron and manganese.

1. Sequestration with polyphosphates shall be considered for polishing filtered water; however, it shall not be used where the residual iron, manganese, or combination thereof exceeds 1.0 mg/L.

2. Phosphate feed rates shall be determined by the product manufacturer and shall not exceed 10 mg/L.

3. Feed equipment shall be in accordance with the requirements of 12VAC5-590-860.

4. Stock phosphate solution shall be disinfected in accordance with manufacturer recommendations unless the phosphate solution is fed directly from the covered shipping container.

5. Sodium silicate or other silicate-based chemicals for the sequestration of iron and manganese shall be approved by the department on an individual basis. Operational data from actual full-scale facilities treating waters of similar quality or pilot tests may be required.

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

F. Iron and manganese testing equipment shall be provided. Iron testing equipment shall be capable of accurately measuring iron concentration as low as 0.1 mg/L. Manganese testing equipment shall be capable of accurately measuring manganese concentration as low as 0.05 mg/L.

G. The department may approve proprietary treatment processes for the removal of iron and manganese on an individual basis. Operational data from actual full-scale facilities treating waters of similar quality or pilot tests may be required. The provisions of 12VAC5-590-290 may apply.

12 Va. Admin. Code § 5-590-920

Derived from VR355-18-009.08 § 3.29, eff. August 1, 1991; Amended, Virginia Register Volume 37, Issue 20, eff. 6/23/2021.

Statutory Authority: §§ 32.1-12 and 32.1-170 of the Code of Virginia.