Section 58.01.08.535 - DESIGN STANDARDS FOR IRON AND MANGANESE CONTROL SYSTEMSIron 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 (1) 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 Department. The Department may require a pilot plant study in order to gather all information pertinent to the design in accordance with Subsection 501.19.
01.Removal by Oxidation, Detention and Filtration.a. Oxidation may be by aeration or by chemical oxidation with chlorine, potassium permanganate, ozone or chlorine dioxide.b. Detention time: i. A minimum detention time of thirty (30) minutes must be provided following aeration to ensure that the oxidation reactions are as complete as possible. This minimum detention may be omitted only where a pilot plant study indicates no need for detention. The detention basin may be designed as a holding tank without provisions for sludge collection but with sufficient baffling to prevent short circuiting.ii. Sedimentation basins must be provided when treating water with high iron or manganese content, or where chemical coagulation is used to reduce the load on the filters. Provisions for sludge removal must be made.c. Rapid rate pressure filters are normally used for iron and manganese removal. Pressure filters may not be used in the filtration of surface or other polluted waters or following lime-soda softening.i. The rate of filtration may not exceed three (3) gallons per minute per square foot of filter area except where in-plant testing as approved by the Department has demonstrated satisfactory results at higher rates.ii. The filters must be designed to provide for:(1) Loss of head gauges on the inlet and outlet pipes of each battery of filters.(2) An easily readable meter or flow indicator on each battery of filters.(3) Filtration and backwashing of each filter individually with an arrangement of piping as simple as possible to accomplish these purposes.(4) Minimum side wall shell height of five (5) feet. A corresponding reduction in side wall height is acceptable where proprietary bottoms permit reduction of the gravel depth.(5) The top of the wash water collectors to be at least eighteen (18) inches above the surface of the media,(6) The underdrain system to efficiently collect the filtered water and to uniformly distribute the backwash water at a rate not less than fifteen (15) gallons per minute per square foot of filter area.(7) Backwash flow indicators and controls that are easily readable while operating the control valves.(8) An air release valve on the highest point of each filter.(9) An accessible manhole to facilitate inspection and repairs for filters thirty-six (36) inches or more in diameter. Sufficient handholds will be provided for filters less than thirty-six (36) inches in diameter.(10) A means to observe the wastewater during backwashing and construction to prevent cross connection.02.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. 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.b. An anthracite media cap of at least six (6) inches or more as required by the Department must be provided over manganese coated media.c. Normal filtration rate must be three (3) gallons per minute per square foot.d. Normal wash rate will be eight (8) to ten (10) gallons per minute per square foot with manganese greensand and fifteen (15) to twenty (20) gallons per minute with manganese coated media.e. Sample taps must be provided prior to application of permanganate, immediately ahead of filtration, at points between the anthracite media, and at the filter effluent. The sample taps must satisfy the requirements of Subsection 501.09.03.Removal by Ion Exchange. This process is not acceptable where either the raw water or wash water contains dissolved oxygen or other oxidants.04.Biological Removal. Biofiltration to remove manganese, iron, or a combination of manganese and iron requires on-site piloting testing to establish effectiveness. The final filter design must be based on the on-site pilot plant studies.05.Sequestration by Polyphosphates. This process may not be used when iron, manganese or a combination thereof exceeds one point zero (1.0) mg/1. The total phosphate applied must not exceed ten (10) mg/1 as PO4. Where phosphate treatment is used, satisfactory chlorine residuals must be maintained in the distribution system. Possible adverse affects on corrosion must be addressed when phosphate addition is proposed for iron sequestering. a. Stock phosphate solution must be kept covered and disinfected by carrying approximately ten (10) mg/1 free chlorine residual unless it is demonstrated to the satisfaction of the Department that the phosphate solution is not able to support bacterial growth and the phosphate solution is being fed from the covered shipping container or an approved disinfected tank. Phosphate solutions having a pH of two point zero (2.0) or less may also be exempted from this requirement by the Department.b. Polyphosphates may not be applied ahead of iron and manganese removal treatment. The point of application must be prior to any aeration, oxidation or disinfection if no iron or manganese removal treatment is provided.06.Sequestration by Sodium Silicates. Sodium silicate sequestration of iron and manganese is allowed only for groundwater supplies prior to air contact. On-site pilot studies 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.a. Sodium silicate addition is applicable to waters containing up to two (2) mg/1 of iron, manganese or combination thereof.b. Chlorine residuals must be maintained throughout the distribution system to prevent biological breakdown of the sequestered iron.c. The amount of silicate added must be limited to twenty (20) mg/1 as SiO2, but the amount of added and naturally occurring silicate may not exceed sixty (60) mg/1 as SiO2.d. Sodium silicate must not be applied ahead of iron or manganese removal treatment.07.Sampling Taps. Smooth-nosed sampling taps must be provided for control purposes. Taps will be located on each raw water source, each treatment unit influent and each treatment unit effluent. The sample taps must satisfy the requirements of Subsection 501.09.Idaho Admin. Code r. 58.01.08.535