Design Guide for Community Water Systems - The Water, Sanitation ...

4.7. Iron and Manganese ControlIron and manganese control, as used in this section, refers solely to treatmentprocesses designed specifically for this purpose. The treatment process used willdepend upon the character of the raw water. The selection of one or more treatmentprocess must meet specific local conditions as determined by engineeringinvestigations, including chemical analysis of representative samples of water to betreated, and receive the approval of the department. It may be necessary to operatea pilot plant in order to gather all information pertinent to the design. Allowancesmust be made for deterioration of groundwater quality, over time, and for variationsin ground water quality at different locations. Testing equipment and sampling tapsshall be provided as specified in sections 2.8 and 2.10.4.7.1. Removal by oxidation, detention and filtration.a. Oxidation. Oxidation may be by aeration, as indicated in Section 4.6or by chemical oxidation with chlorine, potassium permanganate,ozone, or chlorine dioxide.b. Detention.1. Reaction-A minimum detention time of two hours shall beprovided following aeration for water containing iron ormanganese to insure that the oxidation reactions are as completeas possible. This minimum detention time may be decreased onlywhere indicated by a pilot plant study. The detention basin shouldbe designed with sufficient baffling to prevent short-circuiting.i. Provisions shall be made for adding chemicals for pHadjustment and enhancement of the oxidation process.ii. Provisions shall be made for providing rapid mix of 30seconds.2. Sedimentation-A sedimentation basin in place of a detention basinshall be provided when treating water containing 4 mg/L or moreiron and/or manganese, or where chemical coagulation is used toreduce the load on the filters. Provisions shall be made for addingchemicals for pH adjustment and enhancement of the oxidationprocess. Coagulant addition and rapid mixing should also beprovided. Facilities for rapid mixing flocculation andsedimentation should be designed in accordance with section 4.1.Provisions for residuals removal shall be made. The detentionbasin shall be designed with sufficient baffling to prevent shortcircuiting.The detention time in the sedimentation basin shall bebased on the total concentration of iron and/or manganese in thewater to be treated.i. The following are the minimum detention times at differentconcentration ranges of iron and /or manganese exceeding 4mg/L:1. 4mg/L to 9 mg/L - four hours detention time;2. 10mg/L to 20mg/L - six hours detention time; andAug. 29, 2003Page 78