Montana DEQ - Circular DEQ 2 - Design Standards for ... - Force Flow

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CHAPTER 110SUPPLEMENTAL TREATMENT PROCESSES111. PHOSPHORUS REMOVAL BY CHEMICAL TREATMENT111.1 General111.11 MethodAddition of lime or the salts of aluminum or iron may be used for thechemical removal of soluble phosphorus. The phosphorus reacts with thecalcium, aluminum or iron ions to form insoluble compounds. Theseinsoluble compounds may be flocculated with or without the addition of acoagulant aid such as a polyelectrolyte to facilitate separation bysedimentation.111.12 Design Basis111.2 Process Requirements111.21 Dosage111.121 Preliminary TestingLaboratory, pilot or full scale studies of various chemicalfeed systems and treatment processes are recommended forexisting plant facilities to determine the achievableperformance level, cost-effective design criteria, andranges of required chemical dosages.The selection of a treatment process and chemical dosagefor a new facility should be based on such factors asinfluent wastewater characteristics, effluent requirements,and anticipated treatment efficiency.111.122 System FlexibilitySystems must be designed with sufficient flexibility toallow for several operational adjustments in chemical feedlocation, chemical feed rates, and for feeding alternatechemical compounds.The design chemical dosage must include the amount needed to react withthe phosphorus in the wastewater, the amount required to drive the chemicalreaction to the desired state of completion, and the amount required due toinefficiencies in mixing or dispersion. Excessive chemical dosage shouldbe avoided.153
Chapter 110Supplemental Treatment Process111.22 Chemical SelectionThe choice of lime or the salts of aluminum or iron should be based on thewastewater characteristics and the economics of the total system. Whenlime is used, it may be necessary to neutralize the high pH prior tosubsequent treatment in secondary biological systems or prior to dischargein those flow schemes where lime treatment is the final step in the treatmentprocess.111.23 Chemical Feed PointsSelection of chemical feed points must include consideration of thechemicals used in the process, necessary reaction times between chemicaland polyelectrolyte additions, and the wastewater treatment processes andcomponents utilized. Flexibility in feed locations must be provided tooptimize chemical usage.111.24 Flash MixingEach chemical must be mixed rapidly and uniformly with the flow stream.Where separate mixing basins are provided, they should be equipped withmechanical mixing devices. The detention period should be at least 30seconds.111.25 FlocculationThe particle size of the precipitate formed by chemical treatment may bevery small. Consideration should be given in the process design to theaddition of synthetic polyelectrolytes to aid settling. The flocculationequipment should be adjustable in order to obtain optimum floc growth,control deposition of solids, and prevent floc destruction.111.26 Liquid - Solids SeparationThe velocity through pipes or conduits from flocculation basins to settlingbasins should not exceed 1.5 feet per second (0.46 m/s) in order tominimize floc destruction. Entrance works to settling basins should also bedesigned to minimize floc shear.Settling basins must be designed in accordance with Chapter 70. Fordesign of the sludge handling system, special consideration should be givento the type and volume of sludge generated in the phosphorus removalprocess.111.27 FiltrationEffluent filtration must be considered where effluent phosphorusconcentrations of less than 1 mg/l must be achieved.154
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Montana DEQ - Circular DEQ 2 - Design Standards for ... - Force Flow

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