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The City of Phoenix in Arizona is currently in the process of updating its Water Quality Master Plan inorder to continue development of strategies to meet water quality goals, including reduction ofdisinfection byproducts (DBP), which are expected to be an area of concern for upcoming waterquality regulations. During the first phase of the Water Quality Master Plan Update, it was determinedthat City of Phoenix Water Treatment Plants will need to undergo enhanced coagulation to achieveadequate removal of total organic carbon (TOC) to ensure compliance with the Stage 2 D/DBP rule.Even though the extent of TOC removal by enhanced coagulation has already been established for theCity of Phoenix surface water sources through numerous bench-scale evaluations, the operationalcomplexity with respect to limits of coagulant dose and residuals handling has not been sufficientlyevaluated. For this reason, a plant-scale enhanced coagulation test with aluminum sulfate and ferricchloride was performed. The study was designed to assess the advantages and disadvantages ofenhanced coagulation in terms of natural organic removal, and to evaluate impacts on residualshandling and operational cost.The plant-scale enhanced coagulation testing was performed at the City of Phoenix Val Vista WaterTreatment Plant (WTP). The Val Vista WTP is a conventional water treatment plant consisting of twoparallel treatment trains (East Plant and West Plant) with a total capacity of 220 mgd, and includes aSolids Handling Facility. The Solids Handling facility is made up of two process groups: the UsedWater Recovery System (UWRS), and the Solids Dewatering System. The Used Water RecoverySystem includes equalization basins, backwash clarifiers, and a gravity thickening complex to recoverwater from residuals process streams. The Solids Dewatering System includes centrifuges, solardrying beds, and evaporation lagoons.During the plant-scale testing, residuals produced at the water treatment process (i.e. sedimentationbasin blow-downs and filter backwash water) were routed to the gravity thickening complex. After thegravity thickening process, thickened sludge was transferred to the Solids Dewatering System forfurther separation using centrifuges. During the study, the effects of enhanced coagulation on filterperformance, gravity thickening operation, and the dewatering process were assessed. In addition, acomparison of the costs associated with thickening, dewatering, and disposal between ferric and alumresiduals, was performed. Includes 3 references, tables, figures.

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Edition: Vol. - No. Published: 06/17/2004 Number of Pages: 14File Size: 1 file , 680 KB