AWWA ACE99573

AWWA ACE99573 Balancing Environmental and Potable Water Quality Needs in Indirect Potable Reuse Projects
Conference Proceeding by American Water Works Association, 01/01/1999

Thompson, Donald M; Holtz, Dave; Morrison, Matt; Olson, Erik

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The City of West Palm Beach, Florida (City), in conjunction with Palm Beach County, operated a Demonstration Project over a one-year period to provide cost and performance data for treatment of secondary wastewater effluent to indirect potable reuse standards. The City utilized an Advance Wastewater Treatment (AWT) Plant that used a solids contact clarifier (SCC) and a deep bed denitrification filter (DNF) followed by chlorine disinfection and wetlands polishing. For the West Palm Beach Wetlands Based Water Reclamation Project, it is anticipated that the treated effluent will be routed to natural receiving wetlands that recharge the surficial aquifer in the vicinity of water supply wells. For this reason, the quality of the effluent was evaluated for compliance with Class III water quality standards and wetlands antidegradation requirements. Over the first year of operation, the AWT effluent occasionally exhibited elevated iron levels in excess of the Class III Surface Water Quality Standard of 1.0 mg/l. In addition the effluent total phosphorus concentrations were well in excess of the concentrations exhibited in the potential receiving wetlands. Such iron and phosphorus concentrations in the AWT effluent could prevent or severely restrict the application of the reclaimed water to the wetlands without the addition of new unit processes. During operation of the Demonstration Project, several characteristics of the treatment process were observed that were potentially related to the excessive iron and phosphorus concentration in the AWT effluent. Based upon the AWT Plant water quality and process observations, two actions were deemed necessary to optimize the coagulation/flocculation/sedimentation process: optimize the coagulation and flocculation step including coagulation type, coagulation dosage, and pH condition during coagulation as well as determine the need for a coagulation/flocculation aid polymer and necessary polymer dosage; and, minimize the potential for biological growth in the secondary effluent transmission main, INF, and SCC.