PRO CE S S PAG E Greetings from the FWEA Wastewater Process Committee! In 2020, the FWEA Process Committee conducted a thorough review of the historical Earl B. Phelps Award scoring criteria. After a detailed, line-by-line review, the FWEA Process Committee recommended updates to the criteria to reduce subjectivity and the potential for inspector bias. For example, instead of scoring points based only on carbonaceous biochemical oxygen demand (CBOD5) and total suspended solids (TSS) removal efficiencies, nitrogen and phosphorus removal efficacies were included in the scoring system, even for facilities not permitted for nutrient removal. Overall, a significant number of subjective scoring systems were refined and a detailed, treatment-based objective scoring system was implemented for the 2021 Earl B. Phelps Award evaluation. The evaluation criteria are now heavily focused on effluent quality, including nutrient removal. This allows treatment facilities to compete (in their respective size range and configuration) to earn the Earl B. Phelps Award based on objective, treatment-based excellence. This month’s column highlights the 2021 Advanced Secondary Earle B. Phelps Award winner (City of Cape Coral Southwest Water Reclamation Facility) and the significant aeration control system improvements completed over the past year that resulted in substantial blower energy reduction, while consistently exceeding nitrogen removal regulatory requirements.
Award-Winning City of Cape Coral’s Southwest Water Reclamation Facility: Optimizing Aeration Control Produces Multiple Benefits Matt Astorino and Matt Tebow
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Background
he Water Independence for Cape Coral program was started in the late 1980s and was designed to reduce the impact irrigation has on the Mid Hawthorne Aquifer, one of the main sources for drinking water supply for the City of Cape Coral (city). The city has been recognized as having one of the largest municipal residential reuse water systems in the United States, with a daily average of 31.42 million gallons per day (mgd). The city’s irrigation is supplied by treated wastewater from its two wastewater facilities, Southwest Water Reclamation Facility (SWWRF) and Everest WRF, and supplemented by freshwater
canal water pumped from the city’s five freshwater canal pumping stations. The city’s SWWRF was originally constructed in 1992 using a carousel-style oxidation ditch to treat an annual average daily flow (AADF) of 6.6 mgd. The SWWRF was expanded in 2008 to 15 mgd AADF and currently treats approximately 7 to 8.5 mgd seasonally.
Treatment System and Components The headworks consists of two mechanical step screens and one manual bar screen, grit removal provided by four stacked trays, vortextype grit removal units, odor control, and two cyclone/classifier units, followed by a common influent mixing channel. The secondary treatment (activated sludge) process utilizes the anaerobic-
City of Cape Coral Southwest Reclamation Facility
4 January 2022 • Florida Water Resources Journal
anoxic-aerobic (A2O) process. Although not a regulatory requirement, the A2O process is capable of biological removal of both nitrogen and phosphorus. Three A2O process basins receive flow from the common influent mixing channel, with each basin having an anaerobic zone, followed by an anoxic zone and an aerobic zone. Each basin has four floating mixers, with two mixed liquor internal recycle pumps that pump from the end of the aerobic zone to the beginning of the anoxic zone. Mixed liquor from the three basins flows to a common reaeration channel; the combined flow is then split and gravity-fed to five secondary clarifiers (two at 100-foot-diameter and three at 120-foot-diameter) for settling. The sludge pump station, with multiple return activated sludge (RAS) and waste activated sludge (WAS) pumps, discharges to the common influent mixing channel or sludge holding tanks, respectively. Effluent from the secondary clarifiers is gravity-fed to two sets of effluent automatic backwash (traveling bridge) filters. The effluent from the backwash filters then flows by gravity and is split between two chlorine contact chambers (CCC). High-level disinfection is provided by liquid sodium hypochlorite. The reclaimed water is then stored in three 5-million-gallon (MG) tanks, or due to wet weather or low demand, pumped into the deep injection well. The SWWRF provides reclaimed water to the city’s reuse service area system, also known as the Water Independence for Cape Coral system. The SWWRF includes a 6.8-MG reject Continued on page 6
