The Fountain Hills Sanitary District WWTP was constructed in Fountain Hills, Ariz., in 1974 and received an aggressive upgrade in November 1999.
The plant was in need of an upgrade because the original treatment equipment had reached the end of its life expectancy, and the tremendous growth and changing environmental regulations called for it. Fountain Hills’ secondary and tertiary treatment processes all required expansion or retrofit. The upgrade included the replacement of 16 submersible mixers with four AquaDDm direct-drive mixers from Aqua Aerobic Systems, Inc. in the plant’s two anoxic basins and the use of a MixAir system, also from Aqua Aerobic, in the two aerobic digesters. The two aeration basins, which made up the plant’s secondary treatment process, continue to be utilized. In order to produce reuse quality effluent for the growing community and meet more stringent environmental regulations at an economical cost, Fountain Hills opted to also upgrade the tertiary process by combining two state-of-the-art filtration systems.
This filtration combination consists of three Aqua Aerobic AquaDisk cloth media filters and a Pall Microza hollow-fiber microfiltration membrane system.
Fountain Hills’ new wastewater treatment facility was up and running in February 2001. The new system produces effluent quality exceeding conventional methods and with a low life cycle cost.
The reclamation effluent produced by the cloth media filters is used for park and golf course irrigation, and to fill Fountain Lake, which exhibits the highest fountain in the U.S. A portion of the filters’ effluent is also distributed to the membrane system to produce microfiltered effluent for injection into deep wells for ground water recharge. This allows 2 MGD of water to be stored when the demand for water is low, such as the winter, and have it available when demand is high, such as summer.
Filtration process
Following biological treatment, including nitrogen removal, the wastewater travels to the secondary clarifiers before entering three 6-disk concrete AquaDisk filters. The operation of the filters begins when clarified effluent flows by gravity through the cloth media of the stationary hollow disks and filtrate exits through the hollow center collection tube.
As solids accumulate on the surface of the media, the water level rises. Once a predetermined level is reached, a backwash cleaning mode is automatically initiated. Backwash waste and settled solids are pumped to a digester or plant headworks.
Chlorinated effluent intended for park or golf course irrigation is discharged directly to end-users. Effluent destined for groundwater injection is pumped to the hollow-fiber membrane system.
Design characteristics
Each of the AquaDisk filters has a capacity of six disks. However, only four disks were initially installed in the Fountain Hills application to meet current flow conditions. Simply installing the additional disks can increase capacity up to 3 MGD.
Generally, only a portion of the total plant flow requires advanced filtration with membranes. Because of the reuse quality effluent provided by the filters, capital and operating costs were reduced by downsizing the microfiltration system.
Land restrictions resulted in the installation of the membrane system 1–2 miles from the main plant. Because of the high chemical resistance of the PVDF membrane filters, effluent from the filters is first chlorinated before being pumped to the advanced treatment facility.
“We are very satisfied with the AquaDisk filter,” said Clark Moskop, Fountain Hills Sanitary district WWTP operation supervisor. “It is a fine piece of equipment and it’s been all we wanted and more.”
