Kruger provided a comined solution for the City of Flagstaff upgrade to the Wildcat Hill Wastewater Treatment Facility. The effectiveness of Kruger's AnoxKaldnes Hybas™ system, followed by the Hydrotech Discfilter, has allowed the Wildcat Hill Wastewater Treatment Facility to produce a high quality effluent for their reclaimed water that is distributed around the area while also maintaining the existing footprint of the facility.

In order to achieve more stringent effluent limits, the City of Flagstaff worked with Black and Veatch to upgrade the Wildcat Hill Wastewater Treatment Facility, located in northern Arizona. The facility produces a high quality effluent, as well as reclaimed water, which is distributed throughout the region to construction companies and golf courses. The remaining treated water is discharged into the Rio de Flag Creek. The plant has a design influent annual average flow of 6.0 MGD.

The Wildcat Hill Wastewater Treatment Facility consists of Primary, Secondary, and Tertiary treatment. The primary treatment includes two (2) bar screens and a grit removal chamber, followed by four (4) clarifiers. Secondary treatment previously consisted of biofilters. These were replaced with a Kruger AnoxKaldnes Hybas™ system, which consists of media, air grids, screens and screen supports.The effluent leaving the Hybas enters five (5) secondary clarifiers.Traveling bridge media filters were previously utilized for tertiary treatment, followed by chlorination and dechlorination.Two (2) Kruger Hydrotech Discfilters were installed to provide for filtration in the new design.

Biosolids are processed through two (2) anaerobic digesters, a centrifuge, and two (2) stabilization ponds.This produces Class B sludge used for land application during the summer months.

In order to meet more stringent effluent limits, the Wildcat Hill WWTF incorporated Kruger's Hybas and Hydrotech Discfilter system to treat a design flow of 6.0 MGD for biological treatment at a minimum temperature of 14°C. The facility was required to meet effluent limits of soluble BOD < 10 mg/L, TSS < 10 mg/L, NH3-N < 0.5 mg/L, and NOx-N < 8 mg/L.

The AnoxKaldnes Hybas™ system consists of two (2) trains. Each train contains an anoxic basin, followed by two (2) oxic Hybas™ basins.The Hybas™ basins contain a total of 83,720 ft³ of AnoxKaldnes™ K3 media, medium bubble air grids, and screens to retain the media. The Hybas™ system contains both free-floating biomass (activated sludge) and biomass attached to the AnoxKaldnes™ media. The free-floating biomass passes through the reactor, is settled out, and recycled back to the reactor. The media with the attached biomass are retained in the reactor with cylindrical screens.

Following the secondary clarifiers, the system is required to provide turbidity reduction to a final effluent average of < 2 NTU based on Arizona Class A requirements.Two (2) Kruger HSF2220-2F Discfilter units were provided to meet these requirements and to provide one filter unit redundancy.The Discfilter has a compact footprint and low operating headloss.This allowed the site to utilize one of the four concrete basins housing the traveling bridge media filters for installation of the Discfilters.The units were easy to fit into the existing basin dimensions and met the hydraulic profile requirements, making the Discfilter installation a convenient solution for this application.

The effectiveness of Kruger's AnoxKaldnes Hybas™ system, followed by the Hydrotech Discfilter, has allowed the Wildcat Hill Wastewater Treatment Facility to produce a high quality effluent for their reclaimed water that is distributed around the area while alsomaintaining the existing footprint of the facility.