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Wastewater Treatment Plants (WWTP)

Chandler Airport WRF Grit System

Chandler, AZ

Owner/Client: City of Chandler

Wilson Engineers was retained to perform the design and construction services for the Airport WRF – Grit Removal Facilities Project. This project includes the design of two grit removal systems located on the downstream side of the Headworks Building.  The grit removal project includes two separate 22 MGD capacity stacked cell grit/sand separator units that are capable of removing 95% of grit larger than 75 microns.  The grit facilities design also includes a grit dewatering building which houses the two grit classifiers.  Additional improvements within the facility include modifications to the existing odor control system to treat addition foul air from the grit dewatering building, relocation of plant wide 15 kV and fiber optic loop and incidental yard piping and site work. The project is currently in construction and the work is expected to be completed by Spring 2018.

Chandler Ocotillo WRF Expansion

Chandler, AZ

Owner/Client: City of Chandler

Wilson Engineers is part of the team that was selected for the design and construction phases of a 5 MGD expansion to the Ocotillo Water Reclamation Facility. This project includes a new liquid treatment train consisting of Headworks (with coarse screens followed by fine screens), membrane bioreactor basins, submerged membrane filters, chlorine contact basins and a reclaimed water pump station. The solids treatment include sludge holding basins and dewatering building housing belt filter presses and a cake conveyor and storage silo. Ancillary facilities include chemical facilities and several odor control facilities. Wilson Engineers performed process mechanical, electrical and I&C design of an influent pump station and headworks facilities (15 MGD average flow) and the electrical and instrumentation design for the entire project. The project is currently under construction with an expected substantial completion date of February 2018. 

Ocotillo WRF Process Upgrades

Chandler, AZ

Owner/Client: City of Chandler

The City of Chandler Ocotillo WRF has been in operation since the mid 1980’s.  Over the past 30 years the City has experienced changing influent loading conditions and much of the process equipment is nearing the end of its useful life.  The purpose of this project was to replace or rehabilitate major process equipment and implement modifications to the biological process to enhance the reliability of the treatment process.  Major items included in the project were: Rehabilitation of influent screens, repairs to the headworks odor control system, new mixers in the aeration basins, existing blower replacement, design of new process instrumentation in the aeration basins, a new secondary clarifier, plant control system upgrades and miscellaneous upgrades to the existing chemical feed facilities. 

Airport WRF Expansion to 22 MGD

Chandler, AZ

Owner/Client: City of Chandler

The City of Chandler selected Wilson Engineers to design and provide construction management for a 7-MGD expansion to the existing 15-MGD Airport WRF.  Wilson served as the lead design firm providing overall project management, preliminary and detailed design of all facilities, regulatory and administrative permitting, construction administration, and inspection services.  As part of the project, Wilson completed several tasks which included generation of hydraulic and BioWin computer models of the facility and identified modifications and additions needed as a result of changes in the influent waste water characteristics due to a higher percentage of industrial wastewater in the influent.  Design included significant additions and modifications to all liquid stream processes, solids stream processes and ancillary facilities. Process monitoring probes were installed along the secondary process for real-time monitoring of treatment performance. Wilson developed over 200 Maintenance of Plant Operations (MOPOs) plans with input from Plant Staff to minimize unanticipated interruptions to plant operations.


CMAR alternative project delivery method with multiple design phases was utilized to allow early procurement to reduce the overall construction duration.  The Project was awarded the 2015 Engineering Excellence Grand Award from ACEC, the 2015 Wastewater Project of the Year from AZ Water Association, the 2015 Project of the Year from APWA, and the 2015 Best Project of the Year in “Water/Environment” from ENR Southwest.

Sahuarita 1.5 MGD Expansion

Sahuarita, AZ

Owner/Client: Willcox

The Town of Sahuarita selected Wilson Engineers to provide the design and construction administration services for a 1.5 MGD facility upgrade to replace the existing 0.49 MGD oxidation ditch facility and 0.20 MGD temporary package plant.  Wilson Engineers provided detailed design and permitting services for this project.  The 1.5 MGD plant expansion included an extended aeration design with biological nutrient removal and swing zones within the aeration basins to provide treatment flexibility to the operators. The main treatment processes included fine screening, activated sludge basins, secondary clarifiers, filtration, UV disinfection, and mechanical dewatering. In addition, three new buildings were designed to service the functional aspects of the treatment plant and at the same time be aesthetically pleasing for both visitors and staff. The Town’s major concern with the expansion project was to remain on schedule in accordance with the consent order provisions. Wilson Engineers worked closely with the Construction Manager at Risk CMAR selected by the Town during the design process to ensure the project was constructed on time (July ’09) and on budget ($21.9 M).

Kyrene RF Expansion

Tempe, AZ

Owner/Client: City of Tempe


The City of Tempe selected Wilson to complete an evaluation of different expansion options for the existing Tempe Kyrene Reclamation Facility to increase capacity from 4.5 MGD to 9 MGD.  The evaluation included comparing the conventional activated sludge process and a membrane bioreactor process among others.

After completion of the evaluation, Wilson designed a facility with a membrane bioreactor (MBR) process.  New facilities designed as part of the upgrades included an influent pump station, headworks building, UV disinfection, and odor control facilities.  The existing aeration basins were modified and two new basins were installed to treat additional flows.  The existing rectangular secondary clarifiers were retrofitted with submerged membranes and converted into membrane basins. 

Jomax Water Reclamation Plant

Peoria, AZ

Owner/Client: City of Peoria


Wilson Engineers provided design services for a new 0.75 MGD Jomax Water Reclamation Facility in the Northwest Valley. Wilson’s services include Program Management, Permitting, Treatment Plant design, and Non-Potable Water System design. The facility included an influent pump station, biological nutrient removal basins, secondary clarifiers, RAS/WAS post equalization pump station, rapid mix and flocculation facilities, traveling bridge filters, UV disinfection system, solids dewatering building, sludge storage tank, and a 1.5 million-gallon non-potable water reservoir. Additional facilities include the Beardsley Raw Water Pump Station, non-potable booster station, and odor control, as well as electrical power supply equipment, instrumentation and controls, storm water retention, yard piping, on-site improvements and security system.

Jomax WRF 2.25 MGD Expansion

Peoria, AZ

Owner/Client: Vistancia CFD/City of Peoria

The project included a 1.5 MGD capacity expansion to the existing 0.75 MGD Jomax Water Reclamation Facility. The facility improvements included expanding the existing influent pump station, providing additional capacity to the existing secondary treatment process by adding new aeration basins and one secondary clarifier.  The tertiary treatment improvements included addition of one traveling bridge filter and disinfection system was upgraded by addition of new UV lamps.  Additional facilities included a solids dewatering system, expansion of the existing effluent pump station, odor control facilities and a new two-story headworks facility equipped with 6mm influent screens and a vortex type grit removal system.

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