City Of Scottsdale Water Campus

1. Introduction

The Scottsdale Water Campus stands as one of the most technologically advanced water reclamation and recharge facilities in the arid Southwest. Located in the Sonoran Desert, where water scarcity drives innovation, this facility is the cornerstone of the City of Scottsdale’s sustainable water portfolio. The campus integrates a conventional Water Reclamation Plant (WRP) with a state-of-the-art Advanced Water Treatment (AWT) facility. Unlike traditional wastewater plants that discharge into surface waters, the Water Campus operates as a Zero Liquid Discharge (ZLD) facility regarding surface waterways, directing 100% of its effluent toward beneficial reuse—specifically golf course irrigation and large-scale aquifer recharge.

Commissioned in 1998, the facility has gained international recognition for its pioneering use of Vadose Zone Injection wells and, more recently, for obtaining Arizona’s first permanent permit for Direct Potable Reuse (DPR). With a combined capacity of treating over 20 million gallons daily (MGD), the Water Campus is not merely a waste processing site but a water production factory, critical to the region’s 100-year water supply designation. Recent upgrades, including the addition of ozonation and expanded reverse osmosis trains, position the Scottsdale Water Campus as a global model for indirect and direct potable reuse technologies.

2. Facility Overview

A. Service Area & Coverage

The Water Campus serves the rapidly growing residential and commercial sectors of North and Central Scottsdale, encompassing roughly 184 square miles. The service area is characterized by high-end residential developments, resorts, and premier golf courses, creating a unique influent profile with lower industrial contribution compared to typical urban centers. The collection system feeding the plant includes over 2,000 miles of pipeline and is distinct from the southern collection system, which diverts flow to the regional 91st Avenue Wastewater Treatment Plant.

B. Operational Capacity

The facility operates as a dual-stage system:

• Water Reclamation Plant (WRP): Designed for 23 MGD, currently processing an average daily flow of approximately 20 MGD. Peak wet weather capacity exceeds 30 MGD.
• Advanced Water Treatment (AWT): Originally commissioned at 6 MGD, expanding to 10 MGD, and recently expanded to 20 MGD. The AWT treats tertiary effluent from the WRP to drinking water standards for aquifer recharge.

Historical trends indicate a steady increase in flow correlating with northern development, stabilized by aggressive water conservation mandates. The plant currently operates at approximately 85-90% of its hydraulic capacity during peak seasonal loads.

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C. Discharge & Compliance

The facility operates under an Aquifer Protection Permit (APP) rather than a standard surface discharge NPDES for river release. The “receiving water body” is the local groundwater aquifer.
Primary Discharge Points:

• Turf Irrigation: Tertiary effluent is pumped to 23 local golf courses.
• Aquifer Recharge: AWT permeate (ultrapure water) is injected into the vadose zone to replenish the groundwater table.
• Brine Management: RO concentrate is discharged into the sewer collection system for treatment at the regional 91st Avenue WWTP.

3. Treatment Process

The Scottsdale Water Campus utilizes a complex multi-barrier treatment train. The process is divided into the conventional WRP train and the AWT purification train.

Part I: Water Reclamation Plant (WRP)

A. Preliminary Treatment

Raw wastewater enters the headworks where it passes through mechanical bar screens (6mm) to remove large debris. Following screening, flow enters vortex grit removal chambers where inorganic solids (sand, gravel) are settled out to protect downstream pumps. Odor control at the headworks utilizes biotrickling filters and activated carbon scrubbers to neutralize H2S emissions.

B. Secondary Treatment

The WRP utilizes a conventional Activated Sludge process configured for biological nutrient removal (BNR).
Configuration: Modified Ludwig-Ettinger (MLE) process.
Aeration Basins: The basins feature anoxic zones for denitrification followed by aerobic zones for nitrification. Fine bubble diffusion provides oxygen transfer.
Clarification: Mixed liquor flows to rectangular secondary clarifiers where solids settle. Return Activated Sludge (RAS) is pumped back to the anoxic zone, while Waste Activated Sludge (WAS) is thickened and sent to solids handling.

C. Tertiary Treatment

Secondary effluent is polished via disk filtration (cloth media filters) to reduce turbidity to < 2 NTU. This filtered water is then chlorinated using sodium hypochlorite for disinfection. This stream, known as Class A+ Reclaimed Water, is suitable for open access irrigation (golf courses).

Part II: Advanced Water Treatment (AWT)

A portion of the tertiary effluent (up to 20 MGD) is diverted to the AWT facility for purification to potable standards for recharge.

D. Ozonation (Pre-treatment)

Recently added to the train, ozone is generated on-site and injected into the feed water.
Purpose: Oxidizes pharmaceutical compounds, personal care products (PPCPs), and reduces membrane fouling downstream.
Dosage: Automated based on Total Organic Carbon (TOC) levels.

E. Membrane Filtration

Ultrafiltration (UF): The ozonated water passes through UF membranes (0.04-micron pore size). This stage removes suspended solids, bacteria, and protozoa, acting as a pretreatment to protect the RO membranes.
Reverse Osmosis (RO): The heart of the AWT. High-pressure pumps force water through semi-permeable membranes, removing dissolved salts, viruses, organics, and PFAS. The system operates at approximately 85% recovery.

F. Advanced Oxidation Process (UV-AOP)

The RO permeate passes through Ultraviolet (UV) reactors dosed with Hydrogen Peroxide. This UV-AOP step provides a final barrier against any remaining low-molecular-weight organics (like NDMA) via photolysis and hydroxyl radical oxidation.

G. Post-Treatment & Recharge

Because RO water is corrosive, the pH is adjusted using lime stabilization or decarbonation towers before the water is sent to the Vadose Zone Injection Wells. These specialized dry wells allow water to percolate through hundreds of feet of soil (natural filtration) before reaching the aquifer.

Solids Handling

The Scottsdale Water Campus does not process biosolids to final disposal on-site. Primary and thickened waste activated sludge is discharged into the sewer interceptor system, where it flows by gravity to the regional 91st Avenue Wastewater Treatment Plant (owned by the Sub-Regional Operating Group – SROG). This eliminates the need for digesters and dewatering equipment at the Scottsdale site, significantly reducing the facility’s footprint and odor potential.

4. Infrastructure & Facilities

A. Physical Plant

The campus is architecturally designed to blend with the desert environment. Key structures include the Administration Building, the Water Quality Laboratory (a state-certified facility capable of detecting contaminants at parts-per-trillion levels), the AWT building (housing membrane trains), and the enclosed WRP basins. The site also features the Reclaimed Water Distribution System (RWDS) pump station, capable of delivering over 30 MGD to the irrigation network.

B. Vadose Zone Injection Wells

A critical infrastructure component is the network of approximately 70 vadose zone injection wells. Unlike deep well injection, these wells are approximately 150-180 feet deep, terminating in the unsaturated zone above the aquifer. This allows for an additional soil-aquifer treatment (SAT) benefit as the water percolates down to the groundwater table (approx. 400-500 feet below surface).

C. Energy Systems

The facility is a major energy consumer due to the high-pressure RO pumps. Energy efficiency measures include the installation of Variable Frequency Drives (VFDs) on all major pumps and blowers. The city has also implemented solar photovoltaic (PV) shade structures in the parking areas, contributing to the facility’s power needs.

5. Recent Upgrades & Major Projects

Reclaimed Water Distribution System (RWDS) Pump Station Improvements (2022-2023)

Upgrades to the vertical turbine pumps and electrical gear to handle increased irrigation demand and improve reliability during peak summer months. This included the replacement of aging VFDs and SCADA integration improvements.

Future Projects (2025-2027)

The city is planning the RO Concentrate Management Project. Currently, brine is sent to the sewer. Future plans involve potential brine minimization technologies or dedicated pipelines to manage salinity loads more sustainably as the region faces stricter salinity controls.

6. Regulatory Compliance & Environmental Performance

A. Permit Requirements

The facility operates under some of the strictest standards in the nation due to the potable reuse component.

• Turbidity: Must maintain < 0.1 NTU for membrane effluent.
• Nitrogen: Total Nitrogen < 10 mg/L (APP standard).
• Pathogens: 5-log removal of virus, 5-log removal of Giardia, 4-log removal of Cryptosporidium (via multiple barriers).
• Disinfection Byproducts: Strict limits on TTHMs and HAA5s.

B. Direct Potable Reuse (DPR) Permit

In 2019, the ADEQ issued the Scottsdale Water Campus the state’s first permanent permit for Direct Potable Reuse. While the facility primarily practices Indirect Potable Reuse (recharge), this permit allows the facility to serve purified water directly to customers (used currently for the “Safe Water One” brewing and demonstration campaigns) without an environmental buffer, proving the water exceeds all Safe Drinking Water Act standards.

7. Challenges & Future Planning

A. Salinity Management

As the region cycles water more times through reuse, Total Dissolved Solids (TDS) levels naturally rise. The RO process removes salt, creating a brine concentrate. Managing this brine stream without overwhelming the regional wastewater system (SROG) is a primary engineering challenge for the next decade.

B. Colorado River Shortage

With Tier 1 and Tier 2 shortages declared for the Colorado River, the value of the Water Campus has skyrocketed. The facility is central to Scottsdale’s drought contingency plan. Future planning involves maximizing every drop of effluent for recharge, potentially reducing the amount available for turf irrigation in favor of aquifer banking.

C. Emerging Contaminants (PFAS)

While the RO and GAC/Ozone systems are effective at removing PFAS, regulatory limits are moving toward near-zero. The facility is continuously monitoring influent levels and optimizing carbon replacement cycles and membrane performance to ensure compliance with impending EPA MCLs for PFAS/PFOA.

8. Technical Specifications Summary

9. Related Facilities

• Gainey Ranch Water Reclamation Plant: A smaller satellite facility (1.7 MGD) in Scottsdale that also feeds the reclaimed water system.
• 91st Avenue Wastewater Treatment Plant: The regional plant located in Phoenix. Scottsdale owns capacity in this plant, which treats solids from the Water Campus and flow from southern Scottsdale.
• Chaparral Water Treatment Plant: Scottsdale’s surface water treatment plant treating CAP (Central Arizona Project) water.

10. Frequently Asked Questions

Technical Questions

Q: What is the TOC reduction across the AWT train?
A: The AWT typically reduces Total Organic Carbon from ~6-8 mg/L (tertiary effluent) to non-detectable levels (< 0.5 mg/L) in the final permeate.

Q: How does the facility handle RO concentrate (brine)?
A: The brine is discharged into the sanitary sewer system, where it mixes with raw sewage and flows to the regional 91st Avenue WWTP. It is not discharged to the environment locally.

Q: Is the facility capable of Direct Potable Reuse (DPR)?
A: Yes. The facility holds Arizona’s first permit for DPR. While the infrastructure primarily serves Indirect Potable Reuse (Recharge), the water quality meets all potable standards immediately post-treatment.

Q: What membranes are used in the RO system?
A: The facility generally uses thin-film composite polyamide membranes. Specific suppliers have included Hydranautics and Dow Filmtec during different operational phases.

Public Interest Questions

Q: Is this “Toilet to Tap”?
A: The industry term is “Advanced Water Purification.” While the water originates as wastewater, the multi-barrier purification process (Ozone, RO, UV) renders it chemically purer than most bottled water before it is returned to the ground.

Q: Can the public tour the facility?
A: Yes, the Scottsdale Water Campus is famous for its educational outreach. Tours are regularly available and highly recommended for engineering students and industry professionals.

Q: Where does the water go after treatment?
A: It goes two places: 1) Through purple pipes to irrigate golf courses (saving drinking water), and 2) Into the ground to recharge the aquifer for future use.