Arizona Wastewater Treatment Plants

1. Introduction

Arizona’s wastewater infrastructure is defined by its arid geography and the necessity of the “One Water” management philosophy. Unlike coastal states that discharge treated effluent into oceans, Arizona reclaims approximately 95% of its treated wastewater for agriculture, industrial cooling, turf irrigation, and underground aquifer recharge. The state’s infrastructure is overseen by the Arizona Department of Environmental Quality (ADEQ), which enforces some of the strictest Aquifer Protection Permit (APP) standards in the nation.

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The sector is currently navigating a critical transition period. Rapid population growth in Maricopa and Pinal counties is driving the need for new greenfield capacity, while mature municipalities like Phoenix and Tucson are retrofitting aging bio-solids handling and secondary treatment systems. There are currently over 300 permitted wastewater treatment facilities in the state, serving a population of over 7.4 million. The regulatory environment is shifting toward Direct Potable Reuse (DPR), with ADEQ finalizing rules that will allow utilities to treat wastewater to drinking water standards without an environmental buffer.

2. Recent Developments & Projects

In the last 36 months, Arizona utilities have shifted focus from simple capacity expansion to advanced resource recovery. The Infrastructure Investment and Jobs Act (IIJA) and state-level appropriations have injected over $250 million into the Water Infrastructure Finance Authority of Arizona (WIFA) for distribution.

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Notable recent trends include:

• Regionalization of Assets: Smaller municipal plants are being interconnected to larger regional facilities (like the SROG partnership) to optimize flow management and reduce per-gallon treatment costs.
• Biogas Utilization: Major facilities, including the 91st Ave WWTP, have completed massive Renewable Natural Gas (RNG) projects, turning digester gas into a revenue stream via the regional natural gas grid.
• Drought Resilience: The City of Phoenix and satellite cities are actively designing Advanced Water Purification facilities to offset reductions in Central Arizona Project (CAP) water allocations.

3. Top 20 Largest Treatment Plants

The following table ranks the largest wastewater treatment plants in Arizona by design capacity. The list is dominated by the Sub-Regional Operating Group (SROG) in Phoenix and the Pima County Regional Wastewater Reclamation Department in Tucson.

Detailed Profiles: Top 5 Largest Facilities

4. Plants with Approved Budgets & Expansion Projects

A. Major Projects Under Construction (2024-2026)

B. Projects in Design/Planning Phase (2025-2028)

• Advanced Water Purification (AWP) Facility – Phoenix
  • Budget: Est. $400 – $600 Million
  • Scope: A large-scale Direct Potable Reuse (DPR) facility located at 91st Ave. Will treat effluent to drinking water standards using Ozone-BAC or RO-UV/AOP.
  • Status: Pilot testing complete; Engineering design procurement underway.

• Val Vista Water Treatment Plant Rehabilitation
  • Budget: $110 Million
  • Scope: Major electrical and mechanical upgrades to existing infrastructure shared by Mesa and Phoenix.
  • Status: Design Phase.

• Buckeye WRF Expansion Phase 3
  • Budget: $75 Million
  • Scope: Doubling capacity to meet explosive housing growth in the far West Valley.
  • Status: Planning/Pre-design.

Summary Statistics: Arizona Capital Investment

5. Regulatory & Compliance Landscape

Arizona’s regulatory framework is uniquely tailored to aquifer protection. The Arizona Pollutant Discharge Elimination System (AZPDES) governs surface discharges, but the Aquifer Protection Permit (APP) program is the primary driver for treatment standards, as most plants discharge to the ground (recharge).

• Class A+ Reclaimed Water: The gold standard in Arizona. Requires filtration and disinfection with zero detectable fecal coliforms and turbidity below 2 NTU. This allows for unrestricted reuse (parks, schools, golf courses).
• PFAS/PFOA: ADEQ is currently conducting statewide sampling. While no enforceable state MCL exists yet, major utilities (Tucson Water, Phoenix) are proactively installing treatment or shutting down impacted wells.
• Direct Potable Reuse (DPR): Arizona is finalizing a regulatory pathway for “Advanced Water Purification,” which will remove the requirement for an environmental buffer (aquifer) before reuse water enters the drinking water distribution system.

6. Infrastructure Challenges & Opportunities

The Salt Balance Problem: As water is reused multiple times in a closed loop (One Water), Total Dissolved Solids (TDS) increase (salinity). Inland utilities cannot easily discharge brine. This presents a massive opportunity for vendors specializing in Brine Minimization and Zero Liquid Discharge (ZLD) technologies.

Growth vs. Water Supply: The Assured Water Supply rules require developers to prove 100 years of water. In areas where groundwater is restricted (Pinal County), developers are partnering with utilities to fund advanced wastewater treatment to create “recharge credits,” essentially manufacturing their own water supply to allow construction to proceed.

7. Technology Trends in Arizona

• Vadose Zone Recharge Wells: Unlike traditional injection wells, these use gravity to recharge aquifers in the unsaturated zone. Widely used due to lower O&M costs.
• Ozone-Biofiltration (Ozone-BAC): Gaining traction over Reverse Osmosis for reuse projects because it destroys contaminants without creating a brine stream that is difficult to dispose of in a landlocked state.
• Advanced Metering Infrastructure (AMI) & AI: Used extensively to detect leaks and optimize distribution networks.

8. Resources for Engineers & Operators

• AZ Water Association: The state chapter of AWWA/WEF. Hosts the annual conference in Phoenix (Spring). Link to Association
• WIFA (Water Infrastructure Finance Authority): The primary issuer of SRF loans and water supply development grants. Link to WIFA
• ADEQ Operator Certification: Manages testing and licensure for Grades 1-4 wastewater operators. Link to Certification

9. FAQ Section

How many wastewater treatment plants are in Arizona?

There are over 300 permitted wastewater treatment facilities in Arizona, ranging from massive regional plants like the 204 MGD 91st Ave plant to small package plants serving remote communities and RV parks.

What is the largest wastewater plant in Arizona?

The 91st Ave Wastewater Treatment Plant is the largest, with a capacity of 204.5 MGD. It is owned by the Sub-Regional Operating Group (SROG), which includes Phoenix, Glendale, Mesa, Scottsdale, and Tempe.

What are the primary drivers for WWTP projects in Arizona?

Unlike the East Coast (CSO/SSO compliance), Arizona projects are driven by 1) Capacity expansion for rapid housing growth, and 2) Advanced treatment for water reuse (aquifer recharge) to generate long-term water storage credits.

Is Arizona implementing Direct Potable Reuse (DPR)?

Yes. Arizona is in the advanced stages of finalizing regulations for DPR (termed Advanced Water Purification). The City of Phoenix and Scottsdale are actively planning facilities that will treat effluent to drinking water standards for direct introduction into the potable supply.