Alexandria Renew Enterprises AlexRenew Wastewater Treatment Plant

1. INTRODUCTION

The AlexRenew Water Resource Recovery Facility (WRRF) serves as the ecological cornerstone for the City of Alexandria and parts of Fairfax County, managing wastewater for over 300,000 residents in one of the nation’s most densely populated urban corridors. Located just south of historic Old Town Alexandria, this 54-MGD advanced treatment facility operates under some of the strictest nutrient discharge limits in the United States due to its impact on the Chesapeake Bay watershed.

Operated by Alexandria Renew Enterprises, a public utility and political subdivision of the Commonwealth of Virginia, the facility distinguishes itself through innovative land use—incorporating community athletic fields atop treatment structures—and cutting-edge nitrogen removal technologies. Currently, the facility is the nexus of “RiverRenew,” a monumental $615 million tunnel system project designed to remediate Combined Sewer Overflows (CSOs). By integrating advanced biological treatment with massive civil infrastructure upgrades, AlexRenew has positioned itself as a model for urban water resilience and environmental stewardship.

2. FACILITY OVERVIEW

A. Service Area & Coverage

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AlexRenew serves a highly urbanized 35-square-mile area encompassing the City of Alexandria and the southeastern portion of Fairfax County. The collection system feeding the plant is a complex hybrid of modern separated sewers and legacy combined sewer systems dating back to the mid-19th century. The service area includes dense residential zones, commercial districts, and significant government infrastructure.

B. Operational Capacity

The facility is designed for an average daily flow of 54 million gallons per day (MGD). While current average flows fluctuate between 35 and 40 MGD, the plant handles significant wet-weather peaks. Upon completion of the RiverRenew Tunnel System, the facility’s wet weather pumping capacity will be stressed-tested to manage capture rates up to 130 MGD to prevent untreated discharges.

C. Discharge & Compliance

Treated effluent is discharged into Hunting Creek, a tributary of the Potomac River, which flows into the Chesapeake Bay. Consequently, the facility operates under a stringent Virginia Pollutant Discharge Elimination System (VPDES) permit heavily focused on nutrient loading. The plant consistently achieves Total Nitrogen (TN) levels below 3.0 mg/L and Total Phosphorus (TP) below 0.18 mg/L, meeting the rigorous requirements of the Chesapeake Bay Preservation Act.

3. TREATMENT PROCESS

AlexRenew utilizes a sophisticated treatment train emphasizing biological nutrient removal (BNR) and innovative sidestream treatment technologies.

A. Preliminary Treatment

Raw wastewater enters the headworks where it passes through mechanical bar screens to remove large debris. Following screening, flow enters vortex grit chambers where inorganic solids (sand, gravel, coffee grounds) are settled out via centrifugal force. Odor control is paramount at this stage; the headworks are fully enclosed and ventilated through chemical scrubbers to prevent nuisance odors in the neighboring residential areas.

B. Primary Treatment

Wastewater flows into rectangular primary settling tanks. Here, flow velocity is reduced to allow heavier organic solids to settle as primary sludge, while grease and oils float to the surface for skimming. The primary effluent flows to the biological stage, while primary sludge is pumped to the solids handling train. The facility achieves typical TSS removal of 60-70% and BOD removal of 30-40% at this stage.

C. Secondary Treatment (Biological Nutrient Removal)

The heart of the facility is its Biological Nutrient Removal (BNR) system. The plant utilizes a modified activated sludge process designed for nitrification and denitrification.

• Configuration: The aeration basins feature anoxic and aerobic zones to facilitate the conversion of ammonia to nitrate (nitrification) and nitrate to nitrogen gas (denitrification).
• Aeration: Fine bubble diffusion provides high oxygen transfer efficiency.

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• Chemical Support: Methanol or glycerin may be added as a supplemental carbon source to drive denitrification during periods of low influent carbon-to-nitrogen ratios.

D. Sidestream Deammonification (ANITA Mox)

A distinctive technical feature of AlexRenew is the use of the ANITA Mox process (Veolia) for treating centrate (nitrogen-rich liquid from dewatering centrifuges). This Moving Bed Biofilm Reactor (MBBR) system utilizes anammox bacteria to convert ammonia and nitrite directly into nitrogen gas. This “short-cut” nitrogen removal reduces the nitrogen load returned to the head of the plant by up to 85%, significantly lowering energy costs and chemical usage for the main liquid train.

E. Tertiary Treatment

To meet the ultra-low phosphorus and solids limits, secondary effluent passes through tertiary filtration. The facility utilizes deep-bed multimedia gravity filters. Alum or Ferric Chloride is added prior to filtration to precipitate remaining dissolved phosphorus, which is then captured in the filter media.

F. Disinfection

Disinfection is achieved using ultraviolet (UV) light irradiation. This eliminates the safety hazards associated with storing chlorine gas or hypochlorite in a dense urban environment and negates the need for dechlorination chemicals before discharge.

G. Solids Handling

Solids are processed to produce Class A Exceptional Quality (EQ) biosolids:

• Thickening: Gravity belt thickeners reduce volume before digestion.
• Digestion: Anaerobic digesters stabilize the sludge, reducing volatile solids and pathogen content while producing biogas.
• Pasteurization: The facility employs a pasteurization step to ensure Class A pathogen reduction.
• Dewatering: High-solids centrifuges dewater the digested sludge.
• End Product: The resulting “Alexandria Gold” (or similarly branded) biosolids are beneficially reused as a soil amendment on local farms and public lands.

4. INFRASTRUCTURE & FACILITIES

A. Physical Plant & Urban Integration

The facility occupies a constrained 30+ acre site. To maximize utility, AlexRenew constructed the Nutrient Management Facility (NMF) with an active community asset on its roof: the Limberchest Jones Athletic Fields. This dual-use structure houses 18 million gallons of treatment capacity underneath a full-size synthetic turf soccer/lacrosse field, demonstrating industry-leading land-use efficiency.

B. Energy Systems

AlexRenew recovers energy through biogas utilization. Methane produced in the anaerobic digesters is captured, cleaned, and used to fire boilers that heat the digesters and facility buildings. This cogeneration approach offsets significant natural gas consumption.

C. Odor Control

Given the proximity to Old Town Alexandria and the Carlyle District, AlexRenew maintains one of the region’s most aggressive odor control programs. Technologies include:

• Three-stage chemical scrubbers (acid, caustic/bleach).
• Activated carbon polishing units.
• Foul air intake from all major process units, covering headworks, primary tanks, and solids handling.

5. RECENT UPGRADES & MAJOR PROJECTS

Nutrient Management Facility (Completed ~2016)

This $140 million upgrade included the construction of the 18-million-gallon wet weather equalization tanks and the installation of the ANITA Mox deammonification system. This project was crucial for stabilizing the plant’s biological processes during peak flow events and securing compliance with Chesapeake Bay nitrogen limits.

6. REGULATORY COMPLIANCE & ENVIRONMENTAL PERFORMANCE

A. Permit Requirements

The facility operates under NPDES Permit VA0025160. Key parameters reflect the sensitive nature of the Chesapeake Bay watershed:

• Total Nitrogen (TN): Annual average limit of 3.0 mg/L (load based).
• Total Phosphorus (TP): Monthly average limit of 0.18 mg/L.
• TSS & BOD5: Standard secondary treatment limits (typically < 10 mg/L monthly average achieved).
• Bacteria: E. coli limits consistent with recreational water usage (126 n/100ml geometric mean).

B. Compliance History

AlexRenew has maintained an exemplary compliance record, frequently receiving the Peak Performance Award (Platinum and Gold status) from the National Association of Clean Water Agencies (NACWA). The facility has consistently met the Chesapeake Bay nutrient loading caps, often generating nutrient credits.

7. OPERATIONAL EXCELLENCE

A. Staffing & Safety

The facility employs a diverse team of over 100 professionals, including licensed wastewater operators (Class I-IV), maintenance technicians, laboratory scientists, and engineers. The safety culture is robust, necessitated by the confined space entry requirements of the new tunnel infrastructure and complex chemical systems.

B. Technology & Innovation

AlexRenew utilizes a centralized SCADA system for real-time process monitoring. The facility engages in active research partnerships, notably piloting ammonia-based aeration control strategies and collaborating with the Water Environment Federation (WEF) on industry best practices for sidestream treatment.

8. CHALLENGES & FUTURE PLANNING

A. Current Challenges

Urban Encroachment: As Alexandria densifies, residential developments are built increasingly close to the plant fence line, making odor control and noise mitigation continuous priorities.
Biosolids Management: Regional pressures on land application sites require constant strategic planning for solids disposal outlets.
Rate Impacts: Financing the $615 million RiverRenew project has required multi-year rate increases, necessitating careful financial stewardship and public communication.

B. Future Planning

Following the completion of RiverRenew in 2025, the facility’s master plan shifts focus to asset management of aging electrical infrastructure and potential adaptation for Indirect Potable Reuse (IPR) capabilities in the long term, should regional water supply needs dictate.

9. COMMUNITY & REGIONAL IMPACT

AlexRenew has redefined the “fence-line” relationship between utilities and the public. The Environmental Center serves as an educational hub, hosting school tours and community events. By placing the Limberchest Jones athletic fields on top of active treatment tanks, the authority turned a “Not In My Backyard” (NIMBY) facility into a community destination (“Yes In My Backyard”). Economically, the utility supports the rapid development of the Alexandria waterfront by ensuring reliable sewer capacity and cleaner waterways.

10. TECHNICAL SPECIFICATIONS SUMMARY

11. RELATED FACILITIES

The AlexRenew system includes several critical off-site assets, including the Commonwealth Interceptor and multiple pumping stations that convey flow from Fairfax County. The new RiverRenew project adds significant remote infrastructure, including diversion chambers at existing outfalls (Outfalls 001, 002, 003, and 004) and the deep tunnel pump station shaft located on the plant site.

12. FAQ SECTION

Technical/Professional Questions

1. What is the primary method for nitrogen removal at AlexRenew?
The plant uses a combination of main-stream biological nutrient removal (MLE/Bardenpho configurations) and the sidestream ANITA Mox deammonification process to treat ammonia-rich centrate.

2. Does the facility produce Class A or Class B biosolids?
AlexRenew produces Class A Exceptional Quality (EQ) biosolids through anaerobic digestion followed by pasteurization.

3. What is the RiverRenew Tunnel Project?
It is a massive civil engineering project involving a 2-mile tunnel and a new 130 MGD pump station designed to capture Combined Sewer Overflows (CSOs) to meet Virginia statutory requirements by 2025.

4. How is disinfection handled without chlorine?
The facility utilizes high-intensity UV (Ultraviolet) light banks to neutralize pathogens before discharge, eliminating the need for chlorination/dechlorination chemicals.

Public Interest Questions

5. Can the public use the fields at the plant?
Yes, the Limberchest Jones Athletic Fields located on top of the Nutrient Management Facility are open for reserved community use and league sports.

6. Does the plant smell?
While wastewater treatment naturally generates odors, AlexRenew employs an extensive multi-stage odor control system (carbon and chemical scrubbers) and covers most process tanks to minimize impact on the surrounding community.

7. Who pays for the plant’s operation?
The facility is funded through wastewater treatment charges on water bills from Alexandria and Fairfax Water customers, as well as connection fees for new development.