New Orleans Sewerage And Water Board Carrollton Water Purification Plant

FACILITY BASIC INFORMATION

• Plant Name: Carrollton Water Purification Plant
• Location: New Orleans, Orleans Parish, Louisiana
• Operating Authority: Sewerage and Water Board of New Orleans (SWBNO)
• Design Capacity: 232 MGD (Million Gallons per Day)
• Current Average Flow: ~135 MGD
• Population Served: ~384,000 (East Bank of New Orleans)
• Service Area: Orleans Parish (East Bank)
• Source Water Body: Mississippi River
• Regulatory Authority: Louisiana Department of Health (LDH), EPA Region 6
• Year Commissioned: Original plant 1909 (Expanded continuously)

TARGET AUDIENCE

• Municipal consulting engineers evaluating river water treatment systems
• Water treatment plant operators and utility managers
• Power systems engineers interested in co-generation and legacy 25Hz grids
• Environmental regulators monitoring Mississippi River downstream quality
• Civil engineering students studying hydraulic infrastructure

1. INTRODUCTION

The Carrollton Water Purification Plant is the hydraulic heart of New Orleans, serving the entire East Bank of the city. As one of the oldest and largest water treatment facilities in the southern United States, it operates with a design capacity of 232 MGD, treating raw water drawn directly from the lower Mississippi River. Operated by the Sewerage and Water Board of New Orleans (SWBNO), the facility is a complex amalgamation of historic early 20th-century engineering and modern treatment retrofits.

Unique among American water utilities, the Carrollton facility functions as an islanded energy grid. It houses a dedicated power complex that generates electricity (historically at 25 Hz cycle) to power not only the water purification pumps but also the city’s massive drainage pumping stations. The plant is currently in a transitional era, managing significant capital projects to modernize its power reliability, mitigate saltwater intrusion risks, and update aging conveyance infrastructure while maintaining continuous service for nearly 400,000 residents and a major tourism economy.

2. FACILITY OVERVIEW

A. Service Area & Coverage

The Carrollton Plant serves the East Bank of Orleans Parish, a dense urban environment characterized by flat topography and below-sea-level elevation. The service area includes the Central Business District, the French Quarter, and major residential neighborhoods. The distribution system comprises approximately 1,600 miles of mains, ranging from 4-inch neighborhood lines to 50-inch transmission mains. The system is fully pressurized, with no gravity storage tanks in the distribution network, necessitating robust high-lift pumping capabilities to maintain system pressure (typically 65-70 psi at discharge).

B. Operational Capacity

While the plant boasts a design capacity of 232 MGD, current average daily flows hover between 130 and 140 MGD. However, the facility must handle extreme variances. Historical peak demand has exceeded 180 MGD during freeze events (due to residents running taps to prevent pipe bursting) and significant drops during population shifts post-Hurricane Katrina. The plant’s hydraulic throughput is heavily dependent on the performance of the High Lift Pump Station, which pushes finished water into the city’s grid.

C. Source Water Characteristics

The plant draws from the Mississippi River, a source characterized by high seasonal turbidity, fluctuating hardness, and potential upstream industrial runoff.

• Turbidity: Ranges from 20 NTU to over 1,000 NTU depending on rainfall and river stage.
• Alkalinity/Hardness: Variable; requires careful chemical adjustment for corrosion control.
• Saltwater Wedge: During periods of extreme drought and low river flow, the salt wedge from the Gulf of Mexico can migrate upstream to the intake, posing a critical chloride threat (as seen in the 2023/2024 low water event).

3. TREATMENT PROCESS

The Carrollton Plant utilizes a conventional treatment train adapted for high-turbidity river water softening and purification. The process is designed to remove suspended solids, harmful bacteria, and organic matter while stabilizing water chemistry.

A. INTAKE AND SCREENING

Raw water is drawn from the Mississippi River via two intake structures located at the river’s edge. Coarse bar screens prevent large debris (logs, river trash) from entering the Low Lift Pump Station. The Low Lift pumps elevate the water from the river level to the head of the plant to facilitate gravity flow through the initial treatment stages.

B. CHEMICAL PRE-TREATMENT & FLOCCULATION

Upon entering the plant, the water undergoes rapid mixing with coagulants.

• Coagulants: Ferric sulfate and/or cationic polymers are added to destabilize suspended particles.
• Flash Mix: High-energy mixing ensures immediate chemical dispersion.
• Flocculation: Water moves to flocculation basins where paddle mixers gently agitate the water, encouraging particle collision and the formation of heavy “floc.”

C. CLARIFICATION (SEDIMENTATION)

The facility utilizes expansive sedimentation basins. Given the high silt load of the Mississippi, efficient sludge removal is critical. The heavy floc settles to the bottom of these basins.

• Primary Clarification: Removes the bulk of heavier solids.
• Softening/Conditioning: Lime is added to adjust pH and precipitate hardness (calcium/magnesium) if necessary, primarily for pipe protection.
• Sludge Handling: Settled sludge is collected via mechanical scrapers and pumped to the sludge processing stream (thickening and eventual discharge/disposal per regulatory permits).

D. FILTRATION

Settled water flows to the rapid sand gravity filters. This infrastructure includes older operational galleries and retrofitted filter beds.

• Media: Dual media (anthracite coal and sand) or mono-media sand configurations resting on gravel support layers.
• Operation: Water passes downward through the media, trapping remaining particulate matter and protozoan cysts (Giardia/Cryptosporidium).
• Backwash: Filters are periodically backwashed based on head loss or time intervals, using finished water to scour the media.

E. DISINFECTION AND STABILIZATION

SWBNO employs a chloramination strategy to maintain residual disinfectant levels throughout the extensive distribution system.

• Primary Disinfection: Chlorine (gas or hypochlorite) is applied to achieve required CT (Concentration x Time) values for viral and bacterial inactivation.
• Ammoniation: Ammonia is added downstream of chlorination to form chloramines. This reduces the formation of Trihalomethanes (THMs) and Haloacetic Acids (HAAs), which are carcinogenic disinfection byproducts common in organic-rich river water.
• Fluoridation: Hydrofluorosilicic acid is added for dental health compliance.
• Corrosion Control: Orthophosphate or polyphosphate blends are dosed to coat distribution pipes, inhibiting lead and copper leaching from aging service lines.

F. PROCESS CONTROL

The plant utilizes a SCADA (Supervisory Control and Data Acquisition) system to monitor tank levels, pump status, and online water quality analyzers (turbidity, chlorine residual, pH). However, significant manual intervention and monitoring remain part of the operational culture due to the vintage of certain subsystems.

4. INFRASTRUCTURE & POWER GENERATION

A. The Power Complex

The most engineering-intensive aspect of the Carrollton site is its integrated Power Complex. Historically, the plant operated on a 25 Hz cycle (common in the early 1900s) rather than the standard 60 Hz used by the US grid today.

• Steam Turbines: Legacy steam-driven turbines provided the backbone of power for both water and drainage pumps.
• Gas Turbines: Combustion Turbine Generators (CTGs) were added in recent decades to provide backup and peak power.
• Frequency Conversion: Because much of the SWBNO’s heavy drainage equipment still utilizes 25 Hz motors, the plant requires complex frequency changers to convert grid power (60 Hz) or modern generator power to the legacy 25 Hz standard.

B. Pumping Infrastructure

• Low Lift Pump Station: River intake pumps.
• High Lift Pump Station: Pressurizes the finished water for distribution. These are critical assets; a failure here results in an immediate boil water advisory due to pressure loss allowing potential groundwater infiltration.

C. Water Hammer Towers

Two massive surge protection towers (water hammer towers) were recently constructed. These structures mitigate hydraulic transients (pressure surges) that occur if pumps suddenly trip offline, protecting the aging distribution pipes from catastrophic bursts.

5. RECENT UPGRADES & MAJOR PROJECTS

The SWBNO is currently executing a multi-billion dollar Capital Improvement Program (CIP) to address deferred maintenance and modernization.

Power Complex Substation (2021-2024)

• Budget: ~$30+ Million (Estimate)
• Scope: Construction of a dedicated electrical substation to connect the Carrollton plant directly to the Entergy (local utility) transmission grid.
• Engineering Goal: To reduce reliance on aging on-site steam and gas turbines. This allows the plant to run primarily on reliable grid power while retaining on-site generation for emergency backup only.
• Status: Commissioning phases active as of 2024.

Water Hammer Hazard Mitigation (Completed ~2020)

• Budget: ~$50 Million (FEMA funded)
• Scope: Construction of two composite elevated storage tanks/surge towers.
• Technical Highlight: These towers provide transient surge protection. If power fails, the stored water maintains positive pressure in the mains long enough to prevent vacuum conditions that could suck contaminants into the pipes.

Smart Metering (AMI) Rollout (Ongoing)

• Scope: Replacing mechanical analog meters with Advanced Metering Infrastructure (AMI).
• Goal: To improve billing accuracy, detect leaks on the customer side faster, and reduce non-revenue water loss.

Joint Infrastructure Recovery Request (JIRR)

Following Hurricane Ida and recent turbine failures, SWBNO has been working with state and federal partners for emergency funding to replace the entire legacy power generation suite with modern frequency changers and 60 Hz standardized equipment.

6. REGULATORY COMPLIANCE & ENVIRONMENTAL PERFORMANCE

A. Drinking Water Standards

The facility operates under the oversight of the Louisiana Department of Health (LDH). Key compliance parameters include:

• Turbidity: Must be ≤ 0.3 NTU in 95% of monthly samples (Surface Water Treatment Rule).
• Disinfection Byproducts: Compliance with Stage 2 D/DBP Rule for TTHMs (80 ppb) and HAA5 (60 ppb).
• Lead and Copper: Compliance with the LCR (Lead and Copper Rule). SWBNO utilizes orthophosphate for corrosion control, but the city has a significant inventory of lead service lines which are currently being inventoried and replaced under federal mandates.

B. Compliance Challenges

The facility faces challenges maintaining consistent pressure. In New Orleans, if system pressure drops below 20 psi, a precautionary Boil Water Advisory is automatically issued. Historically, power failures at the Carrollton plant have caused pressure drops leading to frequent advisories, though reliability has improved with recent tower installations.

7. CHALLENGES & FUTURE PLANNING

A. Saltwater Intrusion

During drought years (notably 1988, 2012, 2023), low Mississippi River flow allows the dense saltwater wedge from the Gulf of Mexico to creep upstream. The Carrollton intake is vulnerable to chloride spikes.
Mitigation Strategy: SWBNO coordinates with the Army Corps of Engineers to construct underwater sills (barriers) in the river. In 2023, plans were developed to barge fresh water and construct a temporary pipeline from upstream, highlighting the need for long-term resilient intake solutions (e.g., Reverse Osmosis capabilities or upstream intakes).

B. Power Reliability & The “25 Hz” Problem

The reliance on unique 25 Hz equipment means SWBNO cannot simply buy off-the-shelf pumps or motors. The strategic plan involves a total migration to 60 Hz standards, allowing for easier procurement and grid connectivity. This is a massive electromechanical undertaking requiring phased replacement of major pump motors.

C. Non-Revenue Water

Due to expansive clay soils (subsidence) and aging cast-iron pipes, the distribution system suffers from high leakage rates. Reducing water loss remains a top priority to lower chemical and energy costs per gallon delivered.

8. TECHNICAL SPECIFICATIONS SUMMARY

9. FAQ SECTION

Technical Questions

Q1: Why does the Carrollton Plant generate its own power?
A: Historically, the plant used 25 Hz pumps for efficiency in the early 1900s. To maintain these legacy pumps, the plant had to generate its own 25 Hz electricity. Modernization efforts are shifting the plant to standard 60 Hz grid power.

Q2: How does the plant handle Mississippi River turbidity?
A: The plant uses a robust train of coagulation, flocculation, and massive sedimentation basins. The primary clarifiers are designed to handle heavy solids loading, with mechanical sludge scrapers removing tons of sediment daily before filtration.

Q3: What is the “Water Hammer” hazard?
A: If high-lift pumps fail suddenly, the moving water column in the pipes stops and reverses, creating a pressure wave (transient) that can burst pipes. The new towers absorb this energy to protect the infrastructure.

Public Interest Questions

Q4: Is the water safe to drink during a Boil Water Advisory?
A: No. An advisory implies pressure dropped below 20 psi, creating a risk that groundwater entered the pipes. Water must be boiled for 1 minute to kill potential bacteria until the advisory is lifted.

Q5: Does the plant remove salt from the water?
A: Currently, the Carrollton Plant is a freshwater treatment plant and does not have Reverse Osmosis (RO) desalination capabilities. During saltwater intrusion events, the utility relies on dilution or alternative water sources.