Charlotte Water McDowell Creek Wastewater Treatment Plant

1. Introduction

The McDowell Creek Wastewater Treatment Plant (WWTP) serves as a critical environmental safeguard for the rapidly growing northern Mecklenburg County region. Operated by Charlotte Water, this 12-MGD facility is strategically located within the Mountain Island Lake watershed—the primary drinking water source for the City of Charlotte and surrounding municipalities. Consequently, the plant operates under some of the most stringent nutrient removal standards in the state of North Carolina.

Originally commissioned to support local development, the facility has evolved into a highly sophisticated advanced treatment complex. Following a major multi-phase expansion completed circa 2020, the plant now utilizes advanced Biological Nutrient Removal (BNR) and tertiary filtration to ensure effluent quality exceeds regulatory requirements. As a model of modern wastewater infrastructure, the McDowell Creek WWTP demonstrates how high-density suburban growth can be balanced with rigorous environmental protection of sensitive receiving waters.

2. Facility Overview

A. Service Area & Coverage

The McDowell Creek WWTP services the northern sector of Charlotte Water’s jurisdiction. The sewershed encompasses the towns of Huntersville and Cornelius, as well as portions of Davidson and unincorporated Mecklenburg County. This area is characterized by a mix of high-density residential developments, commercial corridors along I-77, and light industrial zones. The collection system relies on a network of gravity mains feeding into major lift stations that convey flow to the plant’s headworks.

B. Operational Capacity

• Design Capacity: 12.0 MGD
• Current Average Daily Flow: Approximately 6.0 – 7.5 MGD (subject to seasonal variation)
• Peak Hydraulic Capacity: ~30 MGD (peak hourly flow)

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Historically, the plant operated at a lower capacity (6 MGD, then 9 MGD). Rapid population growth in the Lake Norman area necessitated the most recent expansion to 12 MGD to prevent hydraulic overloads and ensure capacity for projected growth through 2030.

C. Discharge & Compliance

The facility discharges treated effluent into McDowell Creek, which flows directly into Mountain Island Lake (Catawba River Basin). Because Mountain Island Lake is a Class WS-IV water body (Water Supply), the plant is subject to rigorous NPDES permitting regarding Total Phosphorus (TP) and Total Nitrogen (TN). The facility consistently achieves compliance, often discharging water with lower nutrient concentrations than the background levels of the receiving stream.

3. Treatment Process

The McDowell Creek WWTP employs a tertiary treatment train designed specifically for high-efficiency nutrient removal. The process flow is configured to handle variable hydraulic loads while maintaining biological stability.

A. Preliminary Treatment

Raw wastewater enters the headworks facility where it undergoes mechanical screening and grit removal.

• Screening: Multi-rake mechanical bar screens remove rags, plastics, and large debris to protect downstream pumps. Screenings are washed, compacted, and disposed of in a sanitary landfill.
• Grit Removal: Vortex grit chambers utilize centrifugal force to separate inorganic solids (sand, gravel, coffee grounds). This prevents abrasion on mechanical equipment and volume loss in the bioreactors.
• Odor Control: The headworks is enclosed and ventilated to biological scrubbers to mitigate nuisance odors for nearby residential neighbors.

B. Secondary Treatment (BNR)

The core of the treatment process is the activated sludge system, configured for Biological Nutrient Removal (BNR).

• Process Type: The plant utilizes a multi-stage BNR process (typically a 5-stage Bardenpho or similar A2O modification).
• Zones:
  • Anaerobic Zone: Promotes the growth of Phosphate Accumulating Organisms (PAOs) for biological phosphorus removal.
  • Anoxic Zone: Facilitates denitrification, converting nitrate to nitrogen gas.
  • Aerobic Zone: Provides dissolved oxygen for BOD oxidation and nitrification (ammonia conversion to nitrate) via fine bubble diffusion.
  
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• Secondary Clarification: Mixed liquor flows to large circular secondary clarifiers where biological floc settles. Return Activated Sludge (RAS) is pumped back to the anaerobic zone, while Waste Activated Sludge (WAS) is removed for solids processing.

C. Tertiary Treatment

To meet strict effluent limits (often < 1.0 mg/L TN and < 0.5 mg/L TP), the plant employs advanced polishing:

• Filtration: Effluent from secondary clarifiers passes through deep bed sand filters or cloth media disk filters. This stage removes remaining suspended solids and particulate-bound phosphorus.
• Chemical Polishing: Facilities for alum or ferric salt addition are available to precipitate any remaining soluble phosphorus prior to filtration if biological removal is insufficient.

D. Disinfection

The plant utilizes Ultraviolet (UV) Disinfection. Unlike chlorination, UV creates no disinfection byproducts (DBPs) such as trihalomethanes, which is critical for protecting the aquatic life in Mountain Island Lake. The UV system alters the DNA of bacteria and viruses, rendering them unable to reproduce.

E. Solids Handling

Solids management at McDowell Creek is integrated into Charlotte Water’s regional bio-solids strategy.

• Thickening/Dewatering: WAS is thickened (typically via Rotary Drum Thickeners or gravity belts) and dewatered using high-speed centrifuges to produce a sludge cake.
• Disposal: The dewatered cake is typically transported to the larger McAlpine Creek Wastewater Management Facility or regional composting facilities for final processing and beneficial reuse (land application) as a soil conditioner (Terra-Nu).

4. Infrastructure & Facilities

A. Physical Plant

The site is compact, requiring efficient use of vertical space and hydraulic profiles. The layout includes the Administration Building (housing SCADA control rooms and local laboratory), the Headworks Building, Blower Buildings, and the Chemical Feed structures. The architecture is designed to blend with the surrounding suburban environment where possible.

B. Energy Systems

Energy efficiency is a key operational metric. The plant utilizes Variable Frequency Drives (VFDs) on all major pumps and aeration blowers to match energy consumption with biological demand. High-efficiency turbo blowers provide the air for the aeration basins, significantly reducing the electrical load compared to legacy positive displacement blowers.

C. Odor Control

Given the proximity to residential neighborhoods (such as the Birkdale area), odor control is paramount. The facility utilizes bio-towers and chemical scrubbers at high-generation points (headworks and solids handling). Negative pressure is maintained in these buildings to prevent fugitive emissions.

5. Recent Upgrades & Major Projects

Future Capital Improvements (2024-2028)

Charlotte Water’s Capital Improvement Plan (CIP) indicates ongoing investment in asset preservation for McDowell Creek, including:

• Filter Rehabilitation: Upgrades to tertiary filter media and backwash systems.
• UV System Renewal: Replacement of aging UV banks with higher efficiency lamp technology.
• Collection System: Upgrades to the major pump stations feeding the plant to reduce inflow and infiltration (I&I) during wet weather events.

6. Regulatory Compliance & Environmental Performance

A. NPDES Permit

The facility operates under a National Pollutant Discharge Elimination System (NPDES) permit issued by the North Carolina Department of Environmental Quality (NCDEQ).
Permit Number: NC0036277 (Verify via NCDEQ Laserfiche).

B. Key Effluent Parameters

Due to the discharge into a WS-IV watershed, the plant faces stricter limits than standard secondary treatment plants:

• BOD/TSS: Typically < 5.0 mg/L (Monthly Average)
• Ammonia-Nitrogen: < 1.0 - 2.0 mg/L (Seasonal variation)
• Total Phosphorus: Strict mass loading limits.
• Fecal Coliform: < 200 CFU/100mL (Monthly Geometric Mean)

C. Environmental Stewardship

Charlotte Water maintains a rigorous stream monitoring program downstream of the outfall. The McDowell Creek plant has consistently received NACWA (National Association of Clean Water Agencies) Peak Performance Awards (Silver and Gold) for permit compliance.

7. Operational Excellence

Staffing: The plant is staffed 24/7/365. It requires operators with North Carolina Grade IV Biological Wastewater certification—the highest level of certification in the state—due to the complexity of the BNR and tertiary processes.

Automation: The facility utilizes a robust SCADA (Supervisory Control and Data Acquisition) system that provides real-time monitoring of Dissolved Oxygen (DO), Oxidation-Reduction Potential (ORP), and flows. This allows for automated pacing of chemical feeds and aeration, optimizing treatment while minimizing chemical and energy costs.

8. Challenges & Future Planning

Urban Encroachment: As Huntersville develops, residential zones are moving closer to the plant boundaries. This necessitates stricter odor control and noise mitigation strategies than typical rural plants.

Nutrient Regulations: Regulations regarding nutrient discharge into the Catawba River basin are expected to tighten further. Future planning involves evaluating Membrane Bioreactor (MBR) technology or other intensified treatment processes if limits decrease below current technical capabilities of conventional BNR.

Biosolids Logistics: As regional traffic increases, the logistics of hauling dewatered cake to processing facilities becomes more costly and time-consuming, driving interest in further volume reduction technologies.

9. Technical Specifications Summary

10. Frequently Asked Questions

Technical & Professional

Q: What is the current capacity of the McDowell Creek WWTP?
A: The plant has a permitted design capacity of 12.0 MGD following the Phase II expansion.

Q: Does the plant perform Biological Nutrient Removal (BNR)?
A: Yes. The plant utilizes a multi-stage activated sludge process specifically designed to remove Nitrogen and Phosphorus to protect the Mountain Island Lake watershed.

Q: How are biosolids handled at the facility?
A: Waste activated sludge is thickened and dewatered onsite (typically via centrifuges) and then transported to Charlotte Water’s regional facilities (like McAlpine) or land application sites.

Public Interest

Q: Does the plant smell?
A: While wastewater treatment naturally generates odors, McDowell Creek employs advanced odor control scrubbers and bio-filters to capture and treat air from the headworks and solids buildings to minimize impact on neighbors.

Q: Is the water discharged safe for the environment?
A: Yes. The effluent is treated to tertiary standards and disinfected with UV light. It meets or exceeds all state and federal requirements for discharge into a water supply watershed.

Q: Who do I contact for a tour?
A: Tours are generally arranged through Charlotte Water’s public affairs or education department. Due to safety and security, they are typically reserved for educational groups or industry professionals.