Charlotte Water Sugar Creek Wastewater Treatment Plant

1. INTRODUCTION

The Sugar Creek Wastewater Treatment Plant (WWTP) serves as a cornerstone of environmental protection for the highly urbanized central and southern districts of Charlotte, North Carolina. Operated by Charlotte Water, this facility is permitted for a hydraulic capacity of 20 million gallons per day (MGD). Originally commissioned in the early 20th century as one of the city’s first treatment works, the plant has evolved through successive capital improvement cycles into a modern, highly automated resource recovery facility.

Situated directly adjacent to the Little Sugar Creek Greenway, the plant operates within a dense mixed-use and residential corridor, necessitating rigorous odor control and aesthetic integration. Beyond its primary function of pathogen and nutrient removal, the Sugar Creek WWTP is a regional leader in sustainability, featuring a Combined Heat and Power (CHP) cogeneration system that converts biogas into electricity, offsetting a significant portion of the plant’s energy demand. It stands as a critical asset in the protection of the Catawba River basin ecosystem.

2. FACILITY OVERVIEW

A. Service Area & Coverage

The Sugar Creek WWTP services a distinct sewershed encompassing the highly developed Uptown Charlotte area, the Myers Park and Dilworth neighborhoods, and the Tyvola Road corridor. The collection system feeding the plant is characterized by older infrastructure, primarily gravity mains, which presents unique challenges regarding Inflow and Infiltration (I/I) during wet weather events. The service area is largely built-out, meaning flow increases are driven closer by densification (vertical growth) rather than suburban sprawl.

B. Operational Capacity

While permitted for 20 MGD, the facility typically treats an average daily flow (ADF) ranging between 11 and 14 MGD, providing sufficient reserve capacity for peak wet weather flows. The hydraulic profile is designed to handle peak hourly flows significantly higher than the average to accommodate storm surges common in the North Carolina Piedmont region. The plant operates 24/7/365, managed by state-certified operators utilizing advanced SCADA monitoring.

C. Discharge & Compliance

Treated effluent is discharged into Little Sugar Creek, a tributary that eventually feeds into the Catawba River. Given the impaired historical status of Little Sugar Creek, the NPDES permit limits for the facility are stringent, particularly regarding Dissolved Oxygen (DO), Ammonia-Nitrogen, and Fecal Coliform. The facility consistently achieves compliance, aiding in the gradual ecological restoration of the creek, which now supports aquatic life and recreational activities along its banks.

3. TREATMENT PROCESS

The Sugar Creek WWTP utilizes a multi-stage conventional activated sludge process supplemented by tertiary filtration and ultraviolet disinfection.

A. Preliminary Treatment

Raw influent enters the headworks where it passes through mechanical coarse and fine bar screens to remove large debris, rags, and plastics. Following screening, flow enters vortex grit removal chambers. These systems use centrifugal force to separate inorganic solids (sand, gravel, eggshells) from the organic wastewater stream. The extracted grit and screenings are washed, compacted, and disposed of in landfills. This stage is critical for protecting downstream pumps and reducing wear on mechanical equipment.

B. Primary Treatment

Wastewater flows into rectangular primary clarifiers. Here, the velocity of the water is reduced to allow settleable solids to drop to the bottom as primary sludge, while fats, oils, and grease (FOG) float to the surface for skimming. The primary sludge is pumped to the solids handling train. This physical separation removes approximately 30-40% of BOD and 50-60% of TSS before biological treatment.

C. Secondary Treatment (Biological)

The core treatment occurs in the aeration basins using an Activated Sludge process. The basins are configured for biological nutrient removal (BNR), specifically targeting nitrification (conversion of ammonia to nitrate). Air is introduced via fine-bubble diffusers to sustain the aerobic bacteria that consume organic matter.

Mixed liquor from the aeration basins flows to secondary clarifiers, where the biological biomass (floc) settles out. A portion of this settled biomass is returned to the aeration basins as Return Activated Sludge (RAS) to maintain the biological population, while the excess growth is removed as Waste Activated Sludge (WAS).

D. Tertiary Treatment

To meet stringent effluent limits, secondary effluent undergoes tertiary filtration. Sugar Creek utilizes Deep Bed Sand Filters (or similar media filtration) to polish the water, removing remaining suspended solids and particulate-bound phosphorus. This step is essential for ensuring the effectiveness of the downstream UV disinfection process.

E. Disinfection

Historically a gas chlorination facility, Sugar Creek upgraded to Ultraviolet (UV) Disinfection. The filtered water passes through banks of UV lamps submerged in channels. The UV light penetrates the cell walls of pathogens (bacteria, viruses, protozoa), disrupting their DNA and preventing reproduction. This method eliminates the need for hazardous chlorine gas storage and the subsequent need for dechlorination chemicals, resulting in a safer effluent for aquatic life.

F. Solids Handling & Energy Recovery

Solids handling at Sugar Creek is a sophisticated process focused on volume reduction and energy recovery:

• Thickening: Primary and waste activated sludges are thickened (often via gravity thickeners or rotary drum thickeners).
• Anaerobic Digestion: Thickened sludge acts as feed for anaerobic digesters. In these heated, oxygen-free tanks, bacteria break down the organic matter, reducing volatile solids by 40-50%.
• Biogas Utilization: A byproduct of digestion is methane-rich biogas. This gas is captured, scrubbed, and fed into a Combined Heat and Power (CHP) engine cogeneration system. This system generates electricity to power plant equipment and produces heat used to warm the digesters, creating a semi-closed energy loop.
• Dewatering: Digested sludge is dewatered using high-speed centrifuges to produce a “cake” (biosolids).
• Disposal: The Class B biosolids are typically land-applied as a soil conditioner on permitted agricultural fields, recycling nutrients back to the earth.

4. INFRASTRUCTURE & FACILITIES

A. Physical Plant

The site is physically constrained by Tyvola Road and the Little Sugar Creek floodplain, requiring a compact, vertical engineering approach. The architecture of recent additions, particularly the administration and headworks buildings, has been designed to blend with the surrounding commercial aesthetic.

B. Energy Systems & Cogeneration

Sugar Creek is a model for Charlotte Water’s energy initiatives. The CHP system significantly reduces the plant’s reliance on the grid. By utilizing the biogas generated onsite, the facility mitigates greenhouse gas emissions (methane) and stabilizes operating costs against fluctuating energy prices. Energy efficiency is further enhanced by the use of Variable Frequency Drives (VFDs) on major pumps and blowers.

C. Odor Control

Given the proximity to the high-value Park Road and Montford Drive commercial districts, odor control is paramount. The facility utilizes covered headworks and primary clarifiers, ducting foul air to chemical scrubbers and/or biological distinct odor control units designed to remove hydrogen sulfide and mercaptans before releasing air to the atmosphere.

5. RECENT UPGRADES & MAJOR PROJECTS

Phase 2 Upgrades & Reliability Improvements (Completed ~2018-2020)

• Project Scope: Comprehensive modernization of the headworks, influent pumping, and disinfection systems.
• Budget: Approx. $35 – $45 Million.
• Contractors: Crowder Construction Company (General Contractor).
• Technical Highlights:
  • Construction of a new Influent Pump Station (IPS) to handle peak wet weather flows more effectively.
  • Replacement of aging bar screens and grit removal systems with higher capture-efficiency equipment.
  • Full conversion from gaseous chlorine to UV disinfection, enhancing safety and environmental compliance.
  • Installation of a new standby generator complex to ensure resiliency during power outages.

Combined Heat and Power (CHP) Project

• Scope: Installation of biogas conditioning and cogeneration engines.
• Drivers: Duke Energy incentives and Charlotte Water’s sustainability goals.
• Result: The system allows the plant to offset a significant percentage of its electrical load and provides thermal energy for the digestion process.

6. REGULATORY COMPLIANCE & ENVIRONMENTAL PERFORMANCE

A. Permit Requirements

The facility operates under NPDES Permit NC0024937 issued by the North Carolina Department of Environmental Quality (NCDEQ). Critical parameters include:

• BOD5 & TSS: Strict removal efficiencies required (typically >85% removal).
• Ammonia Nitrogen: Seasonal limits to prevent toxicity to aquatic life.
• Fecal Coliform: Limits to ensure water quality suitable for secondary recreation.
• Metals: Monitoring required due to the urban nature of the influent.

B. Environmental Stewardship

Charlotte Water and the Sugar Creek facility have received numerous Peak Performance Awards from the National Association of Clean Water Agencies (NACWA) for permit compliance. The facility plays a vital role in the “Little Sugar Creek Restoration,” transforming a waterway once listed as impaired into an asset that anchors the city’s greenway system.

7. OPERATIONAL EXCELLENCE

The facility is staffed by a dedicated team of operators, mechanics, and laboratory technicians. Operators must hold North Carolina Biological Water Pollution Control System Operator certifications, with senior staff holding the highest level (Grade IV). The plant utilizes a robust SCADA system for real-time monitoring of dissolved oxygen profiles, tank levels, and motor amp draws, allowing for precise process control adjustments to minimize energy waste while maximizing treatment.

8. CHALLENGES & FUTURE PLANNING

A. Aging Infrastructure vs. Urban Density

While the treatment trains have been modernized, the underlying collection system and some structural concrete components date back decades. Rehabilitating these assets within a constrained, high-traffic footprint requires complex logistics and phased construction to maintain continuous operations.

B. Nutrient Regulations

As the Catawba River basin faces increased pressure from regional growth, nutrient limits (Nitrogen and Phosphorus) are expected to tighten. Future planning likely includes optimization of the BNR process or the addition of chemical polishing to meet potentially lower phosphorus limits.

C. Resiliency

Flood mitigation is a constant consideration. Being located next to the creek it discharges into, the plant must be protected against 100-year and 500-year flood events to prevent washout of the biomass or sanitary sewer overflows.

9. COMMUNITY & REGIONAL IMPACT

The Sugar Creek WWTP demonstrates that essential utility infrastructure can coexist with urban amenities. The plant’s integration with the Little Sugar Creek Greenway offers a unique educational opportunity, where the public can see the clean effluent entering the creek. Economically, the plant provides the sanitary capacity requisite for the continued high-density development of Charlotte’s South End and Midtown districts.

10. TECHNICAL SPECIFICATIONS SUMMARY

11. RELATED FACILITIES

Sugar Creek is one of five major wastewater treatment plants operated by Charlotte Water. It works in conjunction with:

• McAlpine Creek WWMF: The largest plant in the system (64 MGD), located downstream.
• Mallard Creek WRF: Serves the university area (12 MGD).
• Irwin Creek WWTP: Serves the west side (15 MGD).
• McDowell Creek WWTP: Serves the northern Huntersville area (12 MGD).

12. FAQ SECTION

Technical Questions

1. Does Sugar Creek WWTP perform Biological Nutrient Removal (BNR)?
Yes, the activated sludge basins are configured to support nitrification and partial denitrification to reduce ammonia and nitrogen levels in the effluent.

2. How is grit handling managed at the facility?
Following mechanical screening, the plant utilizes vortex grit chambers to separate inorganic solids. The grit is washed and dewatered prior to landfill disposal.

3. What is the hydraulic retention time (HRT) of the aeration basins?
While variable based on flow, typical conventional activated sludge plants target an HRT of 4-8 hours. Specific operational data depends on the current flow mode (dry vs. wet weather).

4. Is the facility manned 24 hours a day?
Yes, Charlotte Water staffs the facility 24/7 with certified operators to monitor SCADA and perform physical rounds.

Public Interest Questions

5. Why doesn’t the plant smell bad despite being in the city?
The plant employs aggressive odor control technologies, including covering primary treatment tanks and using chemical or biological air scrubbers to treat foul air before it leaves the buildings.

6. Is the water released into the creek clean?
Yes. The water undergoes physical, biological, and chemical (UV) treatment. It is often clearer and has higher dissolved oxygen levels than the creek water itself.

7. Does the plant generate its own power?
It generates a portion of its own power through a Combined Heat and Power (CHP) system that burns methane gas produced by the sludge digestion process.