Renewable Water Resources Mauldin Road Water Resource Recovery Facility Greenville

FACILITY BASIC INFORMATION

• Plant Name: Mauldin Road Water Resource Recovery Facility (WRRF)
• Location: 661 Mauldin Road, Greenville, SC 29607
• Operating Authority: Renewable Water Resources (ReWa)
• Design Capacity: 29.0 MGD
• Current Average Flow: ~18-22 MGD
• Population Served: Approx. 500,000 (Regional System Total)
• Service Area: Greenville County (City of Greenville, Mauldin, Simpsonville)
• Receiving Water Body: Reedy River
• NPDES Permit Number: SC0020010
• Year Commissioned: Original commissioning 1929 (Multiple major expansions)

1. INTRODUCTION

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The Mauldin Road Water Resource Recovery Facility (WRRF) serves as the flagship treatment asset for Renewable Water Resources (ReWa), the regional wastewater authority for Upstate South Carolina. Located along the banks of the Reedy River, this facility is not only the largest in ReWa’s portfolio with a design capacity of 29 million gallons per day (MGD), but it also stands as a technological benchmark for the Southeast United States. The plant is historically significant, tracing its roots to the region’s first treatment efforts in the 1920s, yet it currently operates as a modern model of the circular economy.

Distinguished by its adoption of advanced biosolids management technologies, Mauldin Road was one of the first facilities in the region to implement the Thermal Hydrolysis Process (THP) for sludge treatment. This strategic investment allows the facility to serve as a regional solids handling hub, processing biosolids from satellite plants while generating renewable energy through combined heat and power (CHP) systems. As Greenville continues its rapid population growth, the Mauldin Road WRRF remains critical to protecting the water quality of the Reedy River basin while pioneering energy neutrality in wastewater operations.

2. FACILITY OVERVIEW

A. Service Area & Coverage

The Mauldin Road WRRF serves the core urban density of Greenville County. The collection system feeding the plant encompasses the City of Greenville, the City of Mauldin, and portions of Simpsonville and Travelers Rest. The influent profile is a mix of residential (high density), commercial, and light industrial wastewater. As a regional authority, ReWa manages over 350 miles of trunk sewer lines and connects to municipal sub-districts, consolidating flow to major treatment hubs like Mauldin Road.

B. Operational Capacity

The facility is permitted for a design flow of 29.0 MGD. Current average daily flows typically range between 18 and 22 MGD, providing a capacity utilization of approximately 65-75%. This headroom is strategic, allowing ReWa to accommodate the significant hydraulic surges associated with wet weather events in the Upstate region and to support the projected double-digit population growth expected in Greenville County over the next decade.

C. Discharge & Compliance

Treated effluent is discharged into the Reedy River, a tributary of the Saluda River. The discharge location is environmentally sensitive, situated immediately upstream of Lake Conestee Nature Park, a major regional wildlife sanctuary. Consequently, the facility operates under strict NPDES limitations regarding BOD, suspended solids, and increasingly, nutrient loads (Phosphorus and Nitrogen) to prevent eutrophication in downstream reservoirs. The facility maintains a distinguished record of compliance, frequently earning the NACWA (National Association of Clean Water Agencies) Platinum Peak Performance Award for consecutive years of perfect permit compliance.

3. TREATMENT PROCESS

A. Preliminary Treatment

Raw wastewater enters the headworks via large diameter interceptors following the Reedy River basin. Preliminary treatment consists of mechanical bar screens to remove large debris, rags, and plastics. Following screening, flow passes through vortex grit removal chambers where inorganic solids (sand, gravel, coffee grounds) are settled out to protect downstream pumps and biosolids equipment. The headworks is enclosed and ventilated through chemical scrubbers for odor control, given the facility’s proximity to commercial and residential zones.

B. Primary Treatment

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Flow is directed to primary clarifiers where gravity settling removes approximately 60-70% of Total Suspended Solids (TSS) and 30-40% of Biological Oxygen Demand (BOD). Primary sludge is pumped directly to the solids handling train, while the supernatant flows to the secondary treatment stage. The efficiency of primary treatment here is critical for reducing the organic load on the aeration basins.

C. Secondary Treatment

Mauldin Road utilizes a conventional activated sludge process modified for nutrient removal capabilities. The biological reactors (aeration basins) use fine-bubble diffusion to oxygenate the mixed liquor. The specific configuration allows for nitrification, converting ammonia to nitrate. Following aeration, the mixed liquor enters secondary clarifiers where biological floc settles. Return Activated Sludge (RAS) is recycled to the head of the aeration basins, while Waste Activated Sludge (WAS) is thickened and sent to the digestion complex.

D. Tertiary Treatment & Disinfection

To meet stringent pathogen limits without introducing chlorinated byproducts into the Reedy River, the facility utilizes a large-scale Ultraviolet (UV) disinfection system. The UV channels ensure inactivation of bacteria and viruses prior to discharge. Post-aeration is utilized to ensure the final effluent meets the dissolved oxygen (DO) requirements of the receiving stream.

E. Solids Handling (Advanced Thermal Hydrolysis)

The defining technical feature of the Mauldin Road WRRF is its solids handling train, modernized under the “Digester Greenville” project. The process flow includes:

• Thickening: Primary sludge and WAS are thickened prior to processing.
• Thermal Hydrolysis Process (THP): The facility utilizes the CAMBI THP system. Sludge is subjected to high pressure and temperature (approx. 165°C) essentially “pressure cooking” the biomass. This step lyses cells, reduces viscosity, and increases the biodegradability of the volatile solids.
• Anaerobic Digestion: The hydrolyzed sludge is fed to anaerobic digesters. Because of the THP pre-treatment, the digesters can operate at double the conventional loading rate with significantly higher volatile solids reduction (VSR).
• Dewatering: Digested sludge is dewatered using high-speed centrifuges. The THP process results in a dewatered cake with higher solids content (often >30%) compared to conventional digestion.
• End Product: The final product is a Class A Biosolid, free of pathogens and low in odor, which ReWa markets as a soil amendment.

4. INFRASTRUCTURE & FACILITIES

A. Physical Plant

The site spans a significant footprint along the Reedy River corridor. It houses the central administration for ReWa, including engineering, operations, and water quality laboratory departments. The site layout is linear, following the hydraulic grade line toward the river.

B. Energy Systems & CHP

The facility operates a Combined Heat and Power (CHP) system. Methane-rich biogas generated in the anaerobic digesters is captured, scrubbed to remove siloxanes and hydrogen sulfide, and fed into cogeneration engines. These engines generate electricity to offset grid consumption and produce waste heat. This thermal energy is recovered and looped back to provide the steam required for the CAMBI Thermal Hydrolysis Process, creating a highly efficient energy loop.

C. Odor Control

Odor mitigation is a Tier-1 priority. The facility utilizes a multi-stage approach including covering primary clarifiers, enclosing headworks, and utilizing biotrickling filters and carbon adsorption units. The switch to THP and Class A biosolids has also significantly reduced the odors associated with the final sludge product.

5. RECENT UPGRADES & MAJOR PROJECTS

Digester Greenville (Completed ~2020)

• Project Scope: A transformative overhaul of the solids handling infrastructure. This project involved the installation of the CAMBI Thermal Hydrolysis Process (THP), new anaerobic digester rehabilitation, and new dewatering centrifuges.
• Capital Investment: Approximately $45 Million.
• Drivers: The need to increase solids processing capacity without building new digester tanks, the desire to produce Class A biosolids for beneficial reuse, and the goal of energy recovery.
• Technical Highlight: This was the first installation of CAMBI THP technology in South Carolina. It allows the plant to accept sludge from satellite ReWa facilities, centralizing processing at Mauldin Road.
• Results: Reduced biosolids volume by over 50%, saving millions in hauling costs. Increased biogas production significantly, fueling the CHP system.

Upcoming: Membrane Bioreactor (MBR) Conversion (Planning/Future)

While currently utilizing conventional activated sludge, long-term master planning for ReWa has evaluated the potential conversion or expansion using Membrane Bioreactor technology at various sites to meet future nutrient limits (Phosphorus < 0.1 mg/L) imposed by downstream water quality constraints in the Reedy River basin.

6. REGULATORY COMPLIANCE & ENVIRONMENTAL PERFORMANCE

A. Permit Requirements

The facility operates under NPDES Permit SC0020010. Critical parameters include:

• BOD5: Monthly average limits typically < 15 mg/L (seasonally variable).
• TSS: Monthly average limits < 30 mg/L.
• Ammonia-Nitrogen: Strict seasonal limits to prevent toxicity.
• Phosphorus: The Reedy River has a Total Phosphorus (TP) TMDL (Total Maximum Daily Load), requiring the plant to optimize biological phosphorus removal (Bio-P) and chemical precipitation capabilities.

B. Compliance History

ReWa’s Mauldin Road facility is a consistent recipient of the NACWA Platinum Peak Performance Award, recognizing facilities that achieve 100% compliance with their NPDES permits for five or more consecutive years. This demonstrates a high level of operational control and redundancy.

7. OPERATIONAL EXCELLENCE

A. Staffing & Certification

The facility is staffed 24/7/365. Operators are required to hold South Carolina Biological Wastewater Treatment licensure, with senior operators holding “A” level certifications. The site also houses ReWa’s central certified laboratory, which performs compliance testing for the entire district.

B. Technology Integration

The plant utilizes a robust SCADA (Supervisory Control and Data Acquisition) system that provides real-time monitoring of dissolved oxygen profiles, digester pressures, and flow pacing. The integration of the CHP and THP systems requires sophisticated automated controls to balance gas production with steam generation requirements.

8. CHALLENGES & FUTURE PLANNING

A. Nutrient Management

The primary engineering challenge for Mauldin Road is the Total Maximum Daily Load (TMDL) for nutrients in the Reedy River. As regulations tighten regarding Total Phosphorus and Total Nitrogen, the facility will likely require further tertiary treatment upgrades, potentially including deep-bed denitrification filters or membrane filtration.

B. Wet Weather Management

Inflow and Infiltration (I&I) in the older sections of the Greenville collection system can cause hydraulic peaking at the plant. ReWa has invested heavily in the “Dig Deep” tunnel project—a massive gravity sewer tunnel—to provide storage and conveyance capacity, smoothing out peak flows arriving at Mauldin Road.

9. TECHNICAL SPECIFICATIONS SUMMARY

10. FAQ SECTION

Technical Questions

Q: What is the specific advantage of the THP system at Mauldin Road?
A: The Thermal Hydrolysis Process reduces sludge viscosity, allowing digesters to be loaded at double the conventional rate. It significantly increases biogas production for energy recovery and produces a Class A biosolid that is pathogen-free.

Q: Does Mauldin Road have nutrient removal capabilities?
A: Yes, the facility is designed for nitrification and biological phosphorus removal to meet the sensitive requirements of the Reedy River TMDL.

Q: What is the peak hydraulic capacity?
A: While permitted for 29 MGD average flow, the hydraulic peak capacity is significantly higher (estimated >60 MGD) to handle wet weather surges, supported by equalization basins.

General Interest

Q: Does the plant smell?
A: While wastewater treatment naturally produces odors, Mauldin Road utilizes advanced chemical scrubbers and carbon filters. The switch to THP digestion has also dramatically reduced the odor of the final biosolids product.

Q: Where does the water go?
A: Treated, clean water is discharged into the Reedy River, where it supports the ecosystem of the downstream Lake Conestee Nature Park.