DeKalb County South River Water Reclamation Facility

1. INTRODUCTION

The Pole Bridge Creek Advanced Wastewater Treatment Facility (AWTF) is a cornerstone of the DeKalb County Department of Watershed Management’s infrastructure, serving the rapidly growing southeastern quadrant of the county. Treating an average of 14 million gallons per day (MGD) with a design capacity of 20 MGD, this facility plays a pivotal role in the protection of the South River watershed—a water body historically impacted by urbanization and combined sewer overflows.

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Operating under strict Georgia Environmental Protection Division (EPD) regulations, the facility utilizes advanced biological nutrient removal and tertiary filtration to meet stringent effluent limits, particularly for phosphorus and fecal coliform. As DeKalb County operates under a federal Consent Decree to address sanitary sewer overflows (SSOs) and aging infrastructure, the Pole Bridge Creek AWTF has been the recipient of significant recent capital investment. These upgrades focus on modernization, energy efficiency, and hydraulic reliability, establishing the plant as a critical asset in the county’s $1.3 billion capital improvement strategy.

2. FACILITY OVERVIEW

A. Service Area & Coverage

The facility serves a distinct hydraulic shed in Southeast DeKalb, covering approximately 25 square miles. This area includes portions of Lithonia and unincorporated DeKalb County. The service area is characterized by a mix of mature suburban residential developments and light industrial zones. The collection system feeding the plant is gravity-dominated, though it is supported by several major lift stations including the Pole Bridge Lift Station. The collection system has historically struggled with Inflow and Infiltration (I/I), leading to significant peaking factors during wet weather events.

B. Operational Capacity

While permitted for 20 MGD, the plant typically operates at 60-70% of its hydraulic capacity during dry weather. However, the hydraulic peaking factor is substantial. During significant storm events common to the Southeast, peak instantaneous flows can challenge the headworks and primary treatment capacity. Long-term planning by DeKalb DWM projects moderate growth in the sewershed, with a focus on infill development, necessitating sustained treatment reliability rather than massive capacity expansion.

C. Discharge & Compliance

The facility discharges directly into the South River. Because the South River is listed on Georgia’s 303(d) list for impairments (primarily fecal coliform and legacy PCBs), the NPDES permit limits are stringent. The facility is required to maintain high levels of Dissolved Oxygen (DO) in the effluent and strictly limit Total Suspended Solids (TSS) and Ammonia-Nitrogen to prevent further degradation of the receiving water’s aquatic habitat.

3. TREATMENT PROCESS

A. PRELIMINARY TREATMENT

Raw influent enters the headworks via gravity interceptors. The preliminary treatment stage is critical for protecting downstream pumping and aeration equipment.

• Screening: The facility utilizes mechanical coarse and fine bar screens to remove rags, plastics, and large debris. Recent upgrades have replaced aging climber screens with more efficient perforated plate screens to improve capture rates and reduce maintenance.
• Grit Removal: Following screening, flow enters vortex grit chambers. Given the age of the collection system, grit loading can be high, particularly during first-flush rain events. Grit is washed and dewatered before landfill disposal.
• Flow Equalization: Limited equalization exists to manage diurnal peaks, though wet weather operations rely heavily on effective process control adjustments.

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B. PRIMARY TREATMENT

The plant employs conventional circular primary clarifiers. These units reduce the organic loading on the secondary system by settling out heavy solids and skimming floating fats, oils, and grease (FOG). Primary sludge is pumped directly to the solids handling complex, while the clarified effluent (primary effluent) flows to the aeration basins. The hydraulic retention time (HRT) in this stage is approximately 2-3 hours at average flow.

C. SECONDARY TREATMENT

The core of the treatment capability is an activated sludge process configured for biological nutrient removal.

• Bioreactors: The aeration basins are operated in an anoxic/oxic configuration to facilitate nitrification and denitrification. This allows the plant to meet strict Ammonia-Nitrogen limits.
• Aeration: Air is supplied via centrifugal blowers delivering oxygen to fine-bubble membrane diffusers located on the basin floors. This system was retrofitted in the last decade to improve oxygen transfer efficiency (OTE).
• Secondary Clarification: Mixed liquor flows to circular center-feed secondary clarifiers where biological floc settles. Return Activated Sludge (RAS) is pumped back to the anoxic zone, while Waste Activated Sludge (WAS) is diverted to solids processing.

D. TERTIARY TREATMENT

To meet the low TSS and Phosphorus limits required for discharge into the South River, the facility employs tertiary filtration.

• Deep Bed Filters: The plant utilizes deep bed sand filters. These gravity filters polish the secondary effluent, capturing remaining suspended solids and particulate phosphorus. This stage is essential for meeting the permit limit of < 15 mg/L TSS (monthly average).
• Chemical Polishing: Alum or Ferric Chloride can be dosed upstream of the filters to precipitate soluble phosphorus if biological removal in the secondary stage is insufficient.

E. DISINFECTION

Historically a chlorination/dechlorination facility, the plant was converted to Ultraviolet (UV) disinfection to eliminate the safety hazards associated with chlorine gas and reduce disinfection byproducts (DBPs) in the receiving stream. The system uses horizontal low-pressure high-output (LPHO) lamp banks submerged in open channels. Dosage is automatically paced based on flow rate and UV transmittance (UVT) to ensure compliance with fecal coliform limits (typically 200 CFU/100mL monthly geometric mean).

F. SOLIDS HANDLING

Solids management is a significant operational component:

• Thickening: Primary sludge and WAS are thickened utilizing Gravity Belt Thickeners (GBTs) or Rotary Drum Thickeners (RDTs) to reduce hydraulic volume.
• Digestion: Thickened sludge undergoes aerobic digestion. While less energy-efficient than anaerobic digestion, aerobic digestion is simpler to operate and produces less odor, which is critical given the proximity of residential neighborhoods.
• Dewatering: Digested biosolids are dewatered using high-solids Belt Filter Presses (BFPs).
• Disposal: The dewatered cake is hauled off-site to a sanitary landfill. DeKalb County is currently evaluating long-term strategies for biosolids reuse, but landfilling remains the primary disposal method.

4. INFRASTRUCTURE & FACILITIES

Physical Plant: The site encompasses approximately 40 acres of fenced industrial area, surrounded by a natural buffer zone. The layout separates the liquid treatment train from the solids handling complex to optimize truck traffic for biosolids hauling.

Energy Systems: The plant is a major energy consumer, with aeration blowers accounting for nearly 50% of total electrical load. Recent capital projects have focused on installing Variable Frequency Drives (VFDs) on all major pumps and blowers to match energy consumption with biological demand. The facility is equipped with redundant diesel generators capable of running the full treatment process during grid outages—a necessity for preventing SSOs during severe weather.

Odor Control: Due to encroaching residential developments, odor control is paramount. The headworks and solids handling buildings are enclosed and ventilated through chemical scrubbers (utilizing bleach and caustic loops) and activated carbon polishing units to maintain neutral air quality at the fence line.

5. RECENT UPGRADES & MAJOR PROJECTS

Future Planning (2025-2027)

DeKalb County DWM is currently assessing the need for “Phase 2” nutrient removal upgrades. As the Georgia EPD potentially lowers phosphorus limits for the South River basin, the Pole Bridge Creek facility may require structural modifications to its biological basins or the addition of tertiary disk filters to replace the aging sand filters.

6. REGULATORY COMPLIANCE & ENVIRONMENTAL PERFORMANCE

Permit Requirements (NPDES GA0020303)

The facility operates under strict limitations due to the impaired status of the South River. Key parameters typically include:

• BOD5: Monthly average limit of < 10 mg/L.
• TSS: Monthly average limit of < 15 mg/L.
• Ammonia (NH3-N): Seasonal limits, typically < 1.0 mg/L in summer and < 2.0 mg/L in winter.
• Fecal Coliform: 200 CFU/100mL (May-Oct), 1,000 CFU/100mL (Nov-Apr).
• Total Phosphorus: Often monitored with a target of < 1.0 mg/L, trending toward tighter limits.

Compliance History

Under the Federal Consent Decree (CD), DeKalb County has aggressively targeted SSOs. The Pole Bridge Creek plant itself generally maintains compliance with effluent limits. The primary challenges in the basin are related to collection system spills rather than plant treatment failure. The plant has received Gold Awards from the Georgia Association of Water Professionals (GAWP) for achieving 100% permit compliance in specific operational years.

7. CHALLENGES & OPERATIONAL CONTEXT

Inflow & Infiltration (I/I)

The most significant engineering challenge for the Pole Bridge Creek facility is the hydraulic peaking caused by I/I. During heavy rains, flow to the plant can triple rapidly. This washes out the biological solids inventory (MLSS) from the secondary clarifiers if not carefully managed using step-feed strategies or flow equalization.

Aging Workforce

Like many municipal utilities, DeKalb faces a shortage of Class I licensed wastewater operators. The county has implemented aggressive training programs and apprenticeship models to backfill retiring senior operators, ensuring institutional knowledge is retained for the complex biological processes.

8. TECHNICAL SPECIFICATIONS SUMMARY

9. FAQ SECTION

Technical & Engineering Questions

Q: What is the specific nutrient removal capability of the plant?
A: The plant is designed for nitrification (ammonia removal) and partial denitrification. It utilizes chemical precipitation (alum) for phosphorus removal to meet discharge standards.

Q: How does the plant handle wet weather flows?
A: The plant relies on robust headworks screening and robust clarifier performance. While on-site equalization is limited, the plant operators utilize storage in the collection system and process adjustments to manage peak hydraulic loads.

Q: Is this the same facility as the Snapfinger Creek plant?
A: No. DeKalb County operates both the Pole Bridge Creek AWTF (20 MGD) and the Snapfinger Creek AWTF (36 MGD). Both discharge to the South River basin but are distinct facilities serving different sewersheds.

Q: What SCADA system is utilized?
A: The facility utilizes a centralized SCADA system, largely based on Rockwell Automation/Allen-Bradley PLCs and Wonderware or similar HMI software, integrated into the county-wide telemetry network.

Public & General Interest

Q: Does the plant produce bad odors?
A: The plant employs chemical scrubbers and carbon filters at the headworks and solids handling buildings to neutralize odors. Occasional odors may occur during maintenance or extreme weather, but they are actively managed.

Q: Where does the water go after treatment?
A: The highly treated effluent is discharged into the South River, where it eventually flows into the Ocmulgee River, contributing to the water resources of downstream communities and ecosystems.

Q: How can I tour the facility?
A: Tours are typically arranged through the DeKalb County Department of Watershed Management’s public outreach office. They are often available for engineering students, industry groups, and community organizations.