Citizens Energy Group Belmont Advanced Wastewater Treatment Plant Indianapolis

TARGET AUDIENCE

• Municipal consulting engineers evaluating High Purity Oxygen (HPO) and tertiary filtration systems.
• Wastewater treatment plant operators studying CSO tunnel integration.
• Environmental regulators reviewing wet weather compliance strategies.
• Engineering firms pursuing combined sewer overflow (CSO) abatement projects.
• Industry professionals interested in thermal solids processing.

1. INTRODUCTION

The Belmont Advanced Wastewater Treatment Plant (AWTP) serves as the cornerstone of wastewater infrastructure for central Indiana, operating as the largest treatment facility in the state. Managed by Citizens Energy Group since the utility transfer from the City of Indianapolis in 2011, Belmont treats an average daily flow exceeding 100 million gallons (MGD) and serves the metropolitan population of Indianapolis and Marion County. The facility is strategically located along the White River and plays a pivotal role in the region’s environmental health.

Historically commissioned in the 1920s, Belmont has evolved into a highly complex, advanced secondary and tertiary treatment facility. It utilizes High Purity Oxygen (HPO) activated sludge technology and extensive tertiary filtration to meet stringent effluent limits. The plant is currently the focal point of one of the nation’s largest infrastructure initiatives—the DigIndy Tunnel System—a $2 billion program designed to mitigate Combined Sewer Overflows (CSOs). The recent integration of the Deep Rock Tunnel Pump Station has transformed Belmont into a modern hub for wet weather flow management, setting benchmarks for compliance with Federal Consent Decrees.

2. FACILITY OVERVIEW

A. Service Area & Coverage

The Belmont AWTP services the majority of the Consolidated City of Indianapolis (Marion County). The collection system is a hybrid network comprising approximately 3,000 miles of sewers. Crucially, a significant portion of the older downtown Indianapolis area operates on a Combined Sewer System (CSS), which conveys both sanitary sewage and stormwater. The service area encompasses dense urban residential zones, heavy industrial corridors, and commercial districts. The facility also accepts flows from satellite communities through wholesale agreements.

B. Operational Capacity

The facility is designed with substantial hydraulic flexibility to handle the flashy nature of the combined collection system:

• Average Daily Design Flow: 120 MGD
• Peak Secondary Treatment Capacity: 300 MGD
• Peak Hydraulic Capacity (Primary): Exceeds 300 MGD during storm events (managed via flow equalization and bypass subject to permit).

With the activation of the DigIndy tunnel system, the plant’s operational strategy has shifted to maximize treatment of stored wet weather flows during dry periods, effectively increasing the utilization rate of the secondary treatment train.

C. Discharge & Compliance

Treated effluent is discharged into the West Fork of the White River via Outfall 001. The facility operates under NPDES Permit No. IN0023183, issued by the Indiana Department of Environmental Management (IDEM). Due to the low dilution ratio of the White River during summer months, the plant faces strict limits on Carbonaceous Biochemical Oxygen Demand (CBOD), Total Suspended Solids (TSS), Ammonia-Nitrogen (NH3-N), and E. coli. The facility operates under a Federal Consent Decree aimed at reducing untreated CSO discharges by approximately 97% upon full completion of the DigIndy program in 2025.

3. TREATMENT PROCESS

The Belmont AWTP utilizes a sophisticated treatment train characterized by High Purity Oxygen (HPO) activated sludge, biological roughing towers, and tertiary media filtration.

A. PRELIMINARY TREATMENT

Incoming wastewater enters the headworks where it undergoes physical screening and grit removal.

• Screening: Mechanical bar screens remove large debris, rags, and plastics to protect downstream pumps. The recent tunnel pump station includes dedicated heavy-duty coarse and fine screens to handle the “first flush” debris stored in the deep tunnels.
• Grit Removal: Aerated grit chambers facilitate the settling of sand, gravel, and heavy inorganic particulate matter.
• Odor Control: The headworks and tunnel reception shafts utilize biotrickling filters and carbon adsorption units to mitigate H₂S and organic odors.

B. PRIMARY TREATMENT

Flow enters rectangular primary clarifiers where gravity settling removes approximately 60% of suspended solids and 30-40% of BOD. Primary sludge is pumped to the solids handling complex, while primary scum is skimmed and removed. The primary tanks are covered in specific areas to capture odors, which are directed to chemical scrubbers.

C. SECONDARY TREATMENT (Biological)

Belmont utilizes a multi-stage biological system:

• Bio-Roughing Towers: Prior to the activated sludge basins, flow is directed over plastic media trickling filters (bio-towers). This acts as a roughing stage to reduce high BOD loads and treat industrial shocks before the main aeration stage.
• High Purity Oxygen (HPO) Activated Sludge: The core of the secondary treatment is an HPO system (UNOX type design). Unlike conventional air-activated sludge, this system uses covered basins and injects >90% pure oxygen generated on-site.
  • Cryogenic Oxygen Generation: The plant operates cryogenic air separation units (ASU) to produce high-purity oxygen from ambient air.
  • Advantages: The HPO process allows for a higher Mixed Liquor Suspended Solids (MLSS) concentration, smaller tank footprint, and ability to handle high organic loading rates typical of the industrial contributions in Indianapolis.

• Secondary Clarifiers: Mixed liquor flows to secondary clarifiers where biological floc settles. Return Activated Sludge (RAS) is recycled to the HPO basins, and Waste Activated Sludge (WAS) is thickened for processing.

D. TERTIARY TREATMENT

To meet stringent effluent limits, particularly for suspended solids and associated pollutants:

• Deep Bed Sand Filters: The facility employs a large battery of rapid gravity sand filters. These filters polish the secondary effluent, reducing TSS to single-digit mg/L levels and removing particulate BOD.
• Nitrification: While the HPO system focuses on carbonaceous removal, nitrification (conversion of ammonia to nitrate) is achieved through a combination of the trickling filters and solids retention time management within the biological system, optimized for cold-weather performance.

E. DISINFECTION

Method: Chlorination/Dechlorination.

• Chlorination: Sodium hypochlorite is applied to the filtered effluent in contact tanks to inactivate pathogens (E. coli).
• Dechlorination: Sodium bisulfite is added prior to the outfall to neutralize residual chlorine, preventing toxicity to aquatic life in the White River.
• Seasonality: Disinfection is typically required during the recreation season (April 1 – October 31), though operational adjustments are made based on permit conditions.

F. SOLIDS HANDLING

Belmont is a regional hub for biosolids processing, handling solids from both Belmont and the Southport AWTP.

• Thickening: Gravity belt thickeners (GBT) and dissolved air flotation (DAF) units thicken WAS and primary sludge.
• Dewatering: A battery of belt filter presses dewaters the sludge cake to approximately 20-25% solids.
• Thermal Processing (Incineration): The facility operates Multiple Hearth Incinerators (MHIs). Incineration reduces the volume of solids by over 90%, leaving a sterile ash. The plant utilizes advanced air pollution control systems (wet scrubbers, WESPs, and RTOs) to meet strict Clean Air Act (Title V) requirements.

4. INFRASTRUCTURE & FACILITIES

A. Physical Plant

The site spans over 100 acres along the river. The complex includes the Operations Control Center, a comprehensive environmental laboratory, maintenance shops, and the Cryogenic Oxygen Plant. The architecture is strictly industrial, with recent additions (Deep Rock Tunnel Pump Station) featuring modern concrete substructures plunging over 250 feet below grade.

B. Energy Systems

The Cryogenic Oxygen Plant is the largest energy consumer on-site. Citizens Energy Group has implemented energy management strategies to optimize oxygen production based on real-time biological demand. The incineration process utilizes waste heat recovery where feasible to preheat combustion air, reducing natural gas consumption.

C. Odor Control

Given the plant’s proximity to residential neighborhoods, odor control is a critical operational parameter. Technologies include:

• Chemical Scrubbers: Packed tower scrubbers using hypochlorite and caustic soda for headworks and solids processing areas.
• Biofilters: Used for tunnel vents to treat high-volume, low-concentration air streams.
• Thermal Oxidation: Regenerative Thermal Oxidizers (RTOs) are employed on incinerator exhaust streams to destroy volatile organic compounds (VOCs) and odors.

5. RECENT UPGRADES & MAJOR PROJECTS

6. REGULATORY COMPLIANCE & ENVIRONMENTAL PERFORMANCE

A. Permit Requirements

The Belmont AWTP operates under a challenging NPDES permit due to the White River’s limited assimilative capacity. Key parameters include:

• CBOD5: Monthly average limits typically ≤ 10 mg/L (Summer).
• TSS: Monthly average limits typically ≤ 12 mg/L.
• Ammonia-Nitrogen: Seasonal limits, often < 1.5 mg/L in summer to prevent toxicity.
• Phosphorus: Indiana has implemented a 1.0 mg/L limit for major dischargers, requiring chemical precipitation (ferric chloride/alum) or biological removal optimization.

B. Compliance History

Since the implementation of the Consent Decree and the phased opening of the DigIndy tunnel segments, the frequency and volume of CSOs have dropped dramatically. The plant consistently achieves high removal efficiencies for conventional pollutants. The facility has received NACWA (National Association of Clean Water Agencies) Peak Performance Awards for permit compliance.

7. OPERATIONAL EXCELLENCE

Citizens Energy Group maintains a certified workforce of operators and maintenance technicians. The facility utilizes a robust Rockwell Automation SCADA system for process monitoring. The on-site laboratory is state-certified, conducting daily analysis for process control and compliance reporting. Operational excellence focuses heavily on energy efficiency—specifically optimizing the specific energy consumption (kWh/lb BOD removed) of the oxygen generation system.

8. CHALLENGES & FUTURE PLANNING

A. Current Challenges

• Aging Solids Infrastructure: The incinerators require significant maintenance and capital investment to meet Maximum Achievable Control Technology (MACT) air standards.
• Tunnel Operations: Managing the “first flush” from the deep tunnel, which can be highly septic and high in solids, requires careful pacing to avoid upsetting the biological process.
• Nutrient Removal: Future regulatory tightening on Total Nitrogen and Total Phosphorus may require retrofits to the existing HPO basins or additional tertiary treatment steps.

B. Future Planning

The 2025 completion of the DigIndy system marks a shift from construction to operational optimization. Future CIP projects are expected to focus on:

• Modernization of the solids handling complex (potentially shifting away from incineration).
• Electrical distribution system upgrades.
• Rehabilitation of the tertiary filter media and underdrains.

10. TECHNICAL SPECIFICATIONS SUMMARY

11. RELATED FACILITIES

Southport Advanced Wastewater Treatment Plant: The second major facility in Indianapolis (also operated by Citizens), treating approximately 125 MGD peak. Sludge from Southport is pumped to Belmont for incineration.

Deep Rock Tunnel Pump Station: Located on the Belmont campus, this 250-foot deep pumping complex is the mechanical heart of the DigIndy system.

12. FAQ SECTION

Technical Questions

1. What is the advantage of the High Purity Oxygen (HPO) system at Belmont?
The HPO system allows the plant to maintain a high biomass concentration (MLSS) in smaller reactor volumes compared to conventional aeration. This is crucial for treating the high organic loads from Indianapolis’s industrial sector within the existing site footprint.

2. How does the DigIndy Tunnel connect to Belmont?
The tunnel terminates at a deep shaft on the Belmont property. The Deep Rock Tunnel Pump Station (DRTPS) lifts the stored combined sewage >200 feet to the surface, where it enters the headworks for full treatment.

3. Does Belmont have nutrient removal capabilities?
Yes. The plant achieves nitrification and phosphorus removal to meet permit limits. Phosphorus is managed via chemical precipitation, while nitrification occurs through the biological towers and activated sludge system.

4. What is the ultimate disposal method for biosolids?
Biosolids are dewatered and incinerated on-site. The resulting ash is disposed of in landfills, though the utility evaluates reuse options periodically.

Public Interest Questions

5. Why is the DigIndy project important for the White River?
Before DigIndy, billions of gallons of mixture (sewage and rainwater) overflowed into the river during storms. The project captures this water, sends it to Belmont for treatment, and is expected to reduce overflows by up to 97%.

6. Does the plant smell?
Wastewater treatment inherently generates odors. However, Belmont employs extensive odor control systems, including chemical scrubbers and thermal oxidizers on the incinerators, to minimize impact on the surrounding community.

7. Who owns the Belmont plant?
The plant is owned and operated by Citizens Energy Group, a Public Trust, which acquired the water and wastewater utilities from the City of Indianapolis in 2011.

Disclaimer: This article is for informational purposes for engineering and industry professionals. Data presented is based on publicly available regulatory filings, annual reports, and engineering publications as of late 2023. For official operational data, please consult Citizens Energy Group or IDEM records.