City Of Springfield Southwest Wastewater Treatment Plant

1. Introduction

The Southwest Wastewater Treatment Plant (SWTP) serves as the cornerstone of wastewater infrastructure for the City of Springfield, Missouri. As the largest treatment facility in southwest Missouri, the SWTP is critical to the environmental health of the James River Basin and the downstream Table Rock Lake watershed. Commissioned originally in 1959 and significantly expanded through multiple capital improvement phases, the facility currently operates with a design average flow of 42.5 million gallons per day (MGD).

Operated by the City of Springfield Department of Environmental Services, the SWTP is a model of regulatory compliance in a sensitive watershed. The facility employs advanced biological nutrient removal (BNR) and tertiary filtration to meet stringent effluent limits, particularly for phosphorus and nitrogen. With over $50 million invested in recent improvements focusing on solids handling and energy recovery, the plant not only protects regional water quality but also serves as a case study in municipal resource recovery and sustainability.

2. Facility Overview

A. Service Area & Coverage

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The SWTP services the southern two-thirds of the City of Springfield, the City of Battlefield, and portions of unincorporated Greene County. The service area is characterized by a mix of residential density, commercial corridors, and light industry. The collection system feeding the plant is extensive, navigating the region’s challenging karst topography, which historically contributes to significant inflow and infiltration (I&I) during wet weather events.

B. Operational Capacity

While the design capacity stands at 42.5 MGD, the plant manages substantial flow variations.

• Average Daily Flow: ~28–32 MGD
• Peak Hydraulic Capacity: Capable of handling over 100 MGD during storm events through equalization and peak flow management strategies.

The facility is currently operating at approximately 70-75% of its organic loading capacity, allowing for moderate regional growth before major process expansion is required.

C. Discharge & Compliance

Treated effluent is discharged into Wilson’s Creek, a tributary of the James River. Because the James River feeds into Table Rock Lake—a primary recreational reservoir—the SWTP operates under strict nutrient limits to prevent eutrophication. The plant consistently achieves high removal rates for Total Phosphorus (TP) and Total Nitrogen (TN), often performing well below the limits established in its Missouri Department of Natural Resources (MDNR) operating permit.

3. Treatment Process

The SWTP utilizes a complex treatment train designed to handle variable hydraulic loads while maintaining high-quality effluent.

A. Preliminary Treatment

Raw influent enters the headworks where it passes through mechanical bar screens (typically 6mm spacing) to remove large debris, plastics, and rags. Following screening, flow velocity is reduced in vortex grit removal chambers, settling out sand, gravel, and heavy particulates to protect downstream pumps. The headworks facility is enclosed and treated with chemical scrubbers for odor control.

B. Primary Treatment

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Flow enters rectangular and circular primary clarifiers where gravity settling removes approximately 60% of Total Suspended Solids (TSS) and 30-40% of Biochemical Oxygen Demand (BOD). Primary sludge is pumped to the solids handling complex, while primary effluent flows to the aeration basins.

C. Secondary Treatment (BNR)

The core of the SWTP is its Activated Sludge Process configured for Biological Nutrient Removal (BNR).

• Configuration: The basins utilize anaerobic, anoxic, and aerobic zones to facilitate nitrification, denitrification, and biological phosphorus removal.
• Aeration: Fine-bubble diffused aeration provides oxygen in the aerobic zones, controlled by dissolved oxygen (DO) sensors to optimize energy consumption.
• Clarification: Mixed liquor flows to 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 sent to thickening.

D. Tertiary Treatment

To meet stringent limits (often < 0.5 mg/L Phosphorus), the plant employs Deep Bed Sand Filters. These gravity filters polish the secondary effluent, capturing remaining suspended solids and particulate phosphorus that escaped secondary clarification. This stage is critical for compliance with the James River TMDL.

E. Disinfection

Historically a chlorination facility, the SWTP utilizes Ultraviolet (UV) Disinfection (and/or Ozonation in pilot/specific configurations) to neutralize pathogens without introducing chemical byproducts into the receiving stream. The effluent is re-aerated if necessary to meet dissolved oxygen minimums before discharge.

F. Solids Handling

The SWTP is a regional hub for biosolids processing.

• Thickening: Gravity belt thickeners or dissolved air flotation (DAF) concentrate WAS.
• Digestion: Anaerobic digesters stabilize the sludge, reducing volatile solids and pathogen content. The process generates methane gas (biogas).
• Dewatering: Digested sludge is dewatered using high-solids centrifuges or belt filter presses.
• Disposal: The resulting Class B biosolids are land-applied on local agricultural fields as a fertilizer and soil conditioner, closing the nutrient loop.

4. Infrastructure & Facilities

Energy Recovery & Sustainability

The SWTP is notable for its commitment to energy efficiency. The facility employs Combined Heat and Power (CHP) cogeneration units. These engines burn the biogas produced in the anaerobic digesters to generate electricity and heat. The recovered heat is used to maintain optimal temperatures in the digesters, while the electricity offsets the plant’s grid consumption. This system significantly reduces the facility’s carbon footprint and operational costs.

Odor Control

Given the proximity to residential areas and the Wilson’s Creek National Battlefield, odor control is a priority. The plant utilizes biofilters and chemical scrubbers at the headworks and solids processing buildings. The City maintains a dedicated odor complaint logging system to address community concerns rapidly.

5. Recent Upgrades & Major Projects

Ongoing: Collection System Renewal (Tiered CIP)

The City allocates annual funding ($10M+ typically across the utility) for the “Overflow Control Plan” to address I&I. This involves trenchless pipe lining, manhole rehabilitation, and lift station upgrades throughout the Southwest basin to reduce peak wet weather flows arriving at the plant.

6. Regulatory Compliance & Environmental Performance

The SWTP operates under a Missouri State Operating Permit (NPDES delegated). The facility faces some of the strictest nutrient limits in the state due to the “impaired” status of the James River for nutrients.

• Phosphorus Limit: Typically 0.5 mg/L (monthly average) or lower based on TMDL allocations.
• Nitrogen: Monitoring and limits on Ammonia-Nitrogen to prevent toxicity to aquatic life.
• Bacteria: E. coli limits apply during the recreational season (April 1 – October 31).

The facility consistently earns NACWA (National Association of Clean Water Agencies) Peak Performance Awards, recognizing its history of compliance and operational excellence.

7. Challenges & Future Planning

Aging Infrastructure

Like many plants built in the mid-20th century, the SWTP faces the challenge of replacing mechanical and electrical assets that are nearing the end of their useful life. The City employs a robust Asset Management Program to prioritize replacements based on risk and criticality.

Wet Weather Management

Springfield sits atop karst topography (limestone with sinkholes and fissures). During heavy rains, groundwater enters the sewer system, causing rapid spikes in flow at the plant. Future planning focuses heavily on equalization basin management and continued aggressive I&I reduction in the collection system.

Future Regulations

The utility is planning for potential future regulations regarding “compounds of emerging concern” (CECs), such as PFAS. While no limits are currently enforced, the City actively monitors regulatory trends to anticipate necessary process modifications.

8. Technical Specifications Summary

9. Frequently Asked Questions

1. Does the Springfield SWTP remove phosphorus?
Yes. The plant uses both biological phosphorus removal (in the aeration basins) and physical removal (via tertiary sand filters) to meet strict limits aimed at protecting Table Rock Lake.

2. What is the difference between the Southwest and Northwest plants in Springfield?
The Southwest Plant is the larger of the two major facilities (42.5 MGD) and handles the majority of the city’s flow. The Northwest Plant is smaller and serves the northern basin, discharging toward the Sac River watershed.

3. How is the biogas used?
Methane generated in the digesters is cleaned and fed into cogeneration engines to produce electricity and heat for on-site use, reducing the plant’s external energy demand.

4. Is the plant affected by flooding?
The plant is located near Wilson’s Creek. While the process tanks are elevated/protected, the hydraulic load entering the plant increases drastically during floods due to inflow and infiltration in the collection system, requiring the use of large flow equalization basins.

5. Can engineering firms or students tour the facility?
Yes, the City of Springfield Environmental Services department typically accommodates educational and professional tours. Requests should be made through the City’s official website.