City Of Topeka North Topeka Wastewater Treatment Facility

FACILITY BASIC INFORMATION

• Plant Name: North Topeka Wastewater Treatment Plant
• Location: 1600 NW Button Road, Topeka, Shawnee County, Kansas 66618
• Operating Authority: City of Topeka Utilities Department (Water Pollution Control Division)
• Design Capacity: 8.0 MGD (Average Daily Design Flow)
• Current Average Flow: ~3.6 MGD
• Peak Hydraulic Capacity: 16.0 MGD
• Population Served: Approx. 35,000 (North Topeka Basin)
• Service Area: North Topeka, Soldier Township, and northern growth corridors
• Receiving Water Body: Kansas River (via Soldier Creek confluence)
• NPDES Permit Number: KS-0036684
• Year Commissioned: Original construction 1950s; Major expansion 1980s; Upgrades 2010s

1. INTRODUCTION

The North Topeka Wastewater Treatment Plant (North Topeka WWTP) serves as a critical infrastructure anchor for the City of Topeka’s northern expansion basin. While smaller than the city’s primary Oakland Wastewater Treatment Plant, the North Topeka facility operates as a fully independent treatment system designed to manage an Average Daily Design Flow of 8.0 million gallons per day (MGD) with peak hydraulic capabilities reaching 16.0 MGD. Operated by the City of Topeka Utilities Department, the facility is vital for managing sanitary flows from the Soldier Creek basin and supporting residential and industrial growth north of the Kansas River.

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In recent years, the facility has been the subject of significant capital investment aimed at modernization, specifically transitioning from gaseous chlorine to Ultraviolet (UV) disinfection and enhancing headworks screening reliability. As the Kansas Department of Health and Environment (KDHE) tightens nutrient discharge limits for the Kansas River watershed, the North Topeka WWTP represents a focal point for engineering evaluations regarding biological nutrient removal (BNR) upgrades. The plant stands as a model of efficient mid-sized municipal treatment, balancing aging infrastructure management with modern compliance mandates.

2. FACILITY OVERVIEW

A. Service Area & Coverage

The facility services the northern geographic sector of Topeka, distinct from the central and southern basins served by the Oakland plant. The collection system feeding the North Topeka WWTP spans approximately 20 square miles, covering the growing residential districts of North Topeka and Soldier Township. The influent stream is characterized by a mix of domestic wastewater and light industrial/commercial flow. The collection system relies on a network of gravity interceptors and critical lift stations that convey flow to the Button Road site.

B. Operational Capacity

The plant is currently operating at approximately 45% of its hydraulic design capacity, with an average daily flow hovering between 3.5 and 4.0 MGD. This surplus capacity positions North Topeka as a strategic asset for economic development, allowing the city to approve new industrial or residential connections without immediate plant expansion. However, like many Midwest facilities, the plant experiences significant wet-weather peaking factors due to inflow and infiltration (I/I) in the older sections of the collection system, occasionally testing the hydraulic limits of the headworks and clarifiers.

C. Discharge & Compliance

Treated effluent is discharged into the Kansas River, a sensitive water body subject to rigorous monitoring under the National Pollutant Discharge Elimination System (NPDES). The discharge point is located near the confluence of Soldier Creek and the Kansas River. Compliance is overseen by the KDHE. The facility has maintained a strong record of compliance regarding Carbonaceous Biochemical Oxygen Demand (CBOD) and Total Suspended Solids (TSS), though attention has shifted heavily toward nutrient monitoring (Total Nitrogen and Total Phosphorus) in anticipation of future permit cycles.

3. TREATMENT PROCESS

The North Topeka WWTP utilizes a conventional activated sludge process train. The facility provides preliminary screening, grit removal, primary clarification, biological treatment, secondary clarification, and UV disinfection before discharge.

A. PRELIMINARY TREATMENT

Raw wastewater enters the headworks where it passes through mechanically cleaned bar screens to remove large debris, rags, and plastics. This is a critical protection step for downstream pumps. Following screening, flow enters a grit removal system designed to settle out inorganic solids (sand, gravel, coffee grounds) that could cause abrasion to mechanical equipment or occupy volume in the digesters. The headworks is equipped with odor control systems to mitigate nuisance odors for nearby residents.

B. PRIMARY TREATMENT

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Flow proceeds to primary clarifiers (circular configuration). Here, hydraulic velocity is reduced to allow heavier organic solids to settle as primary sludge, while grease and oils float to the surface for skimming. The primary treatment stage is designed to remove approximately 30-35% of the influent BOD and 50-60% of the TSS, significantly reducing the organic load on the secondary biological system.

C. SECONDARY TREATMENT

The biological heart of the plant is the Activated Sludge system. Settled effluent from the primary clarifiers flows into aeration basins. Large centrifugal blowers supply oxygen to the mixed liquor, fostering the growth of aerobic microorganisms that consume dissolved organic matter. The basins are configured to allow for process flexibility, including step-feed options during high-flow events.

Mixed liquor flows from the aeration basins to the secondary clarifiers. These circular units allow the biological floc to settle, separating the clear treated water from the biomass. A portion of the settled solids is returned to the aeration basins as Return Activated Sludge (RAS) to maintain the microbial population, while excess growth is removed as Waste Activated Sludge (WAS).

D. DISINFECTION

Historically, the plant utilized gaseous chlorine for disinfection. However, in a major safety and environmental upgrade completed in the mid-2010s, the facility converted to Ultraviolet (UV) disinfection. The flow passes through channels containing banks of UV lamps. The UV light penetrates the cell walls of pathogens (bacteria, viruses), altering their DNA and preventing reproduction. This method eliminates the need for dechlorination chemicals (like sulfur dioxide) and removes the hazards associated with storing pressurized chlorine gas on-site.

F. SOLIDS HANDLING

Solids handling at North Topeka is managed via aerobic digestion. Primary sludge and WAS are pumped to aerobic digesters where the solids are stabilized and volatile solids are reduced. The stabilized biosolids are typically land-applied on permitted agricultural fields, recycling nutrients back into the soil. The facility maintains capabilities for liquid sludge hauling.

G. PROCESS CONTROL

The entire treatment train is monitored via a SCADA (Supervisory Control and Data Acquisition) system. This allows operators to monitor dissolved oxygen levels, pump status, tank levels, and UV intensity in real-time. The City maintains a laboratory for process control testing (settleability, pH, microscopy), while permit-compliance samples are processed to certified standards.

4. INFRASTRUCTURE & FACILITIES

A. Physical Plant

The North Topeka WWTP is situated on a dedicated site off NW Button Road. The layout is functional and linear, designed to utilize hydraulic gravity flow where possible to reduce pumping costs. The site includes an administration building, maintenance shops, and chemical storage facilities (principally polymer for sludge thickening).

B. Energy Systems

Energy management is a key operational focus. The aeration blowers represent the largest electrical load at the facility. Upgrades to Variable Frequency Drives (VFDs) on major pumps and blowers have been implemented to match energy consumption with actual flow and loading demands, preventing over-aeration and reducing electrical costs.

C. Odor Control

Given the proximity to the developing North Topeka area, odor control is managed strictly at the headworks and solids handling processing areas. Biofilters and chemical scrubbers are utilized to treat foul air extracted from these critical points before it is released into the atmosphere.

5. RECENT UPGRADES & MAJOR PROJECTS

UV Disinfection System Improvements (2013-2015)

• Project Scope: Complete replacement of the chlorine gas disinfection system with a Trojan UV disinfection system. Included structural modifications to the contact basins and new electrical feeds.
• Drivers: Enhanced operator safety (elimination of chlorine gas), environmental compliance (reduction of disinfection byproducts), and reduced chemical dependency.
• Technical Highlights: Installation of low-pressure, high-output lamp technology with automatic wiping systems to maintain transmittance efficiency.

Headworks and Screening Improvements

• Project Scope: Replacement of aging mechanical bar screens and washer/compactors.
• Drivers: Older screens were allowing “ragging” of downstream pumps and reducing the efficiency of the biosolids handling process.
• Results: Significantly reduced maintenance hours spent unclogging RAS/WAS pumps and improved grit capture.

SCADA & Electrical Modernization (Ongoing)

• Project Scope: Integration of North Topeka telemetry into the central City of Topeka utilities network, allowing for remote monitoring from the Oakland plant if necessary during emergencies.
• Investment: Part of a city-wide multi-million dollar utility automation strategy.

Upcoming Projects (2025-2028 Planning Horizon)

The City is currently evaluating the Nutrient Removal Retrofit. As KDHE pushes for lower Total Nitrogen and Total Phosphorus limits in the Kansas River, the North Topeka plant will likely require modifications to its aeration basins to create anoxic and anaerobic zones necessary for biological nutrient removal (BNR). Engineering studies are underway to determine if chemical precipitation (ferric/alum) or biological selection is the most cost-effective path for this specific facility.

6. REGULATORY COMPLIANCE & ENVIRONMENTAL PERFORMANCE

A. Permit Requirements

The facility operates under NPDES Permit No. KS-0036684. Key discharge parameters include:

• CBOD5: Monthly average limits typically ≤ 25 mg/L.
• TSS: Monthly average limits typically ≤ 30 mg/L.
• E. Coli: Seasonal limits (April-October) utilizing geometric mean calculation.
• Ammonia (NH3-N): Limits vary by season and pH, protecting aquatic life in the Kansas River.

B. Compliance History

The North Topeka WWTP generally maintains a robust compliance record. Occasional challenges have arisen during extreme wet-weather events where hydraulic peaking stresses the secondary clarifiers, a common issue in combined or older separate sanitary systems. The City has been proactive in inflow/infiltration (I/I) studies to mitigate these surges.

7. OPERATIONAL EXCELLENCE

The plant is staffed by a team of KDHE-certified operators. The operational philosophy emphasizes preventative maintenance and process stability. Because the plant is loaded below design capacity, operators have the luxury of longer solids retention times (SRT), which aids in nitrification (ammonia removal) even without specific BNR infrastructure. The facility serves as a training ground for operators seeking Class III and Class IV certifications due to its approachable size but complex activated sludge biology.

8. CHALLENGES & FUTURE PLANNING

Nutrient Reduction

The primary engineering challenge for the next decade is the implementation of nutrient reduction technologies within the existing footprint. Retrofitting existing aeration basins for BNR often reduces their hydraulic capacity, which conflicts with the need to manage wet-weather peaks. Engineers will need to balance these competing hydraulic and biological constraints.

Biosolids Management

As regulations regarding land application of biosolids become stricter and land availability fluctuates, the City is constantly evaluating the long-term sustainability of its solids handling program. Future plans may involve further dewatering technologies (centrifuges or screw presses) to reduce hauling volume.

Aging Infrastructure

While mechanical systems have been upgraded, the concrete structures (clarifiers and basins) date back decades. Concrete rehabilitation and coating projects are anticipated in the 10-year Capital Improvement Plan (CIP).

10. TECHNICAL SPECIFICATIONS SUMMARY

11. RELATED FACILITIES

The North Topeka WWTP operates in conjunction with the Oakland Wastewater Treatment Plant, the city’s primary facility located south of the river. While the two plants have distinct collection systems, they share administrative, laboratory, and maintenance resources. Additionally, the North Topeka plant is supported by several large lift stations that convey sewage from the lower elevations of the Soldier Creek valley to the treatment works.

12. FAQ SECTION

Technical Questions

1. What is the Peak Peaking Factor for the North Topeka WWTP?
The plant generally operates with a peaking factor of 2.0 (16 MGD peak / 8 MGD design), though I/I events can create instantaneous spikes.

2. Does the North Topeka plant utilize anaerobic digestion?
No. Unlike the larger Oakland plant which may utilize anaerobic processes for energy recovery, the North Topeka facility utilizes aerobic digestion for solids stabilization.

3. Are there plans for Water Reuse?
Currently, the City of Topeka does not have a large-scale water reuse program for the North Topeka effluent, as the discharge is returned to the Kansas River to maintain flow requirements.

4. How is the UV system cleaned?
The UV system utilizes an automatic mechanical wiping system that cleans the quartz sleeves at set intervals to prevent fouling and ensure UV transmittance.

Public Interest Questions

5. Does the plant smell?
The facility employs odor control scrubbers at the headworks (where raw sewage enters). While faint odors are inherent to wastewater treatment, the plant is designed to contain these within the fenceline.

6. Where does the treated water go?
After treatment and disinfection, the clean water is discharged into the Kansas River, meeting all state and federal water quality standards.