City Of Lincoln Northeast Wastewater Treatment Facility

TARGET AUDIENCE

• Municipal consulting engineers evaluating biological nutrient removal (BNR) upgrades
• Wastewater treatment plant operators and managers
• Environmental regulators (NDEE/EPA) monitoring Salt Creek basin compliance
• Engineering firms pursuing secondary treatment expansion projects
• Civil and Environmental Engineering students and researchers

1. INTRODUCTION

The Lincoln Northeast Water Resource Recovery Facility (NE WRRF) is a cornerstone of the sanitary infrastructure serving Nebraska’s capital city. Operating as one of two major treatment facilities under the City of Lincoln Transportation and Utilities (LTU) department, the Northeast plant is strategically critical for managing the region’s growth. While the older Theresa Street WRRF serves the city’s core, the Northeast facility handles flows from the rapidly expanding northern and eastern sectors.

Originally commissioned in the late 1970s, the facility has transitioned from a standard secondary treatment plant into a sophisticated Water Resource Recovery Facility. Recent capital improvements have focused on increasing hydraulic capacity to 22 MGD (Average Daily Flow) to relieve pressure on the Theresa Street plant and meeting stringent nutrient discharge limits for the Salt Creek watershed. The facility is a prime example of load-shedding strategies in municipal wastewater, utilizing a major lift station and force main network to balance flows between two facilities to optimize regional treatment efficiency.

2. FACILITY OVERVIEW

A. Service Area & Coverage

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The Northeast WRRF serves the Salt Creek basin drainage area, covering the northern and eastern portions of the City of Lincoln. The service area is characterized by a mix of established residential neighborhoods, rapidly developing suburban tracts, and light industrial zones. The collection system is integrated with the Theresa Street basin; the Northeast Pump Station serves as a critical control point, capable of diverting flow between the two plants based on hydraulic capacity and maintenance needs.

B. Operational Capacity

Following recent master planning and expansion phases, the facility’s operational parameters are defined as follows:

• Design Average Daily Flow (ADF): 22.0 MGD
• Peak Instantaneous Flow: ~60 MGD
• Hydraulic Peaking Factor: Approximately 2.5 – 3.0

Historically, the plant operated closer to 10-12 MGD. However, the Lincoln Wastewater System Facilities Master Plan designated the Northeast facility as the primary site for future capacity expansion due to land constraints at the downtown Theresa Street location. Consequently, flow rates are trending upward as the city actively diverts more influent to this location.

C. Discharge & Compliance

Treated effluent is discharged into Salt Creek, a tributary of the Platte River. The discharge is regulated under the Nebraska Pollutant Discharge Elimination System (NPDES) administered by the Nebraska Department of Environment and Energy (NDEE). Salt Creek is an effluent-dominated stream during dry weather, meaning the facility’s performance directly dictates the ecological health of the waterway. Strict limits are in place for Ammonia-Nitrogen (NH3-N), E. coli, and increasingly, Total Phosphorus and Total Nitrogen, driven by statewide nutrient reduction strategies.

3. TREATMENT PROCESS

The Lincoln Northeast WRRF utilizes a conventional activated sludge process with specific modifications for nutrient removal and solids handling. Unique to this system is the “liquids-focused” nature of the plant; the majority of solids processing occurs at the sister facility.

A. PRELIMINARY TREATMENT

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Influent wastewater enters the Headworks building, designed to protect downstream mechanical equipment.

• Screening: Multi-rake mechanical bar screens (typically 6mm or ¼ inch spacing) remove rags, plastics, and large debris.
• Grit Removal: Vortex grit chambers utilize centrifugal force to settle out inorganic solids (sand, gravel, eggshells) while keeping organics in suspension.
• Odor Control: The headworks is enclosed and ventilated through biological scrubbers (biofilters) to mitigate H2S and organic odors before air release.

B. PRIMARY TREATMENT

Flow proceeds to primary clarifiers where gravity settling occurs.

• Configuration: Circular primary clarifiers with center-feed wells and peripheral overflow weirs.
• Mechanism: Sludge rakes sweep settled solids to a central hopper. Surface skimmers remove fats, oils, and grease (FOG).
• Performance: Target removal of 60-70% Total Suspended Solids (TSS) and 30-35% Biochemical Oxygen Demand (BOD) to reduce loading on the biological stage.

C. SECONDARY TREATMENT

The biological treatment core is an Activated Sludge system optimized for nitrification.

• Aeration Basins: The facility utilizes fine-bubble diffused aeration to maximize oxygen transfer efficiency. The basins are configured to support nitrification (conversion of ammonia to nitrate).
• Process Control: Dissolved Oxygen (DO) probes and Oxidation-Reduction Potential (ORP) sensors are integrated into the SCADA system to automate blower output, optimizing energy consumption.
• Secondary Clarifiers: Mixed liquor flows to circular secondary clarifiers. Large diameter units ensure sufficient settling time to separate treated water from the biomass.
• RAS/WAS: Return Activated Sludge (RAS) is pumped back to the aeration basins to maintain Mean Cell Residence Time (MCRT). Waste Activated Sludge (WAS) is removed to control population growth.

D. DISINFECTION

To ensure pathogen inactivation prior to discharge into Salt Creek:

• Technology: Ultraviolet (UV) Disinfection.
• Configuration: In-channel low-pressure, high-output lamp banks.
• Rationale: Lincoln transitioned away from chlorination to eliminate the safety hazards of chlorine gas and the need for dechlorination chemicals (sulfur dioxide), protecting aquatic life from residual toxicity.

E. SOLIDS HANDLING (Inter-plant Strategy)

A defining engineering feature of the Lincoln system is its centralized solids processing.

• Sludge Transport: Primary sludge and thickened WAS generated at the Northeast WRRF are not digested on-site. Instead, they are pumped via a dedicated solids force main to the Theresa Street WRRF.
• Processing at Sister Plant: At Theresa Street, these solids undergo Anaerobic Digestion. The resulting biogas is harvested for energy recovery (Biogas-to-RNG project), and the remaining biosolids are dewatered and land-applied as a soil conditioner.

4. INFRASTRUCTURE & FACILITIES

A. Physical Plant

The site is situated on the outskirts of Lincoln, allowing ample room for the expansion currently underway. The campus includes the Headworks Building, Primary Clarifier complex, Aeration Basins, Secondary Clarifiers, UV Building, Blower Building, and a dedicated Operations/Lab building.

B. Energy Systems

Power is supplied by the Lincoln Electric System (LES). The plant is a major energy consumer, primarily due to aeration blowers and influent pumping.
Sustainability Note: While biogas generation occurs at Theresa Street, the Northeast facility focuses on demand-side energy management, utilizing VFDs (Variable Frequency Drives) on all major pumps and blowers to match energy draw strictly to hydraulic and biological demand.

C. Automation & SCADA

The facility is fully automated via a centralized SCADA system, allowing operators to monitor DO levels, tank levels, and flow rates in real-time. The system is linked via fiber optics to the Theresa Street control center, allowing for remote monitoring and coordinated load shifting between the two plants.

5. RECENT UPGRADES & MAJOR PROJECTS

6. REGULATORY COMPLIANCE & ENVIRONMENTAL PERFORMANCE

A. Permit Requirements

The facility operates under NPDES Permit NE0021377. Key parameters include:

• Ammonia (NH3-N): Seasonal limits are strictly enforced to prevent toxicity to aquatic life in Salt Creek.
• E. Coli: Limits apply during the recreation season (May 1 – September 30).
• CBOD5 & TSS: Standard secondary treatment limits (typically 25 mg/L monthly average).

B. Watershed Management

Salt Creek is a sensitive water body. The City of Lincoln engages in water quality trading and watershed management planning. The Northeast facility is critical in these efforts, as its effluent constitutes a significant percentage of the creek’s base flow during drought conditions.

7. OPERATIONAL EXCELLENCE

A. Staffing

The plant is staffed by certified wastewater operators licensed by the NDEE. Nebraska classifies plants from Class I to Class IV (highest). As a major mechanical plant, Northeast requires Class IV certified operators or supervision. The staff operates on rotation, with 24/7 monitoring capabilities shared with the central control room.

B. Resilience

The facility is designed with N+1 redundancy for critical pumping and aeration components. Backup power generators ensure that treatment continues during grid outages, preventing raw sewage bypasses into Salt Creek.

8. CHALLENGES & FUTURE PLANNING

A. Nutrient Limits

Like many facilities in the Mississippi River basin, Lincoln faces increasing pressure to reduce Total Nitrogen (TN) and Total Phosphorus (TP) to combat hypoxia in the Gulf of Mexico. Future capital improvement plans (CIP) likely include converting aeration basins to BNR (Biological Nutrient Removal) configurations (e.g., A2O or MLE processes) or adding tertiary filtration.

B. Urban Growth

The northeast quadrant of Lincoln is a primary zone for residential expansion. The plant must stay ahead of the “connection curve,” ensuring capacity is built before the subdivisions are fully occupied.

9. COMMUNITY & REGIONAL IMPACT

The Northeast WRRF enables economic development in Lincoln. By ensuring reliable sewer capacity, the city can approve new commercial and residential developments without moratoriums. Furthermore, the high-quality effluent supports the ecosystem of Salt Creek, which flows through Wilderness Park and other recreational areas downstream.

10. TECHNICAL SPECIFICATIONS SUMMARY

11. FAQ SECTION

Technical Questions

1. Does the Northeast facility digest its own sludge?
No. The Northeast WRRF pumps primary sludge and waste activated sludge (WAS) via a dedicated pipeline to the Theresa Street WRRF for anaerobic digestion and dewatering.

2. Is the facility designed for Biological Nutrient Removal (BNR)?
The facility was originally designed for nitrification (ammonia removal). Recent and future upgrades are focused on optimizing for Total Nitrogen and Phosphorus removal to meet evolving NDEE standards.

3. What is the peaking factor for the Northeast plant?
The plant generally operates with a peaking factor of roughly 2.5 to 3.0, capable of handling ~60 MGD during wet weather events.

Public Interest Questions

4. Does the plant smell?
The City of Lincoln utilizes biological odor control systems at the headworks and covers various process tanks to minimize odors. Occasional odors may occur during maintenance or atmospheric inversions, but they are actively managed.

5. Where does the water go after treatment?
The treated water (effluent) is discharged into Salt Creek. It is clean enough to support aquatic life and meets all state environmental safety standards.