Biological Nutrient Removal
A Smarter Approach to Wastewater Treatment
Understanding the Role of BNR in Wastewater Treatment
Nutrient pollution is a growing challenge for wastewater treatment plants as they work to protect water bodies from excess nitrogen and phosphorus. These nutrients, when discharged untreated, can fuel eutrophication, leading to harmful algal blooms, oxygen depletion and unsafe water for humans and wildlife.
Biological Nutrient Removal (BNR) provides a natural and sustainable solution, using microorganisms to remove nitrogen and phosphorus from wastewater. This reduces reliance on chemical treatments, helping utilities improve effluent quality while minimizing environmental impact. As regulations tighten, understanding how BNR works and its role in wastewater treatment is essential.
At a Glance
BNR is a multi-step process that requires a clear understanding of how nitrogen and phosphorus behave in wastewater. The graphics below break down these nutrient cycles, helping utilities optimize their treatment strategies.
Nitrogen Removal
- Total nitrogen (TN) includes organic and inorganic forms of nitrogen, along with ammonia, nitrate and nitrite.
- Nitrification converts ammonia to nitrate in aerobic conditions using nitrifying bacteria.
- Denitrification then transforms the produced nitrate into nitrogen gas in anoxic conditions, safely releasing it into the atmosphere.
This process is critical for reducing nitrogen pollution and ensuring compliance with environmental standards.
Phosphorus Removal
- Total phosphorus (TP) consists of reactive and non-reactive forms, influencing its bioavailability.
- Phosphorus-accumulating organisms (PAOs) remove phosphorus biologically by cycling through anaerobic and aerobic conditions.
- Understanding different phosphorus fractions, including soluble reactive phosphorus (SRP) and particulate reactive phosphorus (PRP), helps treatment plants fine-tune removal strategies.
Biological phosphorus removal prevents harmful algal blooms and reduces reliance on costly chemical treatments.
The Impact of BNR on Water Quality
With nutrient regulations tightening, wastewater utilities must proactively manage nitrogen and phosphorus levels. Some states, such as Wisconsin, now enforce phosphorus limits below 0.075 mg/L as P, demonstrating the urgency for advanced treatment solutions.
BNR provides a cost-effective, long-term strategy by:
- Preventing harmful algal blooms
- Enhancing effluent quality to meet regulatory standards
- Reducing treatment costs by minimizing chemical use
- Supporting aquatic ecosystem health
Kiewit’s Role in Advancing BNR
Kiewit works with utilities to develop customized BNR solutions, ensuring facilities achieve compliance while optimizing operations. Kiewit’s team provides:
- Nutrient analysis to identify nitrogen and phosphorus fractions in wastewater
- BNR system upgrades to enhance nitrification and phosphorus removal efficiency
- Regulatory compliance strategies to meet evolving environmental standards
- Workshops and consulting to empower clients with knowledge and technical insights
- Advanced process and biological modeling capabilities
Case Study: City of Largo’s Wastewater Reclamation Facility
The City of Largo Wastewater Reclamation Facility (WWRF) in Clearwater, Florida, is a prime example of how BNR protects water quality. Processing 18 million gallons per day (MGD), the facility discharges into Feather Sound, which feeds into Tampa Bay — a sensitive estuarine ecosystem vulnerable to nutrient pollution.
Faced with a consent order from the Florida Department of Environmental Protection (FDEP), the City partnered with Kiewit to implement a design-build solution that improved nitrogen and phosphorus removal. The results were significant:
- Total nitrogen reduced to below the permit limit of 28.5 tons per year (12-month rolling average)
- Total phosphorus maintained below the permit limit of 3.0 mg/L (single sample max) and 2.5 mg/L (weekly average)
- Methanol usage reduced by 15%
The project involved major upgrades, including filter system improvements, clarifier rehabilitation and new electrical systems, all executed while maintaining operations.
Collaboration was key. Through value engineering workshops, the City’s maintenance team identified $2.4 million in cost savings, reinvesting those funds into additional improvements. The project’s success earned it recognition as the 2023 Florida DBIA Project of the Year (Water/Wastewater Division).
The Future of BNR and Sustainable Wastewater Treatment
BNR is more than just a regulatory requirement — it is a pathway to long-term water resource sustainability. As utilities face more stringent nutrient limits and infrastructure challenges, Kiewit continues to provide innovative, cost-effective solutions that balance compliance, efficiency and environmental responsibility.
About the Authors
Steven Greseth is Kiewit’s Market Director of Wastewater and Biosolids Technology. With nearly 30 years of expertise in the industry, Steven has led numerous large, complex and collaborative water and wastewater projects throughout North America and Europe.
Caroline Wilson is a lead process engineer who specializes in designing water treatment systems. With expertise in process calculations, flow diagrams and equipment specifications, Caroline supports projects from design to construction.