The future of nutrient removal: Balancing compliance, cost and performance

Nutrient removal, particularly for nitrogen and phosphorus, is becoming an increasingly important focus for water and wastewater treatment plants across the country. With new stringent regulations on the horizon in the U.S., plant owners and operators must consider nutrient removal technologies to meet compliance while maintaining cost-effectiveness.

Decision-makers need to explore both traditional and novel nutrient removal technologies, comparing their capital and operational costs to help implement successful facility plans for the future.

The shifting regulatory landscape

States, including California, are tightening regulations on nutrient discharge limits due to the environmental impact of excess nitrogen and phosphorus in water bodies. These nutrients contribute to eutrophication, leading to harmful algal blooms, oxygen depletion and adverse effects on aquatic ecosystems.

The California State Water Resources Control Board is proposing stricter total nitrogen (TN) and total phosphorus (TP) limits, mirroring efforts seen in the Chesapeake Bay and Great Lakes regions. Nutrient removal strategies with more stringent limits have been developed in 30 other states, according to the EPA’s Accelerating Improvement of Water Quality report. Compliance deadlines vary, but early adoption of efficient removal technologies can help facilities avoid penalties and environmental degradation.

Emerging and advanced technologies

Publicly owned treatment works (POTWs) have relied on conventional biological and chemical processes for nutrient removal such as trickling filters, activated sludge, and sequencing batch reactors (SBRs). While conventional methods have been effective, they often require high energy, chemical inputs and large treatment footprints, leading to significant operational expenses.

As regulations become more stringent, newer technologies are emerging to improve nutrient removal efficiency while reducing costs and environmental impact. These include:

• Conventional biological nutrient removal (BNR): Infrastructure that uses zones within basins to create environments that support diverse microorganisms that are capable of removing total nitrogen (TN) and total phosphorus (TP) from wastewater.
• Aerobic granular sludge (AGS): Microbial community that allows for simultaneous removal of carbon, nitrogen, phosphorus and other pollutants. The process produces biomass in a granular form which is much more dense than conventional activated sludge floc. This is a proprietary technology that provides more efficient nutrient removal within a smaller footprint
• Densified Activated Sludge (DAS): Non-proprietary systems with densified sludge, which include particles larger than conventional activated sludge and smaller than aerobic granular sludge.
• Hydrocyclones: Utilize centrifugal force to separate solids based on their size and density; Often coupled with other intensification technologies.
• Membrane Bioreactor (MBR): Couples an activated sludge reactor with a membrane filtration process. Can be aerobic (to remove organic matter and oxidize ammonia to nitrate), anoxic (to remove nitrogen from nitrates to nitrogen gas) or anaerobic (to remove organic matter), depending on the presence of oxygen and nitrates or their absence.
• Membrane Aerated Bioreactor (MABR): Fixed-film/biofilm process with high oxygen transfer efficiency that utilizes hydrophobic membrane to deliver oxygen, like a diffuser, directly to bacteria growing on the membrane surface.
• Integrated Fixed Film Activated Sludge (IFAS): Enhances the conventional activated sludge process via the addition of media introduced to the mixed liquor for bacteria growth. Can enable activated sludge systems to achieve gains in treatment capacity without increasing mixed liquor suspended solids (MLSS) levels
• Mobile Organic Biofilms (MOB): Process which involves a biofilm substrate addition that circulates freely throughout the reactor and biological treatment process. Retention screening for the media is required to recover and redistribution to the front of the basin.

Factors to consider when choosing intensification technology

Selecting the right intensification technology requires evaluating several key factors:

• Influent Quality: The composition and concentration of nutrients in incoming wastewater influence technology selection and performance.
• Existing Process: Compatibility with current treatment processes helps determine whether upgrades or retrofits are feasible.
• Existing Footprint: Space constraints may limit the adoption of certain technologies, particularly those requiring additional tanks or infrastructure. It is worth noting that existing space at treatment plants can be constraining, and the need to integrate new processes/technologies or find a way to use existing assets to achieve better treatment capacity or nutrient removal is becoming more challenging.  
• Budget: Both capital and operational costs must be weighed to ensure economic viability.
• Effluent Quality Requirements: Regulatory discharge limits dictate the necessary level of treatment, influencing technology choices and operational strategies.

Expanding capacity and facility upgrades for the anticipated more stringent nutrient removal requirements are also key factors that are directing owners to consider new technologies for nutrient removal systems.

At a water reclamation facility in the Western U.S., a McCarthy Building Companies team, along with an engineering partner, was tasked with expanding the plant’s treatment capacity and providing redundancy of critical unit processes and equipment, to allow portions of the plant to be taken out of service for inspections, repairs, and renewal activities without impacting its ability to treat incoming wastewater. The plant was quickly approaching the influent volume threshold, which would not allow for vital unit processes to be taken out of service due to insufficient redundant capacity.

Responding to the needs on this project and accomplishing its additional goals of meeting future nutrient removal requirements, the plant influent and RAS were directed to the newly constructed BNR 4 basin from the existing splitter structure.

The BNR 4 is designed to be functionally similar to the facilities' existing basins, while incorporating various process improvements to optimize performance and reduce energy use. Similar to the existing BNR Basin 1, BNR 4 is configured in a Westbank configuration to promote biological nitrogen and phosphorus removal. BNR 4 includes one pre-anoxic zone, three anaerobic zones, one anoxic zone, one swing zone, and two parallel aerobic trains with six total zones.

Control automation improvements are being implemented to optimize biological nutrient removal performance as well. BNR technology was the solution that accomplished the owner’s goals and positions the facilities operations to successfully serve the community, while reducing energy needs.  

Comparative cost analysis: Traditional vs. new technologies

When evaluating nutrient removal technologies, both capital and operational costs must be considered. Traditional methods often have lower upfront capital costs but may incur higher operating expenses due to chemical, energy and labor requirements.

Traditional systems generally have well-established capital costs. New technologies like MABRs and AGS present higher initial capital costs but are more energy efficient and have the ability to remove nutrients more efficiently than conventional technologies. As such, at the end of an overall evaluation, they are more cost competitive on an installed basis. 

When factoring in chemicals, energy, heat and labor, the cost landscape shifts significantly. Traditional methods rely heavily on aeration, chemical dosing and sludge handling, leading to higher annual operating expenses. However, novel technologies, such as MABRs or emerging biological nutrient removal processes such as partial denitrification/anammox (PdNA), increase aeration efficiency, significantly lowering power consumption.

Chemical use is minimized in EBPR and electrochemical systems, reducing recurring material costs, while labor efficiency is improved with automated and integrated systems, decreasing workforce demands.

Overall, while emerging technologies may come with a higher initial price tag, their reduced energy consumption, lower chemical dependency and operational efficiencies make them more cost-effective in the long run.

Planning for the future

For plant owners and municipalities, selecting the right nutrient removal technology requires a balance between compliance, budget and long-term sustainability. Key considerations include:

• Regulatory Compliance: Ensuring selected technologies meet upcoming nutrient discharge limits.
• Lifecycle Cost Analysis: Evaluating both capital expenditures and long-term operational savings.
• Scalability and Flexibility: Choosing adaptable solutions to meet future demand growth that address any current pain points and fit within the plant’s parameters.
• Energy and Carbon Footprint: Prioritizing low-energy and sustainable treatment options to align with climate goals.

McCarthy Buliding Comapnies has witnessed more and more municipalities and owners move towards new treatment alternatives and novel technologies for nutrient removal because of the numerous benefits, output enhancements, and lower long-term operating costs.

For example, a project being built in the Midwest is in plans to install AGS because of its efficiency in the treatment of wastewater and its smaller footprint. Plus, with the AGS, large portions of the existing facility, such as trickling filters and final clarifiers, are no longer needed for treatment, which allows for the rehabilitation or removal of those structures, making for an easier expansion in the future. The new technologies are addressing the priority needs of the facility, including the handling of 2050 flows, complete nitrogen removal and anticipated stringent regulation limits, while using more efficient treatment and less space which enhance its flexibility. 

The push for enhanced nutrient removal is shaping the future of wastewater treatment. While traditional methods have served the industry for decades, emerging technologies offer improved efficiency, reduced operational costs and better environmental outcomes.

By strategically investing in modern treatment solutions, plant owners can achieve compliance while optimizing their resources for the long term. As the industry evolves, those who proactively adopt innovative nutrient removal strategies will be best positioned for future success.