A smarter way to meet tightening nutrient discharge limits

As nitrogen regulations tighten, lagoon-based wastewater systems face increasing pressure to perform. From Mexico’s new discharge standards to Iowa’s nutrient reduction strategy, utilities are being pressed to curb nitrogen pollution to meet increasingly stringent regulatory requirements. These rules aim to prevent the overloading of waterways with nutrients like nitrogen and phosphorus — a process called eutrophication, which leads to harmful algal blooms, dead zones, and groundwater contamination. But for rural towns with aging infrastructure, compliance often seems out of reach.

Fluence’s MABR-based technologies — including the modular Aspiral™ Flex units and SUBRE lagoon retrofits — make it possible to achieve total nitrogen removal in a modular, decentralized format that’s ideal for rural towns and small communities.

MABR technology helps municipalities stay ahead of tightening regulations, turning outdated lagoon systems into future-ready assets, without the cost or disruption associated with building a new plant.

Before exploring how technology can help, it’s important to understand why nitrogen is such a regulatory focus — and why traditional lagoons struggle to handle it.

Why Nitrogen Matters in Lagoon Systems

Nitrogen occurs naturally in the environment. Too much of it in waterways is a recipe for environmental disaster. Excess nitrogen — particularly in the forms of ammonia (NH₃), nitrite (NO₂⁻), and nitrate (NO₃⁻) — acts as a fertilizer that fuels harmful algal blooms in rivers, lakes, and coastal waters. When the nutrients are depleted, the algae die off, stripping oxygen from the water as they decay. The result is hypoxic “dead zones” that suffocate aquatic life. These impacts threaten entire ecosystems; they also pose dangers to drinking water supplies and trigger costly cleanups. For these reasons, Total Nitrogen (TN) has become a major focus of water quality regulations worldwide.

Traditional lagoon systems may be simple and cost-effective, but they often struggle to remove nitrogen effectively, especially in colder climates and during high-flow events. Because colder winter weather slows biological processes, the lagoon system’s ability to convert ammonia and nitrate into harmless nitrogen gas is reduced. During stormwater surges, lagoons can become overloaded, leading to incomplete treatment and permit violations. With regulators in places like Mexico and the U.S. Midwest setting stricter discharge limits, municipalities are under growing pressure to modernize their lagoon systems for compliance.

The Rising Tide of Regulation

Across North America, nitrogen regulation is tightening—and fast. In Mexico, new standards rolling out between 2023 and 2025 require that both agricultural and municipal operators significantly reduce nitrogen levels in their effluent. These changes are part of a broader push to combat nutrient pollution, which has degraded rivers, lakes, and coastal waters across the country. Areas reliant on lagoon systems, especially rural communities, face an urgent need for affordable, high-performance upgrades that can meet the new regulatory requirements.

In the U.S. Midwest, nutrient runoff has contributed to the growing dead zone in the Gulf of Mexico. States like Iowa, Missouri, and Wisconsin have developed aggressive nutrient reduction strategies — influenced largely by the Mississippi River/Gulf of Mexico Hypoxia Task Force — that emphasize reducing nitrogen loads at the source.

Though many smaller towns don’t have access to the federal funding available to larger municipalities, their compliance is still required. With limited budgets and aging lagoon systems, such communities need practical, scalable technologies to help them meet ambitious nitrogen goals without having to overhaul their entire treatment system at great expense.

How MABR Enables Effective Nitrogen Removal in Lagoons

Fluence’s membrane aerated biofilm reactor (MABR) systems are uniquely suited to this challenge. Unlike conventional biological treatment processes that require separate tanks and added chemicals, MABR enables simultaneous nitrification and denitrification (SND) in a single tank. Ammonia is converted to nitrogen gas in one streamlined step, significantly boosting nitrogen removal efficiency without increasing system complexity.

One of MABR’s key advantages is its ability to perform in cold climates, down to temperatures as low as 37°F, making it ideal for installations across the U.S. Midwest and other regions with harsh winters. Because the oxygen is delivered directly through membranes rather than bubbles, the biofilm remains active even in low temperatures. Unlike traditional systems, MABR doesn’t need external carbon dosing or separate anoxic zones; this reduces operational costs and the footprint required.

Fluence’s SUBRE MABR modules can be retrofitted directly into existing lagoons, a cost-effective solution for upgrading existing facilities that improves performance with minimal disruption. For standalone or decentralized applications, Aspiral™ Flex offers a compact, packaged, plug-and-play solution. Both formats are modular, energy-efficient, and can deliver reliable total nitrogen removal to ensure regulatory compliance.

Real-World Example: Dow City, Iowa

Dow City, a small town in rural Iowa, faced regulatory compliance challenges with its seasonal discharge lagoon system. But by installing a single Aspiral™ M2+ unit from Fluence, powered by MABR technology, the city upgraded its lagoon to a continual discharge system, improving performance and ensuring compliance without building a new plant.

Before the upgrade, effluent ammonia and total nitrogen (TN) levels regularly exceeded regulatory limits, posing compliance risks, especially in winter. Just weeks after the Aspiral™ unit was installed, ammonia levels dropped below 10 mg/L, and TN levels saw substantial reductions, keeping the discharge within permit limits throughout the year. The upgrade was completed quickly, with little disturbance to the community and minimal operating cost increases.

Future-Proofing Your Lagoon — Without Building a New Plant

Dow City’s experience is just one example of how MABR makes future-proofing lagoon systems achievable, even with limited resources. Modern lagoon upgrades don’t have to come with massive capital costs or years of construction headaches. With MABR technology, municipalities can meet today’s water quality standards and prepare for more stringent future TN regulations without the expense of building a new plant. Its low energy demand, minimal operational and maintenance costs, and modular footprint make MABR ideal for small systems with limited budgets.

MABR technology is modular and scalable, so it offers built-in flexibility for communities that are expected to grow. Whether you need a compact unit today or a larger system tomorrow, MABR solutions can be deployed in stages, expanding to meet community demand. For towns without the upfront capital for infrastructure investments, build-own-operate (BOO) or leasing models make it possible to get compliant now, without waiting for state or federal funding to catch up.

As nutrient regulations ramp up, municipalities need to plan ahead so that they comply with future nitrogen discharge limits. MABR-based systems are a proven, practical way for existing lagoon infrastructure to keep up with modern discharge requirements without breaking the bank. Fluence’s technologies are already solving these problems in Dow City and other places in the Midwest and rural Mexico, helping communities stay ahead of the curve and comply with more efficient wastewater treatment.

Is Your Lagoon Ready for the Next Round of Regulations?

With regulations evolving fast, now is the time to assess your system and explore upgrade paths that won’t drain your budget or delay compliance.
Fluence’s modular MABR solutions make total nitrogen removal possible — without the cost or complexity of building a new plant. Contact our team to learn more about our MABR solutions and which option would be the most appropriate for your lagoon system.