Excess nitrogen in our state’s waters is harmful to human health and aquatic life, and can contribute to algal blooms and low oxygen zones in downstream waters. Nitrogen concentration in rivers has been increasing from historic natural levels due to human influences. In consultation with stakeholders, the MPCA developed the Wastewater Nitrogen Reduction and Implementation Strategy to start implementing actions that reduce wastewater nitrogen loads needed to protect aquatic life and achieve Minnesota’s nitrogen reduction goals.
Statewide sources
Drinking water in the state is protected by existing nitrogen water quality standards. In other bodies of water, nitrogen also causes adverse effects to aquatic life and contributes to national and international nutrient issues that the Gulf of Mexico Hypoxia Task Force and the International Red River Watershed Board are working to address. Minnesota’s Nutrient Reduction Strategy addresses sources of nitrogen for Minnesota’s waterways and establishes a plan to successfully reach our goals.
Although nitrogen discharged by wastewater treatment facilities is less than 10% of the total nitrogen in Minnesota waters, some wastewater treatment facilities discharge nitrate concentrations at levels that can be harmful for aquatic organisms. Wastewater is typically the highest source of nitrogen to waters in areas where there is relatively little farmland, during low flow months, and in some cases to small rivers and streams.
Based on a review of data collected since 2014, municipal wastewater treatment facilities discharge the majority (92%) of the wastewater sector’s nitrogen loads. Industrial facilities discharge a smaller proportion of the overall nitrogen load (8%), although some industrial discharges are significant.
Nitrogen concentrations discharged from wastewater treatment facilities have increased by 16% during the lower flow period from 2020 through 2023 compared to the decade prior.
Nutrient loads and flow volumes
Tool shows estimations of nitrogen and phosphorus discharge from wastewater treatment facilities around Minnesota.
Wastewater Nitrogen Reduction and Implementation Strategy
The MPCA has developed a wastewater nitrogen reduction and implementation strategy with the goals of meeting the nutrient reduction strategy’s goals and providing protections for aquatic life.
New, expanded, and upgraded municipal and industrial WWTFs require significant investments of public and private funds and are typically designed for a 20-year service life. Beginning April 1, 2024, WWTF designs must include the treatment units and hydraulic capacity necessary to achieve future nitrogen effluent limits, in order to maximize the benefit of impending investments and achieve nitrogen reductions as soon as possible.
In developing this strategy, the MPCA consulted with an external stakeholder group comprised of both municipal and industrial representatives. The MPCA presented to the stakeholders its evaluation of the nitrogen loads from municipal and industrial facilities and a variety of options that could be used to achieve the needed reductions.
The resulting wastewater nitrogen reduction strategy is a multi-phase plan that first makes progress toward achieving nitrogen reduction goals by evaluating options and implementing actions to reduce nitrogen in wastewater discharges by using non-regulatory methods like source reduction and wastewater treatment facility optimization.
The second phase of the strategy includes the development of nitrogen water quality-based effluent limits and other total nitrogen effluent limits in permits upon adoption of nitrate water quality standards and state discharge restriction regulations.
MPCA staff will proactively communicate with wastewater treatment facility operators regarding future nitrogen effluent limits so that they can be factored into current and future plans for facility upgrades. The MPCA supports the development of flexible and cost-effective nitrogen reduction options such as water quality trading, development and implementation of nitrogen management plans, and wastewater treatment facility optimization.