Total Nitrogen & Phosphorus Analysis

Nutrient pollution as a threat to water resources

Nutrient pollution is becoming a serious global problem and is threatening our water resources.

In the United States, the Office of Water in the Environmental Protection Agency (EPA) issued a memo  in March 2011, titled Working in Partnership with States to Address Phosphorus and Nitrogen Pollution through Use of a Framework for State Nutrient Reductions. The effort called for accelerated reduction of nutrient pollution by partnering with individual states. In September 2016, deputy assistant administrator Joel Beauvais renewed the call to action to emphasize incremental efforts to protect water quality and public health.

Significant progress has been made in reduction of nutrient pollution across the country. To encourage the continuance of these efforts, in 2017 the EPA will offer $600,000 to support the states and tribal projects that will generate “short-term measurable” reduction efforts.

In Europe, the Nitrate Directive (1991) is one of the earliest pieces of legislation to control nitrate pollution from agricultural activities and protect ground and surface water quality. All 27 member states have action plans to cut nitrate pollutions. Implementation of the Nitrate Directive affects and benefits other directives, such as the Water Framework Directive and the Groundwater Directive.


Reducing nitrite and nitrate in drinking water

In the U.S., nitrate and nitrite are on the National Primary Drinking Water Regulations list with maximum contaminant level of 10mg/L (10 ppm) or 1mg/L (1 ppm). The EU national drinking water quality standards for nitrate and nitrite are 50mg/L (50 ppm) and 0.5mg/L (0.5ppm), respectively.

Since surface water and ground water are the major sources for drinking water, nitrate and nitrite contamination in these water sources threatens the drinking water quality. Although nitrate and nitrite are monitored by public water systems, private wells are exempt from mandatory monitoring, and therefore may contain ground water exceeding the regulatory limit of nitrate and nitrite. Drinking of nitrate-contaminated water poses a risk to both children and adults.

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Analysis of drinking water for nitrite and nitrate can be done with multiple methods. Colorimetric methods provide fast and simple measurement. However, ion chromatography using EPA Method 300.1 is a sensitive method that separates nitrite and nitrate from other common anions in drinking water, providing accurate and reproducible results.


Analysis of microcystins in drinking water

As a result of discharge of nutrient-containing effluent into surface water, algal bloom occurs due to the overgrowth of algae using the available nutrients from the effluent or storm water runoff of agricultural fertilizers. Algal overgrowth produces microcystins, neurotoxins that pose a health threat to both aquatic and human lives if the surface water is used as a source for drinking water. In concert with these efforts to reduce nitrate and nitrite in drinking water, the EPA requires that public drinking water systems monitor microcystins in drinking water according to the Unregulated Contaminants Monitoring Rule (UCMR 4) program using EPA Methods 544 and 545.


Reducing total nitrogen and phosphorus in wastewater

Insufficiently treated wastewater is a source of nutrient contamination, particularly nitrate and phosphorous, in surface water. Recently, many wastewater facilities have been upgraded to improve removal of nutrient pollutants, resulting in a drastic reduction in the amount of nutrients discharged from wastewater.

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Total nitrogen and total phosphorus are regulated in municipal wastewater by the NPDES (National Pollutant Discharge Elimination System) permits. Total nitrogen is the sum of the inorganic nitrogen, organic nitrogen, and ammonia. The sum of organic nitrogen and ammonia, total Kjeldahl nitrogen (TKN), are traditionally measured using EPA methods 351.2 and 351.4, while inorganic nitrite and nitrate are analyzed using EPA Method 353.2.


A new method for analysis of total nitrogen and phosphorus

The traditional method for measuring total nitrogen has the following drawbacks:

  • TKN determination uses toxic mercury
  • TKN determination is subject to interferences by high concentrations of nitrate
  • Multiple methods used for determination of different nitrogen sources add complexity

In a new method developed to reduce complexity, the samples are run on ion chromatography as in EPA Method 300.1, for both digested and undigested samples, to calculate the total nitrogen and total phosphorus. Nitrate, nitrite (undigested samples), and orthophosphate are measured simultaneously, using only one method and one sample preparation for both nitrogen and phosphorus.