Nutrient Quantification: Nitrogen and Phosphorous-Based Compounds

Nutrient measurement is one of the key parameters in determining the quality of an environmental system, such as a stream or water reservoir, and also wastewater that comes from several sectors such as industry and agriculture. Nutrient concentrations at different points along treatment are key parameters in determining the performance and efficiency of a wastewater plant in treating wastewater biologically. Aquatic organisms need nutrients to survive, but excessive levels of the nutrients in water bodies, which can be caused by wastewater discharge, harm humans and the environment. For example, eutrophication nowadays is considered one of the greatest problems that can threaten an ecosystem, especially in coastal environments. Moreover, it also can cause problems related to the stimulation of an anaerobic condition in the water body that can bring about organism mortality and even the reduce the river or lake area.

Regarding the importance of knowing and controlling the concentration of nutrients, the concentration of the nutrients have to be monitored, evaluated and, more importantly, to be treated if there is the condition where the concentration is too high. For example in Europe, there is a regulation from the European Community to limit the total nitrogen (10 to 15 mg/liter) and phosphorus (1 to 2 mg/liter) that should be contained in the water stream[1]. In addition, the concentration of nutrients, especially ammonia, is a common parameter on National Pollutant Discharge Elimination System (NPDES) permits including in Washington State[2] and also the City of Pullman. In Washington State, the maximum daily for total ammonia (as nitrogen) in the effluent is about 10 mg/L with minimum sampling frequency is about once per every quarter.[3]

Nutrients that have been discussed here generally are nitrogen (in the form of ammonia, nitrate, etc), and phosphorus, and generally are contributed from three main sectors, the agricultural sector, such as from fertilizer utilization, the domestic sector (usually from detergent from laundry activities, and household chemical products), and also from the industrial sector.

Total nitrogen is one of the key parameters for determining wastewater characteristics and also design of wastewater treatment processes, especially for biological wastewater treatment. Nitrogen in the wastewater can be categorized as several forms, for example organic nitrogen (nitrogen in the form of protein, amino acid, etc), ammonia, nitrite, and nitrate. Nitrogen in the form of free ammonia has significant toxic effect for the aquatic life especially for fish even in low concentration. It also can cause the streams to be unusable for bathing and as drinking water. Nitrogen can also stimulate eutrophication because its characteristic as an essential nutrient for algae blooming and water hyacinth. It can bring about oxygen depletion that can derive the reduction of dissolved oxygen.

Phosphorus is another nutrient that also has significant roles in the wastewater treatment. It is generally produced from domestic and agricultural wastewater (for example from commercial fertilizer, etc).

To treat ammonia and other forms of nitrogen in wastewater, a biological process called nitrification plays a significant role in converting ammonia into nitrate with the concentration that can be accepted when the wastewater is discharged into the streams and water body. Nitrification is one of the biological processes in wastewater treatment that has purpose of oxidizing and converting the ammonia form to the nitrate form by using support from bacteria described as follows:

  1. Conversion of ammonia to nitrite using bacteria called Nitrosomonas
  2. Conversion of nitrite formed in the first stage to nitrate using bacteria called

 

Generally, because ammonia will consume noticeable oxygen in the conversion process to be nitrate, biological wastewater treatment will suffer oxygen depletion in its process if it is not equipped by nitrification process. This biological wastewater treatment is usually placed in the secondary treatment that has main purposes for performing biological process to reduce organic matters, nutrient, and also as the main treatment for providing wastewater that is ready to be directly discharged to streams. That is why, in some wastewater treatment plants, the nitrogen and phosphorus removal treatment process are designed together with the main treatment like activated sludge and other biological treatment processes.

[1] Sperling, M. (2007). Wastewater Characteristics, Treatment and Disposal, IWA publishing. Ebook

[2] Pelletier, G. (2010). “Spreadsheets for Water Quality-Based NPDES Permit Calculations.” WA Dept. of Ecology,  <http://www.ecy.wa.gov/programs/eap/pwspread/pwspread.html&gt; .Accessed 10-01-14.

[3] WA Dept. of Ecology. (2014). “Industrial Stormwater General Permit – Fact Sheet.”  <http://www.ecy.wa.gov/programs/wq/stormwater/industrial/ISGPDraft2015FactSheet.pdf&gt; Accessed 10-01-14.

 

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