Why is the Percent Total Nitrogen Important to My Wastewater System? How do I determine it?

Nitrogen ElementMicroorganisms consume organic matter to get the energy they need for cell maintenance and reproduction. When the cell has enough energy and the necessary building blocks, it reproduces. For the reproduction process to occur, continuously and at a rapid rate, microorganisms must have a balanced diet consisting of carbon (C), oxygen (O), nitrogen (N), and phosphorus (P). For wastewater treatment, frequent reproduction of viable bacteria is a critical component of an efficient operation.

While it is possible for bacteria to consume BOD (biochemical oxygen demand) without nutrients, to complete synthesis of new cells, bacteria require nitrogen and phosphorus in the proper amounts. Without suffi¬cient numbers of bacteria, a system cannot achieve optimum BOD removal. For healthy bacteria, the biomass should generally have 8-12% nitrogen.

Total nitrogen includes organic nitrogen, ammonia (NH₃), nitrate (NO₃) and nitrite (NO₂). To determine the percent nitrogen in biomass, the total nitrogen in the sample (solids included) and the total nitrogen in the filtered bulk water are determined. The value for the bulk water is subtracted from the sample’s total nitrogen value, to determine the nitrogen in the sample solids. The resulting value is then divided into the volatile suspended solids (VSS) value to determine the percentage.

Determination of total nitrogen can be done in a number of ways, including a persulfate digestion (which is used in the Environmental Business Specialists or EBS lab). The persulfate method determines the total nitrogen content by oxidizing all nitrogenous compounds to nitrate. The alkaline oxidation occurs at 100 – 110°C (105°C for the Hach method). An alkaline persulfate digestion converts all forms of nitrogen to nitrate. Sodium metabisulfite is added after the digestion to eliminate halogen oxide interferences. The nitrate concentration is determined once the conversion of N (nitrogen) to NO₃ (nitrate) has occurred. Nitrate (NO₃) then reacts with chromotropic acid under strongly acidic conditions to form a yellow complex with an absorbance maximum at 410 nm.

Nutrients are one of the eight growth pressures important to a waste water system (along with pH, dissolved oxygen (DO), health and abundance of the biomass, BOD loading, inhibition/toxicity, retention time and temperature). Determining the percent total nitrogen in the biomass is an important step when troubleshooting an upset system. If it is determined that the percent total nitrogen in the biomass is in the ideal range, additional sources of nitrogen can be added to encourage biomass growth and BOD removal. If it is determined that the percent total nitrogen in the biomass is within the ideal range, one can begin looking for other sources of the upset. If it is determined that the percent total nitrogen in the biomass is above the ideal range, an EBS representative can assist you in optimizing nitrogen addition, thus creating an opportunity to save money.

For more information and/or a full procedure, please contact EBS at info@ebsbiowizard.com.


Learn about the microorganisms in your wastewater treatment system.