Nitrogen

1. Basic Information

• Atomic number: 7
• Symbol: N
• Atomic weight: 14.0067
• Group on the periodic table: Group 15 (pniktogen)
• Period on the periodic table: Period 2

2. Physical and Chemical Properties

• A non-metallic element that at room temperature and atmospheric pressure is a diatomic gas
• Colorless, odorless, and tasteless
• Only slightly soluble in water
• Forms many important compounds, including ammonia, nitric acid, and organic compounds such as amino acids, proteins, and nucleic acids
• Boiling point: -195,8°C
• Melting point: -210°C

3. Presence in Water & Health Effects

• Nitrogen exists in the form of nitrate (NO3-) and nitrite (NO2-) dissolved in water
• Natural sources include decomposition of organic matter and thunderstorms
• Major anthropogenic sources are fertilizers and animal/human waste
• High concentrations of nitrate (>10 mg/L NO3-N) in drinking water can cause methemoglobinemia in infants
• Nitrite can react with amines and amides to form nitrosamines which are carcinogenic

4. Applications & Removal Methods in Water Treatment

• Ion exchange using anion exchange resins can remove nitrate and nitrite
  • Type 1 strong base resins such as AmberSep™ 21K XLT are effective for water with low sulfate/nitrate ratio
  • For high sulfate/nitrate ratios, nitrate selective resins such as AmberLite™ PWA5 are more suitable
• Reverse osmosis and nanofiltration can also remove nitrate and nitrite
• Biological denitrification using anaerobic bacteria converts nitrate to nitrogen gas

5. Regulatory Guidelines & Standards

• The maximum limit for nitrate concentration in drinking water according to WHO is 50 mg/L as NO3-
• The maximum limit for nitrite according to WHO is 3 mg/L as NO2-.
• The US EPA sets a combined maximum contaminant level (MCL) for nitrate and nitrite of 10 mg/L as nitrogen

6. Environmental Impact & Sustainability Considerations

• Excessive nitrogen concentrations in waters can lead to eutrophication and harmful algae blooms
• Water treatment methods that remove nitrogen must properly manage the residue/concentrate so as not to pollute the environment
• Energy-efficient technologies such as denitrification are preferred over energy-intensive methods such as reverse osmosis where possible

7. Future Trends & Research

• Biological removal of nitrate and nitrite is becoming a growing research field
  • Use of membrane bioreactors (MBRs) can combine filtration with denitrification
  • Assessment of new microbes for more efficient denitrification
• Electrodialysis and capacitive deionization are promising technologies for the removal of various ions, including nitrate

8. Interesting Facts

• About 78% of Earth's atmosphere is nitrogen, but most of it cannot be directly utilized biologically
• In the field of water treatment, biological filaments of the genus Thiothrix can cause froth and odor problems due to high nitrate concentrations in wastewater