Common nitrogen-containing salts in aqueous solutions and their removal/purification technologies
Nitrogen in water occurs in several forms, and these forms behave differently during treatment. Ammonia (NH3) and ammonium (NH4+) are related by a pH- and temperature-dependent equilibrium. Nitrate (NO3−) and nitrite (NO2−) are oxidized inorganic nitrogen species. In water, salts dissociate into ions; this overview therefore includes common nitrogen compounds, not only salts.
For treatment selection: Confirm whether results are reported as mg/L nitrogen (as N) or as the whole ion. Relevant conditions include pH, temperature, dissolved oxygen, redox conditions, concentration, competing ions and the required water or product quality.
Common nitrogen compounds in aqueous solutions
| Compound or form | Formula | Typical application / industry / where used | Typical aqueous streams where encountered |
|---|---|---|---|
| Ammonia / ammonium | NH3(aq) / NH4+ | Fertilizer production, chemicals, food processing and biological wastewater treatment; ammonia and ammonium are aqueous species rather than one salt. | Municipal and industrial wastewater, fertilizer production wastewater, livestock-affected water, landfill leachate and some anoxic groundwaters. |
| Ammonium chloride | NH4Cl | Fertilizers, metal finishing, batteries and chemical manufacture. | Fertilizer and chemical process water, metal-finishing rinse water and wastewater from battery manufacture. |
| Ammonium sulfate | (NH4)2SO4 | Nitrogen fertilizer and chemical manufacture. | Fertilizer production wastewater, process condensates and agricultural runoff. |
| Ammonium nitrate | NH4NO3 | Fertilizer manufacture and use. | Fertilizer production wastewater, contaminated runoff and groundwater affected by agricultural activities. |
| Ammonium bicarbonate | NH4HCO3 | Food and chemical processing and some fertilizer applications. | Process waters where ammonium and bicarbonate are both present. |
| Ammonium phosphates | NH4H2PO4 / (NH4)2HPO4 | Fertilizers and nutrient formulations. | Fertilizer manufacture wastewater, agricultural runoff and nutrient-rich wastewater. |
| Sodium nitrate | NaNO3 | Fertilizer and chemical manufacture. | Fertilizer production wastewater, agricultural drainage and some industrial process waters. |
| Potassium nitrate | KNO3 | Fertilizers and specialty chemical production. | Fertilizer manufacture wastewater and agricultural drainage. |
| Calcium nitrate | Ca(NO3)2 | Fertilizers, concrete additives and chemical manufacture. | Fertilizer production wastewater, agricultural drainage and industrial process water. |
| Sodium nitrite | NaNO2 | Metal treatment, chemical manufacture and corrosion-inhibitor formulations. | Metal-finishing and chemical process wastewater; nitrite may also occur as an intermediate during nitrogen conversion. |
| Urea | CO(NH2)2 | Fertilizers, resins and chemical manufacture. Urea is a nitrogen-bearing compound, not a salt. | Fertilizer runoff and wastewater from fertilizer, resin and chemical production; biological breakdown can release ammonia. |
This list is representative, not exhaustive. Organic nitrogen compounds can also be present and may be converted into ammonia, nitrite or nitrate during treatment.
Solubility and nitrogen speciation
Many common ammonium and nitrate salts are readily soluble, so increasing concentration alone may not remove dissolved nitrogen. Ammonia and ammonium proportions change with pH and temperature; nitrate is generally mobile in water, while nitrite is often an intermediate in biological nitrogen conversions. Oxidizing ammonia to nitrate changes its form but does not, by itself, remove total nitrogen. For background, see the nitrogen cycle.
Removal and recovery options
| Water-quality challenge | Possible treatment approaches | Notes |
|---|---|---|
| Nitrate or nitrite in source or drinking water | Anion exchange, reverse osmosis or electrodialysis; see also nitrate removal. | Selection depends on target concentration, water composition, residual stream management and applicable requirements. |
| Ammonia / ammonium in wastewater | Biological nitrification followed by denitrification; ion exchange or air stripping may be considered for specific streams. | Air stripping depends on pH and temperature and requires appropriate handling of the off-gas. Nitrification alone converts nitrogen form; denitrification can remove nitrogen as gas when properly designed and operated. |
| Total nitrogen in industrial wastewater | Biological treatment, including moving-bed biofilm reactor (MBBR) systems, or combinations with physical-chemical treatment. | Biodegradability, carbon availability, toxicity, temperature and discharge targets influence design. |
| Ammonium together with phosphate | Selective precipitation, including struvite crystallization where chemistry is suitable; see struvite precipitation. | Recovery and residual management depend on feed chemistry and product-quality requirements. |
| Concentrated brines or residual streams | Membrane concentration, evaporation and zero liquid discharge (ZLD) options. | Concentrates require a defined disposal or recovery route; high salinity and mixed ions affect feasibility. |
Applicable requirements vary by location and intended water use. Elevated nitrogen can contribute to nutrient enrichment and, in receiving waters, oxygen depletion. A representative water analysis and clearly defined treatment objective are needed to select a process.
Discuss your nitrogen treatment challenge
Lenntech can assess nitrogen removal, purification and recovery options for a specific water or wastewater composition. The appropriate process depends on the nitrogen species, concentration, co-contaminants, flow and required effluent or recovered product quality.
For process feasibility and scale-up support, see process feasibility assessment.
Discuss a water-treatment challenge
To discuss a specific water or wastewater composition or nitrogen-removal objective, contact Lenntech at info@lenntech.com.