How to Remove Nitrogen from waste water by using common process?


Nitrogen Removal :

Nitrogen is the algal nutrient most commonly removed as part of advanced wastewater treatment. In municipal waste water it is present as an organic nitrogen or ammonia.

This is because it is expensive to aerate sewage sufficiently to oxidize the ammonia to nitrate through the action of nitrifying bacteria.In the removal process,ammonia is stripped in the form of NH3 gas from the water by air.

Common process for removal of nitrogen from polluted water :

1. Air stripping ammonia :

                    Ammonium ion is the initial product of biodegradation of nitrogen waste. It is removed by raising the pH to approximately 11 with lime, and stripping ammonia gas from the water by air in a stripping tower. Scaling, icing, and air pollution are the main disadvantages.

2. Ammonium ion exchange :

                 Clinoptilolite, a natural zeolite, selectively removes + ammonium ion by ion exchange: Na+ { – clinoptilolite} + NH 4 → NH 4 { – clinoptilolite} + Na+ . The ion exchanger is regenerated with sodium or calcium salts.


3. Biosynthesis :

                The production of biomass in the sewage treatment system and its subsequent removal from the sewage effluent result in a net loss of nitrogen from the system.


4. Nitrification-denitrification :


            This approach involves the conversion of ammoniacal nitrogen to nitrate by bacteria under aerobic conditions.

2NH4 +3O2 4H  →    + 2NO2+ H2O   


2NO2 + O2→ 2NO3

Followed by production of elemental nitrogen ( denitrification) :


 4NO 3 + 5{CH2O} + 4H +→  2N 2 (g) + 5CO 2 (g) + H2O

Typically, denitrification is carried out in an anaerobic column with added methanol as a food source (microbial reducing agent).


5. Chlorination :

Reaction of ammonium ion and hypochlorite (from chlorine) results in denitrification by chemical reactions:

NH4 + HOCl          →        NH2Cl + H2O + H +


        2NH2 Cl + HOCl → N 2 (g) + 3H++ 3 Cl + H2O


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About the Author: Waleed Ahmed


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