Biotechnology and Bioinformatics (1+1)

 6.1.3.4. Nitrification

Nitrification involves the two step conversion of ammonia to nitrite and nitrite to nitrate by autotrophic aerobic microorganisms which are Nitrosomonas sp. and Nitrobacter  sp. The process for ammonium oxidizing bacteria is

                      Nitrosomonas

         NH₄ ⁺  + ³ /₂O₂⁺              à            NO₂ ^–  +  2 H⁺ + H₂O  + Energy

                                      Nitrobacter

            NO₂ ^-   + 1.5O₂⁺         à           NO₃ ^–  +  energy

Both  Nitrosomonas sp. and  Nitrobacter  sp. are chemoautotrophic and obligate aerobes. Thus, they require no organic growth factors and are capable of growing in completely inorganic media using carbon dioxide as the sole source of carbon. The inorganic energy sources for the two species are NH₃ and NO₂ respectively.

Autotrophic denitrification 

 An alternative to heterotrophic biological denitrification is autotrophic denitrification which uses inorganic substance as electron donor, these substance include hydrogen and sulphur which utilize inorganic carbon compounds (CO₂ , HCO₃) as their carbon source. 

  

Autotrophic denitrification with sulphur uses Thiobacillus denitrificans. This bacterium can reduce nitrate to nitrogen gas while oxidizing elemental sulfur or reduced sulphur compounds (S^2-, S₂ O₃^2-, SO₃^2-) to sulphate, thereby eliminating the need for organic compounds.

 3. Phosphate removal

Phosphorus is released from bacterial biomass in the anaerobic stage and is assimilated by these bacteria in excess as polyphosphate (Poly P) during the aerobic stage.

In the aquaculture systems, stable ortho phosphate concentrations were found throughout the culture period. Phosphorus immobilization took place in the anoxic treatment stages of the system where it accumulated to up to 19 % of the sludge dry weight.