10
K. Ramani et al.
under environment which is unfavourable for autotrophic nitrification, e.g. acidic
environment.
2.2 Denitrification
It involves the use of chemoorganotrophic, phototrophic and lithoautotrophic bacteria
and fungi which reduces the nitrite or nitrate to gaseous nitrogen compounds [30, 31]
under anoxic or oxygen-reduced environment [32]. Denitrification is a kind of anoxic
respiration, where electrons generated from molecular hydrogen, reduced sulphur
compounds, or organic compounds are transferred to nitrite or nitrate instead of
oxygen, which helps in ATP generation. Enzymes involved during the denitrification
are the nitrite reductase, nitrate reductase, nitric oxide reductase and nitrous oxide
reductase [33, 34]. Dinitrogen is the major end product of this process while nitrous
oxide and nitric oxide are also produced in low concentrations. However, nitrous
oxide and nitric oxide are also released as the end product of denitrification process
when the concentration of dissolved oxygen is too high [35]. The onset of aerobic
denitrification is dependent on the regulation of the redox-sensing factors which acts
as a transcription regulator.
2.3 Nitrogen Removal
Nitrogen removal form the wastewater can also be accomplished by the use of newly
discovered anaerobic metabolism of proteobacterial ammonia oxidizers and anaerobic ammonia oxidizing planctomycetes. In this section the application of the newly
discovered microorganisms is discussed.
2.3.1 Partial Nitrification
It involves the oxidation of ammonium present in the wastewater to nitrite, not to
nitrate and therefore subsequent oxidation of nitrite to nitrate must be prevented.
In order to increase nitrogen removal efficiency, partial nitrogen removal can be
combined with anammox process and also with conventional denitrification process.
When combined with conventional denitrification process it gives significant advantage of resource utilization [36]. It requires less aeration since the subsequent
denitrification step reduces nitrite to molecular nitrogen not the nitrate.
Oxidation of nitrite to nitrate is prevented by two different methods. First, by using
difference in activation energy between nitrite oxidation and ammonia (44 kJ/mol
and 68 kJ/mol respectively). The SHARON (Single reactor for high activity ammonium removal over nitrite) process use different growth rate of nitrite and ammonia
K. Ramani et al.
under environment which is unfavourable for autotrophic nitrification, e.g. acidic
environment.
2.2 Denitrification
It involves the use of chemoorganotrophic, phototrophic and lithoautotrophic bacteria
and fungi which reduces the nitrite or nitrate to gaseous nitrogen compounds [30, 31]
under anoxic or oxygen-reduced environment [32]. Denitrification is a kind of anoxic
respiration, where electrons generated from molecular hydrogen, reduced sulphur
compounds, or organic compounds are transferred to nitrite or nitrate instead of
oxygen, which helps in ATP generation. Enzymes involved during the denitrification
are the nitrite reductase, nitrate reductase, nitric oxide reductase and nitrous oxide
reductase [33, 34]. Dinitrogen is the major end product of this process while nitrous
oxide and nitric oxide are also produced in low concentrations. However, nitrous
oxide and nitric oxide are also released as the end product of denitrification process
when the concentration of dissolved oxygen is too high [35]. The onset of aerobic
denitrification is dependent on the regulation of the redox-sensing factors which acts
as a transcription regulator.
2.3 Nitrogen Removal
Nitrogen removal form the wastewater can also be accomplished by the use of newly
discovered anaerobic metabolism of proteobacterial ammonia oxidizers and anaerobic ammonia oxidizing planctomycetes. In this section the application of the newly
discovered microorganisms is discussed.
2.3.1 Partial Nitrification
It involves the oxidation of ammonium present in the wastewater to nitrite, not to
nitrate and therefore subsequent oxidation of nitrite to nitrate must be prevented.
In order to increase nitrogen removal efficiency, partial nitrogen removal can be
combined with anammox process and also with conventional denitrification process.
When combined with conventional denitrification process it gives significant advantage of resource utilization [36]. It requires less aeration since the subsequent
denitrification step reduces nitrite to molecular nitrogen not the nitrate.
Oxidation of nitrite to nitrate is prevented by two different methods. First, by using
difference in activation energy between nitrite oxidation and ammonia (44 kJ/mol
and 68 kJ/mol respectively). The SHARON (Single reactor for high activity ammonium removal over nitrite) process use different growth rate of nitrite and ammonia