Recent Advances in Understanding the Role of Wastewater …
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oxidizers at high temperature (more than 26 °C) [37, 36] and runs at a hydraulic retention time higher than nitrite oxidizers growth rate but lower than ammonia oxidizers.
SHARON process has no sludge retention therefore the nitrite oxidizers are washed
out from this process. SHARON process is not suitable for all the wastewater since
it depends on high temperature. Rotterdam wastewater treatment plant is a typical
example of scaled up SHARON process for treatment of sludge liquor [38].
Second method which prevents the oxidation of nitrite to nitrate is the modified
SHARON process which makes use of sludge retention [39]. It works at surplus
ammonium and low oxygen concentration (less than 5% air saturation), which prevent
the growth of nitrite oxidizers and thereby prevent the oxidation of nitrite and makes it
stable. Mechanistic evidence for the impaired growth of nitrite oxidizers by ammonia
and low oxygen concentration is still not clear.
2.3.2 Anaerobic Ammonia Oxidation (ANAMMOX)
It is a denitrification process of nitrite, employing the use of ammonia as electron
donor [40, 41]. The process requires a nitrification step which converts ammonia
to nitrite. Modified SHARON process has been used to produce ammonium/nitrite
mixtures by removing the anoxic step and not supplying methanol [41, 42]. The first
scaled up anammox reactor is installed in Rotterdam, Netherland. It is in addition to
the SHARON process. Depending on the reactor design and the ammonium concentration of the wastewater, the dinitrogen gas produced during the process can be
used to partially mix the reactor and thereby reducing the power consumption. The
recycling part of the nitrogen gas can be used for additional mixing of the reactor.
The reactor should be well mixed to prevent the formation of toxic sulphide and to
maintain redox potential in denitrification zone. Reactor should not be overloaded
because high nitrite concentration is detrimental for the microorganisms (more than
180 mg N/L NO 2
− for Candidatus Kueneniastuttgartiensis and more than 70 mg N/L
NO 2
− for Candidatus Brocadiaanammoxidans) [43, 44]. Anammox process has been
conducted on laboratory scale in different reactor: fluidized bed [44], fixed bed [39]
and sequencing batch [45] and found to be suitable for all the processes. The major
challenges of the anammox process is its long start up time, because of the slow
growth rate of the anammox planctomycetes (100–150 days before the inoculation
of the reactor with activated sludge) [42]. This problem may be overcome and seeding
can become possible once the anammox plants are in full scale operation.
2.3.3 Canon
It stands for completely autotrophic nitrogen removal over nitrite. It is a combination
of partial nitrification and anammox process in a single aerated reactor [46, 39,
47]. The word canon refers to cooperation of the two groups of bacteria: perform
sequential reactions simultaneously (Eqs. 1 and 2). The nitrifiers group of organisms
involves in the oxidation of ammonia to nitrite and consume oxygen and thereby
11
oxidizers at high temperature (more than 26 °C) [37, 36] and runs at a hydraulic retention time higher than nitrite oxidizers growth rate but lower than ammonia oxidizers.
SHARON process has no sludge retention therefore the nitrite oxidizers are washed
out from this process. SHARON process is not suitable for all the wastewater since
it depends on high temperature. Rotterdam wastewater treatment plant is a typical
example of scaled up SHARON process for treatment of sludge liquor [38].
Second method which prevents the oxidation of nitrite to nitrate is the modified
SHARON process which makes use of sludge retention [39]. It works at surplus
ammonium and low oxygen concentration (less than 5% air saturation), which prevent
the growth of nitrite oxidizers and thereby prevent the oxidation of nitrite and makes it
stable. Mechanistic evidence for the impaired growth of nitrite oxidizers by ammonia
and low oxygen concentration is still not clear.
2.3.2 Anaerobic Ammonia Oxidation (ANAMMOX)
It is a denitrification process of nitrite, employing the use of ammonia as electron
donor [40, 41]. The process requires a nitrification step which converts ammonia
to nitrite. Modified SHARON process has been used to produce ammonium/nitrite
mixtures by removing the anoxic step and not supplying methanol [41, 42]. The first
scaled up anammox reactor is installed in Rotterdam, Netherland. It is in addition to
the SHARON process. Depending on the reactor design and the ammonium concentration of the wastewater, the dinitrogen gas produced during the process can be
used to partially mix the reactor and thereby reducing the power consumption. The
recycling part of the nitrogen gas can be used for additional mixing of the reactor.
The reactor should be well mixed to prevent the formation of toxic sulphide and to
maintain redox potential in denitrification zone. Reactor should not be overloaded
because high nitrite concentration is detrimental for the microorganisms (more than
180 mg N/L NO 2
− for Candidatus Kueneniastuttgartiensis and more than 70 mg N/L
NO 2
− for Candidatus Brocadiaanammoxidans) [43, 44]. Anammox process has been
conducted on laboratory scale in different reactor: fluidized bed [44], fixed bed [39]
and sequencing batch [45] and found to be suitable for all the processes. The major
challenges of the anammox process is its long start up time, because of the slow
growth rate of the anammox planctomycetes (100–150 days before the inoculation
of the reactor with activated sludge) [42]. This problem may be overcome and seeding
can become possible once the anammox plants are in full scale operation.
2.3.3 Canon
It stands for completely autotrophic nitrogen removal over nitrite. It is a combination
of partial nitrification and anammox process in a single aerated reactor [46, 39,
47]. The word canon refers to cooperation of the two groups of bacteria: perform
sequential reactions simultaneously (Eqs. 1 and 2). The nitrifiers group of organisms
involves in the oxidation of ammonia to nitrite and consume oxygen and thereby