Biological Nitrogen Removal
There are many possible solutions, and the process or technology to be used is dependent on the factors.
In many cases these processes and technologies may be combined together to provide a complete solution.
Below is a list of the processes and technologies our company adopted to perform nitrogen removal.
- 1. Modified Ludzack-Ettinger Process (MLE)
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This process consists of the modification of a conventional activated sludge process where an anoxic zone
is created or added upstream of the aerobic zone. The process uses an internal recycle that carries nitrates created
in the nitrification process in the aerobic zone along with the mix liquor to be mixed in the influent to the anoxic zone.
The amount of nitrates potentially removed in the anoxic zone depends on the recycle flow and availability of influent BOD.
Anoxic/Oxic process is designed for WWTPs that must meet stringent TN limits without a TP limit.
Nitrate-rich mixed liquor and RAS are returned to the anoxic zone where they are combined with the influent wastewater.
In the primary anoxic zone, bacteria consume BOD using oxygen from the nitrate molecule. Secondary anoxic zones
can be added after the oxic stage for additional de-nitrification producing effluent with TN of less than 3 mg/L.
- 2. Four-Stage Bardenpho Process
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This process is similar to the MLE process but has a second anoxic zone after the aerobic zone where an external brcarbon source
is typically added to aid in the denitrification process. This process is suitable for achieving very low total nitrogen values.
- 3. Moving Bed Biofilm Reactor (MBBR)
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This is a fluidized fixed-film process using a small plastic media (carriers)
in anoxic or aerobic zones that allows the attached growth to occur.
The MBBR process operates without the presence of suspended phase and is typically retrofitted into
an existing basin when other conventional processes, such as MLE or Bardenpho,
will not fit. This process can be used for nitrification and denitrification, in addition to BOD removal.
The reactor is more compact than a conventional activated sludge process. These reactors can be used
before the secondary treatment process, with the main process train, or after the secondary treatment process.
The versatile nature of this process affords a lot of flexibility with the reactor configurations.
- 4. Integrated Fixed-Film Activated Sludge System (IFAS)
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This is a fixed-film process which combines the benefits of an MBBR process with an activated sludge process.
They can be arranged in many configurations, just like many of the conventional activated sludge processes.
This system is more compact and has smaller footprint than the conventional process configurations since
it combines the suspended growth and attached growth phases. Because of the presence of the attached growth phase,
IFAS process is also more resilient to hydraulic and/or pollutant load variations. This advantage is shared by the MBBR process as well.
- 5. Membrane Biological Reactors (MBR)
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This is a process which can use many configurations with the biological portion of the process and typically
includes anoxic and aerobic zones followed by a membrane that acts as a filter to remove the solids
from the mixed liquor and therefore eliminates the need for a secondary clarifier.
This process typically provides high MLSS concentrations to achieve the nitrogen removal.
- 6. Sharon Process
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SHARON is a robust and cost effective system for the removal of nitrogen from wastewater.
The process is used for treatment of high strength ammonia liquors such as sludge dewatering liquors and the liquid fraction of pig manure.
The process results in stable nitrite formation, rather than complete oxidation to nitrate.
Nitrate formation by nitrafying bacteria (such as Nitrobacter) is prevented by adjusting temperature,
pH, and retention time to select for nitrifying bacteria (such as Nitrosomonas).
The treatment of ammonium rich wastewater, like sludge digester effluent, can be significantly
improved when new biotechnological processes, the combination of a partial nitrification process (SHARON)
and anoxic ammonium oxidation (Anammox) process for the treatment of ammonia rich influents are introduced.
The effluent of the SHARON process was ideally suited as influent for the Anammox reactor.
When compared to traditional nitrification/de-nitrification the savings are:
· 25 % on energy, due to lower oxygen demand;
· 40 % on carbon source for denitrification;
· 30 % on sludge production.
