Nitrogen removal is an essential process in wastewater treatment. The following are the three main nitrogen removal processes:


  1. Nitrification: Nitrification is the process of converting ammonia to nitrate through the action of nitrifying bacteria. The process occurs in two stages: ammonia is first oxidized to nitrite, and then nitrite is oxidized to nitrate. The process requires oxygen and is typically carried out in an aerobic reactor.
  2. Denitrification: Denitrification is the process of converting nitrate to nitrogen gas through the action of denitrifying bacteria. The process occurs in the absence of oxygen and typically takes place in an anoxic reactor.
  3. Simultaneous nitrification and denitrification (SND): SND is a process that combines nitrification and denitrification in a single reactor. The process is carried out by a single group of bacteria that can switch between nitrification and denitrification depending on the availability of oxygen and carbon sources. SND is an efficient process that can remove both nitrogen and organic matter from wastewater simultaneously.

Nitrification is a biological process in advanced wastewater treatment that involves the conversion of ammonia (NH3) to nitrate (NO3-) through two sequential microbial reactions. This process is essential for removing nitrogen compounds from wastewater, as excessive nitrogen discharges can lead to water pollution and eutrophication in natural water bodies.

The two key steps of nitrification are:


1. Ammonia Oxidation (Step 1):

Ammonia-oxidizing bacteria (AOB) convert ammonia (NH3) to nitrite (NO2-) in the presence of oxygen. This reaction is carried out by a group of bacteria known as Nitrosomonas and Nitrosococcus. 

The overall reaction can be represented as follows:

2 NH3 + 3 O2 → 2 NO2- + 2 H2O + 4 H+ 

2. Nitrite Oxidation (Step 2):

Nitrite-oxidizing bacteria (NOB), primarily belonging to the genus Nitrobacter and Nitrospira, further convert nitrite (NO2-) to nitrate (NO3-). 

This reaction is also aerobic and proceeds as follows:

2 NO2- + O2 → 2 NO3-

Both steps of nitrification require oxygen as they are aerobic processes. The oxygen is usually provided through aeration in wastewater treatment plants to ensure sufficient dissolved oxygen levels for the microbial activity.

It is important to note that nitrification is a delicate process, and factors like pH, temperature, and dissolved oxygen levels can significantly influence the efficiency of nitrifying bacteria. If conditions are not optimal, the nitrification process may be hindered, leading to incomplete nitrogen removal.

After nitrification, the wastewater is left with nitrate (NO3-), which can be further removed through denitrification, another advanced treatment process that converts nitrate to nitrogen gas under anaerobic conditions. This is particularly important to minimize the release of nitrates into the environment, as they can negatively impact water quality and aquatic ecosystems.

Brief overview of nitrification:

  • Nitrification is a microbial process that converts ammonia (NH3) to nitrite (NO2-) and then to nitrate (NO3-).
  • The two main groups of bacteria involved in nitrification are Nitrosomonas and Nitrobacter.
  • Nitrosomonas oxidizes ammonia to nitrite, and Nitrobacter oxidizes nitrite to nitrate.
  • Nitrification requires oxygen, so it is an aerobic process.
  • Nitrification is an important step in the nitrogen cycle, as it converts ammonia into a form that can be used by plants.
  • Nitrification is also used in wastewater treatment to remove nitrogen from wastewater.

Here is a more detailed explanation of the nitrification process:

  • The First Step in nitrification is the oxidation of ammonia to nitrite. This is carried out by the bacteria Nitrosomonas. Nitrosomonas bacteria use ammonia as their source of energy, and they produce nitrite as a byproduct.
  • The Second Step in nitrification is the oxidation of nitrite to nitrate. This is carried out by the bacteria Nitrobacter. Nitrobacter bacteria also use nitrite as their source of energy, and they produce nitrate as a byproduct.
  • Nitrification is an aerobic process, so it requires oxygen. If there is not enough oxygen available, then the nitrification process will slow down or stop.
  • Nitrification is an important step in the nitrogen cycle. Nitrogen is an essential nutrient for plants, and nitrate is the form of nitrogen that is most easily used by plants. Therefore, nitrification helps to make nitrogen available to plants.
  • Nitrification is also used in wastewater treatment to remove nitrogen from wastewater. Wastewater often contains high levels of ammonia, which can be toxic to fish and other aquatic life. Nitrification can be used to convert ammonia into nitrate, which is less toxic.

Denitrification Simultaneous nitrification 

Simultaneous nitrification and denitrification (SND) is a wastewater treatment process that combines the two processes of nitrification and denitrification in a single reactor. This can be done by creating micro-anoxic zones within the reactor, where the oxygen levels are low enough to allow denitrification to occur.

Nitrification is the process of converting ammonia (NH3) to nitrate (NO3-). This is done by two groups of bacteria, Nitrosomonas and Nitrobacter. Nitrosomonas oxidizes ammonia to nitrite, and Nitrobacter oxidizes nitrite to nitrate. Denitrification is the process of converting nitrate (NO3-) to nitrogen gas (N2). This is done by a group of bacteria called denitrifiers. Denitrifiers use nitrate as an electron acceptor, and they produce nitrogen gas as a byproduct.

SND has several advantages over traditional wastewater treatment processes that separate nitrification and denitrification into two reactors. First, SND can achieve higher levels of nitrogen removal. Second, SND can be more energy-efficient, as it does not require as much aeration. Third, SND can be more compact, as it does not require two separate reactors.

However, SND also has some disadvantages. First, SND can be more sensitive to changes in the influent wastewater quality. Second, SND can be more difficult to control. Third, SND can produce nitrous oxide (N2O), which is a greenhouse gas.

Overall, SND is a promising wastewater treatment process that can achieve high levels of nitrogen removal in a more energy-efficient and compact way. However, SND is still a relatively new process, and there is more research that needs to be done to understand and optimize it.

Here are some of the factors that can affect the success of SND:

  • The type of wastewater being treated.
  • The concentration of ammonia in the wastewater.
  • The temperature of the wastewater.
  • The pH of the wastewater.
  • The presence of other nutrients, such as phosphorus.
  • The type of bacteria used in the reactor.
  • The design of the reactor.

If you are considering using SND for your wastewater treatment system, it is important to work with a qualified engineer to ensure that the system is designed and operated properly.

Denitrification : 


Denitrification is a microbially facilitated process where nitrate (NO3−) is reduced and ultimately produces molecular nitrogen (N2) through a series of intermediate gaseous nitrogen oxide products.

Denitrification is an anaerobic process, which means that it does not require oxygen. It is carried out by a group of bacteria called denitrifiers. Denitrifiers use nitrate as an electron acceptor, and they produce nitrogen gas as a byproduct.

Denitrification is an important step in the nitrogen cycle. Nitrogen is an essential nutrient for plants, and nitrate is the form of nitrogen that is most easily used by plants. However, nitrate can also be a pollutant, and it can contribute to eutrophication. Denitrification helps to remove nitrate from the environment, and it helps to prevent eutrophication.

Denitrification is also used in wastewater treatment. Wastewater often contains high levels of nitrate, and denitrification can be used to remove nitrate from wastewater. This helps to protect the environment, and it also helps to prevent the spread of diseases.

The denitrification process can be expressed as a redox reaction:

2 NO3− + 10 e− + 12 H+ → N2 + 6 H2O

This reaction shows that nitrate is reduced to nitrogen gas, and that 10 electrons and 12 protons are transferred in the process. The electrons are provided by organic matter, which is oxidized by the denitrifiers. The protons are produced when water is oxidized.

Denitrification is a complex process, and there are many factors that can affect it. Some of the factors that can affect denitrification include:

  • The type of wastewater being treated.
  • The concentration of nitrate in the wastewater.
  • The temperature of the wastewater.
  • The pH of the wastewater.
  • The presence of other nutrients, such as phosphorus.
  • The type of bacteria used in the reactor.
  • The design of the reactor.

Denitrification is an important process in the nitrogen cycle, and it is also used in wastewater treatment. By understanding the denitrification process, we can better manage and protect our environment.

Phosphorus Removal : Introduction

Phosphorus is an essential nutrient for plants, but it can also be a pollutant. High levels of phosphorus in water can lead to eutrophication, which is the excessive growth of algae. This can cause a number of problems, including fish kills, decreased water quality, and increased risk of harmful algal blooms.

Phosphorus removal is an important part of wastewater treatment. There are a number of different ways to remove phosphorus from wastewater, including:

  • Chemical precipitation: This method involves adding a chemical to wastewater that will react with phosphorus to form a solid precipitate. The precipitate can then be removed by filtration or sedimentation.
  • Biological phosphorus removal: This method relies on the growth of phosphorus-accumulating organisms (PAOs). PAOs are bacteria that can store phosphorus in their cells. When the PAOs are in an anaerobic environment, they release phosphorus into the wastewater. The phosphorus can then be removed by filtration or sedimentation.
  • Ion exchange: This method uses a resin to remove phosphorus from wastewater. The resin is a material that has a strong affinity for phosphorus. When the wastewater passes through the resin, the phosphorus is exchanged for another ion, such as chloride. The phosphorus-loaded resin can then be regenerated by washing it with a solution of concentrated chloride.

The best method for phosphorus removal will depend on a number of factors, including the type of wastewater being treated, the concentration of phosphorus in the wastewater, and the cost of the treatment process.

Here are some of the benefits of phosphorus removal:

  • It can help to prevent eutrophication.
  • It can improve water quality.
  • It can reduce the risk of harmful algal blooms.
  • It can protect fish and other aquatic life.

Here are some of the challenges of phosphorus removal:

  • It can be a costly process.
  • It can be difficult to operate and maintain phosphorus removal systems.
  • The effectiveness of phosphorus removal systems can be affected by changes in the influent wastewater quality.

Overall, phosphorus removal is an important part of wastewater treatment. By removing phosphorus from wastewater, we can help to protect our environment and improve water quality.

Phosphorus removal by Chemical Precipitation

Chemical precipitation is a method of phosphorus removal that involves adding a chemical to wastewater that will react with phosphorus to form a solid precipitate. The precipitate can then be removed by filtration or sedimentation.

The most common chemicals used for phosphorus precipitation are alum (aluminum sulfate), ferric chloride, and lime (calcium hydroxide). These chemicals react with phosphorus to form insoluble precipitates, such as aluminum phosphate, ferric phosphate, and calcium phosphate.

The amount of chemical required for phosphorus precipitation will depend on the concentration of phosphorus in the wastewater. The pH of the wastewater will also affect the effectiveness of the precipitation process. In general, the pH of the wastewater should be between 6 and 8 for optimal phosphorus removal.

The precipitate formed by chemical precipitation can be removed by filtration or sedimentation. Filtration is the most common method for removing precipitates from wastewater. The precipitate is trapped in a filter, and the filtered water is then discharged. Sedimentation is another method for removing precipitates from wastewater. The precipitate settles to the bottom of a tank, and the clear water is then discharged.

Chemical precipitation is a relatively simple and effective method for phosphorus removal. However, it can be a costly process, and it can produce sludge that requires further treatment.

Here are some of the advantages of chemical precipitation for phosphorus removal:

  • It is a relatively simple and effective process.
  • It can be used to remove a wide range of phosphorus concentrations.
  • It can be used to remove phosphorus from both domestic and industrial wastewater.

Here are some of the disadvantages of chemical precipitation for phosphorus removal:

  • It can be a costly process.
  • It can produce sludge that requires further treatment.
  • The effectiveness of the process can be affected by changes in the influent wastewater quality.

Overall, chemical precipitation is a viable method for phosphorus removal. However, it is important to consider the cost and effectiveness of the process before deciding whether to use it.

Principles of process, Chemicals applied

The principles of chemical precipitation for phosphorus removal are based on the following:

  • The addition of a chemical to wastewater that will react with phosphorus to form a solid precipitate. The most common chemicals used for phosphorus precipitation are alum (aluminum sulfate), ferric chloride, and lime (calcium hydroxide). These chemicals react with phosphorus to form insoluble precipitates, such as aluminum phosphate, ferric phosphate, and calcium phosphate.
  • The pH of the wastewater will also affect the effectiveness of the precipitation process. In general, the pH of the wastewater should be between 6 and 8 for optimal phosphorus removal.
  • The precipitate formed by chemical precipitation can be removed by filtration or sedimentation. Filtration is the most common method for removing precipitates from wastewater. The precipitate is trapped in a filter, and the filtered water is then discharged. Sedimentation is another method for removing precipitates from wastewater. The precipitate settles to the bottom of a tank, and the clear water is then discharged.

The chemicals that are applied in chemical precipitation for phosphorus removal are:

  • Alum (aluminum sulfate): Alum is a common chemical used for phosphorus precipitation. It reacts with phosphorus to form aluminum phosphate, which is an insoluble precipitate. Alum is a relatively inexpensive chemical, and it is effective at removing phosphorus from wastewater.
  • Ferric chloride: Ferric chloride is another common chemical used for phosphorus precipitation. It reacts with phosphorus to form ferric phosphate, which is an insoluble precipitate. Ferric chloride is more expensive than alum, but it is more effective at removing phosphorus from wastewater.
  • Lime (calcium hydroxide): Lime is a chemical that is used to raise the pH of wastewater. A higher pH makes it more difficult for phosphorus to dissolve in water, which makes it easier to remove by precipitation. Lime is relatively inexpensive, and it is effective at raising the pH of wastewater.

The choice of chemical for phosphorus precipitation will depend on a number of factors, including the cost of the chemical, the effectiveness of the chemical, and the pH of the wastewater.

Here are some of the factors that can affect the choice of chemical for phosphorus precipitation:

  • The cost of the chemical: Alum is a relatively inexpensive chemical, while ferric chloride is more expensive.
  • The effectiveness of the chemical: Alum is effective at removing phosphorus from wastewater, while ferric chloride is more effective.
  • The pH of the wastewater: Lime is used to raise the pH of wastewater, which makes it more difficult for phosphorus to dissolve in water.

Overall, chemical precipitation is a viable method for phosphorus removal. However, it is important to consider the cost and effectiveness of the process before deciding whether to use it.

Chemistry of phosphorus precipitation

The chemistry of phosphorus precipitation is based on the following reactions:

  • Alum: Alum reacts with phosphorus to form aluminum phosphate, which is an insoluble precipitate. The reaction is as follows:
Al2(SO4)3 + 2PO43- → AlPO4↓ + 3SO42-
  • Ferric chloride: Ferric chloride reacts with phosphorus to form ferric phosphate, which is an insoluble precipitate. The reaction is as follows:
FeCl3 + 3PO43- → FePO4↓ + 3Cl-
  • Lime: Lime reacts with water to form calcium hydroxide, which is a base. Calcium hydroxide raises the pH of wastewater, which makes it more difficult for phosphorus to dissolve in water. The reaction is as follows:
Ca(OH)2 + H2O → Ca(OH)2

Process configuration

The process configuration for phosphorus precipitation can vary depending on the specific plant design. However, a typical process configuration would include the following steps:

  1. The wastewater is pre-treated to remove suspended solids and other materials that could interfere with the precipitation process.
  2. The chemical is added to the wastewater.
  3. The pH of the wastewater is adjusted to the desired level.
  4. The precipitate is allowed to settle.
  5. The clear water is discharged.
  6. The sludge is removed from the bottom of the tank and disposed of.

The process configuration for phosphorus precipitation can also be combined with other wastewater treatment processes, such as biological treatment or filtration. This can help to improve the overall efficiency of the treatment process.

Here are some of the factors that can affect the process configuration for phosphorus precipitation:

  • The concentration of phosphorus in the wastewater: The higher the concentration of phosphorus in the wastewater, the more chemical will be required.
  • The pH of the wastewater: The pH of the wastewater will affect the effectiveness of the precipitation process.
  • The type of chemical used: The type of chemical used will affect the effectiveness of the precipitation process.
  • The design of the treatment plant: The design of the treatment plant will affect the efficiency of the precipitation process.

Overall, the chemistry of phosphorus precipitation and process configuration are important factors to consider when designing a phosphorus removal system. By understanding these factors, you can help to ensure that the system is effective and efficient.

Sure, here is some information about biological precipitation for phosphorus removal:

Principles of the process : 

Biological precipitation is a process that uses microorganisms to remove phosphorus from wastewater. The microorganisms, called phosphorus-accumulating organisms (PAOs), are able to store phosphorus in their cells. When the PAOs are in an anaerobic environment, they release phosphorus into the wastewater. The phosphorus can then be removed by filtration or sedimentation.

The principles of biological precipitation for phosphorus removal are based on the following:

  • The use of microorganisms to remove phosphorus from wastewater. The microorganisms, called PAOs, are able to store phosphorus in their cells.
  • The use of an anaerobic environment to promote the release of phosphorus from PAOs. In an anaerobic environment, the PAOs are unable to use oxygen as an electron acceptor, so they turn to phosphorus instead.
  • The removal of phosphorus from wastewater by filtration or sedimentation. The phosphorus can be removed from wastewater by filtration or sedimentation.

Microorganisms involved in the process

The microorganisms involved in biological precipitation for phosphorus removal are called phosphorus-accumulating organisms (PAOs). PAOs are a type of bacteria that are able to store phosphorus in their cells. PAOs are found in wastewater, and they are able to grow in both aerobic and anaerobic environments.

The most common PAOs are:

  • Acinetobacter
  • Klebsiella
  • Enterobacter
  • Pseudomonas

Process configurations

The process configuration for biological precipitation for phosphorus removal can vary depending on the specific plant design. However, a typical process configuration would include the following steps:

  1. The wastewater is pre-treated to remove suspended solids and other materials that could interfere with the biological process.
  2. The wastewater is passed through an anaerobic reactor.
  3. The phosphorus is released from the PAOs and precipitated.
  4. The precipitate is removed by filtration or sedimentation.
  5. The clear water is discharged.

The process configuration for biological precipitation for phosphorus removal can also be combined with other wastewater treatment processes, such as biological treatment or filtration. This can help to improve the overall efficiency of the treatment process.

Here are some of the factors that can affect the process configuration for biological precipitation for phosphorus removal:

  • The concentration of phosphorus in the wastewater: The higher the concentration of phosphorus in the wastewater, the more PAOs will be required.
  • The type of wastewater: The type of wastewater will affect the type of PAOs that are present.
  • The design of the treatment plant: The design of the treatment plant will affect the efficiency of the biological precipitation process.

Overall, biological precipitation for phosphorus removal is a viable method for phosphorus removal. However, it is important to consider the factors mentioned above when designing a biological precipitation system. By understanding these factors, you can help to ensure that the system is effective and efficient.