What is nitrification in wastewater treatment?
This two step process in which ammonia is changed to nitrite and then nitrate is called nitrification. Why do we need to do nitrification in the wastewater treatment plant? For one thing, ammonia left in the treated effluent can be toxic to fish. Also, the nitrifiers in the receiving waters will be working to convert that ammonia to nitrate.
How do inhibitory wastes affect nitrification?
Small increases in inhibitory wastes can cause a dramatic reduction in nitrification. Nitrifiers grow slowly and only account for a small portion of the bacterial assemblage in an aeration system.
Why do we need to nitrate the effluent from a wastewater plant?
For one thing, ammonia left in the treated effluent can be toxic to fish. Also, the nitrifiers in the receiving waters will be working to convert that ammonia to nitrate. That conversion will use up oxygen. By nitrifying the plant effluent, the oxygen demand on the receiving waters will be reduced.
What is the role of nitrifying activated sludge?
In nitrifying activated sludge process only 3-10% of bacteria is autotrophic (nitrifiers). Nitrifiers possess cytomembranes, which are extensions of the cell membrane away from the cell wall and toward the cytoplasm. These are the active sites for oxidation of ammonium and nitrite ions.
What is nitrification inhibitor?
Nitrification Inhibitors These are the bacteria responsible for converting ammonium to nitrite (Nitrosomonas) and nitrite to nitrate (Nitrobacter). These compounds protect against both denitrification and leaching by retaining fertilizer N in the ammonium form.
What is nitrification in wastewater treatment?
Untreated domestic wastewater contains ammonia. Nitrification is a biological process that converts ammonia to nitrite and nitrite to nitrate. If standards require that the resulting nitrate be removed, one treatment alternative is the process of denitrification, in which nitrate is reduced to nitrogen gas.
What conditions inhibit nitrification?
Nitrification in soils saturated with water (i.e., water potential approaching 0 kPa) is inhibited due to lack of available oxygen.
What causes nitrification in wastewater?
Thus, many domestic and industrial wastewater treatment plants are required to remove the ammonia before discharge of the treated water. Excess nitrogen in the form of ammonia in finished water can be the principal cause of nitrification since ammonia serves as the primary substrate in the nitrificaiton process.
What is the purpose of nitrification?
Nitrification. Nitrification is the process that converts ammonia to nitrite and then to nitrate and is another important step in the global nitrogen cycle.
What do you mean by nitrification?
Definition of nitrification : the oxidation (as by bacteria) of ammonium salts to nitrites and the further oxidation of nitrites to nitrates.
What factors affect nitrification?
Among the various factors, soil matrix, water status, aeration, temperature, and pH have strong influence on nitrification. The information on factors that influence nitrification is useful when developing strategies for regulating nitrification in soils by employing chemical or biological nitrification inhibitors.
What is an example of nitrification?
In a process called nitrification, or nitrogen fixation, bacteria such as Rhizobium living within nodules on the roots of peas, clover, and other legumes convert diatomic nitrogen gas to ammonia.
Why is a nitrification inhibitor used in the BOD test?
An important part of this standard procedure is the addition of a nitrification inhibitor allylthiourea (ATU), added at the beginning of the BOD measurement in order to suppress the oxidation of ammonium to nitrate. This is added as the presence of nitrifying microorganisms can produce artificially high BOD results.
What affects nitrification and wastewater?
Environmental conditions of pH, alkalinity, temperature, dissolved oxygen concentration and organic loading affect the nitrification process in activated sludge plants. The reactions are generally coupled and proceed rapidly to the nitrate form; therefore, nitrite levels at any given time are usually low.
What happens in nitrification?
Nitrification is the process by which ammonia is converted to nitrites (NO2-) and then nitrates (NO3-). This process naturally occurs in the environment, where it is carried out by specialized bacteria. Ammonia is produced by the breakdown of organic sources of nitrogen.
How is nitrogen removed from sewage?
There are two steps for removing nitrogen in biological treatment: nitrification and denitrification. In this process, nitrifiers, including ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB), convert total ammonia (free ammonia and un-ionized ammonia) to nitrate.
What are the conditions for nitrification?
A healthy and stable population of nitrifiers (Nitrosomonas and Nitrobacter) will not exist without the following conditions: 1 Oxygen: Nitrifiers are obligate aerobes, i.e. they require free molecular oxygen and are killed off by anaerobic conditions. Maximum nitrification occurs at a D.O. (Dissolved Oxygen) level of 3.0 mg/l. Significant nitrification occurs at a D.O. level of 2.0 to 2.9 mg/l. Nitrification ceases at D.O. levels of <0.5 mg/l. Approximately 4.6 kg of oxygen are required for every kg of ammonium ions oxidized to nitrate (This compares with a requirement of 1 kg of oxygen to oxidize 1 kg of carbonaceous B.O.D.). An absence of oxygen for <4 hours does not adversely affect nitrifiers when oxygen is restored. To ensure effective nitrification always maintain a D.O. level of ≥1.5 mg/l. 2 Temperature: Nitrification is temperature sensitive. The optimum temperature for nitrification is generally considered to be 30°C.
What concentration of ammonium ions inhibits nitrifying bacteria?
Substrate inhibition usually occurs at a concentration of 400-500 mg/l ammonium ions or when ammonium ions are converted to nitrite ions at a faster rate than nitrite ions are converted to nitrate ions. BOD: Soluble and simplistic forms of cBOD can inhibit the activity of nitrifying bacteria.
How much oxygen is needed to oxidize nitrate?
Approximately 4.6 kg of oxygen are required for every kg of ammonium ions oxidized to nitrate (This compares with a requirement of 1 kg of oxygen to oxidize 1 kg of carbonaceous B.O.D.). An absence of oxygen for <4 hours does not adversely affect nitrifiers when oxygen is restored.
What is the source of carbon in nitrifying activated sludge?
These bacteria are collectively known as nitrifiers and are autotrophic, i.e. they get their carbon source from inorganic carbon (carbonates, bicarbonates) or carbon dioxide. In nitrifying activated sludge process only 3-10% of bacteria is autotrophic (nitrifiers). Nitrifiers possess cytomembranes, which are extensions of ...
What is the name of the nitrite ions that are produced under a low pH?
Free ammonia (NH3) is produced from ammonium ions under a high pH in the aeration tank. Free nitrous acid (NHO2) is produced from nitrite ions under a low pH in the aeration tank. This type of inhibition is known as substrate inhibition.
What is the maximum oxygen level for nitrification?
they require free molecular oxygen and are killed off by anaerobic conditions. Maximum nitrification occurs at a D.O. (Dissolved Oxygen) level of 3.0 mg/l. Significant nitrification occurs at a D.O. level of 2.0 to 2.9 mg/l. Nitrification ceases at D.O. levels of <0.5 mg/l.
Where are ammonium and nitrite ions found?
These are the active sites for oxidation of ammonium and nitrite ions. It is on the cytomembranes of Nitrosomonas and Nitrobacter, where ammonium ions and nitrite ions, respectively, come in contact with enzymes that add oxygen to each ion.
What is biological nitrification?
Biological nitrification is the microbe-mediated process of oxidizing ammonia to remove nitrogenous compounds from wastewaters. Domestic sewage typically contains 20 to 40 mg/L of ammonia nitrogen (NH 4- N). Organic matter containing nitrogen, e.g., protein and nucleic acid, also biodegrades to release ammonia.
What is the main cause of nitrification?
Excess nitrogen in the form of ammonia in finished water can be the principal cause of nitrification since ammonia serves as the primary substrate in the nitrificaiton process. Ammonia, nitrate and nitrite can typically be found in surface water supplies as a result of natural processes.
What is the process of oxidizing ammonia to nitrate?
As shown in the nitrification process , ammonia is first oxidized to nitrite ions, then the nitrite ions are oxidized to nitrate ions. Each oxidation is carried out by a different group of bacteria, the ammonia oxidizing bacteria (AOB) and the nitrite oxidizing bacteria (NOB).
Why is pH important in nitrification?
First, a reduction of total alkalinity may accompany nitrification because a significant amount of bicarbonate is consumed in the conversion of ammonia to nitrite. A model that was developed in 1974 indicates that 8.64 mg/L of bicarbonate (HCO 3) will be utilized for each mg/L of ammonia-nitrogen oxidized. While reduction in alkalinty does not impose a direct public health impact, reductions in alkalinity can cause reductions in buffering capacity, which can impact pH stability and corrosivity of the water toward lead and copper. Secondly, nitrifying bacteria are very sensitive to pH. Nitrosomonas has an optimal pH between approximately 7.0 and 8.0, and the optimum pH range for Nitrobacter is approximately 7.5 to 8.0. Some utilities have reported that an increase in pH (to greater than 9) can be used to reduce the occurrence of nitrification.
What are the operations of nitrifying bacteria?
Operational practices that ensure short residence time and circulation within the system can minimize nitrification problems.
How does ammonia stripping work?
Ammonia stripping is the removal of nitrogen from wastewater when the nitrogen is in gaseous ammonia form . Ammonia is a volatile substance, which means that is has a tendency to leave the wastewater and enter the atmosphere. Ammonia (NH 3) and ammonium (NH 4) exist in equilibrium with each other based on the pH. Most of the ammonia-nitrogen in municipal wastewater is in the ammonium form because of its neutral pH range (between 6 and 8). Therefore, chemicals such as lime or sodium hydroxide must be added to raise the pH to the 10.5 to 11.5 range. This will effectively "convert" the ammonium in the wastewater to ammonia. The stripping effect is achieved by introducing the high pH wastewater into th etop of a tower packed with fixed media (or "packing"). Air is blown into the bottom of the tower and flows in a countercurrent fashion with the incoming wastewater. The intimate contact between wastewater droplets and fresh air encourages the ammonia to volatilize from the wastewater to the exiting air stream.
How do bacteria remove nitrogen from wastewater?
Bacteria remove nitrogen from wastewater by a two step biological processes: nitrification followed by denitrification. Technically, it is a three step process: ammonification precedes nitrification and denitrification.
What is biological nitrification?
Biological nitrification is the microbe-mediated process of oxidizing ammonia to remove nitrogenous compounds from wastewaters. Domestic sewage typically contains 20 to 40 mg/L (ppm) of ammonia nitrogen (NH4-N). Organic matter containing nitrogen, e.g., protein and nucleic acid, also biodegrades to release ammonia. Releasing this ammonia into receiving streams has a direct toxic effect on fish and other animals and, in addition, causes significant oxygen depletion as illustrated in the following equation.
What is the process of oxidizing ammonia?
As shown in the nitrification process equations, ammonia is first oxidized to nitrite ions, then the nitrite ions are oxidized to nitrate ions. Each oxidation is carried out by a different group of bacteria, the ammonia oxidizing bacteria (AOB) and the nitrite oxidizing bacteria (NOB). Each group of bacteria has multiple species and a wastewater treatment process may contain several species of each group. In fact, the process may also include Archaea which are distinct from the bacteria but function similarly in many cases.
