Technical assistance: wastewater treatment

NH3-N, or ammonia nitrogen, is part of total nitrogen TN. When large amounts of nitrogen pollutants enter water bodies, it leads to the excessive growth of plants such as algae, causing eutrophication of the water. It gives water an unpleasant, fishy smell: In waters that are eutrophic, many algae grow in excessive amounts, causing the water to have a musty and foul odor, **which reduces the quality of the water. It reduces the transparency of water bodies, severely affecting their aesthetic value for tourism and viewing: in eutrophic waters, blue-green algae and other green algae grow on the surface of the water, forming a layer of green scum. These algae, which are the dominant species in such waters, cause the water to become turbid and significantly reduce its transparency. Consumption of dissolved oxygen in water bodies: Due to the dense algae in the surface layer, sunlight has difficulty penetrating deep into the lake, which significantly limits photosynthesis in the deeper waters and thus reduces the sources of dissolved oxygen. At the same time, after dying, algae continuously settle to the bottom of the lake, where they decompose, consuming a large amount of dissolved oxygen in the water. Releasing toxic substances into water bodies ； Many algae are capable of secreting and releasing toxic and harmful substances, which harm not only animals. Moreover, it has a severe impact on human health, leading to a reduction in the stability and diversity of aquatic organisms and disrupting the ecological balance of water bodies. Once water bodies become eutrophic, their normal ecological balance is disrupted; biological populations experience significant fluctuations, with some species decreasing markedly while others increase significantly, thereby reducing the stability and diversity of aquatic organisms and disrupting the ecological balance of water bodies. Biological denitrification is now commonly used to reduce N content. Biological nitrogen removal is carried out through three steps: ammonification, nitrification, and denitrification. 1. Ammoniation reaction. Organic ammonium compounds are decomposed by ammonifying bacteria, converting into ammonium nitrogen. 2. Nitrification reaction. Under the action of nitrifying bacteria, ammonium nitrogen is further decomposed and oxidized, which occurs in two stages. (1) Under the action of nitrosifying bacteria, ammonium nitrogen is converted into nitrite nitrogen. (2) Nitrite nitrogen is further oxidized to nitrate nitrogen under the action of nitrifying bacteria. 3. Denitrification reaction. Denitrification is the process by which nitrate nitrogen and nitrite nitrogen are reduced to N2 under the action of denitrifying bacteria, thereby removing nitrogen from the water.

Ammonia nitrogen pollution is widespread in drinking surface water in China. When nitrogen-containing organic substances such as human and animal feces contaminate natural water, they are broken down by microorganisms under aerobic conditions to form ammonia nitrogen. An increase in ammonia nitrogen levels in the water indicates that it may have been recently contaminated by human or animal feces. Surface water flowing through marshy areas also contains high levels of ammonia nitrogen ； Under the action of anaerobic microorganisms, nitrates in groundwater are reduced to nitrites and ammonia, which can also increase the concentration of ammonia nitrogen. Ammonium nitrogen can form nitrite through the nitrification of ammonia, and ultimately form nitrate. Generally, the degree of water pollution can be determined by changes in the levels of ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen in the water body. Hereafter, ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen will be referred to as the “three nitrogens”. Drinking water with high concentrations of nitrates and nitrites can pose two health risks to the human body: inducing methemoglobinemia and producing carcinogenic nitrosamines. Under the action of gastrointestinal bacteria, nitrates can be reduced to nitrites, which can bind to hemoglobin to form methemoglobin, thereby causing hypoxia. Babies, especially those under 3 months old, are particularly sensitive to nitrates and prone to methemoglobinemia. When about 10% of the hemoglobin in the blood is converted to methemoglobin, infants can develop symptoms of hypoxia such as cyanosis. Furthermore, nitrites can also form nitrosamines with secondary amines, and the latter are associated with the development of esophageal cancer. Ammonia nitrogen exists in water in the form of dissolved molecular ammonia (also known as free ammonia, NH3) and as ammonium salts (NH4+). The ratio between these two forms depends on the pH value and water temperature, and the content of ammonia nitrogen is expressed in terms of the amount of nitrogen present. The main sources of ammonia nitrogen in water are domestic sewage and certain industrial wastewater (such as those from the coking and ammonia synthesis industries), as well as surface runoff (mainly referring to fertilizers used in agriculture that enter rivers, lakes, and reservoirs through surface runoff). Ammonia nitrogen in water is typically removed through a digestion-redigestion reaction.

NH3-N refers to ammonium nitrogen. In fresh wastewater with lower water temperatures, organic nitrogen is higher while ammonium nitrogen is lower; in aged wastewater with higher water temperatures, organic nitrogen is lower while ammonium nitrogen is higher. Ammonia nitrogen concentration is one of the most important indicators of water body blackness and odor. Excess nitrogen in water can lead to eutrophication of the water body and has toxic effects on organisms. Organic nitrogen and reduced ammonia nitrogen are highly unstable in wastewater; they can be converted into ammonium nitrogen through ammonification. Ammonium nitrogen is further oxidized to nitrate nitrogen in the presence of oxygen. The purification of wastewater is primarily achieved through oxidation, thereby rendering these substances inorganic and stabilizing them. Therefore, the reduction in the amounts of organic nitrogen and ammonia nitrogen within the total nitrogen content, the change in the proportion of nitrate nitrogen, and the rate of removal of total nitrogen are important indicators of purification effectiveness. In biological nitrogen removal, the form of nitrogen is altered through ammonification, nitrification, and denitrification to remove ammonia nitrogen.

NH3-N refers to the amount of nitrogen present in water in the form of free ammonia and ammonium ions, with the unit being mg/L. In our system, wastewater is treated using activated sludge; within this process, NH3-N is first converted into nitrate and nitrite ions by nitrifying and denitrifying bacteria, and then it is removed either as free N2 or as part of the microorganisms themselves through denitrification processes. 4# rym19821020

This post was last edited by li*ch1968 on 2009-9-1 19:07. In fresh wastewater with lower temperatures, organic nitrogen is higher while ammonia nitrogen is lower; in old wastewater with higher temperatures, organic nitrogen is lower while ammonia nitrogen is higher.

If it is wastewater from a coking plant, an ammonia distillation tower can be used; by adding alkali and carrying out distillation, some of the ammonia nitrogen can be removed, after which biochemical treatment can be applied

For wastewater with an NH3-N concentration of 200–1000 mg·l^-1, the ammonium magnesium phosphate precipitation method is used to remove NH3-N

The MBR method can also be used, but it is employed in combination with the activated sludge method to remove ammonia nitrogen