with the development of industrial and agricultural production and the improvement of people's living standard, the emission of nitrogen compounds has increased rapidly, which has become the main source of pollution in the environment, and has attracted the attention of all walks of life. economic and effective control of ammonia nitrogen wastewater pollution has become a major task faced by environmental workers.
1, the source of ammonia nitrogen waste water
the way of nitrogen entry into water environment mainly includes two aspects: natural processes and human activities. the natural sources and processes of nitrogenous substances entering the water environment include precipitation, dustfall, non urban runoff and biological nitrogen fixation. human activities are also an important source of nitrogen in the water environment, mainly including untreated or treated municipal and industrial wastewater, various leaching solutions, and surface runoff. synthetic chemical fertilizers are the main source of nitrogen nutrients in water, and a large number of nitrogen compounds that are not used by crops are mostly carried into ground water and surface water by farmland drainage and surface runoff. with the development of petroleum, chemical, food and pharmaceutical industries, as well as the continuous improvement of the people's living standards, the content of ammonia nitrogen in municipal sewage and landfill leachate has risen sharply. in recent years, with the development of economy, more and more nitrogen pollutants have been emitted to the environment. nitrogen exists in many forms, such as organic nitrogen, ammonia nitrogen (nh4 -n), nitrate nitrogen (no3--n) and nitrite nitrogen (no2--n) in the wastewater, and ammonia nitrogen is one of the most important forms of existence. ammonia nitrogen in wastewater refers to nitrogen in the form of free ammonia and ion ammonium, mainly from the decomposition of nitrogen containing organic matter in domestic sewage, industrial wastewater such as coking, ammonia synthesis, and drainage of farmland. there are many sources of ammonia pollution, large emissions, and a great change in emission concentration.
2, the harm of ammonia nitrogen waste water
excessive ammonia nitrogen in water environment can cause many harmful effects.
(1) because of the oxidation of nh4 -n, the concentration of dissolved oxygen in the water will be reduced, which causes the water body to be black and stinky, and the water quality is reduced, which will affect the survival of aquatic animals and plants. under favorable environmental conditions, the organic nitrogen contained in the wastewater will be converted into nh4 -n, and nh4 -n is the most reductive inorganic nitrogen form, which will be further converted into no2--n and no3--n. according to the biochemical reaction measurement relationship, 1gnh4 -n oxidized to no2--n and consumed 3.43 g of oxygen and oxidized to no3--n oxygen consumption 4.57g.
(2) too much nitrogen in the water will lead to eutrophication of the water body, resulting in a series of serious consequences. the presence of nitrogen causes the increase in the number of photosynthetic microbes (mostly algae), that is, eutrophication in the water body, resulting in a blockage of the filter pool and the shortened operation cycle of the filter, which increases the cost of water treatment, hinders the water movement, and the final product of the algae metabolism can cause chromaticity and flavor. compound, because of toxins produced by blue-green algae, livestock damage, and fish death; oxygen loss occurs in water due to the decay of algae.
(3) no2--n and no3--n in water have great harm to human beings and aquatic organisms. long term consumption of water with no3--n content of more than 10mg/l will lead to methemoglobin disorder. asphyxia occurs when the content of methemoglobin in the blood reaches 70mg/l. nitrosamines are produced by the action of no2--n and amine in water, while nitrosamines are "three" substances. the reaction of nh4 -n and chlorine will produce chloramine and chloramine is less disinfectant than free chlorine, so when there is nh4 -n, the water treatment plant will need a greater amount of chlorine, so that the water treatment plant will need more chlorine.
increase the cost of processing. in recent years, there have been difficulties and even poisoning incidents of human and animal drinking caused by ammonia nitrogen waste water discharge. there have been some reports in the yangtze river, huaihe, qian tang river and sichuan tuojiang river in china. in the corresponding areas, such as blue algae pollution caused the difficulties of drinking water for millions of residents, and the related waters have been "led". therefore, removing ammonia nitrogen from wastewater has become one of the hotspots of environmental workers.
3, the main technology of ammonia nitrogen waste water treatment
at present, the treatment of ammonia nitrogen wastewater at home and abroad has many kinds of methods, such as broken point chlorination, chemical precipitation, ion exchange, stripping and biological deamination. these technologies can be divided into two categories: physical and chemical method and biological denitrification technology.
3.1 biological denitrification method
the process of removing ammonia nitrogen by microorganism takes two stages. the first stage is nitrification process, and nitrification bacteria and nitrifying bacteria convert ammonia nitrogen into nitrite nitrogen and nitrate nitrogen under aerobic conditions. the second stage is denitrification, and the nitrate nitrogen and nitrite nitrogen in the wastewater are reduced to nitrogen by the denitrifying bacteria (heterotrophic and autotrophic microorganisms are found and many kinds) under the condition of anaerobic or low oxygen. in this process, organic matter (methanol, acetic acid, glucose, etc.) is oxidized as an electron donor to provide energy. the common biological nitrogen removal processes can be divided into 3 categories, namely, the multi-stage sludge system, the single-stage sludge system and the biofilm system.
3.1.1 multistage sludge system
this process can get a good effect of bod5 removal and denitrification. its disadvantages are long process, many structures, high cost of infrastructure, high cost of carbon, high operating cost, and a certain amount of methanol in the effluent.
3.1.2 single stage sludge system
the single stage sludge system includes pre denitrification system, post denitrification system and alternate working system. the biological denitrification process of predenitrification is usually called the a/o process and the traditional biological denitrification process. the a/o process has the advantages of simple process, low structure, low infrastructure cost, no carbon source and high water quality. post denitrification system, because the mixed liquid lacks organic matter, generally needs.
source: polaris environmental protection network
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