Consequences and treatment methods of excessive ammonia nitrogen in water
In fact, when it comes to ammonia nitrogen, it is a routine indicator in sewage monitoring, because its exceeding the standard will bring certain harm. In this article, we will understand the consequences of excessive ammonia nitrogen in water and how to deal with it. [Harm caused by excessive ammonia nitrogen in water] Due to the oxidation of NH4+-N, the concentration of dissolved oxygen in the water body will decrease, causing the water body to become black and smelly, and the water quality will decline, which will affect the survival of aquatic animals and plants. Under favorable environmental conditions, organic nitrogen contained in wastewater will be converted into NH4+-N, NH4+-N is the form of inorganic nitrogen with the strongest reducing power, and will be further converted into NO2--N and NO3--N. According to the stoichiometric relationship of biochemical reactions, the oxidation of 1g NH4+-N to NO2--N consumes 3.43 g of oxygen, and the oxidation to NO3--N consumes 4.57 g of oxygen. Too much nitrogen content in water will lead to eutrophication of water body, and then cause a series of serious consequences. Due to the presence of nitrogen, the number of photosynthetic microorganisms (mostly algae) increases, that is, eutrophication occurs in the water body, resulting in: clogging the filter tank, shortening the operation period of the filter tank, and increasing the cost of water treatment; Movement; the end products of algae metabolism can produce compounds that cause color and taste; livestock damage and fish death due to toxins produced by blue-green algae; oxygen deficiency in water due to algae decay. In addition, NO2--N and NO3--N in the water have a greater harmful effect on humans and aquatic organisms. Drinking water with NO3--N content exceeding 10mg/L for a long time will cause methemoglobinemia, and when the methemoglobin content in the blood reaches 70mg/L, suffocation will occur. The action of NO2--N in water and amines will generate nitrosamines, and nitrosamines are 'three causes' substances. NH4+-N reacts with chlorine to generate chloramine, which has a lower disinfection effect than free chlorine. Therefore, when NH4+-N exists, the water treatment plant will need a larger amount of chlorine addition, thereby increasing the treatment cost. In recent years, people and livestock drinking water difficulties and even poisoning incidents caused by the random discharge of ammonia nitrogen-containing wastewater have occurred from time to time. There have been related reports in the Yangtze River, Huaihe River, Qiantang River, Sichuan Tuojiang River and other river basins. Corresponding areas such as cyanobacteria pollution have caused millions of Residents have difficulty in drinking water, and related waters have been 'implicated' and other major events, so the removal of ammonia nitrogen in wastewater has become one of the hotspots of environmental workers. [How to deal with excessive ammonia nitrogen] What should we do when we detect that the ammonia nitrogen content in the water exceeds the standard through the ammonia nitrogen online monitor? The following are several treatment methods: 1) Traditional biological denitrification method Traditional biological denitrification technology is accomplished through ammonification, nitrification, denitrification and assimilation. The traditional biological denitrification process is mature, and the denitrification effect is better. However, there are disadvantages such as long process flow, large area occupation, external carbon source is often required, large energy consumption, and high cost. 2) The ammonia stripping method includes the steam stripping method and the air stripping method [2~4]. The mechanism is to adjust the wastewater to alkaline, and then pass air or steam into the stripping tower to remove the free ammonia in the wastewater through gas-liquid contact. Ammonia is stripped out. This method has simple process, stable effect, strong applicability and low investment. But it consumes a lot of energy and causes secondary pollution. 3) Ion exchange method The ion exchange method actually uses the exchange reaction between the exchangeable ions on the insoluble ionic compound (ion exchanger) and other same-sex ions (NH4+) in the solution, so that the NH4+ in the wastewater is firmly adsorbed on the ion The surface of the exchanger to achieve the purpose of removing ammonia nitrogen. Although the ion exchange method has achieved certain results in the removal of ammonia nitrogen in wastewater, the amount of resin used is large, and then 4) Breakpoint chlorination method The breakpoint chlorination method is to add excessive chlorine or sodium hypochlorite to oxidize the ammonia nitrogen in the wastewater into nitrogen. chemical denitrification process. The treatment efficiency of this method can reach 90% to 100%, and the treatment effect is stable and not affected by water temperature. However, the operating cost is high, and the by-products chloramines and chlorinated organic compounds will cause secondary pollution. 6) Oxidation method using a strong oxidant (ammonia nitrogen remover) is currently a very fast and effective method for degrading ammonia nitrogen. Because the agent has strong oxidizing properties, it can only be added to the end of the water outlet. This method has low requirements on the on-site process (just stirring or aeration is enough), and is especially suitable for wastewater with relatively low ammonia nitrogen. '④ Breakpoint chlorination method' also belongs to oxidation method.