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I. Sources of nitrate wastewater: Nitrate wastewater has various sources, primarily coming from industrial production and daily life. In industrial production, industries such as machinery, chemicals, electroplating, and photovoltaics often use nitric acid or nitrates in large quantities as raw materials or additives, which directly results in high levels of nitrates in wastewater. Industries such as food, leather, papermaking, and fertilizers cause nitrate pollution to arise indirectly in wastewater during its decomposition process, due to the use of large amounts of nitrogen-containing organic substances. II. Characteristics of nitrate wastewater: A notable feature of nitrate wastewater is its high solubility and good stability, which makes it difficult to remove using traditional simple water treatment methods such as lime softening and filtration. Furthermore, when nitrates are present in water, their concentration is often influenced by factors such as sulfates, which poses additional challenges to the removal of nitrates. III. Nitrate removal processes There are various nitrate removal processes, each with its own applicable scenarios and technical characteristics. This article mainly introduces the following processes, including chemical denitrification, reverse osmosis, electrodialysis, ion exchange, and biological denitrification. 1. Chemical denitrification involves the reduction of nitrates in water to ammonia through chemical methods under alkaline pH conditions. The reaction equation is as follows: NO3- + 8Fe(OH)2 + 6H2O → NH3 + 8Fe(OH)3 + OH-. This reaction takes place with the assistance of a catalyst made of copper, and the Fe/NO3- ratio is 15:1. This process generates large amounts of iron sludge, and the ammonia produced must be removed using air stripping. 2. Reverse osmosis uses a semipermeable membrane to retain nitrates and other soluble ions, resulting in high-quality water output while simultaneously removing various pollutants such as Ca²⁺ and Cl⁻. When the inlet nitrate concentration is 18–25 mg/L, a removal rate of 65% can be achieved after continuous operation for 1000 hours. 3. The electrodialysis electric field drives the directional migration of nitrate ions without the need for chemical reagents, resulting in a high water recovery rate. It is difficult to maintain, sensitive to conductivity, and costly. 4. Ion exchange: The principle behind the removal of nitrates using ion exchange is that NO3- in the solution is removed through exchange with Cl- or HCO3- on the ion exchange resin. After becoming saturated, the resin is regenerated using a NaCl or NaHCO3 solution. Generally, the selectivity order of anion exchange resins for various anions is: HCO3- < Cl- < NO3- < SO42-. Therefore, it is difficult to remove nitrates from sulfuric acid-containing solutions using conventional ion exchange resins. Because the resin exchanges almost all of the sulfates in the water before exchanging them for the nitrates in the water. In other words, the presence of sulfates reduces the resin’s ability to remove nitrates. Using a resin with preferential selectivity for nitrates can effectively solve this problem. This resin preferentially exchanges nitrates, and its exchange capacity for nitrates is not affected by sulfate in the water. 5. Biological denitrifying bacteria reduce nitrates to nitrogen gas through biological metabolic processes and respiration. This method does not produce any toxic substances, either during or after the reaction, and it has low operating costs; no large amounts of chemicals are required. There are also various modified processes available, allowing the reaction sequence and process to be adjusted according to different water quality requirements. The only drawback is its low efficiency – to reduce the nitrogen content in water to low levels, large reaction tanks and long residence times are often necessary. In summary, ion exchange, biological denitrification, and reverse osmosis are common methods for removing NO3-N from water and have been put into practical use. Ion exchange technology is suitable for treating groundwater with low levels of soluble organic matter. The presence of organic matter can contaminate ion exchange resins and reverse osmosis membranes. When the total dissolved solids TDS in water is <500 mg/L and SO42- is <300 mg/L, the ion exchange process can be used. When the TDS in water is >1000 mg/L, reverse osmosis or electrodialysis can be used. As emission standards become stricter, combined processes for removing nitrates are also frequently used in practice, and it is believed that more advanced technologies will emerge for further improvement in the near future.