High salinity and ammonia nitrogen content in industrial wastewater pose a serious threat to the environment and ecosystems. Therefore, desalination and denitrification technologies are particularly important in industrial wastewater treatment. This article aims to explore several mainstream and emerging desalination and denitrification technologies for industrial wastewater, in order to provide useful references for research and practice in related fields.
1. Physicochemical methods: play an important role in the desalination and denitrification of industrial wastewater. Stripping and stripping methods are suitable for treating wastewater with high concentrations of ammonia nitrogen. The principle is to adjust the pH value so that ammonia nitrogen escapes in the form of free ammonia, and then separate it from the water through the stripping action of air or steam. Although this method performs well in treatment effect, it has high energy consumption and is prone to secondary pollution. Electrodialysis uses an electric field to separate ammonia nitrogen from wastewater through the selective permeability of anion and cation exchange membranes. This method is stable and easy to operate, but it has certain limitations on wastewater concentration and is suitable for the treatment of wastewater with medium and low concentrations of ammonia nitrogen.
2. Biological treatment technology: is widely used in industrial wastewater denitrification due to its economy and environmental friendliness. The traditional nitrification-denitrification process converts ammonia nitrogen into nitrogen gas and releases it into the atmosphere through the action of nitrifying and denitrifying bacteria. This process is mature and stable, but it has the disadvantages of high energy consumption and large demand for carbon sources. In contrast, anaerobic ammonia oxidation (Anammox) has obvious advantages. It can directly convert ammonia nitrogen into nitrogen gas without aeration and additional carbon sources, greatly reducing energy consumption and sludge production. However, the reaction rate of anaerobic ammonia oxidation is slow, and a large reactor volume is required.
3. Chemical treatment technology: removes salts and nitrogen compounds from wastewater through chemical reactions. Chemical precipitation methods add chemical reagents (such as magnesium salts and phosphates) to generate insoluble magnesium ammonium phosphate (MAP) precipitates, thereby removing ammonia nitrogen. This method is technically feasible and efficient, but the cost of reagents is high, and the treatment and utilization of precipitates need to be addressed. Oxidation methods use strong oxidants or special light to oxidize and decompose organic matter and ammonia nitrogen into harmless substances. Although oxidation methods perform well in treatment effects, some ammonia nitrogen may be converted into nitrates during the oxidation process, which is not conducive to the removal of total nitrogen.
4. Physical treatment technology: Membrane separation technology has developed rapidly in recent years and has become an important means of desalination and denitrification of industrial wastewater. Reverse osmosis (RO) and nanofiltration (NF) technologies effectively remove dissolved salts and nitrogen compounds from water through the selective permeability of semi-permeable membranes. These technologies are suitable for deep purification, but the equipment investment and operating costs are high, and membrane fouling is prone to occur. Evaporation and concentration methods evaporate water by heating, leaving solid salt crystals, which are suitable for the treatment of wastewater with extremely high salinity. Although the initial investment is large, in the long run, it can significantly reduce the amount of wastewater and recover valuable salt resources.
5. Emerging treatment technologies: such as advanced oxidation processes (AOPs) and electrochemical treatment technologies, also provide new possibilities for desalination and denitrification of industrial wastewater. AOPs effectively decompose refractory organic matter by generating strong oxidizing radicals and can be used as a pretreatment step to reduce the burden on subsequent treatment units. Electrochemical treatment technology removes pollutants through oxidation-reduction reactions on the electrode surface, and has the advantages of simple operation and easy automation control, but it needs to solve the problems of electrode material aging and excessive energy consumption when treating high-salinity wastewater.
6. Summary and outlook: Desalination and denitrification technologies for industrial wastewater need to be comprehensively selected according to wastewater characteristics, treatment requirements, and economic costs. In practical applications, a combination mode of "pretreatment + core process + deep treatment" is often adopted. Case studies show that electrodialysis is suitable for desalination of high-salt wastewater, but membrane fouling needs to be considered; anaerobic ammonia oxidation can significantly reduce energy consumption in the treatment of high-ammonia nitrogen wastewater, but the cultivation of bacterial communities needs careful management; membrane concentration and evaporation crystallization can achieve zero discharge, but high investment and energy consumption need to be balanced through resource recovery; emerging AOPs technology provides a new path for pretreatment, but process parameters need to be optimized to control costs. In the future, technological research and development should focus on the development of low-cost membrane materials, efficient bacterial community cultivation, and energy recovery and utilization, promoting the development of industrial wastewater treatment towards green and sustainable development.
