Zero discharge of sodium nitrate wastewater in the catalyst industry: Ultrafiltration + secondary reverse osmosis + EDI + electrodialysis process

In the catalyst production industry, the treatment of sodium nitrate wastewater has always been a key challenge in environmental protection and resource recovery. Traditional treatment methods often struggle to achieve both efficient purification and zero emission goals. However, an innovative combined process - ultrafiltration + secondary reverse osmosis + EDI + electrodialysis - offers an outstanding solution to this predicament.
Ultrafiltration, as the first step in the entire treatment process, plays a crucial role in pretreatment. It is driven by pressure and uses membranes with pore sizes ranging from 20 to 1000A° to effectively retain macromolecular impurities, colloids, bacteria and other substances in wastewater. Through the ultrafiltration process, the turbidity of wastewater and the content of large-molecule organic substances can be significantly reduced, thereby alleviating the burden on subsequent treatment. For instance, in some practical projects, ultrafiltration can reduce the turbidity of the effluent from wastewater with an allowable influent turbidity of up to 50NTU to 0.1NTU after treatment, significantly improving the wastewater quality and ensuring the stable operation of subsequent membrane treatment units, preventing them from being clogged or contaminated by large particles.

The wastewater that has undergone ultrafiltration pretreatment then enters the secondary reverse osmosis stage. Secondary reverse osmosis uses pressure to force water molecules to pass through reverse osmosis membranes with selective permeability, effectively removing over 98% of dissolved salts and over 99% of colloids, microorganisms, particles and organic matter from water. The water produced by the first-stage reverse osmosis enters the intermediate water tank and is pressurized by the water pump to enter the second-stage reverse osmosis for secondary filtration, further enhancing the purity of the water quality. This process is widely applied in the preparation of pure water in industries with extremely high water quality requirements such as electronics, medical care, and food. In the treatment of sodium nitrate wastewater in the catalyst industry, it can deeply desalinate, significantly reduce the content of sodium nitrate and other salts, and produce high-quality water that meets the reuse standards. Part of the produced water can be reused in the production process, achieving the recycling of water resources.

EDI (Electro-deionization) technology follows closely behind two-stage reverse osmosis, ingeniously combining the advantages of ion exchange resins and electrodialysis technology. Under the action of a direct current electric field, the cations and anions in water migrate towards the anode and cathode respectively. When passing through the ion exchange resin layer, they are adsorbed and removed. Meanwhile, the resin is continuously regenerated through the hydrogen ions and hydroxide ions produced by water ionization. This process does not require the use of acids and bases for chemical regeneration. It not only avoids acid and base pollution but also further deeply removes ionic impurities in the water, producing nearly ultra-pure water. This ensures that the treated water quality meets the strict requirements for water purity in catalyst production, providing a solid guarantee for product quality.

Electrodialysis mainly focuses on the concentration and recovery of salts such as sodium nitrate. Under the action of an electric field, the cations and anions in the sodium nitrate solution migrate towards the two poles respectively. Through selective ion-exchange membranes, efficient separation and concentration of sodium nitrate from water and other impurities are achieved. For instance, in the treatment of sodium nitrate wastewater in the rare earth catalyst industry, a homogeneous membrane electrodialysis device can be used to concentrate 3% to 5% of sodium nitrate wastewater to over 20%, and then it enters the evaporation system for subsequent treatment. This technology has relatively low requirements for the pretreatment of raw water, can adapt to sodium nitrate wastewater of different concentrations and compositions, effectively reduces the amount of water entering the evaporation system, lowers evaporation energy consumption and treatment costs, and at the same time realizes the resource recovery of sodium nitrate, thus having significant economic and environmental benefits.

Through a series of closely coordinated processes including ultrafiltration, secondary reverse osmosis, EDI and electrodialysis, the catalyst industry has achieved the goal of zero discharge of sodium nitrate wastewater. Not only does it efficiently remove pollutants from wastewater and recycle water resources, but it also concentrates and recycles valuable salts such as sodium nitrate for reuse, significantly reducing environmental pollution. At the same time, it lowers the water cost and raw material consumption of enterprises, providing strong technical support for the sustainable development of the catalyst industry and achieving a win-win situation in both environmental protection and economic fields. Become an important model for the green transformation of the industry.