Thread Content
Synthetic ammonia industrial wastewater treatment methods: After decades of continuous technological innovation and transformation, the synthetic ammonia industry has achieved certain results in sewage treatment. However, due to the different product structures, process routes and management levels of each enterprise, pollutants such as COD, ammonia nitrogen, and sulfide in the external drainage of most enterprises still exceed standards, and water pollution problems have not been effectively controlled. At present, the treatment methods for ammonia-containing wastewater are mainly divided into physical and chemical methods and biochemical methods. Physicochemical methods mainly include chemical neutralization method, ammonia stripping method, steam stripping method, etc. The ammonia stripping method and the steam stripping method are commonly used to treat nitrogen-containing wastewater in industrial production. However, the ammonia stripping method cannot operate when the ambient temperature is below 0°C, and scaling is easy to occur on the packing of the stripping tower. The steam stripping method is suitable for the treatment of high-concentration ammonia-containing wastewater with an ammonia nitrogen content of more than 1000mg/L. 1 Breakpoint chlorination method Breakpoint chlorination method is to pass chlorine gas into the wastewater to reach a certain point at which the free chlorine content in the water is low and the ammonia concentration drops to zero. When the amount of chlorine introduced exceeds this point, free chlorine in the water will increase. Therefore, this point is called the break point. Chlorination in this state is called breakpoint chlorination. The mechanism of ammonia removal by breakpoint chlorination is that chlorine reacts with ammonia to generate harmless nitrogen. The reaction equation is:: The amount of chlorine required depends on the concentration of ammonia nitrogen, and the weight ratio of the two is 76: 1. In order to ensure a complete reaction, generally 9-10 mg of chlorine gas is required to oxidize 1 mg of ammonia nitrogen. The optimal reaction range is when the pH value is 6-7, and the contact time is 0.5-2h. The treatment rate of the chlorination method is 90%-100%, the treatment effect is stable, not affected by water temperature, and the investment is low. The disadvantages of the breakpoint chlorination method are the large amount of chlorine added and the high cost. During the process, 4 mol of acid will be produced for every 1 mol of ammonia nitrogen oxidized, which means that every 1 mg/L of alkalinity (calculated as CaCO3) is oxidized to neutralize the acid produced, thus increasing the total dissolved solid content. The by-products chloramine and chlorinated organic matter will cause secondary pollution. It is not suitable for Dashui Chengde zeolite to treat ammonia nitrogen wastewater, and the treatment of high concentration nitrogen-containing wastewater is studied. 2. Chemical precipitation method. Some high-concentration ammonia nitrogen wastewater contains a large amount of substances harmful to microorganisms and is not suitable for biological treatment. Therefore, people consider using chemical methods to remove high-concentration ammonia nitrogen. Among them, chemical precipitation methods have been studied more. Basic principles of chemical precipitation method: Ammonia reacts with chemical precipitant [H3; PO4+MgO or Mg(OH)2] to form a precipitate to remove ammonia nitrogen from wastewater. The unique advantage of this method is that the generated precipitate MgNH4;PO4 is a compound fertilizer required for crops, so this method can be used to achieve the purpose of waste recycling. The reaction mechanism for removing ammonia nitrogen is as follows: This method can remove ammonia nitrogen, heavy metals and certain macromolecular organic matter. It is often combined with other treatment technologies. It is suitable for pretreatment of reverse osmosis, activated carbon adsorption and other advanced treatments, and can also be used for pretreatment or advanced treatment of biochemical treatment. Commonly used flocculants are FeCl3, A12(SO4)3 and anionic and cationic non-ionic polymers. This method has a high removal rate of ammonia nitrogen, up to more than 90%, but the cost is higher than the stripping method, and the sludge produced causes secondary pollution to the environment. However, when it is used for denitrification pretreatment, PO43-type substances can also be used. The sludge can be used as fertilizer, so it has great flexibility, is not affected by temperature, and is simple to operate. Its main cost is chemicals. If you can find a cheap and efficient precipitant, you can * * To reduce treatment costs, you can also use local materials and use seawater or brine to replace magnesium salt. For phosphate, you can use phosphorus-containing wastewater discharged from phosphate fertilizer plants or phosphorus-containing enterprises. Some research shows: When chemical precipitation is used to treat landfill leachate (NH4-N concentration is 1.500mg/L), the removal rate reaches 96%. Zhao Qingliang et al. used chemical precipitation method to * * A study was conducted on West New Territories landfill leachate. The results showed that when the pH value was 8.6, MgCl2·6H2O and Na2HPO4 were added. ； •12H2O can reduce ammonia nitrogen from 5618mg/L to 65mg/L ； Under the same conditions, adding MgO and 85% H3;PO4 can reduce ammonia nitrogen from 5404mg/L to 1688mg/L. Obviously the former is much more effective, but it also introduces a large amount of chloride ions, which will have a negative impact on subsequent biochemical processes. 3. Stripping method: The stripping method is to adjust the pH value of the wastewater to alkaline, then introduce air or steam into the stripping tower to strip off the free ammonia in the wastewater into the atmosphere through gas-liquid contact, and then introduce steam to increase the temperature of the wastewater, thereby increasing the ratio of ammonia that is stripped off at a certain pH value. When using this method to treat ammonia, it should be considered that the total amount of free ammonia emitted should meet the atmospheric emission standards of ammonia to avoid secondary pollution. It includes steam stripping method and air stripping method. The mechanism is to adjust the wastewater to alkalinity, then introduce air or steam into the stripping tower, and remove the wastewater through gas-liquid contact. Low-concentration wastewater is usually blown off with air at normal temperature, while high-concentration wastewater in steelmaking, petrochemical, fertilizer, organic chemical, non-ferrous metal smelting and other industries is often blown off with steam. The steam stripping method has high efficiency, and the ammonia nitrogen removal rate can reach more than 90%, but it consumes a lot of energy and requires not only a steam boiler, but also a heavy maintenance workload. Therefore, ammonia is recycled to reduce installation and operation costs. After stripping treatment, ammonia water with a mass fraction of more than 30% can be recovered. Although the air stripping method is less efficient than the former, it has low energy consumption, simple equipment, and easy operation. When the total amount of ammonia nitrogen in the effluent is not high, it is more economical to use air stripping. Sulfuric acid can also be used as an absorbent for the stripped ammonia nitrogen, and the generated sulfate money can be made into fertilizer. Deng Bin uses the flue gas to treat the remaining ammonia from coking, and collects the generated sulfuric acid together with the organic matter and smoke in the wastewater through a dust collector, and then uses it to make bricks or as a combustion-supporting additive for boiler combustion. In order to reduce energy consumption, ultrasonic purification of wastewater has been proposed. Wang Youle and others used compressed air as the driving force of ultrasonic waves, causing water molecules to undergo alternate compression and expansion to generate cavitation bubbles, thus enhancing the volatilization and mass transfer effects of NH3, making it easier to convert from liquid phase to gas phase. The test was carried out on wastewater with an ammonia nitrogen concentration of 982mg/L, using a gas-liquid ratio of 1000: 1 hour, the ammonia nitrogen removal efficiency using non-ultrasonic waves was 81.53%, and the ammonia nitrogen removal efficiency using ultrasonic waves was 98.72%, an increase of about 17%. 4 Other methods Ion exchange method The ion exchange method uses zeolite with strong selectivity for ammonia ions as the exchange resin to achieve the purpose of removing ammonia nitrogen. Natural zeolite is an aluminosilicate of skeleton piles. Like synthetic zeolite molecular sieves, natural zeolite can selectively adsorb gases, perform catalytic reactions, and has ion exchange capabilities in aqueous solutions. Natural zeolite has a good effect on removing ammonia nitrogen in domestic sewage and industrial wastewater. Clinoptilolite can be used as an ion exchange medium for the selective removal of ammonia from low to medium concentration wastewater. Its selectivity order for different cations: The K+>NH4+>Na+>Ba2+>Fe3+>Al3+>Mg2+>Li+ ion exchange method has the advantages of low investment, simple process, small footprint, convenient operation, and little impact of temperature and poisons on the denitrification rate. It is suitable for medium and low concentration ammonia nitrogen wastewater.