High-concentration ammonia-nitrogen wastewater has a wide range of sources and a large amount of emissions. The wastewater produced by many chemical companies contains high concentrations of ammonia nitrogen, such as fertilizer, coking, petrochemical, pharmaceutical, food, leather, animal husbandry, and clean energy (dimethanol). In addition, the concentration of ammonia nitrogen in the permeate of landfills is particularly high, and can reach about 1500 mg/L. The discharge of such waste water into the water body will cause serious eutrophication of the water body, causing black body odor and even toxic effects on people and organisms.
Ammonia nitrogen wastewater treatment technology
1, blowing off process
The stripping process is usually mainly for wastewater with an ammonia nitrogen concentration of less than 2000 mg/l. The pH value is the main influencing factor of this process. When PH=7, the ammonia nitrogen is mostly present in NH4+. When the pH reaches 11, the dissociation rate of ammonia nitrogen in water is as high as 98%. Therefore, the pH should be strictly controlled during the process operation and adjusted to 11~13. The other factors affecting the ammonia nitrogen stripping are in the order of primary and secondary: temperature, stripping time, gas-liquid ratio. In addition, according to the characteristics of ammonia nitrogen wastewater and the ammonia nitrogen index of the effluent, a first-stage blow-off or a second-stage blow-off is designed. There is a secondary pollution problem in the blow-off. The maximum ground concentration of the discharged pollutants and the distance from the maximum concentration point to the exhaust pipe should be calculated according to the formula specified in the relevant national standards. When the calculation results determine that the ammonia concentration exceeds the standard. The blow off exhaust gas needs to be treated. It is usually absorbed by acid spray and the acid used is 30% sulfuric acid. The stripping tower and the absorption tower are usually made of carbon steel lining FRP.
2, stripping process
The stripping method is suitable for the treatment of ammonia nitrogen wastewater with an ammonia nitrogen concentration above 5000 mg/l. Using water vapor as a heating agent, the gas and liquid are brought into countercurrent contact under high pH conditions, and the mass transfer process is carried out by the difference between the partial pressure of the ammonia gas in the heat carrier and the equilibrium partial pressure of the ammonia concentration in the wastewater. The ammonia nitrogen in the wastewater is gradually released in the form of ammonia gas. This process uses a packed tower to extend the contact time and contact tightness between the gas and water to improve the removal efficiency of ammonia nitrogen. With the stripping method, stripping also has secondary pollution problems. The recovery method of ammonia in the tail gas is usually recovered in the manner of ammonium sulfate or liquid ammonia.
3. Chemical precipitation method
For wastewater with an ammonia nitrogen concentration of 200-1000 mg/L, ammonium ammonia precipitation can be used to remove ammonia nitrogen. The principle is that magnesium hydroxide and phosphoric acid are added to the ammonia nitrogen wastewater, and the ammonia nitrogen is formed by crystal precipitation of the insoluble double salt MgNH4PO4·6H2O (MAP) with ammonia nitrogen under the condition of pH 9-11.
4, ion exchange method
The method is suitable for the treatment of low concentration ammonia nitrogen wastewater, and the removal efficiency can reach 90%-96%. It is adsorbed by a special ion exchanger (zeolite) filter layer, and the sewage is discharged after adsorption. After the ion exchanger is saturated, it is released by sodium salt.
5. Biological law
Due to the biological toxicity of ammonia, the biological nitrogen removal process can be carried out only when the ammonia nitrogen concentration of the wastewater is below 200 mg/L. Our company adopts A/O aerobic and aerobic combined treatment process. This method is a relatively cost-effective nitrogen removal method at present. It is mainly used in urban sewage treatment to effectively remove COD from wastewater while removing ammonia nitrogen. For the treatment of nitriding wastewater, the carbon source should be considered, BOD/TN>3, the process can be operated normally. The hydraulic retention time of the two process sections is designed according to 1:3-1:4, and the O-stage oxidation effluent is refluxed to the A section at a reflux ratio of 100%, which has achieved the purpose of denitrification and denitrification.
6, joint treatment process
For the treatment of high-concentration ammonia-nitrogen chemical wastewater, domestically, according to factors such as wastewater characteristics, operating costs, engineering investment, operational reliability, convenient operation and management, and easy maintenance, several processes can be appropriately selected, such as stripping (blowing). De) + biochemical method, chemical precipitation + biochemical method. The wastewater is largely removed by physical or chemical methods and then biologically treated.
since 2004
