What are the coking wastewater treatment methods and commonly used chemical pumps?
The rapid development of the iron and steel industry has produced a large amount of difficult-to-treat industrial wastewater, especially coking wastewater, which contains a large number of toxic, harmful, and difficult-to-degrade high-concentration organic matter. It has the characteristics of complex components and large changes in water quality and water.
The rapid development of the iron and steel industry has produced a large number of difficult-to-treat industrial wastewater, especially coking wastewater, which contains a large number of toxic, harmful, and difficult-to-degrade high-concentration organic matter. It has the characteristics of complex components and large changes in water quality and water. Value. At present, the treatment of coking wastewater is mainly traditional biological treatment method, flocculation coagulation method, adsorption method and so on. Coking wastewater has poor biochemical properties, which requires a large amount of dilution before biochemical treatment, and the problem of COD (chemical oxygen demand) and ammonia nitrogen after biochemical effluent is difficult to meet the standards at the same time, and further treatment is required. However, some advanced processing technologies have high processing costs, and it is difficult to completely degrade some toxic and harmful substances, and easily cause secondary pollution. Based on the current status of coking wastewater treatment, it is necessary to study efficient and environmentally friendly treatment technologies.
Advanced Oxidation Process (AOPs) uses the highly active hydroxyl radical (· OH) generated in the reaction system to attack organic pollutant molecules, and finally oxidizes organic pollutants to CO2 and H2O and other non-toxic Small molecule acid is a green, environmentally friendly and efficient wastewater treatment technology. At present, advanced oxidation technologies include chemical oxidation, photochemical oxidation, photocatalytic oxidation, and wet catalytic oxidation. Because AOPs have the advantages of strong oxidation and easy control of operating conditions, they have attracted more and more attention in recent years.
Pros and cons of advanced oxidation technology
The method uses a chemical oxidant to convert a liquid or gaseous inorganic or organic substance into a slightly toxic substance, a non-toxic substance, or convert it into an easily separated form. The commonly used oxidants in the field of water treatment are ozone, hydrogen peroxide, potassium permanganate and the like. In the phenol wastewater treatment process, the applications of ozone and hydrogen peroxide are the most common.
At present, many countries in the world already use ozone disinfection, especially in Europe, ozone is more used in water treatment of water plants. Add a solid catalyst to the ozone oxidation system, such as activated carbon with a large surface area. The simultaneous use of ozone and activated carbon plays a catalytic role and can adsorb small molecule products after ozone oxidation. The two jointly increase the OH- in the solution. It has a synergistic effect to generate more hydroxyl radicals.
Hydrogen peroxide is a strong oxidant. It oxidizes quickly in alkaline solutions and does not bring impurity ions to the reaction solution. Therefore, it is well used in the treatment of a variety of organic or inorganic pollutants. Hydrogen peroxide has been used to remove COD from industrial wastewater for a long time. Although the chemical oxidation method is more expensive than ordinary physical and biological methods, this method has irreplaceable effects such as toxic Pre-digestion of harmful or non-biodegradable wastewater, pretreatment of high-concentration / low-flow wastewater, etc. The use of hydrogen peroxide alone to degrade high concentrations of stable, hardly degradable compounds is not effective. It can be improved by using salts of transition metals. The most common method is to use iron salts to activate.
Fenton's reagent method.
Fenton's reagent composed of soluble ferrous salt and hydrogen peroxide mixed at a certain ratio can oxidize many organic molecules, and the system does not require high temperature and pressure. Fe2 + in the reagent can initiate and promote the decomposition of hydrogen peroxide, thereby generating hydroxyl radicals. Some toxic and harmful substances such as phenol, chlorophenol, chlorobenzene and nitrophenol can also be oxidized by Fenton reagents and Fenton-like reagents.
The combination of hydrogen peroxide and ozone, and the combination of hydrogen peroxide and ultraviolet are called Fenton-like technology, and the principle is basically the same as Fenton's technology.
This method is a chemical reaction performed under the action of light. It requires molecules to absorb electromagnetic radiation of a specific wavelength and is excited to produce an excited state of the molecule. Then it changes to another stable state or becomes an intermediate product that initiates a thermal reaction. The decomposition effect of pure ultraviolet radiation is weak. By introducing an appropriate amount of oxidant (such as H2O2, O3, etc.) into the ultraviolet oxidation method, the treatment effect of wastewater and the degradation rate can be significantly improved. There are two ways of photodegradation of organic matter: direct photodegradation and indirect photodegradation. The former refers to the direct reaction of molecules of organic matter after they absorb light energy and the substances in the surrounding environment; the latter refers to certain substances in the environment of organic matter. The process of absorbing light energy in an excited state and then inducing the reaction of organics and pollutants. Among them, indirect photodegradation of organic matter is more important.
The wavelength range that can be used in the photochemical oxidation method is 200nm ~ 700nm, that is, the ultraviolet and visible light ranges. Photochemical oxidation has applications in air pollution treatment and wastewater treatment. It can be divided into UV / O3, UV / H2O2, UV / Fenton and other systems according to the type of oxidant. Regardless of the system, photochemical reactions generally degrade organic matter by generating hydroxyl radicals.
Such as UV / O3 system, liquid-phase ozone will be decomposed under the ultraviolet radiation to generate hydroxyl radicals, and the ultraviolet absorption rate reaches the maximum at 253.7nm. It can oxidize most organic substances into CO2 and water, which is used to treat iron in industrial wastewater. Cyanates, organic compounds, nitrogen acids, alcohols, pesticides, organic compounds containing nitrogen, sulfur or phosphorus, and chlorinated organics and other pollutants.
In this method, a photocatalyst (also called a photocatalyst) produces a catalytic action under the irradiation of a specific wavelength light source, so that the surrounding water molecules and oxygen are excited to form highly active · OH- and · O2 free ion groups. The catalysts used in photocatalytic oxidation technology are TiO2, ZnO, WO3, CdS, ZnS, SnO2 and Fe3O4.
TiO2 is the most commonly used catalyst. In the photocatalytic reaction, the photocatalytic activity of TiO2 is mainly affected by the crystal phase, grain size and specific surface area. When the crystal phase is determined, the grain size and specific surface area become important factors for TiO2 in photocatalysis. The smaller the particle size, the shorter the time for photo-generated electrons and holes to diffuse, and the larger the specific surface area, the more effectively it can adsorb pollution in water. Substances that improve photocatalytic performance. When the catalyst particle size reaches nanometer level, it can also generate quantum effects to improve the light absorption rate and utilization rate, which is an important direction of current catalyst research.
Photocatalytic oxidation has the characteristics of non-toxicity and simple operating conditions. Ultraviolet light, simulated sunlight and sunlight can be used as light sources, and natural conditions (such as air) can be used as catalytic promoters. It has high activity, good stability and can make organic The pollutants are completely degraded without secondary pollution. In recent years, in order to make full use of natural light to degrade various pollutants, people have done a lot of work in improving catalytic activity and expanding the wavelength range of excitation light, which is also called the surface modification of catalysts. Doping TiO2 with transition metal, noble metal deposition can form a new modified energy level, thereby widening its photoresponse range, and performing modification treatments such as photosensitization can improve photocatalytic performance.
The application fields of photocatalytic oxidation mainly include the treatment of dye wastewater, high-concentration organic wastewater, and the removal of difficult-to-degrade micro-pollutants in the advanced treatment stage of drinking water. Generally, the photocatalytic oxidation of TiO2 can only be performed in the wavelength range of ultraviolet light, which limits the promotion and application of photocatalytic technology. In addition, the development of photocatalytic oxidation reactors is immature and it is difficult to achieve large-scale processing.
The method is an advanced oxidation method for removing pollutants by oxidizing organic matter in wastewater into carbon dioxide and water under high temperature and high pressure. The method has the characteristics of wide application range, high processing efficiency, few secondary pollution, fast oxidation rate, recoverable energy and useful materials. In Japan and the United States, such methods have engineering applications, are cutting-edge technologies, and have broad prospects for development. However, this method also has problems, that is, wet oxidation is generally required to be carried out under high temperature and high pressure conditions. The intermediate product is often an organic acid, which requires high equipment materials, expensive catalysts, and is only suitable for small-flow high-concentration wastewater. .
There are two types of wet oxidation methods: subcritical water oxidation and supercritical water oxidation. Supercritical water oxidation technology refers to a new and efficient waste treatment technology for the oxidation treatment of organic pollutants under supercritical conditions. At a certain temperature and pressure, almost all organic matter can be completely oxidized and decomposed in a short period of time, which greatly shortens the waste water treatment time, the treatment device is completely closed, saving space and no secondary pollution.
In water in the supercritical state, the solubility of salt is significantly reduced, and the solubility of organic matter is significantly increased. For example, benzene, hexane, N2, O2, etc. can be completely miscible with water, making its density, viscosity and diffusion coefficient change. The diffusion coefficient decreases with increasing density. Due to the higher temperature and pressure used in the wet oxidation technology, the density of water is reduced, the diffusion coefficient becomes larger, and the mass transfer rate increases sharply.
The application fields of wet oxidation include pesticide wastewater treatment, phenol-containing wastewater treatment, printing and dyeing wastewater, and sludge treatment. After the above-mentioned wastewater is subjected to wet oxidation treatment, the toxicity is greatly reduced, and the biodegradability is also improved. When supplemented with the biochemical treatment, the wastewater can be discharged up to the standard.