Advanced oxidation technology, which brings together the research results of modern optical, electrical, acoustic, magnetic, materials and other related disciplines, mainly including electrochemical oxidation, wet oxidation, supercritical water oxidation, photocatalytic oxidation and ultrasonic degradation Wait.
Factors affecting the redox reaction include the pH of the solution, the temperature, and the concentration of the reactants. The pH of the solution is particularly important, because it will determine the various rational ionization and existence forms in the solution.
的处理，其基本原理是使污染物在电极上发生直接电化学反应或间接电化学反应而得到转化，从而达到削减和去除污染物的目的。 The electrochemical oxidation method is mainly used for the treatment of toxic biodegradable organic wastewater . The basic principle is to convert pollutants to direct or indirect electrochemical reactions on the electrode, thereby achieving the purpose of reducing and removing pollutants. The electrochemical method can be used alone or in combination with other treatment methods. For example, as a pretreatment method, the biodegradability of wastewater can be improved. Generally, the electrochemical treatment process can only target specific wastewater, and the treatment scale is small and the treatment efficiency is small. It is not high, and its power consumption is large, which is not conducive to operating cost control.
Reagent oxidation methods include Fenton reagent treatment method, supercritical water oxidation method (SCWO), and the like.
Fenton reagent is a commonly used catalytic reagent. It is composed of ferrous salts and peroxides. The composition, when the pH value is low enough, iron ions act on hydrogen peroxide to generate hydroxyl radicals, and trigger more free radicals, attack the internal molecular bonds of organic matter, and achieve the purpose of completely inorganicizing or cracking organic matter into small molecules. 试剂在水处理中的作用主要包括对有机物的氧化和混凝两种作用。 The role of Fenton reagent in water treatment mainly includes two effects on oxidation and coagulation of organic matter. It can effectively remove difficult-to-degrade organics that cannot be removed by traditional wastewater treatment technologies.
With the deepening of research, ultraviolet light (UV) and oxalate (C2O42-) were introduced into the Fenton reagent, which greatly enhanced its oxidation ability. Using TiO2 as catalyst and 9 W low-pressure mercury lamp as light source, the pharmaceutical wastewater was treated with Fenton reagent. The decolorization rate was 100% and the COD removal rate was 92.3%. The nitrobenzene compounds were reduced from 8.05 mg / L 0.41 mg / L.
Other catalytic reagents include H2O2 / O3, which is an advanced oxidation technology widely used in drinking water applications, because only hydrogen peroxide needs to be added to the ozone generator. Ozone itself is highly oxidizing and can remove a large amount of organic matter, but it has a poor oxidation effect on certain halogenated hydrocarbons and pesticides. The combination of ozone and hydrogen peroxide can greatly improve the oxidation efficiency. Its main characteristics It works well in water with high turbidity.
。 Supercritical oxidation wastewater treatment technology is a high-level oxidation technology for toxic organic solid waste and industrial wastewater, which is developed based on wet oxidation to rapidly oxidize Fe2 + to Fe3 + from the beginning. 。 SCWO uses a water level medium to take advantage of the fact that there is no resistance to mass transfer at the gas-liquid interface under supercritical conditions (temperature> 374 ° C, P> 22.1MPa). Solubility, light organic gases and CO2 are completely miscible, but inorganic compounds, especially salts, are difficult to dissolve in it. In addition, supercritical water has a higher diffusion coefficient and lower viscosity), and will be dissolved in a very short time All kinds of organic matter are completely oxidized to carbon dioxide and water without causing secondary pollution, which is called ecological water treatment technology . When the organic matter concentration in the wastewater is more than 2%, the heat generated by the oxidation reaction of the organic matter is used to maintain the reaction temperature of the system, and basically no external heating is required.
与其他处理技术相比，具有明显的优点： Compared with other treatment technologies, supercritical oxidation technology has obvious advantages:
① High efficiency, thorough treatment, the removal rate of toxic substances is as high as 99.99% or more;
② fast reaction speed, short residence time (less than 1min), simple reactor structure and small volume;
③ It has a wide range of applications and can be applied to the treatment of various toxic waste water wastes;
④ No secondary pollution, no further treatment is needed, and inorganic salts can be separated from the water, and the treated wastewater can be completely recycled;
⑤ When the content of organic matter exceeds 10%, no additional heating is needed to achieve self-sufficiency of heat.
The high-temperature and high-pressure operating conditions of supercritical water oxidation undoubtedly impose strict requirements on equipment materials. In the actual engineering design, some engineering factors must be paid attention to, such as corrosion, salt precipitation, use of catalysts, and heat transfer.
Wet catalytic oxidation technology is an advanced treatment method for industrial wastewater (a physical and chemical method). At high temperature (200-300 ° C) and high pressure (2-10MPa), the wastewater is passed through a reactor equipped with a high-efficiency oxidation performance catalyst. Looking at the reactor, the organic substances and poisonous structures such as N and S can be included in the reactor. The double bond is broken, and the large molecules are oxidized to small molecules, and the small molecules are further oxidized to harmless substances such as CO2, H2O, and N2, SO42-, which greatly reduces the COD, increases the BOD / COD value, and increases the biodegradability of wastewater. the process of. The reaction time is generally 10min-2.0h.
When using this method to treat wastewater, the wastewater must not contain a large amount of substances that can cause contamination of the catalyst (such as metals) and substances that are likely to cause blockage of equipment or pipelines (such as high-concentration salts). Before the corresponding treatment (such as desalination, distillation, etc.).
Its prominent feature is that hydroxyl radicals are used as the main oxidant to react with organic substances. Organic radicals generated in the reaction can continue to participate in the chain reaction of OH, or by generating organic peroxide radicals, further oxidative decomposition reactions occur. Until it is degraded into the final products CO2 and H2O, so as to achieve the purpose of oxidative decomposition of organic matter. Hydroxyl radical is a very strong chemical oxidant (oxidation potential of the oxidant). Its oxidation potential is much higher than that of ordinary oxidants (such as ozone, chlorine gas, hydrogen peroxide), which means that the oxidation capacity of OH is much higher. For common chemical oxidants.
和流动床两类。 According to the equipment structure, there are two types: fixed bed and fluid bed . The fixed bed is divided into a gas-phase fixed bed and a liquid-phase fixed bed; the fluidized bed should consider the problem of catalyst separation and recovery.
Organic substances that can be treated by wet oxidation are:
①Inorganic cyanide and organic cyanide are easily oxidized;
② Aliphatic and chlorinated aliphatic compounds are susceptible to oxidation;
③ Aromatic hydrocarbons (toluene, etc.) are susceptible to oxidation;
④ Aromatic and halogenated aromatic compounds containing non-halogenated functional groups (such as phenol and aniline) are susceptible to oxidation;
⑤ Halogenated aromatic compounds which do not contain other non-halogenated functional groups (such as chlorobenzene) are difficult to treat by wet oxidation.
Photocatalytic oxidation technology uses photo-excited oxidation to combine oxidants such as O2, H2O2 and light radiation. The light used is mainly ultraviolet light, including processes such as uv-H2O2 and uv-O2, which can be used to treat refractory substances such as CHCl3, CCl4, and polychlorinated biphenyls in sewage. In addition, in the Feton system with ultraviolet light, there is a synergistic effect between ultraviolet light and iron ions, which greatly accelerates the rate of generating hydroxyl radicals by the decomposition of H2O2, and promotes the oxidative removal of organic matter.
This technology can degrade high-concentration organic pollutants in wastewater, which is difficult to degrade organic wastewater that is difficult to biochemically treat. Halogenated aliphatic hydrocarbons, halogenated aromatic hydrocarbons, organic acids, nitroaromatic hydrocarbons, substituted anilines, polycyclic aromatic hydrocarbons, heterocyclic compounds, hydrocarbons, phenols, dyes, surfactants, pesticides, etc. can effectively perform photocatalytic reactions , And finally produce small inorganic molecules. The strong oxidation performance of the photocatalytic reaction is its technical advantage in organic pollution control.
Organic chlorides are the most important type of pollutants in water. They are highly toxic and widely distributed. Halogenated hydrocarbons, halogenated fatty acids, etc. can be completely degraded after treatment with this technology. Chlorophenol, chlorobenzene, etc. generate CO2 and HCl.
Printing and dyeing wastewater entering the water body will cause serious environmental pollution, and some of them also contain carcinogens such as benzene rings, amine groups, and azo groups. This technology can be used for the treatment of dye wastewater.
Pesticide wastewater contains organic phosphorus pesticides, trichlorophenoxyacetic acid, DDVP, DTHP, DDT, trinitronitromethane, etc., which is highly toxic, difficult to degrade and easy to accumulate. Although the photocatalytic removal of pesticides by TiO2 can not make all the pollutants completely mineralized. However, it does not produce more toxic intermediate products, which cannot be compared with other methods. TiO2 photocatalysis has a good effect on the treatment of oily wastewater, surfactant-containing wastewater, landfill leachate, etc. In addition to organic substances, many inorganic substances also have photochemical activity on the surface of TiO2. Current research is more concentrated Treatment of chromium-containing wastewater, cyanide-containing wastewater and recovery of precious metals.
The photocatalytic degradation method can degrade trace organic matters and chlorination processes that cannot be removed by conventional processes in drinking water sources in a short time, and may produce organochlorine compounds that are extremely harmful to human health. TiO2 photocatalysis has a significant effect on the removal of these trace organic pollutants and precursor substances such as humic acids and phenols. The advantage of TiO2 photocatalytic technology in treating microbial pollution is that this technology can not only kill bacteria and viruses in drinking water and decompose them into CO2 and H2O, but also degrade the toxic component endotoxin released after the death of bacteria, thereby avoiding Side effects caused by treatment with silver-based and chlorine-based inorganic fungicides. TiO2 photocatalysis has the same inactivation effect on algae in water, and it also degrades toxins released by algae (such as microalgae toxin), which is not a function of any other sterilization method.
The wet air oxidation method uses air as an oxidant under high temperature and pressure to convert soluble substances in water, including inorganic and organic substances, through oxidation reactions to convert them into harmless new substances, or into forms that can be easily separated and excluded from water ( Gas or solid) to achieve the purpose of treatment.
The key of the wet oxidation method is to generate enough free radicals for the oxidation reaction. Although this method can degrade almost all organic matters, it also has its own disadvantages: due to the harsh reaction conditions, the requirements for equipment are high, the reaction equipment must be resistant to high temperature and pressure, and the fuel consumption is large, which is not suitable for large amounts of water.
Photochemical reaction is a chemical reaction under the action of light, using ozone or hydrogen peroxide as an oxidant, and oxidizing and decomposing pollutants under the irradiation of ultraviolet rays, thereby achieving sewage treatment. The main photochemical oxidation systems are: UV / H2O2 system, UV / O3 system and UV / O3 / H2O2 system.
The UV / H2O2 method can completely harmless the pollutants. The method has a stronger ability to remove organic matter than using hydrogen peroxide or ultraviolet alone. It is also a more economical option and can be assembled in different locations in a short period of time. But it is not suitable for treating soil, because ultraviolet rays cannot penetrate the soil particles. Light is easily blocked by precipitation and reduces UV transmittance. The pH value needs to be controlled to prevent precipitation of metal salts during the oxidation process. The UV / H2O2 system is mainly used for low-concentration wastewater with a concentration of 10-6, and is not suitable for high-intensity polluted wastewater. Using this method to remove trihalomethanes in drinking water can reduce the total organic carbon content in drinking water while removing chloroform, and further improve the water quality. The UV / H2O2 system is used to treat groundwater contaminated with tetrahalomethane, and the removal rate can reach 97.3% ~ 99%, which is equivalent to the cost of activated carbon treatment. In the UV / H2O2 system, each molecule of H2O2 can produce two molecules of hydroxyl groups, which has a better cost-benefit ratio than Fenton's reagent. Compared with other methods such as Fenton reagent and adsorption method, it can not only effectively remove organic pollutants in water, but also not cause secondary pollution, and does not require subsequent treatment.