Gaze et al. call the oxidation process with hydroxyl radical as the main oxidant in water treatment process as AOPs process, and when it is used in water treatment, it is called AOP method. Typical homogeneous AOPs processes include O3/UV, O3/H2O2, UV/H2O2, H2O2/Fe2+ (Fenton reagent) and so on. Ozone treatment at high pH can also be regarded as an AOPs process, and some photocatalytic oxidation is also an AOP process.
The most remarkable feature of advanced oxidation method is that hydroxyl radical is used as the main oxidant to react with organic substances, and the organic radicals generated in the reaction can continue to participate in the chain reaction of HO, or after generating organic peroxide radicals, further undergo oxidative decomposition reaction until they are degraded into final products CO2 and H2O, so as to achieve the purpose of oxidative decomposition of organic substances. Compared with other traditional water treatment methods, advanced oxidation method has the following characteristics: it produces a large number of very active hydroxyl radicals, and its oxidation capacity (2.80v) is second only to fluorine (2.87). As an intermediate product of the reaction, it can induce the later chain reaction, and the reaction rate constants of hydroxyl radical and different organic compounds are very different. When there are many pollutants in the water, one substance will not degrade and the other substance will remain basically unchanged; Ho can not selectively react directly with pollutants in wastewater to degrade it into carbon dioxide, water and harmless substances, and will not produce secondary pollution; Because of poor oxidation ability and selective reaction, ordinary chemical oxidation method can not directly achieve the purpose of completely removing organic matter and reducing TOC and COD, while advanced oxidation method basically does not have this problem. The intermediate products in the oxidation process can continue to react with hydroxyl radicals until they are completely oxidized into carbon dioxide and water, so as to completely remove TOC and COD. Because it is a physical and chemical process, it is easy to control, meets the treatment needs, and even reduces 10-9 pollutants; Compared with the common chemical oxidation method, the advanced oxidation method has fast reaction speed, and the general reaction rate constant is greater than109 mol-1ls-1,which can meet the treatment requirements in a short time. It can be used as a separate treatment or combined with other treatment processes, such as pretreatment of biochemical treatment, which can reduce the treatment cost.
Previous research results have confirmed the practicability of advanced oxidation method in wastewater treatment, and showed a broad treatment prospect in the field of water treatment. In fact, in foreign countries, especially in Europe, advanced oxidation has been widely used in some industrial processes that are insensitive to economic costs. In recent years, China has also adopted UV/H2O2 process to treat papermaking wastewater, and made remarkable progress. The research of O3/UV system for waste gas treatment has begun. In recent years, the application field of advanced oxidation process has been extended to persistent pollutants that are difficult to degrade in water. In addition, the research on new reactor, impinging stream reactor and advanced oxidation coupling required by advanced oxidation process is also being carried out to further strengthen the degradation of wastewater and improve its treatment effect. Advanced oxidation process has also been applied to urban sewage disinfection, hospital sewage treatment and field sewage treatment. With the deepening of advanced oxidation research, it is expected to be widely used in more fields in the near future, and new theories and technologies will also be produced. Application of advanced oxidation technology in pesticide wastewater treatment Update time:1-7141Author: Zhang Yingmin, Li Kaiming, Zhou Weijian, Wang Wei, Zhang Zhaoyun, Jia Yan Abstract: Advanced oxidation technology for pesticide wastewater treatment, including photocatalysis, Fenton method and ozone (O3) oxidation, was summarized. Combined with the progress of pesticide wastewater treatment methods, the achievements and existing problems of various advanced oxidation methods in application are introduced, and the application of advanced oxidation methods in pesticide wastewater treatment is prospected. Keywords: advanced oxidation; Pesticides; In the wastewater treatment of modern agricultural production, pesticides play a very important role in improving crop yield and reducing pests and diseases. China is a big producer of pesticides. Since 200 1, the annual output of pesticides has increased by no less than 5%. In 2007, the national pesticide output reached 654.38+0.73 million t, ranking 654.38+0 in the world. Hundreds of millions of tons of pesticide production wastewater are discharged every year in China, and the treatment rate is less than 10%. Because of the high concentration of organic matter in pesticide wastewater, the pollutants are complex, difficult to biodegrade and toxic, which causes great harm to the environment [1]. At present, the main treatment methods of pesticide wastewater are physical methods (adsorption, stripping, gravity separation, etc. ), biochemical method (aerobic biological treatment, anaerobic biological treatment) and chemical method (incineration, advanced oxidation, etc. ) [2]. Physical methods do not completely remove pollutants, but only change the existing forms and ways of pollutants; The application of biochemical methods in China started very early. In 1980s, some scholars used microorganisms to degrade organophosphorus pesticides [3], but the biochemical method still has the problems of long treatment time and low efficiency, which limits its further development. Advanced oxidation method in chemical method can produce hydroxyl radical (OH) with strong oxidation, and finally oxidize organic pollutants into carbon dioxide, water and mineral salts, which has the advantages of short treatment time and no selectivity [4] and has developed rapidly in recent years. Commonly used advanced oxidation technologies include photocatalysis, Fenton process, ozone (O3) oxidation, catalytic wet oxidation (CWAO) and so on. These technologies can be used alone or in combination, and can also be used as pretreatment processes of pesticide wastewater. This paper briefly introduces the advanced oxidation treatment technology of pesticide wastewater which is widely used at present. 1 photocatalytic oxidation The chemical oxidation reaction under the action of light radiation can be called photocatalytic oxidation. Photochemical reactions require the use of various artificial light sources or natural light. Catalysts are very important substances in photocatalytic reaction, and most of them are semiconductor materials. Common photocatalysts are TiO2, ZnO, SnO2 and Fe2O3 [5]. Photocatalytic degradation of pesticide wastewater has been studied. JARNUZI[6] and others used suspended TiO2 _ 2 as catalyst to treat pesticide PCP by photocatalytic oxidation, and deduced the steps of photocatalytic degradation of PCP. Ge Fei et al. [7] used TiO2 _ 2 membrane shallow pool reactor to treat methamidophos pesticide wastewater. The results showed that the COD removal rate of methamidophos pesticide wastewater reached 85.64% after biochemical treatment, which reached the first-class standard in the national integrated wastewater discharge standard, while the organic phosphorus removal rate reached 65,438+000%, showing the good treatment ability of photocatalytic oxidation reaction. Photocatalytic degradation of pesticide wastewater has the advantages of short degradation time and high efficiency, but it also has the disadvantage of low utilization rate of light source. Photocatalytic oxidation technology combined with other advanced oxidation technologies can improve treatment efficiency and strengthen oxidation capacity, which has attracted researchers' attention in recent years. Jing Guohua and others [8] used UV/Fenton technology to treat triazophos pesticide wastewater. The results show that when Fe2+∶H2O2 is 1∶20, the photolysis effect is good, the reaction rate constant is 0.03min- 1, and the COD removal rate can reach 90%. Peng [9] and others used UV/TiO _ 2/Fenton method to degrade trichlorfon pesticide wastewater. When the pesticide concentration of trichlorfon is 0. 1 mmol/L, the mass concentration of TiO _ 2 is 2g/L, the dosage of Fe3+ is 0. 10 mmol/L, the dosage of H2O2 is 2mmol/L, and the illumination time is 2h, the pesticide of trichlorfon is degraded. In the acidic environment of Fenton oxidation, Fenton reagent can produce highly active OH with oxidation potential as high as 2.8V, which can react with organic compounds for electrophilic addition, dehydrogenation, substitution and electron transfer, thus degrading organic pollutants. Yang Xinping [10] and others used Fenton reagent to treat organochlorine pesticide wastewater with COD of1.29×104 mg/L. The removal rates of COD and chromaticity were 47.8% and 84.4% respectively. Zhu [1 1] and others used Fenton method to treat pesticide wastewater. The dosage of H2O2 in the experiment is 50 mol/L, and the ratio of Fe2+∶H2O2 is 1∶ 10. After treatment for 2 hours, the removal rate of COD and chroma can reach 68.07% and 90.65438, respectively. Fenton reaction also has disadvantages [12]. First of all, it is only carried out under acidic conditions (pH