Drilling wastewater is a kind of special industrial wastewater produced in the process of drilling operation. It contains toxic and harmful substances such as oil, heavy metal salts, refractory organic matter, sediment and bacteria. It has the characteristics of complexity, variability and dispersion. It is in a dark brown opaque colloidal state and has a strong pungent smell and putrid smell Ozone catalytic oxidation technology has become an efficient treatment technology for removing refractory organic pollutants from drilling wastewater because of its advantages of low energy consumption, high degradation efficiency and no secondary pollution Due to the variety of catalysts, different catalysts show different catalytic activities Therefore, in-depth research should be carried out from the characteristics of a specific catalyst and experimental research object or wastewater quality, so as to provide a valuable basis for wastewater treatment process.
Under the condition of low dosage of catalyst, the COD removal rate increases with the increase of catalyst With the increase of catalyst dosage, there will be larger specific surface area and more surface active sites in the reaction system, which can enhance the adsorption of catalyst on ozone and organic matter, produce more hydroxyl radicals and increase the COD removal rate However, when the dosage of catalyst is increased to 100 mg · L-1, the concentration of hydroxyl radicals produced in the reaction system will surge in a short time, and quenching will occur between too many hydroxyl radicals, resulting in the reduction of the total amount of hydroxyl radicals, so that the COD removal rate will decrease It can be seen that there is an optimal catalyst dosage of 50 mg · L-1.
The different pH of the reaction system will affect the production of total hydroxyl radical in the reaction system, resulting in different treatment effects of heterogeneous Cuihua ozonation When the catalyst dosage was 50 mg · L-1 and the pH was 5, 7, 9 and 11, the effect of Mn2O3 catalytic ozonation on COD removal rate was investigated.
The decomposition and solubility of ozone vary with temperature. In order to investigate the effect of reaction system temperature on catalytic ozonation of drilling wastewater, the COD removal rate of drilling wastewater was studied when the reaction system temperature is 10, 20, 30 and 40 ℃.
Under different reaction system temperatures, the COD removal rate of drilling wastewater by heterogeneous catalytic ozonation increases with the extension of reaction time, and increases first and then decreases with the increase of temperature When the reaction time is 25 min and the reaction system temperature is 10 ℃, 20 ℃, 30 ℃ and 40 ℃, the COD removal rates of drilling wastewater treated by heterogeneous catalytic ozonation are 49%, 59.1%, 56.1% and 55.1% respectively When the water temperature is 20 ℃, the treatment effect is the best.
When the temperature of the reaction system is too low, the decomposition rate of ozone and the activity of catalyst decrease, which affects the catalytic ozonation reaction The increase of the temperature of the reaction system is conducive to the reduction of the activation energy of the molecules involved in the catalytic ozone reaction, so as to accelerate the reaction rate of ozone oxidation. The decomposition rate of ozone molecules is also accelerated with the increase of water temperature, which is more conducive to the generation of hydroxyl radicals to degrade COD in drilling wastewater However, when the temperature of the reaction system is too high, ozone has been decomposed into oxygen at high temperature before the adsorption of the catalyst, and hydroxyl radicals with stronger oxidation can not be produced under the action of the catalyst, which affects the removal effect of organic matter by catalytic ozonation reaction Therefore, there is an optimal reaction temperature in heterogeneous catalytic ozonation It can be seen from the experiment that the optimal reaction temperature for heterogeneous catalytic ozonation of drilling wastewater is 20 ℃.
Effect of reaction time on COD removal rate
Under the condition of fixed ozone concentration and ozone flow, different reaction time, i.e. different ozone dosage, has different effects on the treatment of drilling wastewater by heterogeneous catalytic ozonation technology Under the optimum conditions obtained by single factor investigation: ozone flow rate of 0.1 L · min-1, catalyst dosage of 50 mg · L-1, reaction pH of 11, reaction temperature of 20 ℃, stirring intensity of 700 R · min-1, heterogeneous catalytic ozonation technology was used to treat drilling wastewater, COD values at different reaction time points were measured, and the optimum reaction time of heterogeneous catalytic ozonation treatment of drilling wastewater was investigated.
The optimal reaction time for treating drilling wastewater is of great significance to the practical application of heterogeneous catalytic ozonation technology. It is an important parameter for designing the treatment process of drilling wastewater by heterogeneous catalytic ozonation. The amount of reaction time determines the treatment capacity and residence time of the whole process It can be seen from table 2 that the ozone concentration in the liquid phase remains unchanged in the process of ozone oxidation, because the experiment is carried out under the condition of continuous aeration. Therefore, the best reaction time is under the condition of a certain concentration of ozone in the liquid phase As shown in Figure 5, with the increase of reaction time, the COD of drilling sewage decreases and the COD removal rate increases. When the oxidation reaction time is 40 min, the COD of drilling sewage decreases to 79.7 mg · L-1, and the COD removal rate reaches 85.3%. At 35 min and 40 min, the COD removal rates are 82.1% and 85.3% respectively, an increase of only 3.2% It shows that in the process of heterogeneous catalytic ozonation of drilling wastewater, the longer the oxidation reaction time, that is, the increase of ozone dosage, the higher the ozonation efficiency However, with the increase of time, COD decreases less and less per unit time, and ozone utilization efficiency decreases This is because the initial concentration of pollutants is high, oxidants are in close contact with pollutants, and some substances are oxidized into CO2. CO2 forms HCO-3 and CO2-3 in water, which are strong · Oh scavengers. The combined action of the two reduces · Oh, resulting in the reduction of COD removal efficiency; In addition, in the process of heterogeneous catalytic ozonation, macromolecular organics are oxidized into small molecules of acids, alcohols and other organics, while the reaction rate of ozone is slow. In the initial stage of the reaction, there are many catalyst surface active sites, the concentration of ozone decomposed into hydroxyl radicals is large, and the reduction range of COD is also large. With the extension of reaction time, the catalyst surface active sites are adsorbed by small molecules decomposed in the early stage, Then the COD removal rate decreases. Therefore, considering the removal efficiency and economic cost of heterogeneous catalytic ozonation treatment of drilling wastewater, the optimal reaction time of heterogeneous catalytic ozonation treatment of drilling wastewater is 35 min.
In the heterogeneous catalytic ozonation treatment of drilling wastewater, part of CO2 will be produced during the oxidative degradation of organic matter with ozone or hydroxyl radical. CO2 is dissolved in water to form CO2-3 or HCO-3. These two ions are inhibitors of hydroxyl radical. Their existence is bound to inhibit the decomposition and transformation of ozone to hydroxyl radical and affect the treatment effect of heterogeneous catalytic ozonation Therefore, the introduction of a substance that can remove CO2-3 and HCO-3 formed in water will strengthen the effect of heterogeneous catalytic ozonation on drilling wastewater treatment.
After the introduction of enhancer, the removal rate of COD in drilling wastewater is improved to a certain extent 15 min before the reaction, the improvement effect of COD removal rate was not very obvious, only increased slightly. At 20 and 25 min, the COD removal rate increased by 4.8% and 7.1% respectively Since the reaction between ozone or hydroxyl radical and organic matter requires a certain process, less CO2 is generated in the initial stage of the reaction, and less inhibitors of hydroxyl radical such as CO2-3 or HCO-3 are generated, it will not greatly affect the heterogeneous catalytic ozonation reaction in the initial stage After the oxidation reaction is carried out to a certain extent, some organics are completely oxidized and degraded into CO2 and H2O. The emergence of inhibitors of hydroxyl radicals will reduce the removal rate of COD in drilling wastewater treated by heterogeneous catalytic ozonation. The existence of enhancer Ca2 + can be well combined with CO2-3 or HCO-3 and removed, so as to further improve the removal effect of heterogeneous catalytic ozonation.
Compared with ozone alone, the addition of catalyst Mn2O3 significantly improves the COD removal rate of drilling wastewater When the dosage of Mn2O3 is 50 mg · L-1, the COD removal rate reaches 54.3%, which is 16.7% higher than that of ozone oxidation alone With the increase of Mn2O3 dosage, the COD removal rate increased first and then decreased PH has a great influence on heterogeneous catalytic ozonation. When pH is 5 and 11, the COD removal rates are 45.4% and 64.3% respectively When the system temperature is 20 ℃, the maximum COD removal rate is 59.1%, and the COD removal rate increases with the extension of reaction time.
Through orthogonal test, the primary and secondary relationship of influencing factors in heterogeneous catalytic ozonation treatment of drilling wastewater is as follows: catalyst dosage > reaction pH > reaction temperature > reaction time; The optimum process conditions were as follows: the dosage of catalyst was 50 mg · L-1, the reaction pH was 11, the reaction temperature was 25 ℃, and the reaction time was 35 min.
In the treatment of drilling wastewater by heterogeneous catalytic ozonation, the introduction of Ca2 + increased the COD removal rate by 7.1% Hydroxyl radical inhibitors CO2-3 or HCO-3 are produced in the composition of catalytic ozonation. The addition of Ca2 + can effectively consume CO2-3 or HCO-3, thus strengthening the effect of heterogeneous catalytic ozonation.
In the process of catalytic ozonation treatment of drilling wastewater, the material structure changes, its conjugated double bond is transformed into saturated alkanes, and the organic matter is mineralized and degraded.
After Mn2O3 is reused for 10 times, under the best process conditions, the COD removal rate of drilling wastewater reaches 81.6%, which is not much different from the COD removal rate of 82.1% used for the first time; After 15 minutes of reaction, the dissolution amount of manganese ions reached a stable level and was less than 3 mg · L-1, indicating that the catalyst had strong stability and reusability, could strengthen heterogeneous catalytic ozonation reaction in a long time, and the catalyst had durability and stability.
