Advanced Oxidation Processes for Treatment of Harmful Chemicals

First: Shi Wei and Chia-Sen were born in 1974 in the Department of Environmental Engineering of East China University of Science and Technology. In the 1st degree, 65% of the total municipal wastewater and industrial wastewater is currently treated biologically, while more than 95% of urban sewage is biologically treated. . Biological methods are very economical and effective for the treatment of easily degradable organics, but they have poor treatment of refractory chemical substances. In 1987 Glaze et al. proposed the oxidation oxidation process (AOP method): that is, the oxidation process using hydroxyl radical as the main oxidant in the water treatment process. The oxidation potential of hydroxyl radicals is 3.06 volts, which is a very strong and non-selective oxidant, and it has the advantages of high processing efficiency and thorough oxidation, which has increasingly attracted people's attention.

In this study, 2,4-dichlorophenol and aniline were used as target compounds. The effects of common chemical oxidation and A0P methods were tested and compared. The influence of various factors on the treatment efficiency was examined, and the actual sewage treatment effects were also studied. verification.

2. The device is a closed cylindrical plexiglass reactor with a height of 27cm and a diameter of 5cm. A round hole is left in the center of the reactor for the purpose of inserting a UV lamp.

2. Aeration head 3. Ultraviolet lamp 4. Sampling port 5. Exhaust port 6. Reactor from, visible: H22 and 03 alone (PH = 2.5) treatment 2,4-dichlorophenol and aniline oxidation removal rate are It can also be seen from the figure below that the A0P method has different treatment effects for different target compounds.

From the above, it can be seen that the oxidation rate and oxidation efficiency of the COD in water by the immersion oxidation method 03/UV are all in the ordinary oxidation method 03(11)11=2.5). This indicates that the human 0 method has the advantage of having a degree of mineralization of the COD degradation curve when treating aniline with different oxidation time of pollutants/min.

But at the same time, it should be noted that the oxidative decomposition curves of the comparative compounds show that when the A0P process treats harmful chemicals in water, the oxidative decomposition rate of the target compound is much faster than the degree of mineralization, ie, the oxidative decomposition. There are a large number of intermediate products in the process. Therefore, for the actual wastewater treatment, a longer oxidation reaction time is required to achieve a better COD removal rate.

3.3 Factors Influencing the A0P Process Treatment Effect To improve the efficiency of the A0P process in dealing with harmful chemical substances, this study investigated the initial concentration, pH, HCOr, No r, SS and other impact factors using the 3/UV-aniline reaction system. The effect on the treatment effect.

3.3.1 Influence of initial concentration The reaction of organic matter decomposition by AOP method is a first-order reaction, and the reaction rate should not be related to the initial concentration. However, it can be seen that with the increase of the initial concentration of aniline, the reaction rate constant decreases obviously, which is due to the influence of certain oxidation intermediates.

3.3.2 Influence of pH During the reaction process, the pH value is continuously decreased due to the formation of acid species. Therefore, it is necessary to study the effect of pH on the reaction - on the 5th) Initial concentration of aniline Hg Zhao aniline / mgL1 3/ UV (pH = 7.3) process reaction rate constant K with the initial concentration of the curve gradually decreased. When the concentration of HCOr is lOOOmgL-1, the reaction rate constant decreases by 33.6%. This shows that 1:03 has a certain trapping effect on the hydroxyl group. Because the oxidation process in the A0P method will generate a large amount of HCOr and C32-, it will increase with the initial concentration. During the reaction, 11 (:3 and (increase in the amount of 32), the oxidation rate will gradually slow down, which is consistent with the previous concentration effect.

Because -NH2 may be oxidized to NOr during the reaction, it is necessary to study the effect of N3.

3 and 03/UV reaction rate constants change with pH value. It can be seen that the 03/UV process has a higher reaction rate than the 03 process at the same pH value; regardless of the 3 process or 3/UV process, the reaction rate is 8 at pH 8. With the increase of pH value, the reaction rate will decrease slightly when PH>8, that is, the optimal pH value of 03, 3/UV process is 8 ==. This is mainly because the hydroxyl group increases with the increase of pH. The rate of production increases and the relative amounts of HC3 and C32 produced during the reaction also gradually increase. Both hc3- and co32- are hydroxyl-scavenging agents. The interaction of these two factors causes the reaction rate to increase with the increase of pH. Increase first and then decrease.

Since there will always be a certain amount of HCOr in the actual wastewater and HCOr will also be generated during the reaction, it is necessary to consider the effect of HCOr. The primary reaction rate constant of 8 aniline was reduced by 11% to 15%, indicating that NOr has a certain effect on aniline oxidation in the 03/UV process.

3.3.5 Influence of SS Because there is always a large amount of suspended solids (SS) in the actual wastewater, in order to apply the AOP method to practice, changes in the SS concentration must be considered. As can be seen from the figure, the reaction rate increases rapidly with the increase of the sludge amount when the activated sludge is added to less than 20 mg IT1. When the sludge concentration was 20 mgL-1, the reaction rate was the maximum, and when the sludge concentration was greater than this value, the reaction rate gradually slowed as the concentration of activated sludge continued to increase. This is due to the fact that activated sludge has both absorption and influence on the absorption of organic matter by ultraviolet light. Adsorption can accelerate the reaction. The influence of organic matter on the absorption of ultraviolet light can slow the reaction rate. The interaction of two factors leads to the concentration of activated sludge. Ascending enthalpy rises, and the reaction rate increases first and then decreases.

3.3.6 Non-selective In actual wastewater, in addition to the target compounds, there are often many other readily degradable organics. Whether or not the existence of these substances will affect the oxidation and decomposition of target compounds by the A0P method is an important factor affecting whether the A0P method can be applied to actual wastewater treatment. For this reason, a certain amount of sodium acetate is added to the solution containing the target compound in this experiment. Study, the result is shown as 1.

o = 50 mgL-1 pH = 7.3 From 1 shows that even when adding 4 times the sodium acetate of the target compound, the decomposition curve of aniline is almost unchanged, which proves that the A0P method does not have the characteristics of selectivity. This shows that the A0P method is more advantageous for the treatment of complex waste water.

3.4 Practical application Dilute the aniline solution with the domestic wastewater effluent and dilute the aniline solution with distilled water to make a simulated wastewater with a concentration of 50 mgL-1. Both were decomposed with a 3/UV (PH = 7.3) process and the residual aniline and residual COD were measured. The results are shown in Figs.

The degradation curve of the prepared aniline solution PH=7.3 can be seen from 2,13. Regardless of the target compound itself or COD in water, the decomposition rate of the simulated wastewater prepared with domestic wastewater is less than the decomposition rate of the pure solution. This may be caused by a large amount of time/min 3 of HC03 such as HC03 which has a large amount of time/min 3 of degradation of the aniline solution with 3/UV degradation, or other substances that affect the progress of the reaction. Therefore, in the actual treatment, the wastewater needs to be pretreated to improve the processing efficiency of the AOP method.

4 Conclusions Compared with common chemical oxidation methods, AOP has the advantages of fast reaction rate, good oxidative decomposition efficiency and thorough oxidation, but for different compounds, the efficiency of AOP oxidation treatment is not the same.

The rate of decomposition of pollutants by the AOP method is greatly affected by the pH value. At pH 8, the reaction rate decreased with increasing pH. HCOr in water can trap hydroxyl radicals and inhibit the oxidation reaction. However, NOr and Cl have no effect on the AOP oxidation reaction.

The AOP method has no oxidative selectivity. Even if the concentrations of other organic compounds are relatively high, the oxidation rate of the target compound remains basically unchanged, and when the adsorptive suspended solids (SS) are present in the wastewater, the reaction rate can be increased. It shows that the AOP method has practical value in dealing with trace amounts of harmful chemicals.

When the AOP method is used to treat actual waste water, due to the effect of hydroxyl radical trapping agents such as HC03 in the waste water and other factors, the oxidation efficiency is lower than when the single-component artificial water distribution is handled, and attention needs to be paid.