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Phsicochemical Treatment of Hazardous Wastes - Chapter 8

Ba phản ứng chiếm ưu thế trong tia cực tím (UV) / quy trình xử lý ozone (O3) có hiệu quả phân hủy các chất ô nhiễm hữu cơ là photolysis, ozonation, và phản ứng của các gốc hydroxyl. Thế hệ của các gốc hydroxyl là điều cần thiết trong quá trình oxy hóa này vì nó là phản ứng giữa các gốc tự do và các hợp chất hữu cơ mà cuối cùng có thể phá hủy các chất ô nhiễm hữu cơ. Các tham số vật lý, chẳng hạn như nhiệt độ, pH, hợp chất ban đầu, và. | 8_ Ultraviolet Ozone 8.1 Introduction Three dominant reactions during ultraviolet UV ozone O3 treatment processes that effectively decompose organic pollutants are photolysis ozonation and reactions of hydroxyl radicals. The generation of hydroxyl radicals is essential in this oxidation process as it is the reaction between these radicals and organic compounds that can ultimately destroy organic pollutants. Physical parameters such as temperature pH initial compound and ozone concentrations UV intensity and ozone partial pressure will also have considerable effects on the kinetic rate constants and removal efficiency of any compound. The UV ozone process is commonly used to degrade toxic organic compounds often found in surface and groundwater. Many of these compounds originate from the chemical petrochemical pesticide and herbicide industries. The molecular structure of organic pollutants to be oxidized has a significant impact on kinetic rate constants and the removal efficiency of the compound. Parent compounds can be partially oxidized to form by-products during oxidation treatment. These intermediates can further react with hydroxyl radicals creating a scavenging effect that often reduces the degradation rates of parent compounds. 8.2 Decomposition Kinetics of UV Ozone in Aqueous Solution Ozonation processes are rather complex due to the high instability of ozone in aqueous solutions. Ozone absorbs UV photons with the maximal absorption at 253.7 nm. The decomposition of ozone under UV radiation typically occurs through three reactions direct photolysis direct ozonation and reactions between hydroxyl radicals and hydrogen peroxide as shown in the following reactions 2004 by CRC Press LLC Photolysis slow hv O3 H2O S H2O2 O2 8.1 hv H2O2 S 2OH- 8.2 Ozonation HO2- O3 S HO2- O3- 8.3 Hydroxyl radical reactions H2O2 OH- S HO2- H2O 8.4 HO2- OH- S HO2- OH- 8.5 In a gaseous phase enriched with water vapor the mechanism of photolysis