自由餘氯存在下之氯胺酮光降解

Abstract

Ketamine, along with many other pharmaceutical residues found in natural water environments pose potential risk to ecosystem and to public health. This work aimed to establish a kinetic model and to investigate the degradation mechanism of ketamine under solar irradiation in the presence of free available chlorines (FAC), namely FAC photolysis. To my knowledge, this is the first work identifying reactive species other than HO• and ozone during FAC photolysis, and the first effort to develop a kinetic model describing this phenomenon. Compared with the chlorination and natural sunlight photolysis alone, FAC photolysis effectively enhanced the degradation efficiency of ketamine. FAC photolysis can be described with the shifting order-type kinetic, and the model combing two shifting order equations was developed to successfully predict the reaction rates for varying ketamine (25 - 500 μg/L) and FAC concentrations (0.05 - 3 mg Cl2/L) with 13% deviation from the real experimental values at pH 7.

HO• and ozone were found to be the dominant reactants in the presence of FAC; HO• contributed 69 to 83% of ketamine removal in initial 10 minutes of the FAC photolysis at pH 7. At lower pH (higher HOCl/ OCl−), more HO• and O3 were produced enhancing the reaction rates, and resulting in higher mineralization (67% of TOC removal at pH 4; 37% TOC removal at pH 10). Similar results were obtained with five other pharmaceuticals (atenolol, metoprolol, pentoxifylline, gemfibrozil and ibuprofen) investigated. Within 30 minutes of the reaction time, each compound was >90% removed. As FAC residue decreased and entirely depleted, other reactive chlorine species (RCSs), were found to dominate the further ketamine removal at all pH values tested (pH 3-11), and this phenomena was compound dependent. It is hypothesized that these RCSs can react with primary, secondary amine and ether functional groups of ketamine, atenolol, metoprolol and gemfibrozil. FAC photolysis transformation byproducts include DNK, HK, P2, P3, P4. Other byproducts including [M+H+] =216, 220, 258, 275, 326 and 345 were found during FAC photolysis. The rate and amount of these byproducts formed significantly depend on pH values and resulted in different toxicity. Compared with natural photolysis, FAC photolysis undergoes different degradation pathways, resulted in different byproducts (only P2, P3, HK, NK and DNK were found at both systems), different toxicity, and more mineralization. This phenomenon has the potential to be developed into an engineering system; however, the increase of toxicity needs to be evaluated and considered.