Photocatalytic Degradation of Controlled Drugs: Methamphetamine and Codeine
Date Issued
2015
Date
2015
Author(s)
Kuo, Chin-Sheng
Abstract
Methamphetamine (MAT) and codeine which belong controlled drugs are legally used in prescription and often illegally abused for other purpose. They are found in domestic wastewater treatment plants (WWTPs) influents and effluents as well as surface waters in many regions, elevating concerns about their potential impact. These two drugs are not effectively removed by conventional processes of WWTPs. To contemplate advanced treatment, this study investigates the photocatalytic degradation of MAT and codeine by UV-illuminated TiO2. The degradation kinetics and mechanism of these two different drugs by TiO2 under low-wattage UV illumination (9 W with maximum output at 365 nm) were studied. Experimental parameters were varied including the TiO2 loading, initial substance concentration, and pH. During treatment, these two controlled drugs and their intermediates were identified and tracked by HPLC-MS/MS, along with TOC and IC measurements to determine the mineralization extent. In contact with 0.1 g/L of TiO2 under illumination at pH 7, an entire spike amount of 100 μg/L of MAT was completely removed in 3 min and the same initial concentration of codeine was also eliminated in 3 min. The degradation of MAT and codeine followed an apparent first-order kinetics. Near complete mineralization of MAT and codeine from 10 mg/L were achieved in 180 min and in 90 min, respectively, with 0.1 g/L of TiO2 at pH 5, by which the organic nitrogen was converted to NH4+ and NO3-. 76% and 21% of organic nitrogen in MAT was converted to NH4+ and NO3-, respectively. 74% of codeine nitrogen constituent was converted to NH4+ and 22% to NO3-. MAT intermediates include authenticated p-hydroxymethamphetamine (p-OHMAT) and eight tentatively identified compounds. Codeine intermediates include authenticated morphine and five tentatively identified compounds. Based on identified intermediates, two degradation pathways of MAT were deduced that involved cleavage of the side chain as well as hydroxylation of the MAT compound. Also, two degradation pathways of codeine were proposed including one involving ipso-substitution followed by cleavage of the aromatic ring and another involving repeated hydroxylation of the codeine molecule followed by fragmentation of the hydroxylated intermediates. These all degradation pathways occurred via non-selective attacks by hydroxyl radicals generated by irradiated TiO2 that led to continual fragmentation and eventual mineralization. The photocatalytic UV/TiO2 process shows promise in arresting the release of these two controlled drugs and their intermediate derivatives into the water environment.
Subjects
Photocatalysis
Illicit drugs
Intermediates
Degradation mechanism
Kinetics
Mineralization
Type
thesis
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