Departamento de Química Inorgánica, Facultad de Ciencias, Universidad de Granada, 18071 Granada, Spain.
Water Res. 2011 Jan;45(1):393-403. doi: 10.1016/j.watres.2010.08.015. Epub 2010 Sep 28.
The objective of this study was to analyze the efficacy of ultraviolet (UV) radiation in the direct photodegradation of nitroimidazoles. For this purpose, i) a kinetic study was performed, determining the quantum yield of the process; and ii) the influence of the different operational variables was analyzed (initial concentration of antibiotic, pH, presence of natural organic matter compounds, and chemical composition of water), and the time course of total organic carbon (TOC) concentration and toxicity during nitroimidazole photodegradation was studied. The very low quantum yields obtained for the four nitroimidazoles are responsible for the low efficacy of the quantum process during direct photon absorption in nitroimidazole phototransformation. The R(254) values obtained show that the dose habitually used for water disinfection is not sufficient to remove this type of pharmaceutical; therefore, higher doses of UV irradiation or longer exposure times are required for their removal. The time course of TOC and toxicity during direct photodegradation (in both ultrapure and real water) shows that oxidation by-products are not oxidized to CO(2) to the desired extent, generating oxidation by-products that are more toxic than the initial product. The concentration of nitroimidazoles has a major effect on their photodegradation rate. The study of the influence of pH on the values of parameters ɛ (molar absorption coefficient) and k'(E) (photodegradation rate constant) showed no general trend in the behavior of nitroimidazoles as a function of the solution pH. The components of natural organic matter, gallic acid (GAL), tannic acid (TAN) and humic acid (HUM), may act as promoters and/or inhibitors of OH· radicals via photoproduction of H(2)O(2). The effect of GAL on the metronidazole (MNZ) degradation rate markedly differed from that of TAN or HUM, with a higher rate at low GAL concentrations. Differences in MNZ degradation rate among waters with different chemical composition are not very marked, although the rate is slightly lower in wastewaters, mainly due to the UV radiation filter effect of this type of water.
本研究的目的是分析紫外线（UV）辐射在硝基咪唑类药物直接光降解中的效果。为此，i）进行了动力学研究，确定了该过程的量子产率；ii）分析了不同操作变量的影响（抗生素的初始浓度、pH 值、天然有机物化合物的存在以及水的化学成分），并研究了硝基咪唑光降解过程中总有机碳（TOC）浓度和毒性的时间过程。四种硝基咪唑的量子产率非常低，这导致在直接光子吸收过程中，量子过程对硝基咪唑光转化的效果很低。获得的 R（254）值表明，用于水消毒的常规剂量不足以去除此类药物；因此，需要更高剂量的紫外线照射或更长的暴露时间来去除它们。直接光降解过程中 TOC 和毒性的时间过程（在超纯水和实际水中）表明，氧化副产物没有被氧化到 CO（2）的所需程度，产生的氧化副产物比初始产物更具毒性。硝基咪唑的浓度对其光降解速率有重大影响。研究 pH 值对参数ɛ（摩尔吸光系数）和 k'（E）（光降解速率常数）值的影响时，发现硝基咪唑的行为没有随溶液 pH 值的一般趋势。天然有机物的成分，没食子酸（GAL）、单宁酸（TAN）和腐殖酸（HUM），可以通过光产生 H（2）O（2）作为 OH·自由基的促进剂和/或抑制剂。GAL 对甲硝唑（MNZ）降解速率的影响明显不同于 TAN 或 HUM，在低 GAL 浓度下降解速率更高。不同化学成分的水中 MNZ 降解速率的差异并不十分显著，尽管由于这种水的紫外线辐射过滤效应，废水的降解速率略低。
