Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 18 Shuang-qing Road, Beijing 100085, China.
Beijing Municipal Research Institute of Environmental Protection, 59 Beiyingfang Middle Street, Beijing 100037, China.
Water Res. 2017 Oct 15;123:67-74. doi: 10.1016/j.watres.2017.06.037. Epub 2017 Jun 14.
Levofloxacin (LF) is a frequently detected fluoroquinolone in surface water, and permanganate (MnO) is a commonly used oxidant in drinking water treatment. This study investigated the impact of humic acid (HA) on LF degradation by aqueous MnO from both kinetic and mechanistic aspects. In the absence of HA, the second-order rate constant (k) of LF degradation by MnO was determined to be 3.9 M s at pH 7.5, which increased with decreasing pH. In the presence of HA, the pseudo-first-order rate constant (k) of LF degradation at pH 7.5 was significantly increased by 3.8- and 2.8-fold at [HA]:[KMnO] (mass ratio) = 0.5 and 1, respectively. Secondary oxidant scavenging and electron paramagnetic resonance tests indicated that HA could form a complex with Mn(III), a strongly oxidative intermediate produced in the reaction of MnO with HA, to induce the successive formation of superoxide radicals (O) and hydroxyl radicals (OH). The resulting OH primarily contributed to the accelerated LF degradation, and the complex [HA-Mn(III)] could account for the rest of acceleration. The degradation of LF and its byproducts during MnO oxidation was mainly through hydroxylation, dehydrogenation and carboxylation, and the presence of HA led to a stronger destruction of LF. This study helps better understand the degradation of organic micropollutants by MnO in drinking water treatment.
左氧氟沙星（LF）是地表水中经常检测到的氟喹诺酮类药物，而过锰酸钾（MnO）是饮用水处理中常用的氧化剂。本研究从动力学和机理方面研究了腐殖酸（HA）对水中 MnO 降解 LF 的影响。在不存在 HA 的情况下，MnO 降解 LF 的二级速率常数（k）在 pH 7.5 时确定为 3.9 M s，随着 pH 值的降低而增加。在存在 HA 的情况下，pH 7.5 时 LF 降解的拟一级速率常数（k）分别在 [HA]：[KMnO]（质量比）= 0.5 和 1 时显著增加了 3.8 倍和 2.8 倍。次氧化剂清除和电子顺磁共振测试表明，HA 可以与 Mn(III)形成配合物，Mn(III)是 MnO 与 HA 反应中产生的强氧化性中间体，从而诱导超氧自由基（O）和羟基自由基（OH）的连续形成。由此产生的 OH 主要有助于加速 LF 的降解，而配合物 [HA-Mn(III)] 可以解释其余的加速作用。MnO 氧化过程中 LF 和其副产物的降解主要通过羟化、脱氢和羧化，HA 的存在导致 LF 的破坏更强。本研究有助于更好地理解饮用水处理中 MnO 对有机微量污染物的降解。
