Impact of humic acid on the degradation of levofloxacin by aqueous permanganate: Kinetics and mechanism

Abstract

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.

Insights into the Electron-Transfer Mechanism of Permanganate Activation by Graphite for Enhanced Oxidation of Sulfamethoxazole

“…Humic acid (HA) is a typical natural organic matter in real waters. In a previous study, HA was generally considered to have a positive role in the oxidation of organic contaminants in the KMnO 4 system. ,− In this study, HA can slightly accelerate the oxidation of SMX by KMnO 4 , and effects become more obvious with the increase of HA concentration (Figure a). Jiang et al revealed that HA, as a ligand, can stabilize intermediate Mn species formed by the reaction to enhance oxidation of triclosan by KMnO 4 …”

Role of pyrophosphate on the degradation of sulfamethoxazole by permanganate combined with different reductants: Positive or negative

“…Taking KMnO 4 /Na 2 S 2 O 3 system as an example, in order to explore the role of reactive radical species (e.g., , , ), DMPO was used to trap these plausible radicals. As shown in Figure , in the absence of Na 2 S 2 O 3 , DMPO was directly oxidized to DMPO‐OH by permanganate though there is no generated, which is consistent with the literature (Xu et al, ; Xu, Dong, Li, & Qiang, ). The signal of DMPO‐OH was largely stifled when Na 2 S 2 O 3 was added since Na 2 S 2 O 3 could consume KMnO 4 , but there was no sign of sulfur‐containing radicals or hydroxyl radical.…”

Degradation of Diclofenac in Urine by Electro-Permanganate Process Driven by Microbial Fuel Cells

“…As for HA and Cl − , at low concentrations, they might compete with electrons in cathodes, resulting in the reduced generation of RMnS, whereas at higher concentrations they might react with RMnS to generate other reactive species (e.g., • OH, Cl • , etc.) to accelerate the MFC-PM process [24,48]. Additionally, the removal rate of DCF in urea solution was also evaluated to further assess the applicability of the MFC-PM process.…”