Sulfate radicals mediated oxidation of amoxicillin: Optimization of key parameters.

The lack of selectivity of hydroxyl radical species used in Advanced Oxidation Processes (AOPs) to eliminate organic pollutants has swayed the investigation towards more selective oxidizing agents. In the current work, we investigated the oxidation of amoxicillin, the most commonly used antibiotic worldwide, by sulfate radical species generated from the activation of Persulfate (PS) and Peroxymonosulfate (PMS-Oxone®). The optimization of this oxidation using the box-behnken experimental design was conducted. From this study, it was shown that the PS/Fe2+ mixture was capable of dose-dependently inducing a significant amount of degradation of the Amoxicillin compound with a higher degradation rate detected with higher amounts of PS and Fe2+. Sulfate radicals generated from the "Oxidant-Catalyst" mixture were shown to be the predominant oxidizing species involved in this process with the second order rate constant of Amoxicillin degradation found to be equal to 2.79 × 109 M-1. S-1. In the optimization procedure, the box-benhken methodology allowed us to assess the impact of various factors and their interaction on COD removal efficiency (mineralization rate), which is the objective response needed to be optimized. The variables considered were PS as the oxidant, Fe2+ as the catalyst, and pH. It was concluded that among the various parameters tested, pH was the most influential as a decrease in pH values was shown to be positively correlated with a significant increase in COD removal rate. Hence, the highest mineralization rate of Amoxicillin (≈76.10% COD removal) was achieved with PS = 300 µM, Fe2+ = 250 µM, and a pH value of 3.

Oxidative degradation of pentachlorophenol by permanganate for ISCO application.

Potassium permanganate (KMnO4) has been an effective technology for the in situ chemical oxidation (ISCO) of many organic compounds including chlorinated alkanes and alkenes, but it has rarely been applied for oxidizing aromatic organochlorines. This study confirms the ability of permanganate to oxidize an aromatic chlorinated compound, pentachlorophenol (PCP), in an efficient manner at neutral pH. The rate of the reaction between KMnO4 and PCP was calculated and the results indicated that the reaction between PCP and permanganate is relatively fast with a second-order rate constant k″ ∼ 30 M-1 s-1. Besides the kinetic aspect, the authors identified the main reaction by-products, and proposed a possible reaction mechanism scheme. The general pathway shows the formation of chlorinated intermediates, and ultimately, the complete mineralization to chloride, water, and CO2 confirmed by total organic carbon and chloride measurement in solution. Flow-through column experiments, consisting of flushing a PCP-contaminated sandy or natural soil with oxidant, showed the good ability of permanganate to eliminate the pollutant. After 24 h of treatment, 77% and 56% of PCP abatement were obtained for sandy and natural soil, respectively. These findings show the high potential of permanganate for the in situ remediation of aromatic organochlorine contaminated soils.

Fenton-like oxidation of 2,4,6-trinitrotoluene using different iron minerals.

Degradation of 2,4,6-trinitrotoluene (TNT) was investigated in presence of different oxidants (Fenton's reagent, sodium persulfate, peroxymonosulfate and potassium permanganate) and different iron minerals (ferrihydrite, hematite, goethite, lepidocrocite, magnetite and pyrite) either in aqueous solution or in soil slurry systems. Fenton's reagent was the only oxidant able to degrade TNT in solution (k(app)=0.0348 min(-1)). When using iron oxide as heterogeneous catalyst at pH 3, specific reaction rate constants per surface area were k(surf)=1.47.10(-3) L min(-1) m(-2) and k(surf)=0.177 L min(-1) m(-2) for magnetite and pyrite, respectively while ferric iron minerals were inefficient for TNT degradation. The major asset of iron mineral catalyzed Fenton-like treatment has been the complete oxidation of the pollutant avoiding the accumulation of possible toxic by-products. In soil slurry systems, 38% abatement of the initial TNT concentration (2 g/kg) was reached after 24 h treatment time at neutral pH. Rate limiting steps were the availability of soluble iron at neutral pH together with desorption of the TNT fraction sorbed on the clay mineral surfaces.