Treatment of ammunition wastewater by the combined Fe 0 /air and Fenton process (1 st Fe 0 /air-Fenton-2 nd Fe 0 /air)

Degradation and fate of 2,4-dinitroanisole (DNAN) and its intermediates treated with Mg/Cu bimetal: Surface examination with XAS, DFT, and LDI-MS

A novel Mg-based bimetal reagent (Mg/Cu) was used as an enhanced reductive system to degrade insensitive munition 2,4-dinitroanisole (DNAN), a contaminant found in energetic-laden waste. Degradation of DNAN was significantly impacted by dissolved oxygen and studied in anoxic and oxic bimetal systems (i.e., purging with N₂, air, or O₂ gas). Degradation occurred through sequential nitroreduction: first one nitro group was reduced (ortho or para) to form short-lived intermediates 2-amino-4-nitroanisole or 4-amino-2-nitroanisole (2-ANAN or 4-ANAN), and then subsequent reduction of the other nitro group formed 2,4-diaminoanisole (DAAN). The nitro-amino intermediates demonstrated regioselective reduction in the ortho position to 2-ANAN; Regioselectivity was also impacted by the anoxic/oxic environment. Under O₂-purging DNAN degradation rate was slightly enhanced, but most notably O₂ significantly accelerated DAAN generation. DAAN also further degraded only in the oxygenated Mg/Cu system. Adsorption of DNAN byproducts to the reagent occurred regardless of anoxic/oxic condition, resulting in a partition of carbon mass between the adsorbed phase (27%-35%) and dissolved phase (59%-72%). Additional surface techniques were applied to investigate contaminant interaction with Cu. Density functional theory (DFT) calculations identified preferential adsorption structures for DNAN on Cu with binding through two O atoms of one or both nitro groups. X-ray absorption spectroscopy (XAS) measurements determined the oxidation state of catalytic metal Cu and formation of a Cu-O-N bond during treatment. Laser desorption ionization mass spectrometry (LDI-MS) measurements also identified intermediate 2-ANAN adsorbed to the bimetal surface.

Effect of pH on Zero Valent Iron Performance in Heterogeneous Fenton and Fenton-Like Processes: A Review

Heterogeneous Fenton processes with solid catalysts have gained much attention for water and wastewater treatment in recent years. In the field of solid catalysts, zero valent iron (ZVI) is among the most applicable due to its stability, activity, pollutant degradation properties and environmental friendliness. The main limitation in the use of ZVI in heterogeneous Fenton systems is due to its deactivation in neutral and alkaline conditions, and Fenton-like processes have been developed to overcome this difficulty. In this review, the effect of solution pH on the ZVI-Fenton performance is discussed. In addition, the pH trend of ZVI efficiency towards contaminants removal is also considered in oxic solutions (i.e., in the presence of dissolved O₂ but without H₂O₂), as well as in magnetic-field assisted Fenton, sono-Fenton, photo-Fenton and microwave-Fenton processes at different pH values. The comparison of the effect of pH on ZVI performance, taking into account both heterogeneous Fenton and different Fenton-like processes, can guide future studies for developing ZVI applications in water and wastewater treatment.

Novel Cu(II)-EDTA Decomplexation by Discharge Plasma Oxidation and Coupled Cu Removal by Alkaline Precipitation: Underneath Mechanisms

Strong complexation between heavy metals and organic complexing agents makes the heavy metals difficult to be removed by classical chemical precipitation. In this study, a novel decomplexation method was developed using discharge plasma oxidation, which was followed by alkaline precipitation to treat water containing heavy metal-organic complex, that is, Cu-ethylenediaminetetraacetic acid (Cu-EDTA). The decomplexation efficiency of Cu complex reached up to nearly 100% after 60 min's oxidation by discharge plasma, which was accompanied by 82.1% of total organic carbon removal and energy efficiency of 0.62 g kWh^-1. Presence of free Cu²⁺ favored Cu-EDTA decomplexation, whereas the presence of excessive EDTA depressed this process. Cu-EDTA decomplexation was mainly driven by the produced ¹O₂, O₂^•-, O₃, and •OH by discharge plasma. Cu-EDTA decomplexation process was characterized by UV-vis, ATR-FTIR, total organic carbon, and three-dimensional fluorescence diagnosis. The main intermediates including Cu-EDDA, Cu-IDA, Cu-NTA, small organic acids, NH₄⁺, and NO₃^- were identified, accompanied by Cu²⁺ releasing. The followed precipitation process removed 78.1% of Cu²⁺, and Cu-associated precipitates included CuCO₃, Cu₂CO₃(OH)₂, CuO, and Cu(OH)₂. A possible pathway of Cu complex decomplexation and Cu²⁺ removal in such a system was proposed.

Degradation of the antibiotic ornidazole in aqueous solution by using nanoscale zero-valent iron particles: kinetics, mechanism, and degradation pathway

Degradation of ornidazole (ONZ) by nanoscale zero-valent iron (nZVI) particles was investigated for the first time in this work. The results showed that ONZ was almost completely degraded within 30 min by 0.1 g L⁻¹ nZVI at pH 5.8 and 25 °C. The effects of the nZVI dose, initial ONZ concentration, pH, and temperature on ONZ removal were systematically investigated, and removal of ONZ was followed by a pseudo-first-order kinetics model. Experimental results demonstrated that higher nZVI doses, lower initial ONZ concentrations, and lower pH levels could increase the pseudo-first-order rate constant (k_obs) of ONZ removal. While higher temperatures favored removal, the activation energy results suggested that mass transfer was the limiting step during the removal process. The possible effect of oxygen was ruled out by introducing hydroxyl radical scavengers into the experiment. The variation of ONZ concentrations and total organic carbon (TOC) contents in the solution indicated that adsorption was not the main mechanism. The possibility that precipitation was the main mechanism was also excluded by the results for the change in pH and effect of pH. The characterization of nZVI before and after the reaction indicated that ONZ was reduced on the surface of nZVI, which was the main mechanism. Three intermediates and two final products were detected based on the results of UV-vis and high performance liquid chromatography/mass spectrometry (HPLC-MS) analyses. Dechlorination, nitro reduction, N-denitration, and cleavage were all involved in the entire reaction process, and therefore a complicated potential degradation pathway was proposed.

The whole possible process of ONZ removal by nZVI. The reduction on the surface of nZVI was the main mechanism. A potential pathway including dechlorination, nitro reduction, N-denitration, and cleavage was proposed for the degradation process.

Enhanced degradation of gaseous benzene by a Fenton reaction

A wet scrubbing process coupled with advanced oxidation processes (AOP) has raised great interest for the abatement of volatile organic compounds (VOCs) owing to its strong oxidation capacity and few byproducts.