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[en] Accurate estimation of oxidant consumption during in situ chemical oxidation (ISCO) is the key to determining the treatment effectiveness in contaminated sites. We established the estimation model of soil oxidant demand (SOD) and simulation equations of potassium permanganate (KMnO4) dynamic consumption based on the reaction equation of KMnO4 with reductive minerals and the estimation model of SOD. Model validation, model application, and simulation assessment had been accomplished. Results indicated that the simulations are in good agreement with measured data. The confidence level of the SOD estimation model of KMnO4 was over 80%, with sensitivity in decreasing order as follows: organic matter content > initial KMnO4 concentration > reductive minerals (RMs). Particularly, the organic matter played a dominate role in the SOD model estimation. The coefficient of determination (R2) of the SOD dynamic consumption simulation equation was above 0.9. Among the various types of soils, the overall trend of SOD value and reaction period decreased as follows: clay > loam > sand. However, the consumption rate of KMnO4 decreased in the order of clay > sand > loam. In addition, SOD value, reaction period, and reaction rate all increased as the initial concentration of KMnO4 went up. This work can provide a methodology and reference for selecting and estimating of the optimal oxidant doses and reaction period during field application.
[en] Effects of discharge power, O2 content, reaction temperature, catalyst introduction, and presence of NO and dichloromethane (DCM) on the formation of nitrogen oxides (N2O, NO, and NO2) by discharge in N2-O2 mixture have been systematically investigated using a dielectric barrier discharge (DBD) reactor. Results show that discharge in N2-O2 mixture always produces several to hundreds ppm of nitrogen oxides as byproducts. The production of nitrogen oxides increases with the increase of O2 content and the introduction of Al2O3 or RuO2/Al2O3 catalyst. N2O production first increases and then decreases/levels off with increasing discharge power at room temperature, but increases monotonously at 300 °C. NO and NO2 are produced only at relatively high discharge power at room temperature but are produced at all discharge power tested at 300 °C. Increasing the reaction temperature from room temperature to 300 °C significantly reduces the production of N2O but increases that of NO and NO2. The presence of hundreds ppm NO in N2-O2 mixture significantly reduces the production of N2O due to the effective quenching of the vital species for N2O formation (N2(A3Σu+)) by NO. The presence of hundreds ppm DCM, however, hardly affects the production of nitrogen oxides, demonstrating the precedence of nitrogen oxide production over DCM decomposition in N2-O2 plasma.
[en] MgFe2O4-MWCNT/Ag3VO4 photocatalyst was prepared for benefiting the visible region of solar spectrum. Prepared catalyst was characterized by using scanning electron microscope (SEM), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDX). Photocatalytic activity was measured by methylene blue (MB) decolorization under visible light obtained from a 105-W tungsten light bulb. Dye decolorization and its kinetics were followed up by means of a UV-vis spectrophotometer. Kinetic model of decolorization was found to be compatible with first-order kinetics. The effects of pH and concentration of MB solution on the decolorization efficiency were determined. Low and high pH conditions were found to be more effective in increasing the MB decolorization yield and rate. On the other hand, due to the low transparency of concentrated MB solutions, an increase on decolorization time and a lowering in decolorization yield were encountered. Thanks to the magnetic MgFe2O3 nanoparticles, 96% of the catalyst could be recovered by a simple magnetic bar. It was observed that simulated wastewater containing MB was also successfully decolorized showing that visible region-sensitive MgFe2O4-MWCNT/Ag3VO4 photocatalyst can be benefited as a potential, efficient, and reusable material for the removal organic pollutants in aquatic environment.
[en] The investigation and development of technologies to remediate water contaminated with NO3− are constantly increasing. An economically and potentially effective alternative is based on the catalytic hydrogenation of NO3− to N2. With this objective, bimetallic RhMo6 catalysts based on Anderson-type heteropolyanion (RhMo6O24H6)3− were prepared and characteri3ed in order to obtain well-defined bimetallic catalyst. The catalysts were supported on Al2O3 with different textural properties and on silica. The heteropolyanion-support interaction was analysed by temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS). The differences obtained in activity and selectivity to the different products can be assigned to the different interaction between the RhMo6 Anderson phase and the supports. The RhMo6/G, (G: γ-Al2O3) system showed the best catalytic performance. This catalyst exhibited the lowest reduction temperature of Rh and Mo in the TPR assay and a Rh/Mo surface ratio similar to that of the original phase, as observed by XPS analysis. These studies allowed us to verify a synergic effect between Rh and Mo, through which Mo reducibility was promoted by the presence of the noble metal. The catalytic activity was favoured by the active sites generated from the Anderson phase. This fact was confirmed by comparing the activity of RhMo6/G with that corresponding to a conventional catalyst prepared through successive impregnation of both Rh (III) and Mo (VI) salts.
[en] Biodegradation of phenol, o-cresol, and p-cresol was evaluated in continuous flow circulating packed bed bioreactors. Effect of loading rate on the removal rate of phenolic compounds was assessed by varying the influent concentration and flow rate. Regardless of the nature of phenolic compounds at a constant concentration, increase of loading rate caused the removal rate to pass through a maximum and then decline. Influent concentrations of 100 and 300 mg L−1 did not affect the removal rates of phenol and p-cresol, but higher rates were obtained at 500 mg L−1. With o-cresol, increase of influent concentration from 100 to 300 mg L−1 enhanced the removal rate but no further enhancement was observed at 500 mg L−1. The maximum removal rates for phenol, o-cresol, and p-cresol were 67.6–97.8, 38.7–73.8, and 77.2–107.2 mg L−1 h−1 at loading rates of 96.7–171.1, 61.6–163.9, and 87.4–183.9 mg L−1 h−1 (hydraulic residence time 2.9, 1.7–1.8, 1.2–2.8 h), respectively. Toxicity examination of untreated influents singled out phenol as the least toxic compound, while o-cresol and p-cresol showed similar toxicities. Treatment of influent containing 100 mg L−1 of phenolic compound led to the highest decrease in toxicity (> 93%) for all three compounds. With influent concentrations of 300 mg L−1 or higher, the decrease in toxicity of treated effluent was highest for phenol, followed by p-cresol, and then o-cresol. Finally, the observed patterns revealed that the toxicity of treated effluent was affected by the extent of biodegradation, as well as the toxic nature of phenolic compound under treatment.
[en] The research goal was to determine if onsite wastewater system (OWS) density had an influence on the concentrations and watershed exports of Escherichia coli and enterococci in urbanizing watersheds. Eight watersheds with OWS densities ranging from < 0.1 to 1.88 systems ha−1 plus a watershed served by sewer (Sewer) and a mostly forested, natural watershed (Natural) in the Piedmont of North Carolina served as the study locations. Stream samples were collected approximately monthly during baseflow conditions between January 2015 and December 2016 (n = 21). Median concentrations of E. coli (2014 most probable number (MPN) 100 mL−1) and enterococci (168 MPN 100 mL−1) were elevated in streams draining watersheds with a high density of OWS (> 0.77 system ha−1) relative to watersheds with a low (< 0.77 system ha−1) density (E. coli: 204 MPN 100 mL−1 and enterococci: 88 MPN 100 mL−1) and control watersheds (Natural: E. coli: 355 MPN 100 mL−1 and enterococci: 62 MPN 100 mL−1; Sewer: 177 MPN 100 mL−1 and 130 MPN 100 mL−1). Samples collected from watersheds with a high density of OWS had E. coli and enterococci concentrations that exceeded recommended thresholds 88 and 57% of times sampled, respectively. Results show that stream E. coli and enterococci concentrations and exports are influenced by the density of OWS in urbanizing watersheds. Cost share programs to help finance OWS repairs and maintenance are suggested to help improve water quality in watersheds with OWS.