Bahngmi Jung

The influence of humic acid and clay content on the transport of polymer-coated iron nanoparticles through sand

The introduction of nanoscale zero valent iron (nZVI) into the subsurface has recently received significant attention as a potentially effective method for remediation of source zones of chlorinated solvents present as dense nonaqueous phase liquids (DNAPL). One of the challenges in the deployment of nZVI is to achieve good subsurface nZVI mobility to permit delivery of the nZVI to the target treatment zone. Stabilization of nZVI with various polymers has shown promise for enhancing nZVI subsurface mobility, but the impact of subsurface conditions on nZVI mobility has not been fully explored. In this study, the effect of humic acid and kaolinite on the transport of polymer-stabilized nZVI (carboxylmethyl cellulose-surface modified nZVI, CMC90K-RNIP) in sand was investigated using column experiments. In addition, effects of electrolytes on the stability of CMC90K-RNIP in the presence of humic acid, and the stability of humic acid-coated reactive nanoscale iron particles (HA-RNIP) at various humic acid concentrations were investigated. Humic acid enhanced the mobility of bare RNIP, whereas the transport of CMC90K-RNIP was not significantly affected by humic acid injected as a background solution, except at the highest concentration of 500mg/L. At lower pore water velocity, the effect of humic acid on the transport of CMC90K-RNIP was greater than that at high water velocity. Adding kaolinite up to 2% by weight to the sand column reduced the retention of CMC90K-RNIP, but further increases in kaolinite content (to 5%) did not significantly affect nZVI retention. The impact of kaolinite on nZVI retention was more pronounced at lower pore water velocities.

Spectroscopic study of Se(IV) removal from water by reductive precipitation using sulfide.

This study investigates the removal of selenium (IV) from water by reductive precipitation using sodium sulfide at neutral pH. Also, it examines the application of UV light as an activating method to enhance reductive precipitation. Furthermore, this work evaluates the effects of sulfide dose and solution pH on behavior of Se(IV) reduction. Selenium was effectively removed in sulfide solution at both neutral and acidic pH. UV irradiation did not enhance removal efficiency of Se(IV) at conditions tested, but it affected solids morphology and composition. SEM/EDS and XPS results showed that selenite was reduced to elemental Se or Se-S precipitates (e.g. SenS8-n) in sulfide solution. High resolution S 2p XPS spectra suggested the presence of sulfur-containing anions (e.g. S2O3(2-), HSO3(-), etc.) or elemental S (S(0)), monosulfide (S(2-)), and polysulfides (Sn(2-)), which could be produced from sulfide photolysis or reaction with Se. In addition, large aggregates of irregular shape, which suggest Se-S precipitates or elemental sulfur, were found more prominently at pH 4 than at pH 7, and they were more noticeable in the presence of UV with longer reaction times. In addition, XRD patterns showed that gray elemental Se solids were dominant in experiments without UV, whereas Se-S precipitates (Se3S5) with an orange color were found in those with UV.

Visible-Light-Driven Photocatalytic Degradation of Organic Water Pollutants Promoted by Sulfite Addition

Solar-driven heterogeneous photocatalysis has been widely studied as a promising technique for degradation of organic pollutants in wastewater. Herein, we have developed a sulfite-enhanced visible-light-driven photodegradation process using BiOBr/methyl orange (MO) as the model photocatalyst/pollutant system. We found that the degradation rate of MO was greatly enhanced by sulfite, and the enhancement increased with the concentration of sulfite. The degradation rate constant was improved by 29 times in the presence of 20 mM sulfite. Studies using hole scavengers suggest that sulfite radicals generated by the reactions of sulfite (sulfite anions or bisulfite anions) with holes or hydroxyl radicals are the active species for MO photodegradation using BiOBr under visible light. In addition to the BiOBr/MO system, the sulfite-assisted photocatalysis approach has been successfully demonstrated in BiOBr/rhodamine B (RhB), BiOBr/phenol, BiOI/MO, and Bi2O3/MO systems under visible light irradiation, as well as in TiO2/MO system under simulated sunlight irradiation. The developed method implies the potential of introducing external active species to improve photodegradation of organic pollutants and the beneficial use of air pollutants for the removal of water pollutants since sulfite is a waste from flue gas desulfurization process.

Dechlorination of liquid wastes containing chlorinated hydrocarbons by a binder mixture of cement and slag with Fe(II)

Iron-based degradative solidification/stabilization (DS/S-Fe(II)) is a modification of conventional solidification/stabilization (S/S) that incorporates degradative processes for organic contaminant destruction with immobilization. This study investigated the effectiveness of a binder mixture of Portland cement and slag in a DS/S-Fe(II) system to treat trichloroethylene (TCE), 1,1-dichloroethylene (1,1-DCE), vinyl chloride (VC), trichloromethane (CF), and dichloromethane (MC), which are major chlorinated hydrocarbons contained in waste oils and waste organic solvents. For TCE, 1,1-DCE, and VC, degradation experiments were conducted using three different binder combinations with Fe(II) (cement/Fe(II), slag/Fe(II), and cement/slag/Fe(II)). When cement and slag were mixed at a 1:1 ratio (% wt), the TCE and 1,1-DCE dechlorination rate was enhanced compared to that when cement or slag was used alone with Fe(II). Also, batch experiments were conducted in the solid phase consisting of cement, slag, sand, and Fe(II) to treat liquid wastes that contain chlorinated compounds at high concentrations. TCE was completely removed after 5 days in the cement/slag/sand/Fe(II) system, in which the initial TCE concentration was 11.8mM, with Fe(II) concentration of 565 mM. While the CF concentration was decreased by 95% after 5 days when the initial CF and Fe(II) concentration was 0.25 mM and 200 mM, respectively. However, MC was not degraded with the cement/slag/Fe(II) system.

Removal of arsenite by reductive precipitation in dithionite solution activated by UV light

This study investigates the removal of arsenite (As(III)) from water using dithionite activated by UV light. This work evaluated the removal kinetics of As(III) under UV light irradiation as affected by dithionite dose and light intensity, and characterized the nature of the precipitated solids using XPS and SEM-EDS. Photolysis of dithionite was observed by measuring dithionite concentration using UV absorbance at 315nm. This study also investigated the effect of UV light path length on soluble As concentrations to understand resolubilization mechanisms. Total soluble As concentrations were observed to decrease with reaction time due to reduction of arsenite to form solids having a yellow-orange color. The removal mechanism was found to be reductive precipitation that formed solids of elemental arsenic or arsenic sulfide. However, these solids were observed to resolubilize at later times after dithionite had been consumed. Resolubilization of As was prevented and additional As removal was obtained by frequent dosing of dithionite throughout the experiment. As(III) removal is attributed to photolysis of dithionite by UV light and production of reactive radicals that reduce As(III) and convert it to solid forms.

Response to Comment on “Visible-Light-Driven Photocatalytic Degradation of Organic Water Pollutants Promoted by Sulfite Addition”

9 Solar-driven heterogeneous photocatalysis has been widely studied as a promising technique for 10 degradation of organic pollutants in wastewater. Herein, we have developed a sulfite-enhanced 11 visible-light-driven photodegradation process using BiOBr/methyl orange (MO) as the model 12 photocatalyst/pollutant system. We found that the degradation rate of MO was greatly enhanced 13 by sulfite, and the enhancement increased with the concentration of sulfite. The degradation rate 14 constant was improved by twenty-nine times in the presence of 20 mM sulfite. Studies using hole 15 scavengers suggest that sulfite radicals generated by the reactions of sulfite (sulfite anions or 16 bisulfite anions) with holes or hydroxyl radicals are the active species for MO photodegradation 17 using BiOBr under visible light. In addition to the BiOBr/MO system, the sulfite-assisted 18 photocatalysis approach has been successfully demonstrated in BiOBr/rhodamine B (RhB), 19 BiOBr/phenol, BiOI/MO, and Bi2O3/MO systems under visible light irradiation, as well as in 20 TiO2/MO system under simulated sunlight irradiation. The developed method implies the 21 potential of introducing external active species to improve photodegradation of organic 22 Page 1 of 25 ACS Paragon Plus Environment Environmental Science & Technology