细化搜索
结果 991-1000 的 1,955
Electrochemical Degradation of the Reactive Red 141 Dye Using a Boron-Doped Diamond Anode 全文
2013
Aquino, José Mario | Rocha-Filho, Romeu C. | Rodrigo, Manuel A. | Sáez, Cristina | Cañizares, Pablo
The electrochemical degradation of the Reactive Red 141 azo dye was done using a one-compartment filter-press flow cell with a boron-doped diamond anode. The response surface methodology (with a central composite design) was used to investigate the effect of current density (10–50 mA cm⁻²), pH (3–11), NaCl concentration ([NaCl]) (0–2.34 g L–¹), and temperature (15–55 °C) on the system’s performance. The charge required for 90 % decolorization (Q ⁹⁰), the fraction of chemical oxygen demand removal after 6 min of electrolysis (COD⁶), and the fraction of total organic carbon removal after 90 min of electrolysis (TOC⁹⁰) were used to model the obtained results. The lowest values of Q ⁹⁰ were attained at pH <4 in the presence of higher values of [NaCl] (>1.5 g L⁻¹), due to the electrogeneration of active chlorine, present mainly as HClO. The value of COD⁶ was not affected by the solution pH, but increased with [NaCl] up to 1.5 g L⁻¹. Higher temperatures (>40 °C) led to a decrease in COD⁶, as a consequence of side reactions. Higher values of TOC⁹⁰, which can be reached only with strong oxidants (such as ·OH and Cl·), were efficiently attained at low [NaCl] values (<0.7 g L⁻¹) in acidic solutions that inhibit the formation of ClO₃ ⁻ and ClO₄ ⁻. Finally, the obtained results allow inferring that most probably the mineralization of the dye starts with an attack on the chromophore group, followed by the degradation of intermediate species.
显示更多 [+] 显示较少 [-]Persistence and Dissipation Kinetics of Clothianidin in the Soil of Tropical Sugarcane Ecosystem 全文
2013
Ramasubramanian, Thirumalaiandi
Persistence and dissipation kinetics of clothianidin were studied in sandy loam soil of sugarcane ecosystem by adopting a rapid and sensitive analytical method. This single-step analytical method was observed to be superior to multi-step conventional method reported to quantify the residues of clothianidin in soil, in terms of recovery, sensitivity and rapidity besides cost-effectiveness. The recoveries of clothianidin were in the range of 93.19 ± 3.07-95.43 ± 2.09 % at 0.01-0.1 μg/g level of fortification in soil. The limit of quantification of the method was 0.01 μg/g. Dissipation pattern of clothianidin followed first-order kinetics with a good fit (R 2 > 0.96). Half-life of clothianidin was 17.2 and 17.4 days at the single (50 g a.i./ha) and double doses (100 g a.i./ha), respectively. Clothianidin was observed to be more persistent than imidacloprid and thiamethoxam in the soil of tropical sugarcane ecosystem. © 2013 Springer Science+Business Media Dordrecht.
显示更多 [+] 显示较少 [-]Sorption of As(V) by Aluminum-Modified Crop Straw-Derived Biochars 全文
2013
Qian, Wei | Zhao, An-zhen | Xu, Ren-kou
Biochars derived from the straws of rice, soybean, and peanut were prepared and modified with aluminum [Al(III)]. These modifications shifted zeta potential-pH curves of the biochars in a positive-value direction and changed surface charge of biochars from negative to positive under acidic conditions. The isoelectric points for 0.6 M Al(III)-modified rice, soybean, and peanut straw biochars were 8.0, 7.8, and 7.5, respectively. Electrostatic attraction of the positively charged surfaces on Al(III)-modified biochars to arsenate [As(V)] enhanced its sorption. The sorption of As(V) by these Al(III)-modified biochars was investigated in batch experiments. Al(III)-modified biochars had greater sorption capacity under acidic conditions compared with corresponding unmodified biochars. While unmodified biochars sorbed negligible amounts of As(V), their Al(III)-modified forms sorbed 445-667 mmol kg-1 at pH 5.0, which were predicted by the Langmuir equation. Modifications with 0.3 M Al3+ improved sorption capacity of As(V) on soybean straw biochar to 445 mmol kg-1, which was further increased by 50 % after modification with 0.6 M Al3+. These As(V) sorption capacities of biochars modified with 0.6 M Al3+ were larger than those of Fe/Al oxides determined at the same pH, which were < 500 mmol kg-1. Thus, biochars modified with 0.6 M Al3+ could substitute Fe/Al oxides used for water purification. However, the sorption of As(V) by the Al(III)-modified biochars increased with decreasing suspension pH. Thus, As(V) removal by Al(III)-modified biochars is suggested to be conducted under acidic conditions, but at pH > 4.0. © 2013 Springer Science+Business Media Dordrecht.
显示更多 [+] 显示较少 [-]Degradation of Humic Acid by Photocatalytic Reaction Using Nano-sized ZnO/Laponite Composite (NZLC) 全文
2013
Kim, Jong Kyu | Alajmy, Jawaher | Borges, Alisson Carraro | Joo, Jin Chul | Ahn, Hosang | Campos, Luiza Cintra
Humic acids (HA) are known as the precursors of carcinogenic compounds formed by the disinfection of drinking water. While conventional treatments were found to be inefficient HA removal processes in drinking water, advanced oxidation processes have been proven to have a significant effect in the treatment of HA. The degradation of HA was investigated using nano-sized zinc oxide (ZnO)/laponite composite (NZLC). The reactions occurred in a UVC reactor by considering following variables: pH, initial HA concentration, catalyst loading, addition of hydrogen peroxide (H2O2), and catalyst reuse. Water samples containing HA were analysed by ultraviolet/visible spectrophotometer and high-performance size-exclusion chromatography. Initial HA concentrations were tested by the Langmuir-Hinshelwood model with k and K ads values, determined to be 0.126 mg/L.min and 0.0257 L/mg, respectively. The change in pH affected the HA degradation efficiency by the photocatalytic activity where it was higher under acidic conditions rather than alkaline ones. Optimal catalyst loading was proved to be a constrained factor in influencing the photocatalytic efficiency: the increase of catalyst concentration enhanced the HA decomposition efficiency up to an optimum value of 20 g/L, where there was no further degradation with excess loading. The addition of H2O2 was investigated through homogenous and heterogeneous photocatalysis, and, heterogeneous photocatalysis showed higher removal efficiency due to the combined effect of both catalysts and H 2O2. Finally, NZLC was effective for reuse and exhibited an excellent stability after six times of usage. © 2013 Springer Science+Business Media Dordrecht.
显示更多 [+] 显示较少 [-]Comparative Sorption and Mobility of Cr(III) and Cr(VI) Species in a Range of Soils: Implications to Bioavailability 全文
2013
Choppala, Girish | Bolan, Nanthi | Lamb, Dane | Kunhikrishnan, Anitha
The sorption of chromium (Cr) species to soil has become the focus of research as it dictates the bioavailability and also the magnitude of toxicity of Cr. The sorption of two environmentally important Cr species [Cr(III) and Cr(VI)] was examined using batch sorption, and the data were fitted to Langmuir and Freundlich adsorption isotherms. The effects of soil properties such as pH, CEC, organic matter (OM), clay, water-extractable SO₄ ²– and PO₄ ³–, surface charge, and different iron (Fe) fractions of 12 different Australian representative soils on the sorption, and mobility of Cr(III) and Cr(VI) were examined. The amount of sorption as shown by K f was higher for Cr(III) than Cr(VI) in all tested soils. Further, the amount of Cr(III) sorbed increased with an increase in pH, CEC, clay, and OM of soils. Conversely, the chemical properties of soil such as positive charge and Fe (crystalline) had a noticeable influence on the sorption of Cr(VI). Desorption of Cr(VI) occurred rapidly and was greater than desorption of Cr(III) in soils. The mobility of Cr species as estimated by the retardation factor was higher for Cr(VI) than for Cr(III) in all tested soils. These results concurred with the results from leaching experiments which showed higher leaching of Cr(VI) than Cr(III) in both acidic and alkaline soils indicating the higher mobility of Cr(VI) in a wide range of soils. This study demonstrated that Cr(VI) is more mobile and will be bioavailable in soils regardless of soil properties and if not remediated may eventually pose a severe threat to biota.
显示更多 [+] 显示较少 [-]The Potential of Salvia verbenaca for Phytoremediation of Copper Mine Tailings Amended with Technosol and Compost 全文
2013
Novo, Luís A. B. | Covelo, Emma F. | González, Luis
Unreclaimed mine tailings sites are a worldwide problem. This study evaluates the potential of Salvia verbenaca for phytoremediation of copper mine tailings treated with technosol and compost. Ecophysiological results reveal the species ability to thrive in the assessed range of conditions, while the hydrogen peroxide assays exhibit the plant’s capacity to successfully respond to metal toxicity, supporting literature reports about its antioxidant capabilities. Furthermore, the results suggest a selective antioxidant response of S. verbenaca towards Cd, indicative of a protection mechanism against high concentrations of this element. Moderate concentrations of Cu in the roots, adequate translocation and bioconcentration factors, tolerance to metal toxicity, and ecophysiological characteristics classify S. verbenaca as a promising candidate for phytostabilization of mine tailings. The importance of the amendments in order to improve the overall phytostabilization performance is highlighted by the elevated correlations between the treatment properties and the extractable concentrations of trace metals.
显示更多 [+] 显示较少 [-]Impacts of Land Uses on Mercury Retention in Long-Time Cultivated Soils, Brazilian Amazon 全文
2013
Comte, Irina | Lucotte, Marc | Davidson, Robert | Reis de Carvalho, Claúdio José | de Assis Oliveira, Francisco | Rousseau, Guillaume X.
Impacts of Land Uses on Mercury Retention in Long-Time Cultivated Soils, Brazilian Amazon 全文
2013
Comte, Irina | Lucotte, Marc | Davidson, Robert | Reis de Carvalho, Claúdio José | de Assis Oliveira, Francisco | Rousseau, Guillaume X.
Many studies have shown the relationship between fire clearing and mercury contamination of aquatic ecosystems in the Brazilian Amazon. This study aimed at quantifying mercury content in long-time cultivated soils and at assessing the potential of a fire-free alternative clearing technique on mercury retention for long-time cultivated soils compared to traditional slash-and-burn. This case study included five land uses: one crop plot and one pasture plot cleared using slash-and-burn, one crop plot and one pasture plot cleared using chop-and-mulch, and one 40-year-old forest as a control. Low mercury concentrations were recorded in the surface horizon (24.83 to 49.48 ng g⁻¹, 0–5 cm depth). The long-time cultivation (repeated burnings) of these soils triggered large mercury losses in the surface horizon, highlighted by high enrichment factors from surface to deeper horizons. The predominant effect of repeated burnings before the experimental implementation did not let us to distinguish a positive effect of the chop-and-mulch clearing method on soil mercury retention for crops and pastures. Moreover, some processes related to the presence of the mulch may favor mercury retention (Hg volatilization decrease, cationic sites increase), while others may contribute to mercury losses (cationic competition and dislocation, mobilization by the dissolved organic matter).
显示更多 [+] 显示较少 [-]Impacts of land uses on mercury retention in long-time cultivated soils, Brazilian Amazon 全文
2013
Comte I. | Lucotte M. | Davidson R. | Reis de Carvalho C. | de Assis Oliveira F. | Rousseau G.X.
Many studies have shown the relationship between fire clearing and mercury contamination of aquatic ecosystems in the Brazilian Amazon. This study aimed at quantifying mercury content in long-time cultivated soils and at assessing the potential of a fire-free alternative clearing technique on mercury retention for long-time cultivated soils compared to traditional slash-and-burn. This case study included five land uses: one crop plot and one pasture plot cleared using slash-and-burn, one crop plot and one pasture plot cleared using chop-and-mulch, and one 40-year-old forest as a control. Low mercury concentrations were recorded in the surface horizon (24.83 to 49.48 ng g?1, 0–5 cm depth). The long-time cultivation (repeated burnings) of these soils triggered large mercury losses in the surface horizon, highlighted by high enrichment factors from surface to deeper horizons. The predominant effect of repeated burnings before the experimental implementation did not let us to distinguish a positive effect of the chop-and-mulch clearing method on soil mercury retention for crops and pastures. Moreover, some processes related to the presence of the mulch may favor mercury retention (Hg volatilization decrease, cationic sites increase), while others may contribute to mercury losses (cationic competition and dislocation, mobilization by the dissolved organic matter). (Résumé d'auteur)
显示更多 [+] 显示较少 [-]Photocatalytic Activity of 2,4,6-Trichlorophenol by TiO₂ Mesostructures: Effects of Surface Modification, Calcination Temperature and Initial pH 全文
2013
Kim, Hee-Chan | Yi, Sang-hyŏp | Kim, Dong-Ju | Choi, Jae-Woo
A titanium mesostructure was synthesized, and its surface was subsequently modified by adsorbing phosphate. The modified structure was later investigated for photocatalytic activity against the organic contaminant 2,4,6-trichlorophenol with UV irradiation. This research found that the effects of calcination temperature, phosphate concentration for surface modification, amine grafting as a function, and initial pH condition contributed to the enhanced degradation rate of the chlorinated phenol. The results of this study demonstrated an increased photocatalytic degradation rate for 2,4,6-trichlorophenol under the following conditions: (1) titanium mesostructure calcined at 600 °C; (2) adsorption from a 100 mg/L as PO₄-P solution; (3) an amine-functionalized titanium mesostructure synthesized with the molar ration of 1:0.5 (titanium mesostructure: amine group); and (4) acidic condition (pH 4) to promote efficient adsorption of phosphate. This research indicates that phosphate removal and enhanced degradation of organic contaminants could be carried out simultaneously in sewage treatment.
显示更多 [+] 显示较少 [-]Biosorption of Cadmium from Water Using Moringa (Moringa oleifera Lam.) Seeds 全文
2013
Meneghel, Ana Paula | Gonçalves, Affonso Celso, Jr | Rubio, Fernanda | Dragunski, Douglas Cardoso | Lindino, Cleber Antonio | Strey, Leonardo
This study aimed to evaluate the efficacy of using the byproduct of Moringa oleifera Lam. seeds as an adsorbent for removal of cadmium (Cd) from contaminated water. The material characterization was performed by scanning electron microscopy, infrared spectroscopy, and point of zero charge. The effects of the adsorbent mass, solution pH, contact time, and temperature were evaluated. In the preliminary studies, the mass of adsorbent (200–1200 mg) and pH conditions (5.0, 6.0, and 7.0) were varied. The time studies were performed at 20–180 min and the temperature studies at the range of 25–65 °C. The optimal conditions of adsorption obtained were 400 mg of adsorbent mass, 7.0 pH, and 160 min contact time with the adsorbent. The isotherms of adsorption were linearized according to Langmuir, Freundlich, and Dubinin–Radushkevich (D-R) models. The results showed better fit by the Freundlich and D-R models for Cd adsorption, describing a multilayer adsorption and, according to the value of the sorption energy (E), it has chemical nature. The maximum capacity of adsorption (Q ₘ) obtained was 7.864 mg g⁻¹. For a comparative study, the activated carbon (P.A.) was used applying the same optimal conditions used in the adsorption isotherms and desorption process for the biosorbent, obtaining a Q ₘ as 32.884 mg g⁻¹. The average desorption percentage showed that adsorbents have strong interaction with the metal. Based on these results, it was concluded that the biosorbent was effective in remediation of solutions containing Cd and thus the use of this alternative material is a viable option, since it has low cost and it is a byproduct which has not undergone previous treatment.
显示更多 [+] 显示较少 [-]Biosorption of Pb(II) and Fe(III) from Aqueous Solutions Using Oil Palm Biomasses as Adsorbents 全文
2013
Khosravihaftkhany, Shabnam | Morad, Norhashimah | Teng, Tjoon Tow | Abdullah, Ahmad Zuhairi | Norli, Ismail
The removal of lead (II) and iron (III) from aqueous solutions using empty fruit bunch (EFB), oil palm leaves (OPL), oil palm frond (OPF), and oil palm bark (OPB) as biosorbents was investigated. The biosorbents were characterized through scanning electron microscopy, Brunauer–Emmett–Teller analysis, and Fourier transform infrared spectroscopy. Variables such as pH (2–12), biosorbent particle size (200–1,400 μm), adsorbent dosage (0.25–1.75 g/l), and agitation time (5–80 min) were investigated. The suitable pH range, particle size, adsorbent dosage, and agitation time for the removal of both metals were 5 to 6, 200 μm, 1 g/l, and 40 min, respectively. Under optimum conditions, OPB showed the highest adsorption efficiency of 80 % and 78 % for lead and iron, respectively. The adsorption equilibrium data were fitted to three adsorption isotherm models. The Langmuir isotherm showed the best result for both metals. The kinetics of the biosorption process was analyzed using pseudo-first-order and pseudo-second-order models. The latter showed a better fit for both metals. OPB biomass introduced the lowest chemical oxygen demand into the treated solution, with an average amount of 32.9 mg/l.
显示更多 [+] 显示较少 [-]