Soil vapor extraction (SVE) is one of the most effective remediation technologies for soil and groundwater contamination. Soil particles can be mobilized by air perturbation during SVE, resulting in the differentiation of porous media, which has not been well addressed. This paper developed a numerical method to study the flow pattern and quantify the change of porous media for the first time. Based on the mass equilibrium and Darcy’s law, a two-phase water–air flow model was constructed with integration of saturation, relative permeability, and capillary pressure during SVE. Relationship between porosity and saturation was deduced and coupled with the two-phase flow model for quantifying change of porous media in real time. Results reveal that both porosity and permeability increase sharply in the early stage of SVE then gradually to a quasi-steady state. These increases in vadose zone tapered off with distance from the SVE screen and the steady period occurred later as well. The influence radius of a single SVE well and the change degree in porosity and permeability of media were proportional to the extraction vacuum and the driving coefficient C, which is more sensitive than extraction vacuum according to the simulation results. Knowledge from this modeling exercise provides a useful tool to estimate the change of remediated zone and assess the environmental risk of remedial activities at real-world contamination sites.

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.

Reduction of bulk organic matter, nitrogen, and pharmaceutically active compounds from primary effluent during managed aquifer recharge was investigated using laboratory-scale batch reactors. Biologically stable batch reactors were spiked with different concentrations of sodium azide to inhibit biological activity and probe the effect of microbial activity on attenuation of various pollutants of concern. The experimental results obtained revealed that removal of dissolved organic carbon correlated with active microbial biomass. Furthermore, addition of 2 mM of sodium azide affected nitrite-oxidizing bacteria leading to accumulation of nitrite-nitrogen in the reactors while an ammonium-nitrogen reduction of 95.5 % was achieved. Removal efficiencies of the hydrophilic neutral compounds phenacetin, paracetamol, and caffeine were independent of the extent of the active microbial biomass and were >90 % in all reactors, whereas removal of pentoxifylline was dependent on the biological stability of the reactor. However, hydrophobic ionic compounds exhibited removal efficiency >80 % in batch reactors with the highest biological activity as evidenced by high concentration of adenosine triphosphate. © 2013 Springer Science+Business Media Dordrecht.

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.

Natural palygorskite was used as an adsorbent for the removal of copper, cobalt and nickel from an aqueous solution. All assays were performed under controlled conditions to establish the adsorption capacity of the solid. Initially, the clay was characterized by chemical analysis, XRD, infrared spectroscopy and thermogravimetry. Adsorption experiments for the ions in aqueous solution were carried out by a batch method through which the reaction time, initial concentration of cations, temperature and pH of the aqueous solution were systematically varied. First-order, pseudo-second-order and intraparticle diffusion models were used to describe the kinetic data. The results show that the processes were fitted well by the pseudo-second-order model. Moreover, the equilibrium solid–cation systems followed the Langmuir isotherm model. The results indicate that raw palygorskite could be employed as a low-cost material for the removal of heavy metals from aqueous solution.

In this study, residues of passion fruit skin were examined as biosorbent materials, evaluating their capacity to adsorb lead(II) ions in in natura skin (SK-N) and two modified skins, with NaOH (SK-S) and with NaOH and citric acid (SK-SCA). The biomass characterization was done through Fourier transform infrared spectroscopy which confirmed the chemical modification by a peak at 1,730 cm⁻¹. Also, scanning electron microscopy analyses were done, where the increase of residue roughness was observed after the modification. And finally, the values of point of zero charge were determined and were lower than 5.5 for all residues. In the experiments of adsorption in function of pH, it was verified that after pH 4, the adsorbed amount was practically constant. Regarding the necessary time to reach equilibrium, the value that was found was approximately 170 min, and kinetics followed the behavior described by the pseudo-second-order equation. The maximum adsorption capacity was 204 mg g⁻¹ for the SK-SCA biomass. The residues followed Langmuir adsorption model. Through thermodynamic parameters, it was verified that adsorption occurs spontaneously due to the negative values of Gibbs' energy. Moreover, desorption studies showed that adsorbed ions may be recovered in two cycles. Thus, due to the high adsorption capacity of lead ions, passion fruit skin can be utilized in filters to retain this metal in the future.

The present study consisted of an in vitro experiment based on columns to restore a soil affected by the tsunami of 27 February 2010 that struck the Coliumo District, Bio-Bio region, Chile. The agricultural productivity of many coastal lands was severely affected, rendering them unfit for crop production. Composite soil samples were taken at 0 to 20 cm soil depth in Coliumo, Bio-Bio region. The initial physical and chemical analysis showed textural changes, low pH, high levels of electrical conductivity (EC), sodium (Na⁺), and sulfate (SO₄²⁻), whereas bioassay tests showed severe toxicity for lettuce (Lactuca sativa L.) seeds. Germination index (GI), length of hypocotyl (LH), and length of radicle (LR) were used as indicators in the bioassay tests. Two different treatments were used: T1 = soil amended with 7.7 t ha⁻¹ of limestone (CaCO₃) and T2 = soil amended with 7.7 t ha⁻¹ of gypsum (CaSO₄). A control treatment (T0) with unamended soil was included. Each treatment received a total of 1,100 mm of clean water (4 water loads, 275 mm each), which was equivalent to the mean annual precipitation of the area studied. The T2 treatment produced a significant decrease in the concentration of Na⁺ (8.27 to 0.16 meq L⁻¹), decreased EC (1.58 to 0.03 dS m⁻¹), and increased pH from 4.83 to 6.27 in the soil under study. Leaching of Na⁺ and SO₄²⁻ with successive water loads was effective in the soil. The bioindicators as GI, LH and LR revealed that T2 was more effective than T1 and control in removing Na and SO₄ analytes from the soil matrix. The CaSO₄ amendment showed good potential for seed development, but further research on plant growth to maturity is required to determine yield parameters in the affected area.

Tobacco (Nicotiana tabacum L.) stem ash (TSA) was evaluated as an adsorbent for removal of methylene blue (MB) from aqueous solution by batch adsorption method. MB adsorption increased with increase in contact time, initial solution pH, and adsorbent dose. Contact time for adsorption equilibrium was 180 min. The MB adsorption per unit mass of adsorbent (in milligram per gram) increased with the increasing initial dye concentration. Adsorption of MB onto TSA followed the pseudo-second-order kinetic model with a rate constant (k ₂) of 0.017 g mg⁻¹ min⁻¹. The mechanism of adsorption was described with intra-particle diffusion model. It was found that the intra-particle diffusion was not a sole rate-controlling step. Equilibrium adsorption was investigated by the Freundlich, Langmuir, Temkin, and Jovanoic isotherms. On the basis of coefficient of determination, the order of isotherm fit was Langmuir (R ² = 0.974) > Freundlich (R ² = 0.957) = Temkin (R ² = 0.957) > Jovanoic (R ² = 0.764) isotherm. The maximum monolayer adsorption capacity of TSA was 35.7 mg g⁻¹. The dimensionless separation factor (R L) was low (0.137), indicating favorable adsorption of MB onto TSA. The results clearly demonstrate the potential of TSA as a low-cost and an easily available adsorbent for sequestering MB from wastewater.

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.

We study the adsorption and desorption of chromium on two soils (a forest soil and a vineyard soil), both individually or after being combined with ground mussel shell, and on various materials (mussel shell, pyritic material from a dump site, and slate processing fines). The adsorption capacity depends mainly on the initial Cr concentration, on the pH, and on the abundance of noncrystalline Fe. The highest adsorption percentage (94 %) corresponds to the pyritic material, which also shows very low desorption rates (1.4 %), has the lowest pH, and has the highest concentration of noncrystalline Fe. The adsorption isotherms in most cases fit the Freundlich and Lineal models, rather than the Langmuir model, with no easily predictable maximum for chromium adsorption.