Low-temperature thermal desorption of diesel polluted soil: influence of temperature and soil texture on contaminant removal kinetics

Five soil size aggregate fractions, corresponding to coarse (500-840 μm), medium (200-350 μm), fine (75-200 μm) sand, silt (10-75 μm) and clay (<4 μm), were artificially contaminated with diesel, and thermally treated using a laboratory scale apparatus to investigate the effect of soil texture on contaminant adsorption and removal. Ex situ thermal process was simulated using helium as the carrier gas at a flow rate of 1.5 L min(-1), different temperatures (100-300 °C) and different treatment times (5-30 min). The amount of contaminant adsorbed on the soil and the residual amount after thermal treatment was determined by gas chromatography. Results showed that adsorption phenomena and desorption efficiency were affected by the soil texture and that temperature and time of treatment were key factors in remedial process. A temperature of 175 °C is sufficient to remedy diesel polluted sandy and silty soils, whereas a higher temperature (250 °C) is needed for clays. Thermal desorption of diesel polluted soil was shown to be governed by first-order kinetics. Results are of practical interest and may be used in scaling-up and designing desorption systems for preliminary cost and optimal condition assessment.     

Development of sorption materials based on iron(III)-chloride-modified graphene oxide for selective removal of organic pollutants from aquatic media

Abstract

The present work is aimed at developing an effective graphene-based sorbent for liquid-phase sorption of organic pollutants from aquatic media. The material synthesized in accordance with the method proposed represents a nanostructured composite possessing the hydrogel properties: structured three-dimensional carbon framework surface-modified with iron nanoparticles (i.e., graphene oxide (GO)/Fe-H₂O). Moreover, the proportion of dry matter in the hydrogel was revealed by drying to a constant weight at a given temperature (110?°C), and the powdery form (GO/Fe-110) of the composite was obtained. Besides, the aerogel (GO/Fe-250) of the composite developed was formed, for which the hydrogel synthesized was subjected to hydrothermal drying in isopropanol for 6?h under supercritical conditions. The morphological, structural and porous characteristics of all these materials were determined. The sorption capacity of the nanocomposites was estimated for the removal (under dynamic conditions) of the synthetic organic dye, methylene blue, used as a target pollutant. The results of the studies showed that the maximum sorption capacity of the GO/Fe-H₂O, GO/Fe-110 and GO/Fe-250 are ～2500, ～1500 and ～2300?mg g^?1, respectively. Besides, the high rate of the target pollutant removal from the aquatic media is a distinctive feature of the composites developed herein.     

Effect of different extraction agents on metal and organic contaminant removal from a field soil

This paper presents an evaluation of different extracting solutions for the removal of phenanthrene, lead and zinc from a contaminated soil obtained from a former manufactured gas plant site. The field soil contained 50%-88% sand, 11%-35% fines, 2.7%-3.7% organic matter and high concentrations of phenanthrene (260 mg/kg), lead (50.6 mg/kg) and zinc (84.4 mg/kg). A series of batch extraction experiments were conducted using the field soil with different extracting solutions at various concentrations to investigate the removal efficiency and to optimize the concentration of each extractant. The results showed that removal efficiencies of different flushing systems were significantly influenced by their affinity and selectivity for the contaminants in the soil matrix. Non-ionic surfactants (Igepal CA720 and Tween 80) were found to be effective in removing phenanthrene, but they were ineffective in removing lead and zinc. Chelating agents (ethylenediamine tetra acetic acid, EDTA and diethylene triamine penta acetic acid, DTPA) and selected acids were effective in removing lead and zinc, but they were ineffective for the phenanthrene removal. Co-solvents and cyclodextrins were not effective for removal of any of the contaminants. A sequential use of the 0.2 M EDTA followed by 5% Tween 80 or 5% Tween 80 followed by 1 M citric acid was found to be effective for the removal of lead, zinc, and phenanthrene. Overall, it can be concluded that sequential use of different extracting solutions is required for the removal of both heavy metals and organics from field contaminated silty sand soils.     

Removal of indigo carmine dye from water to Mg-Al-CO(3)-calcined layered double hydroxides

Layered double hydroxides (LDHs) calcined, denoted as CLDHs, have been shown to recover their original layered structure in the presence of appropriate anions. In the light of this so-called "memory effect", the removal of indigo carmine (IC), an anionic dye, from aqueous solution by calcined Mg-Al-CO(3) LDHs was investigated in batch mode. We looked at the influence of pH values, dye-adsorbent contact time, initial dye concentration and various temperatures of heating of LDHs on the decolorization rate of IC. The adsorption isotherms, described by Freundlich model are L-type. The characterization of the solids CLDHs, both fresh and after removal of IC, by X-ray diffraction and infrared spectroscopy shows that the IC adsorption on CLDHs is enhanced by reconstruction of a matrix hydrotalcite intercaled by the dye, and the intercalation of the organic ion was clearly evidenced by the net increase in the basal spacing from 0.76 nm for [Mg-Al-CO(3)] to 2.13 nm for the organic derivative.     

Degradation of polycyclic aromatic hydrocarbons (PAHs) in contaminated soils by Fenton's reagent: a multivariate evaluation of the importance of soil characteristics and PAH properties

In this study, we investigated how the chemical degradability of polycyclic aromatic hydrocarbons (PAHs) in aged soil samples from various contaminated sites is influenced by soil characteristics and by PAH physico-chemical properties. The results were evaluated using the multivariate statistical tool, partial least squares projections to latent structures (PLS). The PAH-contaminated soil samples were characterised (by pH, conductivity, organic matter content, oxide content, particle size, specific surface area, and the time elapsed since the contamination events, i.e. age), and subjected to relatively mild, slurry-phase Fenton's reaction conditions. In general, low molecular weight PAHs were degraded to a greater extent than large, highly hydrophobic variants. Anthracene, benzo(a)pyrene, and pyrene were more susceptible to degradation than other, structurally similar, PAHs; an effect attributed to the known susceptibility of these compounds to reactions with hydroxyl radicals. The presence of organic matter and the specific surface area of the soil were clearly negatively correlated with the degradation of bi- and tri-cyclic PAHs, whereas the amount of degraded organic matter correlated positively with the degradation of PAHs with five or six fused rings. This was explained by enhanced availability of the larger PAHs, which were released from the organic matter as it degraded. Our study shows that sorption of PAHs is influenced by a combination of soil characteristics and physico-chemical properties of individual PAHs. Multivariate statistical tools have great potential for assessing the relative importance of these parameters.     

Preparation of nitrogen-doped aluminium titanate (Al2TiO5) nanostructures: Application to removal of organic pollutants from aqueous media

Recently, aluminum titanate (Al₂TiO₅)-based nanostructures have been proved to serve as an efficient photocatalytic material with satisfactory photodegradation capacity. In this study, the citrate sol–gel method was used to synthesize these nanostructures and inspect the significant impacts of nitrogen-doping-originated crystalline defects on their photocatalytic performance in some details for the first time. The results indicated that the penetration of nitrogen atoms into AT crystal lattice, depending on the nitriding time and temperature, can induce a great deal of the residual stress and result in propagating the existing cracks and breaking down the particles. The XPS and FTIR results confirmed the formation of some new bonds in the crystal structure (including O-Ti-N and Ti-N), the substitutional and interstitial replacement of nitrogen atoms with oxygen atoms, oxygen vacancies, and the attachment of nitrogen species at superficial oxygen sites. These events may vary the bandgap values from 2.88 eV for pristine AT to 2.73 eV for the nitrided one, thereby manipulating the charge carrier recombination rate and activation of superficial catalytic reactions in the particles. Numerically, the band structure variations can efficiently increase the photodegradation efficiency of methylene blue (MB) and apparent rate constant (k) by 1.4 times (from 38.9 to 55.9%) and 1.8 times (from 0.0038 to 0.0068 min⁻¹), respectively. Finally, the results show that the synthesized photocatalyst can successfully compete with TiO₂-based photocatalysts in terms of photocatalytic performance.     

Comparison of electrodialytic removal of Cu from spiked kaolinite, spiked soil and industrially polluted soil

Electrokinetic remediation methods for removal of heavy metals from polluted soils have been subjected for quite intense research during the past years since these methods are well suitable for fine-grained soils where other remediation methods fail. Electrodialytic remediation is an electrokinetic remediation method which is based on applying an electric dc field and the use of ion exchange membranes that ensures the main transport of heavy metals to be out of the pollutes soil. An experimental investigation was made with electrodialytic removal of Cu from spiked kaolinite, spiked soil and industrially polluted soil under the same operational conditions (constant current density 0.2 mA/cm(2) and duration 28 days). The results of the present paper show that caution must be taken when generalising results obtained in spiked kaolinite to remediation of industrially polluted soils, as it was shown that the removal rate was higher in kaolinite than in both spiked soil and industrial polluted soil. The duration of spiking was found to be an important factor too, when attempting to relate remediation of spiked soil or kaolinite to remediation of industrially polluted soils. Spiking for 2 days was too short. However, spiking for 30 days resulted in a pattern that was more similar to that of industrially polluted soils with similar compositions both regarding sequential extraction and electrodialytic remediation result, though the remediation still progressed slightly faster in the spiked soil. Generalisation of remediation results to a variety of soil types must on the other hand be done with caution since the remediation results of different industrially polluted soils were very different. In one soil a total of 76% Cu was removed and in another soil no Cu was removed only redistributed within the soil. The factor with the highest influence on removal success was soil pH, which must be low in order to mobilize Cu, and thus the buffering capacity against acidification was the key soil characteristics determining the Cu removal rate.     

Hot water extraction with in situ wet oxidation: kinetics of PAHs removal from soil

Finding environmentally friendly and cost-effective methods to remediate soils contaminated with polycyclic aromatic hydrocarbons (PAHs) is currently a major concern of researchers. In this study, a series of small-scale semi-continuous extractions--with and without in situ wet oxidation--were performed on soils polluted with PAHs, using subcritical water (i.e. liquid water at high temperatures and pressures, but below the critical point) as the removal agent. Experiments were performed in a 300 mL reactor using an aged soil sample. To find the desorption isotherms and oxidation reaction rates, semi-continuous experiments with residence times of 1 and 2 h were performed using aged soil at 250 degrees C and hydrogen peroxide as oxidizing agent. In all combined extraction and oxidation flow experiments, PAHs in the remaining soil after the experiments were almost undetectable. In combined extraction and oxidation no PAHs could be detected in the liquid phase after the first 30 min of the experiments. Based on these results, extraction with hot water, if combined with oxidation, should reduce the cost of remediation and can be used as a feasible alternative technique for remediating contaminated soils and sediments.     

Titania/carbon nanotube composite (TiO2/CNT) and its application for removal of organic pollutants

This review aimed to highlight recent development in the preparation of titania/carbon nanotube composite (TiO₂/CNT) and its application for the removal of organic pollutants in aqueous solution. Current studies indicate that the composite can enhance the absorption of visible light compared with pure TiO₂. Generally, synergistic effects were observed for the degradation of some dyes, phenols, and benzene derivatives. The role of CNTs in the composite was explained to function as a support material, concentrate organic pollutants on the composite surface and more importantly, to extend electron–hole (e–h) recombination time as electron scavenger. However, opposite effects were observed for the degradation of some pharmaceuticals (e.g., carbamazepine and diclofenac). Despite different mechanisms involved, most organic pollutants can be photocatalytically degraded within a few minutes or hours. The summarized results and raised issues in this review will attract more future research for this new photocatalyst, particularly in areas such as synthesis methods, degradation mechanisms, and performance for more diversified structures of organic compounds.     

Removal of heavy metals from kaolin using an upward electrokinetic soil remedial (UESR) technology

An upward electrokinetic soil remedial (UESR) technology was proposed to remove heavy metals from contaminated kaolin. Unlike conventional electrokinetic treatment that uses boreholes or trenches for horizontal migration of heavy metals, the UESR technology, applying vertical non-uniform electric fields, caused upward transportation of heavy metals to the top surface of the treated soil. The effects of current density, treatment duration, cell diameter, and different cathode chamber influent (distilled water or 0.01 M nitric acid) were studied. The removal efficiencies of heavy metals positively correlated to current density and treatment duration. Higher heavy metals removal efficiency was observed for the reactor cell with smaller diameter. A substantial amount of heavy metals was accumulated in the nearest to cathode 2 cm layer of kaolin when distilled water was continuously supplied to the cathode chamber. Heavy metals accumulated in this layer of kaolin can be easily excavated and disposed off. The main part of the removed heavy metals was dissolved in cathode chamber influent and moved away with cathode chamber effluent when 0.01 M nitric acid was used, instead of distilled water. Energy saving treatment by UESR technology with highest metal removal efficiencies was provided by two regimes: (1) by application of 0.01 M nitric acid as cathode chamber influent, cell diameter of 100 mm, duration of 18 days, and constant voltage of 3.5 V (19.7 k Wh/m(3) of kaolin) and (2) by application of 0.01 M nitric acid as cathode chamber influent, cell diameter of 100 cm, duration of 6 days, and constant current density of 0.191 mA/cm(2) (19.1 k Wh/m(3) of kaolin).     

Effect of sequestration on PAH degradability with Fenton's reagent: roles of total organic carbon,humin, and soil porosity

The phenomenon of contaminant sequestration—and the physicochemical soil parameters which drive this process—has recently been studied by several authors with regard to microbial contaminant degradation. Very little work has been done to determine the effects of contaminant sequestration on the chemical treatability (oxidizability) of soil contaminants; the current study was conducted to address this data gap. A suite of six model soils, ranging in organic matter content from 2.32 to 24.28%, were extensively characterized. Measured parameters included: (1) levels of total organic carbon (TOC); (2) contents of humic acid (HA); fulvic acid (FA) and humin; and (3) total porosity and surface area. Each soil was then spiked with coal tar and, after varying periods of aging/sequestration, subjected to slurry-phase Fenton’s reagent oxidation. Percent recoveries of 12 PAHs, ranging from 3 to 6 aromatic rings, were determined. Results indicated that the susceptibility of each PAH to chemical oxidation was a function of TOC in four of the soils (those with TOC greater than approximately 5%), but was strongly dependent on soil porosity for low-TOC soils. The importance of these two parameters changed with increasing sequestration time, with the relative contribution of porosity-mediated sequestration becoming more important over time. Porosity-mediated effects were more rapid and significant with lower-molecular-weight PAHs (e.g. those with three or four aromatic rings) than with higher-molecular-weight, more hydrophobic compounds. These observations are discussed in light of current physicochemical models of the contaminant sequestration process.     

Sorption behavior of cesium on various soils under different pH levels

In the present study we investigated the sorption behavior of Cs in four different soils (sandyloam, loam, clayloam and clay) by using batch experiment. Cs sorption characteristics of the studied soils were examined at 4 mgL(-1) Cs concentration, at various pH levels, at room temperature and with 0.01 M CaCl(2) as a background electrolyte. Among different soils the decrease of k(d) (distribution coefficient) of cesium, at all pH levels, followed the sequence sandyloam > loam > clayloam > clay, indicating that the particle size fractions and especially the clay content plays predominant role on sorption of Cs. The effect of pH on cesium sorption displays a similar pattern for all soils, depending on soil type. At acid pH levels less cesium was sorbed, due to a greater competition with other cations for available sorption sites. The maximum sorption of Cs was observed at pH 8, where the negative charge density on the surface of the absorbents was the highest. For all soils was observed significantly lower Cs sorption at pH 10.     

Effect of different nanostructures of Cu2ZnSnS4 on visible light-driven photocatalytic degradation of organic pollutants

Journal of Materials Science: Materials in Electronics - Surface-modified hydrophilic CZTS nanostructures have been successfully synthesized through hot injection method followed by bi-phase ligand...     

Cosorption of zinc and glyphosate on two soils with different characteristics

Agricultural application of large amounts of glyphosate [N-(phosphonomethyl)-glycine] may affect soil metal behaviors to some extend, because glyphosate can react with many kinds of metals to form metal complexes. Cosorption of Zn and glyphosate on a Red soil (RS, Udic Ferrosols) and a Wushan soil (WS, Anthrosol) was studied. In comparison with the WS, the RS has less adsorption capacity for Zn and higher for glyphosate. The presence of glyphosate decreased Zn adsorption on the two soils, which are resulted from the decreased equilibrium solution pH caused by the added glyphosate, and also the formation of water-soluble complexes of glyphosate with solution Zn(2+) that had lower affinity to soil surface in comparison with Zn(2+) itself. Such effect is more significant on the RS than on the WS, mainly because of the less adsorption quantity of Zn on the former one. On the contrary, the presence of Zn increased the adsorption quantities of glyphosate on the RS and WS, which is resulted from the decreasing pH value of the equilibrium solution caused by Zn(2+) exchange with H(+) ions of soil surface. Such results suggest that glyphosate in field may increase the mobility and bioavailability of Zn and correspondingly increase its environmental risk.     

Electrodialytic removal of heavy metals from different fly ashes. Influence of heavy metal speciation in the ashes

Electrodialytic remediation, an electrochemically assisted extraction method, has recently been suggested as a potential method for removal of heavy metals from fly ashes. In this work, electrodialytic remediation of three different fly ashes, i.e. two municipal solid waste incinerator (MSWI) fly ashes and one wood combustion fly ash was studied in lab scale, and the results were discussed in relation to the expected heavy metal speciation in the ashes. The pH-dependent desorption characteristics for Cr differed between the two MSWI ashes but were similar for Cd, Pb, Zn and Cu. Thus, it was expected that the speciation of Cd, Pb, Zn and Cu was similar in the two ashes. However, in succeeding electrodialytic remediation experiments significant differences in removal efficiencies were observed, especially for Pb and Zn. In analogous electrodialytic remediation experiments, 8% Pb and 73% Zn was removed from one of the MSWI ashes, but only 2.5% Pb and 24% Zn from the other. These differences are probably due to variations in pH and heavy metal speciation between the different ashes. Cd, the sole heavy metal of environmental concern in the wood ash, was found more tightly bonded in this ash than in the two MSWI ashes. Approximately 70% Cd was removed from both types of ashes during 3 weeks of electrodialytic remediation, although the total concentration was a factor of 10 lower in the wood ash. It was suggested that complex Cd-silicates are likely phases in the wood ash whereas more soluble, condensed phases are dominating in the MSWI ashes.     

High efficiency removal of dissolved As(III) using iron nanoparticle-embedded macroporous polymer composites

Novel nanocomposite materials where iron nanoparticles are embedded into the walls of a macroporous polymer were produced and their efficiency for the removal of As(III) from aqueous media was studied. Nanocomposite gels containing α-Fe₂O₃ and Fe₃O₄ nanoparticles were prepared by cryopolymerisation resulting in a monolithic structure with large interconnected pores up to 100 μm in diameter and possessing a high permeability (ca. 3 × 10⁻³ m s⁻¹). The nanocomposite devices showed excellent capability for the removal of trace concentrations of As(III) from solution, with a total capacity of up to 3 mg As/g of nanoparticles. The leaching of iron was minimal and the device could operate in a pH range 3-9 without diminishing removal efficiency. The effect of competing ions such as SO₄²⁻ and PO₄³⁻ was negligible. The macroporous composites can be easily configured into a variety of shapes and structures and the polymer matrix can be selected from a variety of monomers, offering high potential as flexible metal cation remediation devices.     

分体式膜生物反应器(RMBR)有机物降解动力学研究

利用分体式膜生物反应器(RMBR)处理了模拟废水.通过测定不同污泥负荷条件下,系统对有机物的去除效果,探讨了RMBR系统有机物降解动力学模型以及相关动力学参数.结果表明,在整个运行阶段系统中有机物的平均去除率为97.4％,去除率较高.在0.22～0.27kgCOD/(kgMLSS ·d)污泥负荷范围内,COD平均出水浓度满足了《城镇污水处理厂污染物排放标准》中的一级B标准(60 mg/L),而随着污泥负荷的不断增大,出水浓度超出了此标准.根据实验所得RMBR系统动力学参数Vmax为4.21 d-1,Ks为688.74mgCOD/L,有机物降解动力学模型为[(So-Se)·Q]/(X·V)=4.21 Se/(688.74+Se).     

Effect of soil organic matter (SOM) and soil texture on the fatality of indigenous microorganisms in intergrated ozonation and biodegradation

In situ ozonation has been proposed as a method to remediate soils contaminated with organic pollutants. Soil column experiments were performed on eight different soils in order to investigate the effects of soil properties, such as soil organic matter (SOM) and soil texture on the survival and regrowth of indigenous microorganisms after in situ ozonation. Indigenous microorganisms were found to be very sensitive to ozone in the soil column experiments. The microbial fatality revealed a linear relationship with the SOM content in the range of 1.72–2.42% of SOM content, whereas water content was poorly correlated. Four weeks of incubation of ozone-treated soil samples allowed for the regrowth of indigenous microorganisms with inverse relation to ozonation time. The regrowth was also significantly influenced by the SOM content in the same soil texture. Oxidation and removal rate of hexadecane was affected by particle size distribution. Especially, sand exhibited the highest oxidation rate of hexadecane, which resulted from having the lowest SOM content, water content, and surface area with respect to the other samples. The soil samples ozonated for 90–180 min were determined to exhibit the lowest concentration of hexadecane, with the exception of sand, after 4 weeks of incubation. This study provided insight into the influence of SOM and soil texture on indigenous microbial potential to degrade hexadecane in integrated ozonation and biodegradation.     

Role of organic amendments on enhanced bioremediation of heavy metal(loid) contaminated soils

As land application becomes one of the important waste utilization and disposal practices, soil is increasingly being seen as a major source of metal(loid)s reaching food chain, mainly through plant uptake and animal transfer. With greater public awareness of the implications of contaminated soils on human and animal health there has been increasing interest in developing technologies to remediate contaminated sites. Bioremediation is a natural process which relies on soil microorganisms and higher plants to alter metal(loid) bioavailability and can be enhanced by addition of organic amendments to soils. Large quantities of organic amendments, such as manure compost, biosolid and municipal solid wastes are used as a source of nutrients and also as a conditioner to improve the physical properties and fertility of soils. These organic amendments that are low in metal(loid)s can be used as a sink for reducing the bioavailability of metal(loid)s in contaminated soils and sediments through their effect on the adsorption, complexation, reduction and volatilization of metal(loid)s. This review examines the mechanisms for the enhanced bioremediation of metal(loid)s by organic amendments and discusses the practical implications in relation to sequestration and bioavailability of metal(loid)s in soils.