Porous organoclay composite for the sorption of polycyclic aromatic hydrocarbons and pentachlorophenol from groundwater

Adsorption and detoxification of glyphosate and aminomethylphosphonic acid by montmorillonite clays

The co-occurrence of mixtures of glyphosate (GLP) and aminomethylphosphonic acid (AMPA) in contaminated water, soil, sediment, and plants is a cause for concern due to potential threats to the ecosystem and human health. Major routes of exposure include contact with contaminated water and soil and through consumption of crops containing GLP and AMPA residues. Calcium montmorillonite (CM) and acid-processed montmorillonite (APM) clays were investigated for their ability to tightly sorb and detoxify GLP and AMPA mixtures. In vitro adsorption and desorption isotherms and thermodynamic analysis indicated saturable Langmuir binding of both chemicals with high capacities, affinities, enthalpies, and free energies of sorption and low desorption rates. In silico computational modeling indicated that both GLP and AMPA can be readily absorbed onto clay surfaces through electrostatic interactions and hydrogen bonding. The safety and efficacy of the clays were confirmed using well-established living organisms, including an aquatic cnidarian (Hydra vulgaris), a soil nematode (Caenorhabditis elegans), and a floating plant (Lemna minor). Low levels of clay inclusion (0.05% and 0.2%) in the culture medium resulted in increased growth and protection against chemical mixtures based on multiple endpoints. Results indicated that montmorillonite clays may be used to bind mixtures of GLP and AMPA in water, soil, and plants.

Elucidation of substrate interaction effects in multicomponent systems containing 3-ring homocyclic and heterocyclic polynuclear aromatic hydrocarbons

Bacterial growth and degradation experiments were conducted on carbazole (CBZ), fluorene (FLU) and dibenzothiophene (DBT) individually and in various mixture combinations using an efficient polynuclear aromatic hydrocarbon (PAH) degrading bacterial strain, Pseudomonas aeruginosa RS1. In single component systems, bacterial growth on CBZ (specific growth rate, μ = 0.99 day^-1) was much higher compared to that on FLU (μ = 0.38 day^-1) and DBT (μ = 0.33 day^-1) and bacterial growth was inhibited in the presence of FLU and DBT in binary (μ = 0.64 day^-1) and ternary (μ = 0.75 day^-1) mixtures. Multisubstrate additive modelling indicated growth inhibition in all the systems. The degradation of the compounds was significantly inhibited in binary mixtures. While the degradation of the compounds in binary mixtures varied from 35 ± 4% to 73 ± 3%, their degradation varied from 61 ± 5% to 91 ± 4%, when applied as sole substrates and from 77 ± 3% to 96 ± 3%, when applied in a ternary mixture. Degradation experiments were also conducted in ternary mixtures using a 2³ full factorial design and the results were examined using analysis of variance (ANOVA) and Tukey's honest significant difference (HSD) tests. At a low concentration of the heterocyclics, CBZ and DBT (5 mg L^-1 each), the degradation of the PAH, FLU, was significantly enhanced (from 81 ± 1% to 93 ± 0.3%) when its concentration was increased from 5 to 30 mg L^-1. The full factorial design can provide valuable insights into substrate interaction effects in mixtures.

Uncommon Sorption Mechanism of Aromatic Compounds onto Poly(Vinyl Alcohol)/Chitosan/Maleic Anhydride-β-Cyclodextrin Hydrogels

Aromatic hydrocarbons are extensive environmental pollutants occurring in both water and air media, and their removal is a priority effort for a healthy environment. The use of adsorbents is among the several strategies used for the remediation of these compounds. In this paper, we aim the synthesis of an amphiphilic hydrogel with the potential for the simultaneous sorption of a set of monocyclic and polycyclic aromatic hydrocarbons associated with toxicity effects in humans. Thus, we start by the synthesis of a copolymer-based in chitosan and β-cyclodextrin previously functionalized with the maleic anhydride. The presence of β-cyclodextrin will confer the ability to interact with hydrophobic compounds. The resulting material is posteriorly incorporated in a cryogel of poly(vinyl alcohol) matrix. We aim to improve the amphiphilic ability of the hydrogel matrix. The obtained hydrogel was characterized by swelling water kinetics, thermogravimetric analysis, rheological measurements, and scanning electron microscopy. The sorption of aromatic hydrocarbons onto the gel is characterized by pseudo-first-order kinetics and Henry isotherm, suggesting a physisorption mechanism. The results show that the presence of maleic anhydride-β-cyclodextrin and chitosan into hydrogels leads to an increase in the removal efficiency of the aromatic compounds. Additionally, the capacity of this hydrogel for removing these pollutants from a fossil fuel sample has also been tested.

Contribution of inorganic and organic components to sorption of neutral and ionizable pharmaceuticals by sediment/soil

Our previous study showed that the sorption coefficient of certain polar pharmaceuticals to river sediment, especially particular amines, was unexpectedly high. Thus, we conducted sorption experiments of selected polar pharmaceuticals and pyrene derivatives, including amines, carboxylic acids, and neutral compounds, to model clay minerals, i.e., montmorillonite and kaolin, in addition to silica sands and humic substances. The contribution of each component was roughly estimated by simple fractionation of the individual sorption coefficients. Relatively high sorption coefficients (K _d values) were found, especially for amines on clay minerals, which suggest that electrochemical affinity may play an important role. The estimated contribution percentage suggests a relatively large contribution from inorganic constituents, such as clay minerals, for silt loam soil; in contrast, organic components predominantly contribute for sandy river sediments. These findings could be the key to understanding not only the fate and transport but also bioavailability and environmental risks of pharmaceuticals, which are mostly polar and/or ionizable.

Preparation and Characterization of Polymer-Grafted Montmorillonite-Lignocellulose Nanocomposites by In Situ Intercalative Polymerization

Lignocellulose-clay nanocomposites were synthesized using an in situ intercalative polymerization method at 60°C and a pressure of 1 atm. The ratio of the montmorillonite clay to the lignocellulose ranged from 1 : 9 to 1 : 1 (MMT clay to lignocelluloses, wt%). The adsorbent materials were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), and X-ray powder diffraction (XRD). FTIR results showed that the polymers were covalently attached to the nanoclay and the lignocellulose in the nanocomposites. Both TEM and XRD analysis showed that the morphology of the materials ranged from phase-separated to intercalated nanocomposite adsorbents. Improved thermal stability, attributable to the presence of nanoclay, was observed for all the nanocomposites. The nanocomposite materials prepared can potentially be used as adsorbents for the removal of pollutants in water treatment and purification.

Biological impact of environmental polycyclic aromatic hydrocarbons (ePAHs) as endocrine disruptors

Polycyclic aromatic hydrocarbons (PAHs) are often detected in the environment and are regarded as endocrine disruptors. We here designated mixtures of PAHs in the environment as environmental PAHs (ePAHs) to discuss their effects collectively, which could be different from the sum of the constituent PAHs. We first summarized the biological impact of environmental PAHs (ePAHs) found in the atmosphere, sediments, soils, and water as a result of human activities, accidents, or natural phenomena. ePAHs are characterized by their sources and forms, followed by their biological effects and social impact, and bioassays that are used to investigate their biological effects. The findings of the bioassays have demonstrated that ePAHs have the ability to affect the endocrine systems of humans and animals. The pathways that mediate cell signaling for the endocrine disruptions induced by ePAHs and PAHs have also been summarized in order to obtain a clearer understanding of the mechanisms responsible for these effects without animal tests; they include specific signaling pathways (MAPK and other signaling pathways), regulatory mechanisms (chromatin/epigenetic regulation, cell cycle/DNA damage control, and cytoskeletal/adhesion regulation), and cell functions (apoptosis, autophagy, immune responses/inflammation, neurological responses, and development/differentiation) induced by specific PAHs, such as benz[a]anthracene, benzo[a]pyrene, benz[l]aceanthrylene, cyclopenta[c,d]pyrene, 7,12-dimethylbenz[a]anthracene, fluoranthene, fluorene, 3-methylcholanthrene, perylene, phenanthrene, and pyrene as well as their derivatives. Estrogen signaling is one of the most studied pathways associated with the endocrine-disrupting activities of PAHs, and involves estrogen receptors and aryl hydrocarbon receptors. However, some of the actions of PAHs are contradictory, complex, and unexplainable. Although several possibilities have been suggested, such as direct interactions between PAHs and receptors and the suppression of their activities through other pathways, the mechanisms underlying the activities of PAHs remain unclear. Thus, standardized assay protocols for pathway-based assessments are considered to be important to overcome these issues.

Polycyclic aromatic hydrocarbons (PAHs) removal by sorption: A review

Polycyclic aromatic hydrocarbons (PAHs) are organic micro pollutants which are persistent compounds in the environment due to their hydrophobic nature. Concerns over their adverse effects in human health and environment have resulted in extensive studies on various types of PAHs removal methods. Sorption is one of the widely used methods as PAHs possess a great sorptive ability into the solid media and their low aqueous solubility property. Several adsorbent media such as activated carbon, biochar, modified clay minerals have been largely used to remove PAHs from aqueous solution and to immobilise PAHs in the contaminated soils. According to the past studies, very high removal efficiency could be achieved using the adsorbents such as removal efficiency of activated carbon, biochar and modified clay mineral were 100%, 98.6% and >99%, respectively. PAHs removal efficiency or adsorption/absorption capacity largely depends on several parameters such as particle size of the adsorbent, pH, temperature, solubility, salinity including the production process of adsorbents. Although many studies have been carried out to remove PAHs using the sorption process, the findings have not been consolidated which potentially hinder to get the correct information for future study and to design the sorption method to remove PAHs. Therefore, this paper summarized the adsorbent media which have been used to remove PAHs especially from aqueous solutions including the factor affecting the sorption process reported in 142 literature published between 1934 and 2015.

Removal of naphthalene from aqueous systems by poly(divinylbenzene) and poly(methyl methacrylate-divinylbenzene) resins

Treatment of the oily wastewater from crude oil extraction is a growing challenge due to rising concern for the environment. Polyaromatic hydrocarbons (PAHs) deserve special attention because of their high toxicity. There is a need to develop processes able to minimize the discharge of these compounds and analytic techniques to monitor the levels of PAHs in aqueous media. In this study poly(methyl methacrylate-divinylbenzene) (MMA-DVB) and poly(divinylbenzene) (DVB) were assessed with respect to their capacity to retain naphthalene (NAF) in continuous flow and batch processes (adsorption equilibrium and kinetics). The analytic techniques applied were gas chromatography and spectrofluorimetry, which was adapted for quantification of NAF. The batch adsorption studies showed that DVB is more efficient in adsorption than MMA-DVB, and the Freundlich model and pseudo-second-order model better fitted the equilibrium data and adsorption kinetics, respectively. The elution results showed that both resins are highly efficient in removing NAF, with DVB outperforming MMA-DVB. However, MMA is cheaper raw material, making MMA-DVB more competitive for treatment of oily wastewater. The resins were regenerated by eluting about 7.2 and 2.5 L of methanol:water (70:30 v/v), respectively for DVB and MMA-DVB. Regarding to the useful life after regeneration, the resins presented a reduction about 30%, relating to zero concentration of NAF.

Sorption of atrazine, alachlor and trifluralin from water onto different geosorbents

The sorption behavior of the herbicides atrazine, alachlor and trifluralin on two modified organoclays, one model sediment, and one natural sediment in three water matrices (synthetic water, natural groundwater and surface water) was investigated.

Permeable Adsorptive Barrier (PAB) for the remediation of groundwater simultaneously contaminated by some chlorinated organic compounds

In this paper, a Permeable Reactive Barrier (PRB) made with activated carbon, namely a Permeable Adsorptive Barrier (PAB), is put forward as an effective technique for the remediation of aquifers simultaneously contaminated by some chlorinated organic compounds. A design procedure, based on a computer code and including different routines, is presented as a tool to accurately describe mass transport within the aquifer and adsorption/desorption phenomena occurring inside the barrier. The remediation of a contaminated aquifer near a solid waste landfill in the district of Napoli (Italy), where Tetrachloroethylene (PCE) and Trichloroethylene (TCE) are simultaneously present, is considered as a case study. A complete hydrological and geotechnical site characterization, as well as a number of dedicated adsorption laboratory tests for the determination of activated carbon PCE/TCE adsorption capacity in binary systems, are carried out to support the barrier design. By means of a series of numerical simulations it is possible to determine the optimal barrier location, orientation and dimensions. PABs appear to be an effective remediation tool for the in-situ treatment of an aquifer contaminated by PCE and TCE simultaneously, as the concentration of both compounds flowing out of the barrier is everywhere lower than the regulatory limits on groundwater quality.

PAH concentration gradients and fluxes through sand cap test cells installed in situ over river sediments containing coal tar

Short-term performance of permeable sand cap test cells, installed over sediment containing liquid coal tar was monitored on the Grand Calumet River (Hammond, Indiana, USA). The sand cap test cells included two sand-only cells, two test cells containing a sand/peat mixed layer, two test cells containing a sand/organoclay mixed layer, and two sediment control cells. In each test cell, six monocyclic and twelve polycyclic aromatic hydrocarbons (MAHs and PAHs) were monitored over an 18 month period, and interfacial water flow was monitored periodically. Seepage velocities ranged from 3.8 cm per day into the sediments to 3.2 cm per day out of the sediments, with discharge out of the sediments being observed more often. A ferric iron test indicated that stratified oxic-anaerobic layers were formed in the caps. Within the sand caps, concentrations of MAHs and PAHs fluctuated with time, and this fluctuation was more significant near the bottom. Near the top, most of the MAHs and PAHs were attenuated above 95% in the first year of the study, but their attenuation rates decreased in the second year due to recontamination of the surface of the caps by the surrounding sediments. Functional genes involved in PAH degradation were detected by polymerase chain reaction (PCR) in upper and lower sections of the caps for each of the three treatments. Bacterial communities were characterized by PCR amplification of 16s rRNA genes and denaturing gradient gel electrophoresis (DGGE). The results indicate that the rate and direction of sediment porewater flow is an important factor for properly designing any remedial sand cap, and that biodegradation of many of the MAH and PAH compounds was likely a major removal mechanism leading to attenuation through the test cells.

Organically modified clays as binders of fumonisins in feedstocks

This study reports an investigation on the ability of organically modified clays to bind mycotoxins, fumonisins B1 (FB1) and B2 (FB2). Organically modified clays are commercia materials prepared from natural clays, generally montmorillonite, by exchanging the inorganic cation with an ammonium organic cation. A screening experiment conducted on 13 organically modified clays and 3 nonmodified clays, used as controls, has confirmed that the presence of an organic cation in the clay interlayer promoted the adsorption of both fumonisins. On the basis of the results of the screening test, four modified clays and a Na-montmorillonite were selected for the determination of the adsorption kinetics and isotherms. On all the tested materials adsorption took place within one hour of contact with fumonisins solutions. Adsorption isotherms have pointed out that the modified clays exhibited a higher adsorptive capacity than the unmodified clay. It was also demonstrated that, notwithstanding the reduced structural difference between FB1 and FB2, they were differently adsorbed on the modified clays. Addition of 2% modified clays to contaminated maize allowed a reduction of more than 70% and 60% of the amount of FB1and FB2 released in solution. Although in vivo experiments are required to confirm the effectiveness of the organically modified clays, these preliminary results suggest that these materials are promising as fumonisins binders.

Removal of polycyclic aromatic hydrocarbons and phenols from coking wastewater by simultaneously synthesized organobentonite in a one-step process

The optimal condition for a one-step process removing organic compounds from coking wastewater by simultaneously synthesized organobentonite as a pretreatment was investigated. Results showed that sorption of organic compounds by organobentonite was positively correlated to the cation surfactant exchange on the bentonite and the octanol-water partition coefficient (Kow) of the solutes. With 0.75 g/L bentonite and 180 mg/L (60% of bentonite cation exchange capacity) cetyltrimethylammonium bromide, the removal efficiencies of the 16 polycyclic aromatic hydrocarbon (PAHs) specified by the US Environmental Protection Agency in coking wastewater except naphthalene were more than 90%, and that of benzo(a)pyrene was 99.5%. At the same time, the removal efficiencies of COD(Cr), NH3-N, volatile phenols, colour and turbidity were 28.6%, 13.2%, 8.9%, 55% and 84.3%, respectively, and the ratio of BOD5/COD(Cr) increased from 0.31 to 0.41. These results indicated that the one-step process had high removal efficiency for toxic and refractory hydrophobic organic compounds, and could improve the biodegradability of the coking wastewater. Therefore it could be a promising technology for the pretreatment of toxic and refractory organic wastewater.

Removal of o-nitrobenzoic acid by adsorption on to a new organoclay: montmorillonite modified with HDTMA microemulsion

A new organoclay, consisting of montmorillonite modified by a hexadecyl trimethyl ammonium (HDTMA) microemulsion, was synthesized, characterized and used as an adsorbent for the removal of o-nitrobenzoic acid from aqueous solution. Adsorption kinetics, isotherms and effects of operating variables, such as adsorbent dosage, ionic strength and initial solution pH, were also investigated. The results of Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) analysis and BET surface area determination indicated that HDTMA molecules had entered into the interlayer of the montmorillonite. The optimized experimental conditions for the adsorption of o-nitrobenzoic acid by montmorillonite modified by HDTMA microemulsion were 0.5 g adsorbent dosage, 0.4 mL of 0.1 mol lbL(-1) CaCl2 solution, initial solution pH of 6.0 and contact time of 6 h. The adsorption isotherms of o-nitrobenzoic acid fitted the Langmuir model well (R2 = 0.9880). The adsorption kinetics data fitted the pseudo-second-order equation (R2 = 0.9999). These above results indicate that montmorillonite modified by an HDTMA microemulsion can be used as adsorbent for o-nitrobenzoic acid because of its high adsorption capacity and low cost.

Removal of organic pollutants in model water and thermal wastewater using clay minerals

Water treatment method was developed for the removal of different anionic dyes such as methyl orange and indigo carmine, and also for thymol applying sodium bentonite and cationic surfactant - hexadecyltrimethylammonium bromide (HTAB) - or polyelectrolytes (polydiallyldimethylammonium chloride, poly-DADMAC and poly-amines). The removal efficiency of these model substrates was examined in model water using UV-Vis spectrophotometry, HPLC and TOC analysis. The clay mineral and HTAB were added in one step to the polluted model water in Jar-test experiments. The influence of the cation exchange capacity (CEC) of the applied clay mineral and the presence of polyaluminium chloride coagulant (BOPAC) were also tested for the water treatment process. The structures of the in situ produced and pre-prepared organoclay composites were compared by XRD analysis. The rapid formation of organoclay adsorbents provided very efficient removal of the dyes (65-90 % in 3-10 mg/L TOC(0) range) with 200 mg/L sodium bentonite dose, however thymol was less efficiently separated. Adsorption efficiencies of the composites were compared at different levels of ion exchange such as at 40, 60 and 100 %. In the case of thymol, the elimination of inorganic carbon from the model water before the TOC analysis resulted in some loss of the analysed volatile compound therefore the HPLC analysis was found to be the most suitable tool for the evaluation of the process. This one-step adsorption method using in situ formed organoclay was better performing than the conventional process in which the montmorillonite-surfactant composite is pre-preapared and subsequently added to the polluted water. The purification performance of this method was also evaluated on raw and artificially polluted thermal wastewater samples containing added thymol.

The use of cork waste as a biosorbent for persistent organic pollutants-Study of adsorption/desorption of polycyclic aromatic hydrocarbons

The aim of this study is to determine the sorption-desorption behavior of a mixture of thirteen aqueous PAHs on cork waste at a particle of size 0.25-0.42 mm obtained from the remains of cork strips. The final purpose is to use this natural adsorbent as an alternative to activated carbon in an innovative approach for the removal of this class of toxic compounds, and significantly reduce the regeneration costs of the process. The chemical composition of the selected cork revealed that suberin (38.5 %) and lignin (31.6 %) were the main structural components of the cell wall. The high efficiency of cork as a biosorbent of PAHs is shown by the fact that just over 80 % of adsorption occurred during the first two minutes of contact time. Both Freundlich's and Langmuir's isotherms gave good fits to the sorption process. The highest adsorption affinities were exhibited for pyrene, anthracene, and phenanthrene. Desorption studies indicate a high degree of irreversibility for all PAHs, and especially so in the case of high molecular PAHs. The correlation with K(F) and low molecular weight PAHs was the most significant. The quantity of cork required to reduce water pollution was estimated to be between 3 and 15 times less than the quantities required in the case of other materials (i.e. aspen wood and leonardite). This study demonstrates for the first time that cork is a potential biosorbent for PAHs and may have relevance in the future treatment of PAH-contaminated waters.

A procedure to design a Permeable Adsorptive Barrier (PAB) for contaminated groundwater remediation

A procedure to optimize the design of a Permeable Adsorptive Barrier (PAB) for the remediation of a contaminated aquifer is presented in this paper. A computer code, including different routines that describe the groundwater contaminant transport and the pollutant capture by adsorption in unsteady conditions over the barrier solid surface, has been developed. The complete characterization of the chemical-physical interactions between adsorbing solids and the contaminated water, required by the computer code, has been obtained by experimental measurements. A case study in which the procedure developed has been applied to a tetrachloroethylene (PCE)-contaminated aquifer near a solid waste landfill, in the district of Napoli (Italy), is also presented and the main dimensions of the barrier (length and width) have been evaluated. Model results show that PAB is effective for the remediation of a PCE-contaminated aquifer, since the concentration of PCE flowing out of the barrier is everywhere always lower than the concentration limit provided for in the Italian regulations on groundwater quality.

Removal of polycyclic aromatic hydrocarbons from organic solvents by ashes wastes

Polycyclic aromatic hydrocarbons (PAHs) can be formed during the refinery processes of crude petroleum. Their removal is of great importance. The same happens with other organic solvents used for the extraction of PAHs (hexane, acetonitrile...), which can be polluted with PAHs. Kinetic and equilibrium batch sorption tests were used to investigate the effect of wood ashes wastes as compared to activated carbon on the sorption of three representative PAHs from n-hexane and acetonitrile. Mussel shell ashes were discarded for batch sorption experiments because they were the only ashes containing PAHs. The equilibrium time was reached at 16 h. Physical sorption caused by the aromatic nature of the compounds was the main mechanism that governed the PAHs removal process. Our investigation revealed that wood ashes obtained at lower temperature (300 degrees C) did not show any PAHs sorption, while ashes obtained at higher temperature (>500 degrees C) have adsorbent sites readily available for the PAH molecules. An increase in the molecular weight of PAHs has a strong effect on sorption wood ashes wastes. As low the wood ashes particle size as high the sorption of PAHs, as a result of differences in adsorbent sites. The performance of wood ash wastes vs. activated carbon to remove 10 PAHs from organic solvents is competitive in price, and a good way for waste disposal.

Groundwater protection from cadmium contamination by permeable reactive barriers

This work studies the reliability of an activated carbon permeable reactive barrier in removing cadmium from a contaminated shallow aquifer. Laboratory tests have been performed to characterize the equilibrium and kinetic adsorption properties of the activated carbon in cadmium-containing aqueous solutions. A 2D numerical model has been used to describe pollutant transport within a groundwater and the pollutant adsorption on the permeable adsorbing barrier (PRB). In particular, it has been considered the case of a permeable adsorbing barrier (PAB) used to protect a river from a Cd(II) contaminated groundwater. Numerical results show that the PAB can achieve a long-term efficiency by preventing river pollution for several months.

Toxicity of water and sediment from stormwater retarding basins to Hydra hexactinella

Hydra hexactinella was used to assess the toxicity of stormwater and sediment samples from three retarding basins in Melbourne, Australia, using an acute test, a sublethal test, and a pulse test. Stormwater from the Avoca St retarding basins resulted in a LC50 of 613 ml/L, NOEC and LOEC values of 50 ml/L and 100 ml/L, while the 7h pulse exposure caused a significant increase in the mean population growth rate compared to the control. Water samples from the two other retarding basins were found non-toxic to H. hexactinella. This is the first study to employ sediment tests with Hydra spp. on stormwater sediments and a lower population growth rate was observed for organisms exposed to sediment from the Avoca St retarding basins. The behavioral study showed that H. hexactinella tended to avoid the sediment-water interface when exposed to sediment from all retarding basins, compared to the reference sediment. Further work is needed to determine the long-term effects of stormwater polluted sediments and acute effects due to organism exposure to short-term high concentrations during rain events.

Adsorption of naphthalene onto the carbon adsorbent from waste ion exchange resin: equilibrium and kinetic characteristics

Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental pollutants that can result in serious health problems and genetic defects in humans. In this research, a spherical microporous carbon adsorbent (CR-1) had been obtained by carbonization and activation of the waste polysulfonated cation exchange resin. Naphthalene was adopted as a model compound to examine the adsorption effectiveness for removing PAHs from the aqueous solution by CR-1. Nonlinear isotherms models, i.e., Freundlich, Langmuir, Brunauer-Emmett-Teller and Polanyi-Dubinin-Manes models were tested to fit experimental data. The adsorption equilibrium data of naphthalene on CR-1 was fitted well by the Polanyi-Dubinin-Manes model. Through both isotherm modeling and constructing "characteristic curve", Polanyi theory was useful to describe the adsorption process of naphthalene by CR-1, providing evidence that a micropore filling phenomenon is involved. In addition, among the tested kinetic models in this study (e.g., pseudo-first-order and pseudo-second-order equations), the pseudo-first-order equation successfully predicted the kinetic adsorption process.

Studies on adsorption, desorption and biodegradation of pentachlorophenol by the anaerobic granular sludge in an upflow anaerobic sludge blanket (UASB) reactor

PCP-degrading anaerobic granular sludge could be formed in an upflow anaerobic sludge blanket (UASB) reactor that was seeded with anaerobic sludge acclimated to chlorophenol. When hydraulic retention time (HRT) was 20-22 h and PCP loading rate was 200-220 mgL(-1)d(-1), the wastewater containing 170-180 mgL(-1) PCP could be treated effectively in UASB reactor, and PCP removal rate reached up to 99.5%. PCP adsorption and desorption by anaerobic granular sludge follow Freundlich isothermal equation and part of adsorption capacity was not reversible. And the isothermal equation could well describe the variation law of PCP adsorption and desorption by anaerobic granular sludge. The results indicated that the principal removal mechanism of PCP was biodegradation by anaerobic granular sludge, but not adsorption or volatilization.

Coating of silica sand with aluminosilicate clay

The objective of this work was to coat aluminosilicate clays on an inert silica support, and to characterize the properties and stability of the clay-silica coating. Two polymers, polyacrylamide (PAM) and polyvinyl alcohol (PVA), were used to bind kaolinite, illite, and smectite onto silica grains. The clay-polymer composites were studied by X-ray diffraction, FTIR, and electrophoretic mobility. Clay coatings on silica grains were characterized by mass coverage, scanning electron microscopy, specific surface area, and pH stability. Silica sand was successfully coated with clays by using the two polymers, but with PVA, the clay coating had a greater mass coverage and was more stable against pH variations. Less polymer was needed for the clay coating using PVA as compared to using PAM. Clay-polymer complexes and pure clay minerals had similar cation exchange capacities and electrophoretic mobilities, indicating that overall surface charge of the clays was little affected by the polymers. Some decrease in hydrophilicity was observed for illite and smectite when clays where coated with the polymers. The methodology reported here allows the generation of a clay-based porous matrix, with hydraulic properties that can be varied by adjusting the grain size of the inert silica support.

Sorption of pentachlorophenol on pine bark

The minimization of pentachlorophenol (PCP) transport in the environment driven by industrial wastewater discharges can be accomplished by sorption in natural, available and low cost by-products like pine bark. Taking into account that PCP is a chemical which behaviour is highly dominated by the surrounding features, this work intended to evaluate the sorption kinetics and equilibrium parameters according to the pH and temperature as well as the pine bark particle size. The PCP uptake by pine bark showed to be faster in the initial phase followed by a slower process, being 24 h the suitably time to reach the sorption equilibrium in the range of pH studied. The neutral PCP species showed to have higher binding capacity to pine bark than the anionic PCP, which was reflected in a decrease in the distribution coefficient (Kd) of the linear sorption isotherm with the increase of solution pH from 2 to 7. On the other hand, between 10 degrees C and 35 degrees C, the temperature does not seem to play a significant role in the PCP sorption by pine bark, while the sorbent size is a key parameter to enhance the overall process.

Matrix-immobilized organoclay for the sorption of polycyclic aromatic hydrocarbons and pentachlorophenol from groundwater

Sorbent materials consisting of organoclay immobilized onto the surface of a solid support were evaluated for use in pentachlorophenol (PCP) and polycyclic aromatic hydrocarbon (PAH) remediation of groundwater at a creosote-contaminated Superfund site. Cetylpyridinium-exchanged low pH montmorillonite clay (CP-LPHM) was bonded to either sand (CP-LPHM/sand) or granular activated carbon (GAC) (CP-LPHM/GAC) using the free acid form of carboxymethylcellulose as an adhesive. Effluent from an oil-water separator was eluted through equal bed volumes of composite (4 g 3:2 CP-LPHM/GAC or 13 g CP-LPHM/sand), affinity-extracted, and quantitatively analyzed by GC/MS. PCP, naphthalene, fluorene, phenanthrene, pyrene, and total PAHs were initially reduced by both CP-LPHM/GAC (> or =99%, 61%, 99%, > or =99%, 97%, and 94%, respectively) and CP-LPHM/sand (90%, 70%, 94%, 95%, 93%, and 86%, respectively). Complete breakthrough of naphthalene occurred after approximately 15 h of elution through 3:2 CP-LPHM/GAC and 22 h through CP-LPHM/sand. PCP showed complete breakthrough following 18 h of elution through 3:2 CP-LPHM/GAC and 26 h through CP-LPHM/sand. However, 50% breakthrough was not attained for higher molecular weight PAHs, as fluoranthene, pyrene, benzo[a]anthracene, and chrysene continued to be greatly reduced with both 3:2 CP-LPHM/GAC (98%, 95%, 94%, and 95%, respectively) and CP-LPHM/sand (75%, 73%, 76%, and 78%, respectively) after 48 h of continuous elution. Results confirm prior studies, indicating that these organoclay-containing composites have a high capacity for contaminants found in wood preserving waste. Further, results suggest that the inclusion of CP-LPHM may be useful as part of an effective strategy for groundwater remediation of high concentrations of PCP and PAHs, in particular high molecular weight and carcinogenic PAHs.

Sorption of phenol and 4-chlorophenol onto pumice treated with cationic surfactant

In this study the sorption of phenol and 4-chlorophenol on pumice modified with the cationic surfactants hexadecyltrimethyl ammonium bromide (HDTMA) and benzyldimethyl tetradecylammonium chloride (BDTDA) was investigated. Experimental studies indicate that HDTMA-pumice and BDTDA-pumice have the capability to remove phenol and 4-chlorophenol from aqueous solution. The influence of initial concentration and adsorbent dosage was studied. The adsorption of phenol and 4-chlorophenol increased with increasing initial concentration and decreased with increasing amount of adsorbent used. The Freundlich adsorption isotherm was found to describe well the equilibrium adsorption data. The parameters of the Freundlich model have been determined using the adsorption data.

Evaluation of new surfactant expanded zirconium and titanium phosphates for polycyclic aromatic hydrocarbons extraction from waters

A newly synthesized family of materials prepared with surfactant as organic template were tested for the extraction of polycyclic aromatic hydrocarbons (PAHs) from water, using pyrene (Pyr) and benzo[a]pyrene (B[a]P) as PAHs representatives. Particular attention was paid to the evaluation of the recovery factors with dichloromethane as eluent in order to estimate their potential as adsorbing solid phases for PAH remediation or analysis. Eleven lamellar MCM-50 type materials incorporating n-alkyl- (n = 12, 16, 18) trimethylammonium bromide molecules with different concentrations and chain lengths and two hexagonal MCM-41 type materials incorporating octadecyl-trimethyl ammonium bromide were tested. Best results were obtained by preparing lamellar MCM-50 zirconium and titanium phosphates in the presence of n-dodecyl-trimethylammonium at a relative molar concentration (surfactant/phosphate) of 1.

Natural and modified nanomaterials as sorbents of environmental contaminants

Nanotechnology is a revolutionary scientific and engineering concept that will have a large impact on our life. A core piece of this technology is the production of nanomaterials for electronic, chemical, medical, pharmaceutical, and environmental applications. In the last case, natural and modified natural nanomaterials would be good reference points for comparison of the functionality, cost, and potential ecological implications of synthetic nanomaterials. Here we investigated the performance of natural and modified nanomaterials (an allophane and a surface-modified smectite) in adsorbing copper (a common heavy metal contaminant), naphthalene (a representative polycyclic aromatic hydrocarbon), or 17beta-estradiol (an endocrine-disrupting chemical). Allophane is an effective sorbent of copper (Cu): at pH 5.5 it can take up 4448 mg Cu/kg at the equilibrium concentration of 10mg Cu/L. On the other hand, the surface-modified smectite is an excellent sorbent for naphthalene and 17beta-estradiol. It can sorb 1180mg naphthalene/kg at the equilibrium concentration of 1 mg/L or remove 98% of 17beta-estradiol from a solution after 4h of reaction. While the environmental impact and health effects of synthetic nanomaterials are essentially unknown and their use is of concern, natural nanomaterials (e.g., allophane and smectites) have been part of human existence since antiquity. As such, they do not pose much risk either to the physical environment or to human health.