Sorption Of Hydrophobic Compounds Research Articles

Comparative Study of Laterite and Bentonite Based Organoclays: Implications of Hydrophobic Compounds Remediation from Aqueous Solutions

Four cost effective organoclays were synthesized, characterized, and studied for the sorption of hydrophobic compounds (edible oil/grease and hydrocarbon oil) from aqueous solutions. Organoclays were prepared by cation exchange reaction of lattice ions (present onto the surface of laterite and bentonite clay minerals) with two surfactants, hexadecyl trimethyl ammonium chloride (HDTMA-Cl) and tetradecyl trimethyl ammonium bromide (TDTMA-Br). Fourier transform infrared spectroscopy and scanning electron microscopy were used for the characterization of synthesized organoclays. It was found that the amount of surfactant loading and the nature of the surfactant molecules used in the syntheses of organoclay strongly affect the sorption capacity of the clay mineral. Further, it was found that both the laterite and bentonite based organoclays efficiently removed the edible and hydrocarbon oil content from lab prepared emulsions; however, the adsorption capacity of clay mineral was greatly influenced by the nature of hydrophobic compounds as well.

Fate of hazardous aromatic substances in membrane bioreactors

In this work, the removal of hazardous aromatic compounds was investigated in two types of membrane bioreactors (MBRs), based on cross-flow and semi dead-end filtration systems. BTEX and PAH were efficiently eliminated from wastewater during treatment via a membrane bioreactor (90–99.9%) but non-biotic processes, i.e. volatilisation and sorption, contributed significantly. The semi dead-end MBR showed slightly better removal efficiencies than the cross-flow MBR. However, non-biotic processes were more significant in the first process and, finally, degradation rates were higher in the cross-flow MBR. Higher degradation rates were explained by a higher bio-availability of pollutants. Differences in shear stress imposed in cross-flow and semi dead-end filtration systems radically modify the sludge morphology. High shear stress (cross-flow filtration) generates dispersed bacteria and larger quantities of dissolved and colloidal matter. Sorption of hydrophobic compounds (PAHs) on suspended solid was less marked in disaggregated sludge. The results suggest new strategies for improving micro-pollutant degradation in MBRs.

The role of organic matter in the sorption capacity of marine sediments

Past studies have suggested that desiccation enhances hydrophobicity of salt marsh sediment, and that drying and rewetting sediment can be used to investigate sorption mechanisms of amino acids and other organic compounds [Liu, Z., Lee, C., 2006. Drying effects on sorption capacity of coastal sediment: The importance of architecture and polarity of organic matter. Geochim. Cosmochim. Acta 70, 3313–3324]. Here we further develop this technique to study sorption of hydrophobic and hydrophilic organic compounds in a wide range of marine sediments. Our results show that hydrophilic compounds sorb strongly to wet coastal sediments; in dried sediments, sorption of hydrophilic compounds decreases, while sorption of hydrophobic compounds is greatly enhanced. Small compounds with aromatic rings sorb more in dried than wet coastal sediments, suggesting that aromatic groups have a stronger effect on sorption than polar groups like amino and carboxyl moieties. Sorption of lysine, glutamic acid and putrescine decreases greatly when sediment is pretreated with KCl, indicating the importance of cation ion exchange. However, α-amino acids sorb much more than corresponding β- or γ-amino acids, and l-alanine sorbs more than d-alanine, suggesting that amino group location and chiral selectivity play an important role in sorption. Comparison of lysine and tyrosine sorption in different sediments indicates that source and diagenetic state of organic matter are important factors determining sorption capacity. Lysine sorbs much more to organic detritus from salt marsh sediment than to fresh Spartina root materials, marine particles, lignin or humic acids, indicating the importance of structural integrity in sorption. Desorption hysteresis of glutamic acid, putrescine and lysine (in dried sediment) suggests the presence of enzyme-type sorption sites of high sorption energy or multiple binding mechanisms. Taken together, these findings suggest that organic matter plays the major role in amino acid sorption in organic-rich sediments.

Sorption of apolar aromatic compounds to soil humic acid particles affected by aluminum(III) ion Cross-Linking.

Sorption of hydrophobic compounds in soils often shows nonlinearity, competition, and hysteresis. Since such behaviors have been associated with organic polymers in glassy state, it has been postulated that some forms of soil humic substances are glassy. The glassy state is favored by properties that decrease the flexibility of macromolecules, such as cross-linking, presence of unsaturated bonds, and high molecular weight. Polyvalent metal ions, which are abundant in soils, may cross-link humic substances by coordinating to multiple functional groups on different strands. Accordingly, we prepared an Al(3+)-cross-linked humic acid (Al-HA) from the H(+) form (H-HA) of a soil humic acid by a flocculation technique that leaves Al ions bound to organic groups. Sorption of naphthalene and 1,2,4-trichlorobenzene (TCB) on H-HA was nonlinear, competitive, and slightly hysteretic, in agreement with previous studies showing glass transition temperatures of humic acids that lie above room temperature. Nonlinearity, competition, and hysteresis were all enhanced in Al-HA, validating the hypothesis that metal ion cross-linking enhances nonideal sorption. Application of a glassy polymer sorption model reveals that cross-linking increases the affinity of solutes for the hole domain relative to the dissolution domain. The results (i) indicate that isolated, purified soil humic acid behaves like a glassy solid, (ii) indicate that metal-ion cross-linking creates a more rigid-chain structure and supports a link between nonideal sorption and the glassy character of soil organic matter, and (iii) underscore the importance of metal ions on humic structure in relation to sorption of hydrophobic organic compounds.

Sorption of Hydrophobic Compounds by Modified Poly(ethylene oxide) Networks

Various flocculates were prepared by irradiation and chemical modification of poly(ethylene oxide). It was found that the amphiphilic hydrogels are efficient for purification of waste waters and water-organic systems contaminated with dyes and pigments, even at low concentrations (0.035–0.1 wt.-%) of the polymeric PEO network flocculates. The affinity of the modified networks for ionic and nonionic species was studied as a function of the structure and crosslinking density of the networks, their degree of quaternization, and their hydrophilicity coefficients. It was established that hydrophobic organic compounds such as sodium picrate and bromophenol blue are bound predominantly to the lipophilic quaternary ammonium cations. The polyether chains remain inert (in the case of nonionic dyes) or form complexes with the alkali cations (in the case of sodium picrate). It was also found that the microenvironment of the active site (quaternary N+ ion or EO segment) affects the sorption ability of the modified networks.

Sorption of hydrophobic compounds on aquifer materials: analysis methods and the effect of organic carbon

Sorption studies of polynuclear aromatic hydrocarbons (PAH) on low-carbon aquifer materials are reported. Both column and batch partition coefficients ( K d) were affected by synthetic polymeric components, such as Teflon®, in commonly used experimental apparatus. These influences include incorrect (high) estimates for K d and tailing of peaks in column studies. Both batch and column experimental methods are developed, using polymer-free systems, that allow accurate measurement of K d's for hydrophobic PAHs in low-carbon systems. Application of these methods shows that organic carbon contents below the commonly cited threshold level of 0.1% may dominate the partitioning and subsequent transport of phenanthrene in aquifer systems.

Sorption of hydrophobic compounds by sediments, soils and suspended solids—I. Theory and background

This is the first of a two-part series describing the adsorption of hydrophobic pollutants by sediments, soils, and suspended solids. Many pollutants, including a large number of hazardous compounds, are hydrophobic and their environmental behavior varies markedly between sorbed and dissolved states. It is thus necessary to account for sorption reactions in analysis and prediction of the environmental transport and fate of such pollutants. In this first part the energetics of sorption reactions are discussed and models for description of equilibrium relationships are summarized. Factors which affect the sorption of pollutants in natural environmental systems are then considered and evaluated.

Sorption of hydrophobic pollutants on natural sediments

The sorption of hydrophobic compounds (aromatic hydrocarbons and chlorinated hydrocarbons) spanning a concentration range in water solubility from 500 parts per trillion (ppt) to 1800 parts per million (ppm) on local (North Georgia) pond and river sediments was investigated. The sorption isotherms were linear over a broad range of aqueous phase pollutant concentrations. The linear partition coefficients ( K p ) were relatively independent of sediment concentrations and ionic strength in the suspensions. The K p ś were directly related to organic carbon content for given particle size isolates in the different sediments. On an organic carbon basis ( K oc = K p /fraction ) organic carbon), the sand fraction (> 50 μm particle size) was a considerably less effective sorbent (50–90% reduction in K oc ) than the fines fraction (> 50 μm particles). Differences in sorption within the silt and clay fractions were largely related to differences in organic carbon content. Reasonable estimates of K oc ś can be made from octanol/water distribution coefficients, which are widely catalogued or easily measured in the laboratory.