Sorption kinetics of toluene in humin under two different levels of relative humidity

Sorption of organic compounds to two diesel soot black carbons in water evaluated by liquid chromatography and polyparameter linear solvation energy relationship

Substantial variability in sorption capacity of black carbon (BC) has been a major challenge for accurate fate and risk assessment of organic pollutants in soils and sediments. 16 model organic sorbates (logK_OW = 0.38-4.21) encompassing diverse chemical functionalities were used to probe the sorption capacity of two diesel soot samples representative of graphitic BC (BC1, specific surface area (SSA) = 87 m²/g) and amorphous, oxygenated BC (BC2; SSA = 3.6 m²/g). The BC-water sorption coefficients (logK_BC) of the model sorbates were determined using reversed-phase liquid chromatography (RP-LC) on soot-filled columns. It was found that mass-based logK_BC's of BC1 (1.64-3.66 L/kg_BC) exceeded those of BC2 (0.68-3.48 L/kg_BC) consistently for all model sorbates. However, area-normalized logK_BC's of BC2 were larger than those of BC1, suggesting that the overall sorption was more favored on the oxygenated sorbent per area basis. Linear solvation energy relationships (LSERs) for sorption onto BC1 and BC2 were found to be logK_BC = (2.49 ± 0.65)E + (-2.71 ± 0.88)S + (1.17 ± 0.46)A + (2.52 ± 0.34)V and logK_BC = (1.12 ± 0.39)E + (-1.68 ± 0.32)S + (-3.70 ± 0.57)B + (4.37 ± 0.38)V + (-1.51 ± 0.22), respectively. The LSERs indicated that sorption onto soot was generally enhanced with increasing non-specific van der Waals and decreasing cavitation cost (i.e., eE, sS, and vV terms). The logK_BC difference between BC1 and BC2, ΔlogK_BC, appeared to be correlated with the H-bonding capacity of the sorbates but not logK_OW. Analysis of literature and experimental logK_BC's revealed that logK_BC and logSSA across different types of BC (i.e., soot, char, charcoal, activated carbon) were linearly correlated for benzene and toluene (r² = 0.88-0.91). This work illustrates the utility of RP-LC in determining the sorption coefficients of high-capacity sorbents and suggests the possibility of a unified sorption model for the continuum of black carbon.

Sorption equilibrium of emerging and traditional organic contaminants in leafy rape, Chinese mustard, lettuce and Chinese cabbage

Emerging and petroleum contaminants could transfer into food chains by plant uptake, potentially causing food security problems. To build a prediction model, the sorption equilibrium and uptake kinetics of toluene, p-xylene, naphthalene, bisphenol A, and 4-bromo-diphenyl ether in some common leafy vegetables including leafy rape, Chinese mustard, lettuce and Chinese cabbage were examined. The kinetic experiments revealed that high sorption rates were observed for these plants that had high lipid contents. For two emerging contaminants with polar functional groups, their resulting isotherms were strongly linear (R(2) = 0.92 to 1.00), indicating that the sorption was dominated by partitioning. Moreover, regression correlation showed that log Klip, the lipid-water partition coefficient, and log Kow, the octanol-water coefficient, for these organic chemicals were strongly linear-related, following the equation: log Klip = 0.894 × log Kow+0.219 (R(2) = 0.953). The correlation equation allows the prediction of the sorption capacity of plant species for an organic compound when the plant composition and the log Kow of the chemical are determined. This improved model containing different organic chemicals with a wide range of log Kow (2.73-4.80) and including emerging contaminants was established, which shows further utilization for predicting the sorption of organic contaminants by plants.

Sorption of toluene by humic acids derived from lake sediment and mountain soil at different pH

Contamination of soil and groundwater with BTEX compounds (benzene, toluene, ethylbenzene, and xylene) depends on the sorption behavior of these compounds by soil organic matter (SOM) and humic acids (HAs). In this study sorption of toluene by HAs extracted from lake sediment and mountain soil was investigated. HA suspensions were adjusted to pH 4.00, 6.00, or 8.00 and made to the concentration of 200 mg L(-1). Each HA suspension or solution was subjected to particle size analysis using high performance particle sizer (HPPS). The particle size of HA from lake sediment was around 1000-1200 nm while that from mountain soil was 220-320 nm at suspension pH 4.00. Kinetic studies showed that sorption of toluene by the two HAs followed pseudo-first-order and mainly pseudo-zero-order kinetics. At suspension pH 4.00, the sorption of toluene by the two HAs was best described by Langmuir and Temkin adsorption isotherm models. Further, sorption of toluene by the lake sediment HA was significantly greater than that by mountain soil HA. It was thus suggested that the lake sediment HA with larger particle size may develop beneficially chemical conformation for sorption of toluene and related compounds in soil and associated environments.

New option for characterizing the mobility of organic compounds in humic acids

A new NMR option for monitoring the mobility of organic contaminants in SOM in the solid state has been successfully applied for the first time. This recently available noninvasive technique, magic angle spinning pulsed-field gradient (MAS PFG) NMR, combines both NMR spectroscopy and diffusometry to selectively monitor the diffusion of compounds sorbed in porous media or polymer matrices. Using this technique, the diffusion of toluene in humic acid particles has been studied. Measurements were performed under varying temperatures from 25 to 80 degrees C. The obtained diffusion coefficients were found to be in good agreement with those obtained from computer simulations reported elsewhere. Our results show a strong influence of the interaction of toluene with humic acid on its diffusion in the matrix even at elevated temperatures of up to 80 degrees C. The Arrhenius plot of the diffusivities shows a decrease in the activation energy of diffusion above 50 degrees C by a factor of 3. This change of activation energy is attributed to a structural change in the humic acid matrix that influences the mobility of toluene.

Sustainable oil and grease removal from synthetic stormwater runoff using bench-scale bioretention studies

One of the principal components of the contaminant load in urban stormwater runoff is oil and grease (O&G) pollution, resulting from vehicle emissions. A mulch layer was used as a contaminant trap to remove O&G (dissolved and particulate-associated naphthalene, dissolved toluene, and dissolved motor oil hydrocarbons) from a synthetic runoff during a bench-scale infiltration study. Approximately 80 to 95% removal of all contaminants from synthetic runoff was found via sorption and filtration. Subsequently, approximately 90% of the sorbed naphthalene, toluene, oil, and particulate-associated naphthalene was biodegraded within approximately 3, 4, 8, and 2 days after the event, respectively, based on decreases in contaminant concentrations coupled with increases of microbial populations. These results indicate the effectiveness and sustainability of placing a thin layer of mulch on the surface of a bioretention facility for reducing O&G pollution from urban stormwater runoff.