Effects of lipids on the sorption of hydrophobic organic compounds on geosorbents: a case study using phenanthrene

The impact of the lipid fraction of natural geosorbents on the sorption of a polycyclic aromatic hydrocarbon was assessed using several experiments. In the first set of experiments phenanthrene was sorbed on a coastal sediment as well as on its humin and humic acid fractions before and after lipid extraction. Before lipid extraction, sorption shows dominantly partitioning characteristics. However, the extraction of lipids from sediment and humin drastically increases, by up to one order of magnitude, their sorption affinity for phenanthrene at low sorbate concentrations, resulting in increased isotherm nonlinearity. This effect is less pronounced for humic acids. One mechanism proposed for the increasing sorption is that lipids, despite their very low relative abundance in the sediments, can compete with phenanthrene for specific high affinity sorption sites (e.g., matrix pores and adsorption sites). This competition is not surprising considering the similar hydrophobic nature of lipids and phenanthrene. Lipids, or any non-polar molecules, could also act like plasticizers by swelling rigid domains and disrupting high affinity sites. In both cases, the removal of lipids (and extraction solvents) makes those sites available for phenanthrene. These provide alternative explanations to the previously proposed “solvent conditioning effect” believed to occur when geosorbents are treated with non-polar solvents modifying the matrix structure, an effect yet to be proven at molecular scale. To further investigate the impact of lipids on sorption, other independent experiments were performed. In a second experiment, re-addition of lipids to the extracted sediment restored the sorption isotherm linearity observed in the native material supporting the absence of irreversible extraction artifacts. However, high addition of lipids (i.e., after saturation of high affinity sites) seems to also enlarge the low affinity partitioning domain. These results are consistent with dual-mode, hole-filling, sorption models involving diffusion. In the final set of experiments, solid-state ¹⁹F-NMR using F-labeled lipids sorbed onto the sediments confirmed that lipids may be in different domains (mobile or rigid) that interact or not with phenanthrene. The possible effects of lipid removal on sorption have been overlooked and should be considered when geosorbents are pretreated.     

Sorption of pentachlorophenol on surficial sediments: the roles of metal oxides and organic materials with co-existed copper present

The sorption characteristics of pentachlorophenol (PCP) in the surficial sediments were investigated using a selective extraction procedure. The results show that the Gamma(max) of PCP sorption decreased from 1.60mumolg(-1) to 0.69mumolg(-1) by approximately 60% after selective removal of organic materials from the sediments. The sorption of PCP in the sediments after selective removal of Mn oxides increased nearly up to 600% (from 1.60mumolg(-1) to 11.11mumolg(-1)) and, to a less degree, the PCP sorption in the sediments after simultaneous removal of Fe/Mn oxides (Gamma(max)=3.53mumolg(-1)). The analysis of the data using an additional model indicates that the contribution of Mn oxides to PCP sorption was negative, and Fe oxides and organic materials both have greater potential for sorption of PCP with less contribution from residues including Mn and Fe oxides in the residual fractions determined by a sequential extraction procedure and clay and silicate minerals. The differences in the decreased degrees of PCP sorption with increasing of Cu suggest that competition between Cu and PCP for sorption sites mainly takes place on Fe oxides.     

Colloid-facilitated transport of radionuclides through fractured media

The sorption of radionuclides on natural colloids may significantly modify their transport behaviour through fractured media, since radionuclides bound to colloids may not be subject to the important retardation mechanisms of matrix diffusion and sorption onto pore surfaces. This paper reports on theoretical and experimental work aimed at assessing the relevance of colloid-facilitated transport to repository safety analyses, with specific reference to the Swiss case. Transport models are presented, developed in conjunction with field- and laboratory-based studies of deep groundwater in the crystalline basement of northern Switzerland, in which colloid size distributions, compositions and sorption properties have been measured. Various potential mechanisms giving rise to both reversible and irreversible sorption are discussed. In the first case, a simple approach is examined which is based on previously reported models of colloid transport and assumes reversible, linear sorption on colloids, for which experimental data have been obtained. It is shown that transport of radionuclides would not, in general, be significantly enhanced because of this process. A more recently developed and more complex model is then described incorporating irreversible sorption, in which case the transport of radionuclides tends to be strongly dependent on the extent of colloid-fracture wall interaction.     

Hydroxypropyl-β-cyclodextrin extractability and bioavailability of phenanthrene in humin and humic acid fractions from different soils and sediments

Organic matter (OM) plays a vital role in controlling polycyclic aromatic hydrocarbon (PAH) bioavailability in soils and sediments. In this study, both a hydroxypropyl-β-cyclodextrin (HPCD) extraction test and a biodegradation test were performed to evaluate the bioavailability of phenanthrene in seven different bulk soil/sediment samples and two OM components (humin fractions and humic acid (HA) fractions) separated from these soils/sediments. Results showed that both the extent of HPCD-extractable phenanthrene and the extent of biodegradable phenanthrene in humin fraction were lower than those in the respective HA fraction and source soil/sediment, demonstrating the limited bioavailability of phenanthrene in the humin fraction. For the source soils/sediments and the humin fractions, significant inverse relationships were observed between the sorption capacities for phenanthrene and the amounts of HPCD-extractable or biodegradable phenanthrene (p?<?0.05), suggesting the importance of the sorption capacity in affecting desorption and biodegradation of phenanthrene. Strong linear relationships were observed between the amount of HPCD-extractable phenanthrene and the amount degraded in both the bulk soils/sediments and the humin fractions, with both slopes close to 1. On the other hand, in the case of phenanthrene contained in HA, a poor relationship was observed between the amount of phenanthrene extracted by HPCD and the amount degraded, with the former being much less than the latter. The results revealed the importance of humin fraction in affecting the bioavailability of phenanthrene in the bulk soils/sediments, which would deepen our understanding of the organic matter fractions in affecting desorption and biodegradation of organic pollutants and provide theoretical support for remediation and risk assessment of contaminated soils and sediments.     

Application of a mechanistic desorption-biodegradation model to describe the behavior of polycyclic aromatic hydrocarbons in peat soil aggregates

A procedure was developed to obtain three size fractions (2360 < d(p) < 1000, 1000 < d(p) < 710, and 710 < d(p) < 425 microm) of stable aggregates from Koopveen peat soil by application of an intense mixing regime prior to sieving of the soil material. The organic matter content, aggregation structure and the microstructure of these aggregates were determined and the particles were artificially contaminated with naphthalene and phenanthrene via a solvent phase. A nonlinear Freundlich sorption isotherm was determined for the naphthalene contaminated soil aggregates (n = 0.39; K(F) = 1.13 x 10(-2) m(1.17) kg(-0.39)). The applicability of a mathematical model, that describes sorption equilibrium, intraparticle mass-transfer, and nonlinear bacterial degradation kinetics, was tested by fitting results of dynamic desorption and biodegradation experiments, generated in this study and earlier work on the peat soil aggregates. The experimental data were described adequately although strong variations in the values of the fit parameter, the intra-particle porosity (0.30 < epsilon < 0.88), were found. This indicates the necessity of further investigations.     

The effect of structural compositions on the biosorption of phenanthrene and pyrene by tea leaf residue fractions as model biosorbents

To enhance the removal efficiency of polycyclic aromatic hydrocarbons (PAHs) by natural biosorbent, sorption of phenanthrene and pyrene onto raw and modified tea leaves as a model biomass were investigated. Tea leaves were treated using Soxhlet extraction, saponification, and acid hydrolysis to yield six fractions. The structures of tea leaf fractions were characterized by elemental analysis, Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM). The amorphous cellulose components regulated the sorption kinetics, capacity, and mechanism of biomass fractions. The adsorption kinetics fit well to pseudo-second-order model and isotherms followed the Freundlich equation. By the consumption of the amorphous cellulose under acid hydrolysis, both the aliphatic moieties and aromatic domains contributed to total sorption, thus sorption capacities of the de-sugared fractions were dramatically increased (5–20-fold for phenanthrene and 8–36-fold for pyrene). All de-sugared fractions exhibited non-linear sorption due to strong specific interaction between PAHs and exposed aromatic domains of biosorbent, while presenting a relative slow rate because of the condensed domain in de-sugared samples. The availability of strong sorption phases (aromatic domains) in the biomass fractions were controlled by polar polysaccharide components, which were supported by the FTIR, CHN, and SEM data.     

Sorption of phenanthrene by soils contaminated with heavy metals

The fate of polycyclic aromatic hydrocarbons (PAHs) in soils with co-contaminants of heavy metals has yet to be elucidated. This study examined sorption of phenanthrene as a representative of PAHs by three soils contaminated with Pb, Zn or Cu. Phenanthrene sorption was clearly higher after the addition of heavy metals. The distribution coefficient (K(d)) and the organic carbon-normalized distribution coefficient (K(oc)) for phenanthrene sorption by soils spiked with Pb, Zn or Cu (0-1000 mg kg(-1)) were approximately 24% larger than those by unspiked ones, and the higher contents of heavy metals added into soils resulted in the larger K(d) and K(oc) values. The enhanced sorption of phenanthrene in the case of heavy metal-contaminated soils could be ascribed to the decreased dissolved organic matter (DOM) in solution and increased soil organic matter (SOM) as a consequence of DOM sorption onto soil solids. Concentrations of DOM in equilibrium solution for phenanthrene sorption were lower in the case of the heavy metal-spiked than unspiked soils. However, the decreased DOM in solution contributed little to the enhanced sorption of phenanthrene in the presence of metals. On the other hand, the sorbed DOM on soil solids after the addition of heavy metals in soils was found to be much more reactive and have far stronger capacity of phenanthrene uptake than the inherent SOM. The distribution coefficients of phenanthrene between water and the sorbed DOM on soil solids (K(ph/soc)) were about 2-3 magnitude larger than K(d) between water and inherent SOM, which may be the dominant mechanism of the enhanced sorption of phenanthrene by soils with the addition of heavy metals.     

Biodegradation of polycyclic aromatic hydrocarbons in the natural waters of the Yellow River: effects of high sediment content on biodegradation

The contamination of polycyclic aromatic hydrocarbons (PAHs) has become one of the major problems in the Yellow River of China. As the Yellow River is the most turbid large river in the world, it remains unknown to which extent the high suspended sediment content in the river may affect the fate and effect of PAHs. Here we report the effect of sediment on biodegradation of chrysene, benzo(a)pyrene and benzo(g,h,i)perylene with phenanthrene as a co-metabolism substrate in natural waters from the Yellow River. Biodegradation kinetics of the PAHs in the river water with various levels of sediment contents were studied in the laboratory by fitting with a biodegradation kinetics model for organic compounds not supporting growth. The results indicated that the biodegradation rates of PAHs increased with the sediment content in the water. When the sediment contents were 0, 4 and 10 g/l, the biodegradation rate constants of chrysene with the initial concentration of 3.80 microg/l were 0.053, 0.084 and 0.111 d(-1), respectively. Further studies suggested the enhanced biodegradation rate in the presence of sediment was caused by the following mechanisms: (1) the population of PAH-degrading bacteria in the water system was found to increase with the sediment content; the bacteria population on sediment phase was far greater than that on water phase during the cultivation process; (2) the sorption of PAHs on the sediment phase was well described by the dual adsorption-partition model. Although the sorption capacity of PAH per unit weight of sediment decreased with the increase of the sediment content, the amount of sorbed PAH increased with the sediment content; and, (3) the desorption of PAHs from the solid phase led to a higher concentration near the water-sediment interface. Since the bacteria were also attached to the interface, this resulted in an increased contact chance between the bacteria and PAHs.     

Transport and transformation of sulfadiazine in soil columns packed with a silty loam and a loamy sand

Concerning the transport of the veterinary antibiotic sulfadiazine (SDZ) little is known about its possible degradation during transport. Also its sorption behaviour is not yet completely understood. We investigated the transport of SDZ in soil columns with a special emphasis on the detection of transformation products in the outflow of the soil columns and on modelling of the concentration distribution in the soil columns afterwards. We used disturbed soil columns near saturation, packed with a loamy sand and a silty loam. SDZ was applied as a 0.57 mg L(-1) solution at a constant flow rate of 0.25 cm h(-1) for 68 h. Breakthrough curves (BTC) of SDZ and its transformation products 4-(2-iminopyrimidin-1(2H)-yl)aniline and 4-hydroxy-SDZ were measured for both soils. For the silty loam we additionally measured a BTC for an unknown transformation product which we only detected in the outflow samples of this soil. After the leaching experiments the (14)C-concentration was quantified in different layers of the soil columns. The transformation rates were low with mean SDZ mass fractions in the outflow samples of 95% for the loamy sand compared to 97% for the silty loam. The formation of 4-(2-iminopyrimidin-1(2H)-yl)aniline appears to be light dependent and did probably not occur in the soils, but afterwards. In the soil columns most of the (14)C was found near the soil surface. The BTCs in both soils were described well by a model with one reversible (kinetic) and one irreversible sorption site. Sorption kinetics played a more prominent role than sorption capacity. The prediction of the (14)C -concentration profiles was improved by applying two empirical models other than first order to predict irreversible sorption, but also these models were not able to describe the (14)C concentration profiles correctly. Irreversible sorption of sulfadiazine still is not well understood.     

Role of extractable and residual organic matter fractions on sorption of phenanthrene in sediments

Two sediments were demineralized and sequentially fractionated into extracted fractions [free lipid (FL), bound lipid (BL) and lignin (LG)] and residual fractions [free lipid free (FLF), bound lipid free (BLF) and lignin free (LGF)]. The sorption isotherms of phenanthrene (Phen) were examined to evaluate the importance of various fractions on sorption. A lignin extraction procedure was for the first time applied to separate the lignin or degraded lignin fraction from sediment organic matter (SOM). The extracted LG was similar to model lignin in terms of elemental ratios and sorption behavior. FL and LG fractions were quite important, as their contents were much higher than reported values. Phen sorption for the extracted fractions was almost linear, whereas that for the residual fractions was nonlinear, especially for LGF with n 0.56–0.63. As the different organic fractions were removed sequentially, sorption energy distribution on the residual sediment organic matter (SOM) became more heterogeneous. In addition, increasing sorption capacity for the residual fractions, except for BLF with its high polarity, suggested that more sorption sites on the SOM matrix became accessible to Phen. The sorption capacity for LGF was comparable to that of condensed SOM. The residual fraction LGF generally controlled the overall sorption at low Phen concentration, but the extractable fraction FL surpassed the former fraction at high Phen concentration, demonstrating the importance of condensed SOM in the sorption of hydrophobic organic compounds (HOCs) in sediments.     

Sorption kinetic characteristics of polybrominated diphenyl ethers on natural soils

Sorption kinetic characteristics of BDE-28 and BDE-47 on five natural soils with different organic carbon fractions were investigated, and could be satisfactorily described by a two (fast and slow)-compartment first-order model with the ratio of rate constants ranged from 9 to 94 times. The fast compartment made a dominant contribution (71% ∼ 94%) to the total sorption amount in the whole process, and accounted for over 90% of the increase in the total sorption amount at initial 5 h. The influence of the slow compartment on the increase in the total sorption amount became principal (above 90%) in the subsequent stage approximately from 9 h or 25 h to the apparent equilibrium at 265 h. The results proposed the different sorption behaviors of the mathematically classified compartments for BDE-28 and BDE-47, which may correspond to the different soil components, such as soil organic fractions with amorphous and condensed structures, respectively.     

Evaluation of impacts of soil fractions on phenanthrene sorption

Phenanthrene sorption to soils and soil fractions was investigated using two contrasting soils with different clay mineral and organic carbon (OC) contents in an attempt to evaluate the contribution of each soil fraction to phenanthrene sorption and the applicability of the carbon-normalized distribution constant (K(OC)) in soils. Sorbents were characterized using surface analysis, solid-state (13)C NMR analysis, and glass transition temperature (T(g)) analysis to gain a insight into the chemical nature of OC in soils. Dissolved organic carbon (DOC) in the soil solution impeded the phenanthrene sorption, while humins accounted for the predominant phenanthrene sorption in soils. The contribution of OC to phenanthrene sorption in soil would be overestimated if only a K(OC)-approach was adopted, since clay minerals could account for much of the sorption, especially when OC was low in soils. Nitrogen gas was shown to be inappropriate for probing non-polar sorption capacity. The results obtained highlight the importance of clay minerals in governing the sorption of phenanthrene in soil, and emphasize the inapplicability of the carbon-normalized distribution coefficient K(OC) in soils.     

Effect of expandable clays and cometabolism on PAH biodegradability

Pyrene and phenanthrene degradation was examined in both single and binary slurry systems for three different natural soils. It was found that the amount of total expandable clays (smectite and vermiculite) was in a good agreement with the achieved rate and extent of biodegradation. For instance, the intrinsic phenanthrene biodegradation rate was 626 microg/L/day for the soil with the largest expandable clay and 3203 microg/L/day for the soil with the least. Similarly, the smallest total pyrene biodegradation (65%) was found for the soil rich in expandable clays, compared to an 82% pyrene reduction in the soil that had the lowest amount. Mass transfer limitation after compound sorption to the clays was more pronounced for the more hydrophobic pyrene. In the presence of phenanthrene, total pyrene biodegradation increased by 2 to 7% due to cometabolism, while the total phenanthrene biodegradation was only enhanced by 0.5 to 5% in the binary system. This research demonstrated that expandable clays might govern the substrate availability to microorganisms and microbial accessibility to substrates. Therefore, the contribution of organic matter and expandable clays to sorption, desorption and biodegradation should be taken equally into account in order to better understand complex bioremediation issues.     

Potential contributions of clay minerals and organic matter to pentachlorophenol retention in soils

Sorption of pentachlorophenol (PCP) by pure minerals and humic acids were measured to obtain additional perspective on the potential contributions of both clay minerals and soil organic matter (SOM) to contaminants retention in soils. Four types of common soil minerals and two kinds of humic acids (HAs) were tested. The sorption affinity for PCP conformed to an order of HAs > K-montmorillonite > Ca-montmorillonite > goethite > kaolinite. Such a difference in sorption capacity could be attributed to the crucial control of HAs. Clay minerals also had their contribution, especially K-montmorillonite, which played an important, if not dominant, role in the controlling process of PCP sorption. By removing 80% (on average) of the organic carbon from the soils with H(2)O(2), the sorption decreased by an average of 50%. The sorption reversibility had been greatly favored as well. Considering the uncharged mineral fractions in soil before and after H(2)O(2)-treated, the main variation in sorption behavior of the soil might thus be related to the removed organic carbon and the reduced pH. This testified rightly the interactive effect of SOM and clay minerals on PCP sorption as a function of pH.     

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.     

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

Complex mixtures of hazardous chemicals such as polycyclic aromatic hydrocarbons (PAHs) in contaminated soil and groundwater can have severe and long-lasting effects on health. The evidence that these contaminants can cause adverse health effects in animals and humans is rapidly expanding. The frequent and wide-spread occurrence of PAHs in groundwater makes appropriate intervention strategies for their remediation highly desirable. The core objective of this research was to assess the ability of a clay-based composite to sorb and remove toxic contaminants from groundwater at a wood-preserving chemical waste site. Treatment efficiencies were evaluated using either effluent from an oil-water separator (OWS) or a bioreactor (B2). The effluent water from these units was passed through fixed bed columns containing either an organoclay composite or granular activated carbon. The sorbent columns were placed in-line using existing sampling ports at the effluent of the OWS or B2. Individual one-liter samples of treated and untreated effluent were collected in Kimax bottles over the course of 78 h (total of 50 samples). Subsequently each sample was extracted by solid phase extraction methodology, and pentachlorophenol (PCP) and PAH concentrations were quantitated via GC/MS. Columns containing porous organoclay composite, i.e. sand-immobilized cetylpyridinium-exchanged low-pH montmorillonite clay (CP/LPHM), were shown to reduce the contaminant load from the OWS effluent stream by 97%. The concentrations of benzo[a]pyrene (BaP) and PCP were considerably reduced (i.e. >99%). An effluent stream from the bioreactor was also filtered through columns packed with composite or an equivalent amount of GAC. Although the composite reduced the majority of contaminants (including BaP and PCP), it was less effective in diminishing the levels of lower ring versus higher ring PAHs. Conversely, GAC was more effective in removing the lower ring PAHs, except for naphthalene and PCP. The effectiveness of sorption of PCP from the OWS effluent by the composite was confirmed using a PCP-sensitive adult hydra bioassay previously described in our laboratory. The findings of this initial study have delineated differences between CP/LPHM and GAC for groundwater remediation, and suggest that GAC (instead of sand) as the solid support for organoclay may be more effective for the treatment of contaminated groundwater under field conditions than GAC or CP/LPHM alone. Further work is ongoing to confirm this conclusion.     

Dissolved organic matter effects on the performance of a barrier to polycyclic aromatic hydrocarbon transport by groundwater

In order to contain the movement of organic contaminants in groundwater, a subsurface sorption barrier consisting of sand or clay minerals coated with a cationic surfactant has been proposed. The effectiveness of such a sorption barrier might be affected by the presence of dissolved organic matter (DOM) in the groundwater. To study the impact of DOM on barrier performance, a series of batch experiments were performed by measuring naphthalene and phenanthrene sorption onto sand coated with cetylpyridinium chloride (CPC) and bentonite coated with hexadecyltrimethylammonium bromide (HDTMA) in the presence of various concentrations of DOM. The overall soil-water distribution coefficient (K*) of naphthalene and phenanthrene onto CPC-coated sand decreased with increasing DOM concentration, whereas the K* of the compounds onto HDTMA-coated bentonite slightly increased with increasing DOM concentration. To describe the overall distribution of polycyclic aromatic hydrocarbons (PAHs) in the systems, a competitive multiphase sorption (CMS) model was developed and compared with an overall mechanistic sorption (OMS) model. The modeling studies showed that while the OMS model did not explain the CPC-coated sand experimental results, a model that included competitive sorption between DOM and PAH did. The experimental results and the modeling study indicated that there was no apparent competition between DOM and PAH in the HDTMA-coated bentonite system, and indicated that in groundwater systems with high DOM, a barrier using HDTMA-coated bentonite might be more effective.     

Pentachlorophenol sorption by variable-charge soils in methanol-water mixture: pH effect at the low solvent volume fraction

Information on how cosolvents affect sorption of ionizable chemicals by soils with heterogeneous variable-charge mineral surface domains is sparse. In this study, the effect of soil-solution pH in methanol/water solutions on sorption of pentachlorophenol (PCP) by variable-charge soils with a range of hydrophilic (f Hphilic) and hydrophobic (f Hphobic) sorption domains was characterized. PCP sorption by 10 variable-charge soils was measured as a function of apparent pH (pH app) and methanol volume fraction (fc8) decreased log-linearly with increasing fc, but the slope of the relationship was less for anionic PCP. The empirical solvent-sorbent interaction term for anionic PCP (alpha i) was inversely correlated with f Hphilic (r2=0.82), which is consistent with methanol-induced increases in anion exchange. For neutral PCP, the empirical term (alpha n) was positively correlated with f Hphobic (r2=0.84), supporting methanol-induced increases in solution and sorbent hydrophobicity. Sorption of PCP by two soils with varying f Hphilic in the pH app range from 3 to 8 at fc相似文献   

The equilibria of bisolute sorption on soil

The goal of this study was to investigate the effects of both concentration levels and loading sequence or contamination history of each pollutant on the equilibrium sorption of mixed organic pollutants on soils. We measured binary sorption equilibria for a soil using ten concentration levels for both phenanthrene and naphthalene. Both solutes were either simultaneously loaded or sequentially loaded (i.e., the second sorbate was loaded after the sorption of the first sorbate had attained equilibrium) on soil. The results showed different competitive sorption equilibria between phenanthrene and naphthalene. In the presence of phenanthrene and regardless of loading sequence, naphthalene exhibited consistently lower sorption capacities and the ideal adsorbed solution theory (IAST) slightly underestimates the naphthalene sorption equilibria. Conversely, the sorption equilibria of phenanthrene in the presence of naphthalene depended upon the loading sequence of the two sorbates on the soil. Little competition from naphthalene on the sorption equilibria of phenanthrene was observed when phenanthrene was loaded either simultaneously with or sequentially after naphthalene, but appreciable competition from naphthalene was observed when the soil had been pre-contaminated with phenanthrene. IAST slightly underestimates the phenanthrene sorption equilibria observed in the latter system, but it cannot estimate the phenanthrene sorption equilibria in the former two systems. We proposed that adsorption on internal surfaces of ink-bottle shaped pores within relatively flexible sorbent matrix may have caused the competitive sorption phenomena observed in this study. The study suggests that contamination history may have strong influence on the equilibrium sorption of organic pollutant mixtures.     

Removal of lignin and tannin colour from aqueous solution by adsorption onto activated charcoal

Sorptive uptake of lignin and tannin from an aqueous phase by activated charcoal was investigated in the laboratory. The sorption reaction was found to be of a first order. The influence on the rate of sorption of various factors, such as amount of sorbent and pH of the system, have been investigated. Sorption data fit well into the Langmuir adsorption isotherm, indicating formation of a monolayer over a homogeneous sorbent surface. Sorption capacity, rate constant, intraparticle diffusion coefficient, etc. were calculated from the sorption data. Desorption studies indicate the irreversible nature of the sorption reaction, whereas interruption studies suggest film diffusion to be rate limiting.