Sorption Of PCE Research Articles

Effects of polycarboxylate superplasticizer equipped with β-cyclodextrin as the terminal group on the fluidity of montmorillonite-containing cement paste

In this study, β-Cyclodextrin (β-CD) as the terminal group was grafted on polyoxyethylene (PEO) via click reaction for preparing monovinyl β-Cyclodextrin monomer (β-P). Then β-P was employed to synthesize a polycarboxylate superplasticizer with β-CD grafted on the side chain [PAA-g-(β-P) n HPEG]. The functional groups, molecular weights, and molecular weight distributions of synthesized copolymers PAA-g-(β-P) n HPEG were characterized by Fourier transform infrared spectra (FT-IR), 1H nuclear magnetic resonance spectroscopy (1H NMR), and gel permeation chromatography (GPC). The dispersion performance of PAA-g-(β-P) n HPEG in cement paste containing montmorillonite (MMT) clay was tested. Sorption measurement and X-ray diffraction (XRD) analysis revealed that the PAA-g-(β-P) n HPEG intercalated less into the interlayer space of MMT than PAA-g-HPEG only with PEO as the side chain. β-CD as the terminal group grafted on the end of the side chain of PCE effectively hindered PCE sorption on MMT and enhanced the clay-tolerance property of PAA-g-(β-P) n HPEG. This study offered a new idea in designing polycarboxylate superplasticizers to lower their clay sensitivity.

Two-Stage Ozonation – Adsorption Purification of Ground Water from Trichloroethylene and Tetrachloroethylene with Application of Commercial Carbon Adsorbents

ABSTRACT The aim of the research is to choose the most efficient adsorbent for two-stage ozone-sorption purification of groundwater containing both trichloroethylene (TCE) and tetrachloroethylene (PCE) between three carbon sorbents produced in Russia (AUT-M, CAUSORB-221, and AG-3). Sorption isotherms of TCE and PCE on AUT-M and CAUSORB-221 at 296 K were fitted by the Freundlich equation. The better TCE and PCE sorption ability of AUT-M in comparison with CAUSORB – 221 and AG-3 was demonstrated. The optimum parameters for ozonation and sorption stages of groundwater purification from TCE and PCE are elucidated using laboratory and pilot-plant scales. Prolonged test of this technology for purification of ground demonstrated that the higher achievable efficiency of destruction with ozone is 94% for TCE and 38% for PCE. Ozonation-sorption treatment of groundwater allows one to achieve TCE and PCE removal efficiency of 96-97% and 92-94% correspondingly. The most efficient carbon sorbent is microporous carbon fiber AUT-M. Using this sorbent, TCE and PCE concentrations in treated water decrease below the MPC level (5 μg/L) adopted in Russia. It is concluded that the combination of ozonation with sorption of residual contaminants by carbon sorbents is a promising way for the purification of waters containing chlorinated contaminants.

Sorption mechanisms of chlorinated hydrocarbons on biochar produced from different feedstocks: Conclusions from single- and bi-solute experiments

Biochar is increasingly deemed a potential sorbent for contaminants in soil and water remediation. We tested three biochars from different feedstocks (cattle manure, grain husk, and wood chips) produced at relatively low pyrolysis temperature (450 °C), for their sorption behavior towards trichloroethylene (TCE) and tetrachloroethylene (PCE) in single- and bi-solute systems. In single-solute experiments, all biochars show stronger sorption for TCE (about 50% based on solubility-normalized Freundlich coefficients). The lower sorption of PCE is attributed to steric effects, e.g. size exclusion in small micropores and specific interactions. Plant-derived, carbon-rich biochars with high specific surface area and microporosity predominantly sorb via pore-filling, as also observed in activated carbon. Biochar produced from manure, with higher ash content and polarity, and smaller total pore volume (PVtot), shows significant contribution of partitioning. These findings also apply to bi-solute systems. TCE and PCE show different competition behavior depending on biochar properties. Plant-based biochars are pore-filling-dominated and show strong competition. However, competition behavior in microporous biochars depends on the concentration range. Manure biochar with high polarity and low PVtot shows significant partitioning and therefore less competition. Compared to the plant-based chars competition in manure biochar is not concentration-dependent. These results indicate that biochars with a large fraction of non-carbonized phase facilitate non-competitive sorption and might be a valuable sorbent in mixed contaminant systems.

Impact of sorption processes on PCE concentrations in organohalide-respiring aquifer sediment samples

The evaluation of groundwater contaminant e.g. tetrachloroethene (PCE) degradation processes requires complete quantification of and pathway analysis of the groundwater contaminant under investigation. For example the reduction of PCE concentrations in the groundwater by unknown dissolution and/or sorption processes will impede interpretation of the fate and behaviour of such contaminants. In the present study PCE dissolution and sorption processes during anaerobic microbial degradation of chlorinated ethenes were investigated. For this purpose, microcosms were prepared using sediment samples from a PCE-contaminated aquifer, which in previous studies had demonstrated anaerobic organohalide respiration of PCE. Solid/water distribution coefficients (kd) of PCE were determined and validated by loss-on-ignition (LOI) and PCE sorption experiments. The determined kd magnitudes indicated methodological congruency, yielding values for sediment samples within a range of 1.15±0.02 to 5.93±0.34L·kg−1. The microcosm experiment showed lower PCE concentrations than expected, based on spiked PCE and observed anaerobic microbial degradation processes. Nevertheless the amount of PCE spike added was completely recovered albeit in the form of lower chlorinated metabolites. A delay due to dissolution processes was not responsible for this phenomenon. Sorption to sediments could only partially explain the reduction of PCE in the water phase. Accordingly, the results point to reversible sorption processes of PCE, possibly onto bacterial cell compartments and/or exopolymeric substances.

Characteristics and influencing factors of tetrachloroethylene sorption-desorption on soil and its components.

To investigate the effects of soil structure, soil organic carbon (SOC), minerals, initial tetrachloroethylene (PCE) concentration (C0), and ionic strength (Ci) on PCE sorption-desorption, six types of soil were adopted as adsorbents, including two types of natural soil and four types of soil with most of the "soft carbon" pre-treated by H2O2 or with all SOC removed from the original soil by 600 °C ignition. The results showed that all of the sorption-desorption isotherms of PCE were non-linear within the experimental range, and the H2O2-treated samples exhibited higher non-linear sorption isotherms than those of the original soils. The hysteresis index of PCE sorption to original soil is less pronounced than that of the H2O2-treated and 600 °C-heated samples due to the entrapment of sorbate molecules in the "hard carbon" domain, together with the meso- and microporous structures within the 600 °C-heated samples. Both SOC and minerals have impacts on the sorption-desorption of PCE, and the sorption-desorption contribution rate of minerals increased with decreasing SOC content. C0 has almost no influence on the sorption to minerals of the soils, but the contribution rate of minerals decreased with increasing C0 in the desorption stage. As a result of the salting-out effect, PCE sorption capacity was increased by increasing Ci, especially when Ci ≥ 0.1 M. Moreover, desorption increased and hysteresis weakened with increasing Ci, except for the 600 °C-heated samples. In addition, no significant effect of Ci on desorption of PCE and no hysteresis was observed in this experimental range for the 600 °C-heated samples.

Identification of TCE and PCE sorption and biodegradation parameters in a sandy aquifer for fate and transport modelling: batch and column studies.

The main aim of this study was to determine the sorption and biodegradation parameters of trichloroethene (TCE) and tetrachloroethene (PCE) as input data required for their fate and transport modelling in a Quaternary sandy aquifer. Sorption was determined based on batch and column experiments, while biodegradation was investigated using the compound-specific isotope analysis (CSIA). The aquifer materials medium (soil 1) to fine (soil 2) sands and groundwater samples came from the representative profile of the contaminated site (south-east Poland). The sorption isotherms were approximately linear (TCE, soil 1, K d = 0.0016; PCE, soil 1, K d = 0.0051; PCE, soil 2, K d = 0.0069) except for one case in which the best fitting was for the Langmuir isotherm (TCE, soil 2, K f = 0.6493 and S max = 0.0145). The results indicate low retardation coefficients (R) of TCE and PCE; however, somewhat lower values were obtained in batch compared to column experiments. In the column experiments with the presence of both contaminants, TCE influenced sorption of PCE, so that the R values for both compounds were almost two times higher. Non-significant differences in isotope compositions of TCE and PCE measured in the observation points (δ13C values within the range of −23.6 ÷ −24.3 ‰ and −26.3 ÷−27.7 ‰, respectively) indicate that biodegradation apparently is not an important process contributing to the natural attenuation of these contaminants in the studied sandy aquifer.

Nonideal transport of contaminants in heterogeneous porous media: 10. Impact of co-solutes on sorption by porous media with low organic-carbon contents

The impact of co-solutes on sorption of tetrachloroethene (PCE) by two porous media with low organic-carbon contents was examined by conducting batch experiments. The two media (Borden and Eustis) have similar physical properties, but significantly different organic-carbon (OC) contents. Sorption of PCE was nonlinear for both media, and well-described by the Freundlich equation. For the Borden aquifer material (OC=0.03%), the isotherms measured with a suite of co-solutes present (1,2-dichlorobenzene, bromoform, carbon tetrachloride, and hexachloroethane) were identical to the isotherms measured for PCE alone. These results indicate that there was no measurable impact of the co-solutes on PCE sorption for this system. In contrast to the Borden results, there was a measurable reduction in sorption of PCE by the Eustis soil (OC=0.38%) in the presence of the co-solutes. The organic-carbon fractions of both media contain hard-carbon components, which have been associated with the manifestation of nonideal sorption phenomena. The disparity in results observed for the two media may relate to relative differences in the magnitude and geochemical nature of these hard-carbon components.

Degradation of PCE in an anaerobic waste gas by biofiltration

Simulated landfill gas, consisting of an equimolar mixture of carbon dioxide and methane and containing tetrachloroethylene (PCE) as a model impurity compound, was treated in a biofilter under anaerobic conditions. The PCE concentrations ranged from 30 to 100 ppm. Sucrose was added as an additional energy and carbon source. Tetrachloroethylene was dechlorinated completely. The final end-product of biodegradation could not be identified, but chlorinated hydrocarbons (vinyl chloride, dichloroethylene and trichloroethylene) were excluded. After an acclimation period the biofilter’s PCE removal efficiency was higher than 98%. Granular activated carbon (GAC) was chosen as the support material for the biomass. GAC is a good sorbent, and PCE sorption probably played a major role in the successful biodegradation. The experiments, on the other hand, all indicate that tetrachloroethylene removal was due to metabolic degradation rather than sorption on the activated carbon. The removal rate was estimated to be 4.1 g PCE/(hm 3 biofilter volume). To the best of our knowledge, this is the first study reporting PCE biodegradation in an anaerobic, waste-gas environment.

Chlorinated Ethene Reduction by Cast Iron: Sorption and Mass Transfer

Tetrachloroethylene (PCE) and trichloroethylene (TCE) exhibited significant nonlinear sorption to nonreactive sites when exposed to four cast irons. Cast iron is a reactive material that promotes reductive dechlorination and has recently been used for \Iin-situ\N remediation of chlorinated solvent contminated ground water. Comparisons between PCE sorption to cast iron, graphite, and iron-containing minerals indicate that nonreactive soprtion is due to exposed graphite inclusions in the cast iron. Sorption of the homologous series of chloroethenes to a cast iron adheres to Traube’s rule; thus, the extent of sorption is related primarily to compound hydrophobicity. An analytical model incorporating rate-limited sorption/desorption to nonreactive sites was used to assess sorption nonequilibrium. Effective sorption and desorption rate coefficients determined how significant mass transfer limitations to nonreactive sorption sites exist for PCE and not for TCE. The nonreactive sorption observed indicates that flow-through cast iron treatment systems will exhibit significant delayed attainment of steady-state conditions for chlorinated ethenes, particularly PCE and TCE.

Long-term sorption of halogenated organic chemicals by aquifer material. 1. Equilibrium

The sorption of tetrachloroethene (PCE) and 1,2,4,5-tetrachlorobenzene (TeCB) was studied on sandy aquifer material from Borden, ON, by using a batch methodology designed to accurately measure sorption over long equilibration periods. Autoclaving was effective in inhibiting biotransformation, and use of fire-sealed glass ampules precluded volatilization losses. Data analysis techniques were developed to accurately account for partitioning to sample headspace and other losses. Sorption isotherms for PCE and TeCB with Borden solids deviated from linearity when a 4-5 order of magnitude range in aqueous concentration was considered. However, in the dilute range (<50 {mu}/l), the deviations from linearity were inconsequential. The sorption of TeCB was approximately 40 times stronger than for PCE, in qualitative accordance with TeCB's approximately 100-fold greater octanol-water partitioning coefficient. For a given solute, the distribution coefficients differed by a factor of 30 among the various size fractions, being greatest for the largest grains. For most Borden solids, the long-term sorption of PCE and TeCB exceeded by more than 1 order of magnitude the predictions of generalized correlations based on hydrophobic partitioning into organic matter. This difference is believed to be partially the result of mineral contributions to sorption, but may also reflect unattainment of equilibrium in previouslymore » regressed results - in this study, contact times on the order of tens to hundreds of days were required. For Borden solids, pulverization of solid samples was shown to be a viable expedient to obviate the need for excessively long equilibrations.« less