Removal Of Hydrophobic Organic Compounds Research Articles

Selective removal of phenanthrene from SDBS or TX100 solution by sorption of resin SP850

Surfactant enhanced remediation (SER) is a promising technology for the removal of hydrophobic organic compounds (HOCs) from contaminated soils. Recycling of soil washing effluent by selective removing of HOCs from surfactant solutions, using techniques such as sorption, is a keyway to reduce the operation costs of SER. In this study, a potential and economical method to recycle washing effluent and lower operation costs of SER, i.e., selective sorption of phenanthrene from an anionic surfactant (sodium dodecylbenzene sulfonate, SDBS) or a nonionic surfactant (Triton X-100, TX100) solution by a resin, SP850, was developed. A modified selectivity parameter (S*), having a parabolic equation with a maximum S* value, was developed to evaluate the efficiency of the selective sorption process, the optimal surfactant concentration and SP850 dose for SER. For example, at the given SP850 dose of 1.0 g/L, the optimal concentrations of SDBS and TX100 for SER are about 15000 mg/L and 8000 mg/L, respectively. Moreover, the optimal added SP850 dose for recycling washing effluents is 1.5 g/L, which is independent of surfactant concentration. At the relatively high concentrations of surfactant used in SER, the selective sorption is depended on the sorption of phenanthrene by SP850 and the solubility enhancement of phenanthrene into surfactant micelles in solutions. The observed recycling soil washing effluent method by selective sorption using resins (e.g., SP850) as the adsorbents would be helpful for the application of SER in remediating contaminated soils.

A case study of organic micropollutants in a major Swedish water source – Removal efficiency in seven drinking water treatment plants and influence of operational age of granulated active carbon filters

A wide range of organic micropollutants (n = 163) representing several compound categories (pharmaceuticals, pesticides, per- and polyfluorinated alkyl substances, flame retardants, phthalates, food additives, drugs and benzos) were analysed in water samples from the Göta Älv river (Sweden's second largest source water). The sampling also included raw water and finished drinking water from seven drinking water treatment plants and in addition a more detailed sampling at one of the treatment plants after six granulated active carbon filters of varying operational ages. In total, 27 organic micropollutants were detected, with individual concentrations ranging from sub ng L−1 levels to 54 ng L−1. The impact of human activities along the flow path was reflected by increased concentrations downstream the river, with total concentrations ranging from 65 ng L−1 at the start of the river to 120 ng L−1 at the last sampling point.The removal efficiency was significantly (p = 0.014; one-sided t-test) higher in treatment plants that employed granulated active carbon filters (n = 4; average 60%) or artificial infiltration (n = 1; 65%) compared with those that used a more conventional treatment strategy (n = 2; 38%). The removal was also strongly affected by the operational age of the carbon filters. A filter with an operational age of 12 months with recent addition of ~10% new material showed an average removal efficiency of 92%, while a 25-month old filter had an average of 76%, and an even lower 34% was observed for a 71-month old filter. The breakthrough in the carbon filters occurred in the order of dissolved organic carbon, per- and polyfluorinated alkyl substances and then other organic micropollutants. The addition of fresh granulated active carbon seemed to improve the removal of hydrophobic organic compounds, particularly dissolved organic carbon and per- and polyfluorinated alkyl substances.

Effects of Interfaces of Goethite and Humic Acid-Goethite Complex on Microbial Degradation of Methyl Parathion.

Microbial degradation plays an essential role in the removal of hydrophobic organic compounds (HOCs) dispersed in soil and sediment, and its performance is greatly affected by mineral particles which regulate HOCs bioavailability by interfacial adsorption. Likewise, bacteria cells attach to the surfaces of mineral particles as well but how bacterial attachment affects biodegradation is largely unknown. Here we report inhibitory effects of goethite and humic acid (HA)-goethite complex addition on microbial degradation of methyl parathion (MP). Using attenuated total reflectance-Fourier transform infrared spectroscopy, we observed that the adhesion of bacterial cells responsible for MP degradation on goethite occurred and the adhesive strength increased over time. We then replaced goethite with phosphate-adsorbed goethite to weaken the goethite-bacteria association and the inhibition of MP biodegradation was alleviated. These results suggested the formation of goethite-bacteria association hinder MP biodegradation. Meanwhile, our results showed that HA coating prevented bacterial attachment on goethite particles along with a drastically increased MP adsorption by goethite. The combined effect would lead to decreased mass fluxes of MP to bacterial cells and could represent another mechanism responsible for the decreased degradation rate observed in the current study.

Prevention of Groundwater Pollution by Using the Electroosmotic Flushing of Soil Systems

Electrokinetic removal of hydrophobic organic compounds from soil systems of various compositions making it possible to avoid an ingress of toxicants into groundwater has been investigated. Solubilization of impurities was ensured by using aqueous solutions of nonionic surfactants belonging to the group of oxyethylated alkylphenols. The distribution curves of residual impurity content were obtained after the termination of electric treatment of soils following the passage of different volumes of electroosmotic solutions containing surfactants. The specified curves allow us to predict the possibility of achieving the required treatment efficiency.

Adsorptive removal of hydrophobic organic compounds by carbonaceous adsorbents: A comparative study of waste-polymer-based, coal-based activated carbon, and carbon nanotubes

Adsorption of the hydrophobic organic compounds (HOCs) trichloroethylene (TCE), 1,3-dichlorobenzene (DCB), 1,3-dinitrobenzene (DNB) and γ-hexachlorocyclohexane (HCH) on five different carbonaceous materials was compared. The adsorbents included three polymer-based activated carbons, one coal-based activated carbon (F400) and multiwalled carbon nanotubes (MWNT). The polymer-based activated carbons were prepared using KOH activation from waste polymers: polyvinyl chloride (PVC), polyethyleneterephthalate (PET) and tire rubber (TR). Compared with F400 and MWNT, activated carbons derived from PVC and PET exhibited fast adsorption kinetics and high adsorption capacity toward the HOCs, attributed to their extremely large hydrophobic surface area (2700 m2/g) and highly mesoporous structures. Adsorption of small-sized TCE was stronger on the tire-rubber-based carbon and F400 resulting from the pore-filling effect. In contrast, due to the molecular sieving effect, their adsorption on HCH was lower. MWNT exhibited the lowest adsorption capacity toward HOCs because of its low surface area and characteristic of aggregating in aqueous solution.

Investigation of Transport- and Sorption-Related Factors on the Removal of Hydrophobic Organic Compounds in Heterogeneous Soils Using a Hierarchical Modeling Approach

Hydrophobic organic compounds (HOCs) represent a class of generally highly persistent contaminants in groundwater. Factors influencing the transport of HOCs are evaluated through a hierarchical modeling approach, which incorporates particle scale sorption/diffusion with pore scale flow and transport models. The relative contributions of transport- and sorption-related factors on HOCs transport are first elucidated in a simplified single particle system. The comparative roles of different soil organic matter contents and compositions on the fate and transport of HOCs are further investigated by simulation of phenanthrene transport in porous media. This effort represents a proof-of-concept demonstration of bridging comprehensive representations of fluid-flow with mechanistic sorption/desorption processes.

Pilot-scale electrokinetic movement of HCB and Zn in real contaminated sediments enhanced with hydroxypropyl-β-cyclodextrin

This study deals with the efficiency of a pilot-scale electrokinetic (EK) treatment on real aged sediments contaminated with hexachlorobenzene (HCB) and Zn. A total of 0.5 m 3 of sediments were treated under a constant voltage in a polyvinyl chloride reactor. The changes of sediment pH, electrical conductivity (EC), organic content (OC), the transport of contaminants in sediments and the consumption of electric energy were evaluated. After 100 d processing, sediment pH slightly increased compared with the initial values, particularly in the bottom layer close to cathodic section, while sediment EC in most sections significantly decreased. Sediment OC in all sections increased, which implied that hydroxypropyl-β-cyclodextrin (HPCD) was successfully penetrated across sediments by electroosmosis. Significant movement of contaminants was observed across sediments with negligible removals. Both HCB and Zn generally moved from sections near anode and accumulated near cathode. Upon the completion of treatment, the electric energy consumption was calculated as 563 kW h m −3. This pilot-scale EK test indicates that it is difficult to achieve great removal of hydrophobic organic compounds (HOCs), or HOCs and heavy metal mixed contaminants, by EK treatment in large scale with the use of HPCD.

Analysis of a dual liquid phase biofilter for the removal of hydrophobic organic compounds from airstreams

Biofilters are fixed bed bioreactors with immobilized biofilm, which are used for the removal of pollutants from airstreams. Partial coating of the bed packing of a biofilter with an organic non-volatile and non-water miscible solvent before biofilm development is a possible way to improve the performance of the systems for the removal of hydrophobic organic compounds. The heavy solvent enhances the sorption capacity of the biofilter and may improve the rate of pollutant biodegradation. In this research a conceptual model for a dual liquid phase biofilter was developed. Using the model and simulation of the process under different conditions, it was shown that the addition of a solvent to the bed of a biofilter can enhance the biodegradation rate of a hydrophobic pollutant when there is efficient contact between biofilm and heavy solvent layers, and when the process is not reaction limited. The results of simulation moreover showed that the difference between the solubility of the pollutant in the solvent and in biofilm is an important factor that determines the usefulness of heavy solvents in biofilters. When the difference is large the inclusion would be reasonable. The model was calibrated to describe the biofiltration of n-hexane in a silicone oil amended biofilter. The trends predicted by the model are in good agreement with the experimental data.

REMOVAL OF HYDROPHOBIC MICRO‐ORGANIC POLLUTANTS FROM MUNICIPAL WASTEWATER TREATMENT PLANT EFFLUENTS BY SORPTION ONTO SYNTHETIC POLYMERIC ADSORBENTS: UPFLOW COLUMN EXPERIMENTS

Continuous upflow bench‐scale column experiments were carried out to investigate the use of a synthetic form polymer, polypropylene, and polypropylene coated with a thin layer of n‐hexane as sorbents for hydrophobic organic compounds present in the effluent of municipal wastewater treatment plant. Two polycyclic aromatic hydrocarbons, namely, phenanthrene and fluorene, were selected as representative hydrophobic organic compounds for experimental purposes. The effect of flow rate, column diameter and column height on the removal efficiency of polycyclic aromatic hydrocarbons was investigated. Removal efficiency was found to correlate well with hydraulic retention time, showing that retention time is the primary parameter in the design of the adsorption column. Dissolved organic matter did not sorb onto polypropylene or polypropylene coated n‐hexane, and the presence of dissolved organic matter in the aqueous phase did not significantly affect sorption of polycyclic aromatic hydrocarbons. For experiments with polypropylene coated with n‐hexane, an insignificant amount of n‐hexane (less than 0.03 times the aqueous solubility of n‐hexane in water) was lost due to dissolution in the effluent. The potential use of polypropylene coated n‐hexane in upflow column experiments for the removal of hydrophobic organic compounds from the effluent of municipal wastewater treatment plants was demonstrated.

Solubilization and desorption of methyl-parathion from porous media: A comparison of hydroxypropyl- β-cyclodextrin and two nonionic surfactants

The removal of hydrophobic organic compounds (HOCs) from soils and sediments by water flushing is often constrained by sorption interactions. The development of improved methods for remediation of contaminated soils has emerged as a significant environmental priority. Increasing HOCs desorption and mobility in soil using surfactants is considered to be one of the most suitable on-site techniques for soil remediation. A major concern regarding the use of surfactants for environmental restoration is the potential loss to the environment of large amounts of surfactant through sorption of nonionic types. A study was conducted to investigate whether surfactants and cyclodextrins can be used to enhance the transport of methyl-parathion in a contaminated soil. At aqueous concentrations of surfactants tested, the proportion of each surfactant sorbed to the soil increased with increasing surfactant concentrations. The maximal adsorbed mass is about 5130 and 14,200 μg/g for Brij 35 and Tween 80, respectively. In the case of nonionic surfactants, sorption attenuates surfactant effectiveness by increasing the organic carbon content of the soil matrix and retarding transport of methyl-parathion through batch and soil column experiments. However, in contrast with the surfactants, hydroxypropyl- β-cyclodextrin (HPCD) does not interact with the soil tested. The nonreactive nature of cyclodextrins, combined with its large affinity for HOCs suggests that it should have an advantage versus adsorbing surfactants for decreasing HOC distribution coefficients in subsurface systems.

Electrokinetic Removal of Hydrophobic Organic Compounds from Soil

Electrokinetic technique for soil decontamination to remove hydrophobic organic compounds, based on application of direct electric field to soil sample preliminarily treated with solutions of chelating agent and a nonionic surfactant, was developed. The influence of various factors on electroosmotic flow in soddy podzolic soil sample was studied.

A general mathematical model for chemical‐enhanced flushing of soil contaminated by organic compounds

The use of chemical agents to enhance the in situ removal of hydrophobic organic compounds (HOCs) from porous media is an emerging remediation technology. Whereas surfactants and cosolvents are the primary agents examined to date, others, such as natural organic matter and complexing agents, have also been examined for their ability to enhance the solubilization of HOCs. While the mode of action of each type of enhanced‐solubilization agent may be different, they all induce similar responses. In this paper, a general mathematical model is developed to simulate the enhanced‐solubilization process for various chemical agents, including cosolvents, surfactants, natural organic matter, and complexing agents. This model is developed using a master‐equation approach that incorporates the solubilization mechanisms associated with each type of agent. A limited evaluation of the model is conducted by comparing simulations to the results of two laboratory experiments. A sensitivity analysis is performed to illustrate the influence of various factors on contaminant removal.