Complete Removal Of Contaminants Research Articles

Interfacial Acid‐Like Microenvironment and Orbital Modulating Strategy toward Efficient Hydrogen Evolution in Neutral High‐Salinity Wastewater/Seawater

Electrochemical high‐salinity wastewater splitting is a promising technology for green hydrogen (H2) production. However, the kinetics of hydrogen evolution reaction (HER) in neutral media is slow, and the high theoretical potential of oxygen evolution reaction leads to large energy losses. Herein, an iron‐based electrocoagulation‐coupled hydrogen production integrated system (IEHPS) is constructed, which is realized by coupling low‐potential anodic iron oxidation reaction with cathodic HER. The non‐noble metal HxWO3‐Ni catalyst is synthesized by fabricating a proton sponge HxWO3 to achieve an interfacial acid‐like microenvironment and doping it with Ni heteroatom to modulate the 4d orbital of W, thereby weakening the adsorption strength of the W site toward hydrogen. Consequently, the HxWO3 Ni demonstrates remarkable performance characteristics, boasting a mere 131 mV overpotential at 10 mA cm−2 and Tafel slope of 44 mV dec− in neutral media. Operating at an applied voltage of 1.5 V, the IEHPS exhibits a high hydrogen production rate of 235 mL g−1 min−1 in seawater. It achieves nearly complete removal of contaminants like rhodamine B and heavy metal ions within a rapid 8–20 min, with an energy consumption of only 3.7 kWh Nm−3. This study provides a promising pathway for efficient and energy‐saving production of high‐purity hydrogen and effective treatment of high‐salinity wastewater.

Electro-oxidation of ammonia nitrogen using W, Ti-doped IrO2 DSA as a treatment method for mariculture and livestock wastewater.

Animal farming wastewater is one of the most important sources of ammonia nitrogen (NH4+-N) emissions. Electro-oxidation can be a viable solution for removing NH4+-N in wastewater. Compared with other treatment methods, electro-oxidation has the advantages of i) high removal efficiency, ii) smaller size of treatment facilities, and iii) complete removal of contaminant. In this study, a previously prepared DSA (W, Ti-doped IrO2) was used for electro-oxidation of synthetic mariculture and livestock wastewater. The DSA was tested for chlorine evolution reaction (CER) activity, and the reaction kinetics was investigated. CER current efficiency reaches 60-80% in mariculture wastewater and less than 20% in livestock wastewater. In the absence of NH4+-N, the generation of active chlorine follows zero-order kinetics and its consumption follows first-order kinetics, with cathodic reduction being its main consumption pathway, rather than escape or conversion to ClO3-. Cyclic voltammetry experiments show that NH4+-N in the form of NH3 can be oxidized directly on the anode surface. In addition, the generated active chlorine combines with NH4+-N at a fast rate near the anode, rather than in the bulk solution. In electrolysis experiments, the NH4+-N removal rate in synthetic mariculture wastewater (30-40mg/L NH4+-N) and livestock wastewater (~ 450mg/L NH4+-N) is 112.9g NH4+-N/(m2·d) and 186.5g NH4+-N/(m2·d), respectively, which is much more efficient than biological treatment. The specific energy consumption (SEC) in synthetic mariculture wastewater is 31.5 kWh/kg NH4+-N, comparable to other modified electro-catalysts reported in the literature. However, in synthetic livestock wastewater, the SEC is as high as 260 kWh/kg NH4+-N, mainly due to the suppression of active chlorine generation by HCO3- and the generation of NO3- as a by-product. Therefore, we conclude that electro-oxidation is suitable for mariculture wastewater treatment, but is not recommended for livestock wastewater. Electrolysis prior to urea hydrolysis may enhance the treatment efficiency in livestock wastewater.

Upscaling the reaction rates in porous media from pore- to Darcy-scale

Modeling and prediction of reactive transport in porous media are challenging due to the complexity of the characterization of reactions across spatial and time scales. The application of reaction rates obtained from batch experiments to porous media is not valid because it disregards the influences of flow pathways, distribution of residence time, transport limitations within the porous media, as well as neglecting the impact of surface mineralogy heterogeneity. In this study, we presented how the pore-scale modeling can help to improve the Darcy-scale simulations. First, the reactive transport was simulated in a pore-network model and was validated against the experiments. Then, the pore-network results were averaged to obtain the effective reaction rates as a function of pore velocity, the inlet concentration, and the resident concentration. The upscaled function was incorporated into the Darcy-scale model and showed a significant improvement in predicting the concentration profiles. Notably, the use of batch reaction rates in the Darcy model (ADRE-batch) led to significant underestimation, up to 93%, of the required pore volume injection for complete contaminant removal from the simulation domain.

Effective removal of metal-carbide contamination from diamond circuit boards by reactive ion etching

Recently, we have demonstrated the feasibility of using laser-patterned polycrystalline diamond sheets as a substrate for implantable circuit boards. The laser grooves in the diamond can be filled with biocompatible braze alloys such as Au-ABA and polished back to create long-lasting, hermetic circuit boards suitable for implantation in the human body. However, during the process of depositing molybdenum and niobium layers to aid adhesion of the Au-ABA braze, a residual film was found to form, which was resistant to both polishing and chemical etching, resulting in electrical shorting between features on the circuit board. Here, we report an optimised reactive ion etching process to remove the residual metal contamination and electrically isolate fine features on the diamond circuit boards. Samples were evaluated through energy dispersive spectroscopy elemental analysis and electrical testing of the diamond surface, confirming the complete removal of contaminants from the diamond surface.

Electron flux at the Schottky junction of Bi NPs and WO3-supported g-C3N4: an efficient ternary S-scheme catalyst for removal of fluoroquinolone-type antibiotics from water.

Recently, global-scale attempts have been conducted to develop clean technologies and affordable materials to remediate pharmaceutical contaminants of water resources that are resistant to the biodegradation. In line with global efforts, this study reports a facile method to fabricate Bi nanocrystals in situ decorated on WO3 nanoplates and its composite with graphitic carbon nitride (WO3/Bi/g-C3N4) for photocatalytic degradation of fluoroquinolone-type antibiotics (ciprofloxacin and ofloxacin). The designed ternary S-scheme WO3/Bi/g-C3N4 composite material was fully characterized by physicochemical and electrochemical analysis. Depositing the cost-effective and earth-abundant Bi nanocrystals onto WO3 via a facile reduction route has been shown to increase the boosting of electron flux at their interface (Schottky junction). The S-scheme separation is confirmed by the calculation of band positions and the analysis of photogenerated hydroxyl radicals and holes. The complete removal of contaminants was obtained over the WO3/Bi/g-C3N4 photocatalyst after 90 min under visible light irradiation. The present work would provide a rational route for developing Bi NP-based photocatalysis to replace metallic Au, Pt, and Ag NPs.

Treatability Studies on the Optimization of Ozone and Carbon Dosages for the Effective Removal of Contaminants from Secondary Treated Effluent

This study investigates the novel and advanced integrated pilot-scale treatment system of removal of contaminants in the secondary effluent from municipal wastewater. The main intent of this work is to assess the combination of pressure sand filter (PSF), ultrafiltration (UF), ozone (O3), and granular activated carbon (GAC) to treat wastewater and evaluate its suitability for water reuse. The experiments were carried out in a following condition: [Formula: see text], [Formula: see text], and [Formula: see text]. Configuration 1 was found to be more effective when compared to the other two and almost there occurred complete removal of contaminants. Whereas configuration 2 had the lowest removal efficiency of all, and configuration 3 had quite positive results. The influence of process parameters such as ozone dosage, flow rate, and filtration time was optimized. The optimized filtration time was 20 min with the filtration feed flow rate of 300 LPH. The best configuration of this treatment process produced a removal efficiency of about 80 to 90% with the ozone dosage of 8.33 mg/L with a flow rate of 4 l/min, whereas there occurred complete removal by the subsequent action of GAC. Moreover, the biodegradability of wastewaters as measured by the BOD5/COD ratio increased from 0.45 to 0.53. The proposed integrated pilot-scale process was effective in removing contaminants to the required level of discharge in the environment or reuse and it will pave the way to provide significant benefits to wastewater treatment.

Graphene Oxide-Chitosan Aerogels: Synthesis, Characterization, and Use as Adsorbent Material for Water Contaminants.

Porous aerogels, formed by subjecting precursor hydrogels using a freeze-drying process, are certainly one of the most studied and synthetized soft materials, thanks to their important features such as elasticity, swelling behavior, softness, and micro and nanosized pores, which guarantee their applicability in various fields. Typically, these systems are synthetized working with natural or synthetic polymers, but in the last years great interest has been given to proper formulated aerogels able to combine polymeric structures with other moieties such as graphene or graphene oxide. This working strategy can be pivotal in many cases to tune important properties of the final system such as toughness, porosity, elasticity, electrical conductivity, or responsive behavior. In this work we propose the synthesis of chitosan graphene oxide aerogels obtained through self-assembly of graphene oxide sheets and chitosan chains. These three-dimensional systems were chemically characterized with IR and XRD technique and their inner structure was investigated through the scanning electron microscopy (SEM). Moreover, we mechanically characterized the material through dynamic mechanical analysis, showing the stability of these systems. Finally, the adsorption ability of these soft materials has been demonstrated using model molecules to simulate water contaminants showing the efficacy of those graphene-based systems even for the removal of anionic dyes. Complete removal of contaminants was obtained at low concentration of dyes in solution (100 mg/L), while with a higher amount of pollutant in the solution (350 mg/L) high sorption capacity (q > 200 mg/g) was observed.

A Recent Advancement on Treatment Technologies for Handling of Pharma Waste water

The Pharmaceutical Industry produces a wide variety of products in batch or semi-batch processes where the usage of water in many processing equipment plays an important role. The wastewater that is generated from these industries may contain pharmaceutical compounds that are let out in the aquatic environment. The characteristics of pharmaceutical wastewater are clearly mentioned. The wastewater generated in between the processes may contain many chemicals and pharmaceutical compounds that have to be treated. It is very much necessary to analyze the treatment technologies and implement properly, such that the pharmaceutical compounds are disposed of in safe limits. All the various treatments used are presented clearly in this review. Generally, one method employed will not lead to complete removal of contaminants; there must be a combination of the process for efficient removal.

Should Healing Abutments and Cover Screws for Dental Implants be Reused? A Systematic Review.

To systematically review the current scientific evidence to assess if healing abutments and cover screws for dental implants can be resterilized effectively for reuse. A secondary purpose was to investigate if there has been any reported adverse biological or mechanical consequences to implants, or harm to patients with the reuse of healing abutments or cover screws. An electronic search of the English language scientific literature was performed independently by multiple investigators using a systematic search process using the PubMed search engine and Cochrane database. After the application of predetermined inclusion and exclusion criteria, the final list of articles was reviewed to meet the various objectives of this review. The initial electronic search resulted in 657 titles and after the application of predetermined inclusion and exclusion criteria, six articles were identified that satisfied the study objectives. All six articles were observational studies that described a total sample of over 300 used healed abutments obtained from patients. Out of these, three studies showed that routine methods (mechanical, chemical, and steam) used for cleaning and sterilizing used healing abutments did not result in the complete removal of contaminants, while two studies showed that routine methods supplemented with an additional regimen resulted in adequate decontamination. One additional study showed that routine methods sufficiently resulted in adequate decontamination of used healing abutments. There were no true clinical studies identified. There were no studies identified in the literature that reported on any adverse consequences to dental implants, such as infections, bone loss, mechanical complications, implant failure, or harm to patients, by reuse of healing abutments or cover screws. Limited evidence suggests that routine methods used for cleaning and sterilization of used titanium healing abutments may not result in the complete removal of contaminants. However, the biological or mechanical implication of this finding is yet to be determined because presently there are no reports in the literature related to any unfavorable consequences to dental implants, or harm to patients by reuse of healing abutments or cover screws. Nevertheless, due to the popular clinical practice of reusing healing abutments to reduce cost to clinicians and patients, indiscriminate reuse of healing abutments should be avoided, until further supporting evidence is established.

Application of encapsulated magnesium peroxide (MgO2) nanoparticles in permeable reactive barrier (PRB) for naphthalene and toluene bioremediation from groundwater

One of the challenges in the petroleum hydrocarbon contaminated groundwater remediation by oxygen releasing compounds (ORCs) is to identify the remediation mechanism and determine the impact of ORCs on the environment and the intrinsic groundwater microorganisms. In this research, the application of encapsulated magnesium peroxide (MgO2) nanoparticles in the permeable reactive barrier (PRB) for bioremediation of the groundwater contaminated by toluene and naphthalene was studied in the continuous flow sand-packed plexiglass columns within 50 d experiments. For the biodiversity studies, next generation sequencing (NGS) of the 16S rRNA gene was applied. The results showed that naphthalene was metabolized (within 20 days) faster than toluene (after 30 days) by microorganisms of the aqueous phase. By comparing the contaminant removal in the biotic (which resulted in the complete contaminant removal) and abiotic (around 32% removal for naphthalene and 36% for toluene after 50 d) conditions, the significant role of microorganisms on the decontamination process was proved. Furthermore, the attached microbial communities on the porous media were visualized by scanning electron microscopy (SEM). Microbial community structure analysis by NGS technique revealed that the microbial species which were able to degrade toluene and naphthalene such as P. putida and P. mendocina respectively were stimulated by addition of MgO2 nanoparticles. The presented study resulted in a momentous insight into the application of MgO2 nanoparticles in the hydrocarbon compounds removal from groundwater.

EXL-MS: An Enhanced Cross-Linking Mass Spectrometry Workflow To Study Protein Complexes

The analysis of proteins and protein complexes by cross-linking mass spectrometry (XL-MS) has expanded in the past decade. However, mostly used approaches suffer important limitations in term of efficiency and sensitivity. We describe here a new workflow based on the advanced use of the trifunctional cross-linker NNP9. NNP9 carries an azido group allowing the quantitative and selective introduction of a biotin molecule into cross-linked proteins. The incorporation is performed by click-chemistry using an adapted version of the enhanced filter-aided sample preparation (eFASP) protocol. This protocol, based on the use of a molecular filter, allows a very high recovery of peptides after enzymatic digestion and complete removal of contaminants. This in turn offers the possibility for one to analyze very large membrane proteins solubilized in detergent. After trypsin digestion, biotinylated peptides can be easily enriched on monoavidin beads and analyzed by LC-MS/MS. The whole workflow was developed on creatine kinase in the presence of detergent. It led to a drastic improvement in the number of identified cross-linked peptides (407 vs 81), compared to the conventional approach using a gel-based separation. One great advantage of our enhanced cross-linking mass spectrometry (eXL-MS) workflow is its high efficiency, allowing the analysis of a very low amount of material (15 μg). We also demonstrate that higher-energy collision dissociation (HCD) outperforms electron-transfer/higher-energy collision dissociation (EThcD) in terms of number of cross-linked peptides identified, but EThcD leads to better sequence coverage than HCD and thus easier localization of cross-linking sites.

Iron(III) phthalocyanine supported on a spongin scaffold as an advanced photocatalyst in a highly efficient removal process of halophenols and bisphenol A

This study investigated for the first time the degradation of phenol, chlorophenol, fluorophenol and bisphenol A (BPA) by the novel iron phthalocyanine/spongin hybrid material under various process conditions: hydrogen peroxide and UV irradiation. The heterogeneous catalyst, iron phthalocyanine/spongin (SFe), was produced by an adsorption process. The product obtained was investigated by a variety of spectroscopic techniques – X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR) and carbon-13 nuclear magnetic resonance (13C NMR) – as well as elemental and thermal analysis. The study confirmed the stable immobilization of the dye on the biopolymer. The results demonstrate that the degradation of phenols and BPA followed pseudo-second-order kinetics under different experimental conditions. The synergy of SFe, H2O2 and UV was found to produce a significant increase in the removal efficiency and resulted in complete removal of contaminants in a short time of 1 h. The reaction products were identified by high-performance liquid chromatography/mass spectrometry (HPLC-MS) and possible degradation pathways were proposed, featuring a series of steps including cleavage of CC bonds and oxidation.

Intermediate-Scale Investigation of Enhanced-Solubilization Agents on the Dissolution and Removal of a Multicomponent Dense Nonaqueous Phase Liquid (DNAPL) Source

The presence of multicomponent nonaqueous phase liquid (NAPL) source zones in the subsurface can significantly complicate remediation efforts, transport predictions, and the development of accurate risk assessments. A series of flow-cell experiments was conducted to investigate the effectiveness of two different enhanced-solubilization agents for the removal of a multicomponent dense nonaqueous phase liquid (DNAPL) source zone from homogeneous porous media. The source zone consisted of an equal 1:1:1 mole mixture of cis-1,2-dichloroethene (DCE), trichloroethene (TCE), and tetrachloroethene (PCE) with NAPL saturation (Sn) targeted between 8 and 14 %. Solutions (5 wt%) of hydroxypropyl-β-cyclodextrin (HPCD) and sodium dodecyl sulfate (SDS) were flushed through the flow-cell system until nearly complete contaminant removal was achieved. Analysis of elution curves indicate that SDS was approximately 10 times more efficient at removing all three components from the system compared to HPCD. Although enhancement factor magnitudes vary for each specific contaminant component and enhanced-solubilization agent, the lowest-solubility contaminant component (i.e., PCE) consistently experienced the greatest relative solubility enhancement during flushing. SDS was generally superior when evaluated on a recovery basis; however, HPCD outperformed SDS for all contaminant components when compared based on moles-contaminant to moles-reagent removal efficiency analysis. Contaminant mass flux reduction analysis showed that enhanced-solubilization flushing (HPCD and SDS) resulted in general inefficient contaminant removal behavior. Raoult’s Law could be used to successfully predict aqueous contaminant concentrations from the multicomponent DNAPL source zone, indicating that dissolution processes were relatively ideal during both HPCD and SDS enhanced-solubilization flushing. These findings suggest that multicomponent NAPL source dissolution and removal depend upon the flushing agent itself and of the solubility and properties of the individual components of the NAPL mixture. The selection of a particular enhanced-flushing agent should be evaluated carefully prior to remediation as the dissolution, removal, and mass flux behavior of each component can vary significantly.

Lability of polycyclic aromatic hydrocarbons in the rhizosphere

Remediation of soils containing high concentrations of polycyclic aromatic hydrocarbons (PAHs) seldom results in complete removal of contaminants, but residual toxicity often is reduced. In this study, soil from a former manufactured gas plant site was treated for 12 months by phytoremediation and then tested for total PAHs, Tenax-TA extractable (“labile”) PAHs, aqueous soluble PAHs (PAH wp) , and biotoxicity assessed by earthworms survival, nematode mortality, emergence of lettuce seedlings, and microbial respiration. Prior to phytoremediation, the soil had toxic impacts on all bioassays (except the nematodes), and 12 months of remediation decreased this response. Change in labile PAHs was a predictor for change in total PAH for 3- and 4-ring compounds but not for the 5- and 6-ring. Decreases in labile PAHs were correlated ( r 2 ⩾ 0.80) with toxicity in the bioassays except microbial respiration. PAH wp was correlated only with nematode toxicity prior to remediation but with none of the tests after remediation. Total PAHs were not correlated with any of the bioassay tests. Tenax-TA appears to have potential for predicting residual toxicity in remediated soils and is superior to total concentrations for that application.

Reductions in Contaminant Mass Discharge Following Partial Mass Removal from DNAPL Source Zones

Although in situ remediation technologies have been used to aggressively treat dense nonaqueous phase liquid (DNAPL) source zones, complete contaminant removal or destruction is rarely achieved. To evaluate the effects of partial source zone mass removal on dissolved-phase contaminant flux, four experiments were conducted in a two-dimensional aquifer cell that contained a tetrachloroethene (PCE) source zone and down-gradient plume region. Initial source zone PCE saturation distributions, quantified using a light transmission system, were expressed in terms of a ganglia-to-pool ratio (GTP), which ranged from 0.16 (13.8% ganglia) to 1.6 (61.5% ganglia). The cells were flushed sequentially with a 4% (wt.) Tween 80 surfactant solution to achieve incremental PCE mass removal, followed by water flooding until steady-state mass discharge and plume concentrations were established. In all cases, the GTP ratio decreased with increasing mass removal, consistent with the observed preferential dissolution of PCE ganglia and persistence of high-saturation pools. In the ganglia-dominated system (GTP = 1.6), greater than 70% mass removal was required before measurable reductions in plume concentrations and mass discharge were observed. For pool-dominated source zones (GTP < 0.3), substantial reductions (>50%) in mass discharge were realized after only 50% mass removal.

Conceptual Site Models as a Tool in Evaluating Ecological Health: The Case of the Department of Energy'S Amchitka Island Nuclear Test Site

Managers of contaminated sites are faced with options ranging from monitoring natural attenuation to complete removal of contaminants to meet residential health standards. Conceptual site models (CSMs) are one tool used by the U.S. Department of Energy (DOE) and other environmental managers to understand, track, help with decisions, and communicate with the public about the risk from contamination. CSMs are simplified graphical representations of the sources, releases, transport and exposure pathways, and receptors, along with possible barriers to interdict pathways and reduce exposure. In this article, three CSMs are created using Amchitka Island, where the remaining contamination is from underground nuclear test shot cavities containing large quantities of numerous radionuclides in various physical and chemical forms: (1) a typical underground nuclear test shot CSM (modeled after other sites), (2) an expanded CSM with more complex receptors, and (3) a regional CSM that takes into account contaminant pathways from sources other than Amchitka. The objective was to expand the CSM used by DOE to be more responsive to different types of receptors. Amchitka Island differs from other DOE test shot sites because it is surrounded by a marine environment that is highly productive and has a high biodiversity, and the source of contamination is underground, not on the surface. The surrounding waters of the Bering Sea and North Pacific Ocean are heavily exploited by commercial fisheries and provide the United States and other countries with a significant proportion of its seafood. It is proposed that the CSMs on Amchitka Island should focus more on the pathways of exposure and critical receptors, rather than sources and blocks. Further, CSMs should be incorporated within a larger regional model because of the potentially rapid transport within ocean ecosystems. The large number of migratory or highly mobile species that pass by Amchitka provide the potential for a direct pathway to the local human population, known as Aleut, and commercial fisheries, which are remote from the island itself. The exposure matrix for receptors requires expansion for the Amchitka Island ecosystem because of the valuable marine and seafood resources in the region. CSMs with an expanded exposure/receptor matrix can be used effectively to clarify the conceptualization of the problem for scientists, regulators, and the general public.

Regeneration Technology of Cutting Oil Using Electrolytic Bubble Flotation Method-Simultaneous Removal of Fine Aluminum Particles and Sludge Contaminant-

The used cutting oil contains not only fine metals but also sludge and other compounds which cause the source of odors as time elapses. In the present study, the two types of electrolytic bubble flotation reactors, such as the flow type reactor and the batch type reactor, were investigated to remove these compounds and to regenerate the cutting oil with the aim of developing the maintenance-free and innovative cutting oil treatment process. When the flow type reactor was used, 39% of fine aluminum particles and sludge were removed based on weight basis from the filter catch. When the batch type reactor was used, 75% of these were removed. The cutting oil can be used for regeneration and its characteristic was not deteriorated when the treatment time was less than 40 s at 20V. When the cutting oil regeneration system with the batch type reactor followed by the filter was used, the complete removal of contaminant was obtained.

Surface cleaning and characterization of yttria‐stabilized zirconia

AbstractCleaning substrate surfaces and checking the effectiveness of the cleaning method are two very important aspects of reliable surface analysis. The absence of a cleaning process leading to an yttria‐stabilized zirconia (YSZ) surface that is free of contaminants and of unchanged structure has inspired us to investigate a new surface cleaning method based on a combination of high vacuum annealing at 300°C and oxidation with atomic oxygen. The efficiency of the cleaning procedure is examined by studying the surface composition after each stage of the process with low‐energy ion scattering (LEIS or ISS) and x‐ray photoelectron spectroscopy (XPS). The cleaning method results in complete removal of contaminants adsorbed from the ambient atmosphere, such as water and hydrocarbons. No segregation or sputtering effects due to the cleaning procedure are observed. The process also is compared with more conventional methods such as thermal oxidation and plasma etching. Although this study focuses on cleaning polycrystalline YSZ, which is inherently difficult to clean, other oxides and several metals also are investigated. For all the oxides studied, the newly proposed cleaning strategy removes up to ∼90% more contamination than the commonly used method of thermal oxidation. In the case of metals, the surface carbon is replaced by oxygen, which can be removed much easier. Additional segregation of bulk carbon is avoided. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Contaminant Transport Through Single Fracture With Porous Obstructions

Transport of contaminant through a single fracture, modeled as a closely spaced parallel plates aperture, is analyzed theoretically and numerically. Permeable contact regions between the plates are modeled as fixed packs of homogeneous, isotropic, and inert porous material. A nondimensional theoretical expression for estimating the equivalent global permeability of the aperture is presented in terms of the relative volume occupied by the contact regions. Transient transport of contaminant (solute) through this heterogeneous system is analyzed considering injection of fluid with uniform concentration at the inlet of the fracture. For natural systems, it is verified that relative volume and distribution of contact regions affect clean-up time, defined as the time necessary for the complete removal of contaminant, only indirectly by varying the equivalent permeability of the system, otherwise their effect is negligible. The clean-up time of a clear (of contact regions) fracture, is correlated with the Peclet number for 10−1 ≤ Pe ≤ 106.

EFFECT OF SURFACTANT ADDITION ON PHENANTHRENE BIODEGRADATION IN SEDIMENTS

A laboratory study was conducted to determine whether commercial surfactants enhance the bioremediation of PAH-contaminated sediments. Phenanthrene was chosen as a representative PAH; an inoculum of PAH-degrading microorganisms, enriched from an aquatic sediment, was used in sediment-water slurry microcosm biodegradation experiments. Of seven nonionic surfactants tested, only one (Triton X-100) did not inhibit phenanthrene mineralization at concentrations above the critical micelle concentration (CMC). Temporal studies on Triton X-100 revealed that while it initially inhibited mineralization in sediment-free microcosms, after 1 week Triton X-100 slightly improved phenanthrene biotransformation and mineralization in microcosms with and without sediment. For all treatments, phenanthrene disappearance was complete after 9 d, and mineralization reached 50 to 65% after 12 d. Sorption to the sediment appears to have reduced the free aqueous surfactant concentration, thereby reducing surfactant toxicity to the microorganisms. These results suggest that many surfactants are toxic to PAH-degrading microorganisms, and while surfactant addition may not always have adverse effects on biodegradation, the use of surfactants might not be desirable to achieve complete contaminant removal.