Cadmium Release from Four Sorbents during Treatment of Contaminated Soils by Catalyzed H2O2 Propagations (Modified Fenton’s Reagent)

The release of heavy metals from soils and subsurface solids is a significant concern during in situ chemical oxidation treatment. The release of cadmium sorbed on four solids of varied properties was investigated in slurries treated by catalyzed H2O2 propagations (CHP—modified Fenton’s reagent). Cadmium was released in all four solids in CHP reactions conducted at pH 3; however, aqueous cadmium concentrations decreased in CHP reactions conducted at pH 7. Cadmium release at pH 3 was directly proportional to the soil organic carbon (SOC) content of the four solids (R2 = 0.99), and may have been due to destruction of the SOC by hydroxyl radical in the reactions at pH 3. Scavenging of hydroxyl radical minimized the release of cadmium in CHP systems at pH 3, which is consistent with cadmium release resulting from destruction of SOC by hydroxyl radical. Scavenging of hydroxyl radical in CHP systems at pH 7 resulted in increased cadmium release, compared to pH 7 reactions without the hydroxyl radical scavenger isopropanol. Superoxide, the conjugate base of perhydroxyl radical (pKa = 4.8), was proposed as the desorbing species in the scavenged CHP reactions at pH 7. The results of this research demonstrate that cadmium release will likely be minimal in CHP reactions conducted at pH 7 if compounds that increase the activity of superoxide are not present at significant concentrations.     

Destruction of Trichloroethylene and Perchloroethylene DNAPLs by Catalyzed H2O2 Propagations

The destruction of trichloroethylene (TCE) and perchloroethylene (PCE) dense nonaqueous phase liquids (DNAPLs) using catalyzed H2O2 propagations (CHP), an in situ chemical oxidation process based on Fenton’s reagent, was investigated in batch, bench scale reactors. TCE and PCE masses were quantified over time in DNAPLs, aqueous phases, and off gasses, and the rate of DNAPL destruction was compared to the corresponding rate of gas purge dissolution. TCE and PCE DNAPLs were rapidly destroyed by CHP at 1.7 and 4.4 times the rate of gas purge dissolution, respectively. Use of reactions in which a single reactive oxygen species was generated demonstrated that both hydroxyl radical and superoxide were involved in TCE and PCE DNAPL destruction, with superoxide having the major role in the destruction of the DNAPLs. These results show that DNAPLs composed of contaminants highly reactive with hydroxyl radical, such as TCE and PCE, are destroyed primarily through reaction with superoxide.     

Treating Soil PCP at Optimal Conditions Using Heme and Peroxide

The environmental impact of pentachlorophenol (PCP) has been the subject of extensive research in recent years. Investigations of PCP degradation using both biotic and abiotic methods are extensively reported in literature. Based on some preliminary tests (not shown), an abiotic method was found for oxidative PCP degradation in soil under unsaturated conditions and a neutral pH. Reagents used were heme (a catalyst) and peroxide (an oxidant). From two screening tests (not shown), the heme and peroxide were identified as the most important factors on PCP degradation in highly PCP-contaminated soil. The objective of this study was to determine the optimum doses of heme and peroxide for PCP degradation in soil. Using a statistical method, known as response surface methodology, a quadratic function was fit to the data and used to estimate the optimum doses of heme and peroxide at 0.035?g/2?g-soil and 0.105?g/2?g-soil, respectively, in treating PCP-contaminated soil. The model also was used to determine the region in which the response was within the 95% confidence region of the optimum. The lowest heme and peroxide doses required to achieve a response within the 95% confidence region of the optimum were found to be 0.017?g/2?g-soil and 0.095?g/2?g-soil, respectively. Based on the results of the optimization studies, kinetic studies were conducted to examine the rate and extent of PCP degradation in soil over time. The results showed that about 50% of PCP was degraded within the first 30?min, and up to ～ 80% of PCP was degraded within 4?h.     

Diffusive Transport of Permanganate during In Situ Oxidation

The transport of permanganate in low permeability media (LPM) and its ability to degrade trichloroethylene (TCE) in situ were studied through diffusive transport experiments with intact soil cores. A transport cell was developed to measure the effective diffusion coefficient (Deff) of a Br? tracer through intact cores of silty clay LPM obtained from a field site and enable calculation of the apparent tortuosity (τa) of the medium. Then, 5000 mg?L?1 of KMnO4 was added to the cell and diffusive transport and soil matrix interactions were observed. After three months, the soil cores were dissected for morphologic examination and characterization of matrix ions, total organic carbon, MnO4?, and manganese oxides (MnO2). The experiment was then repeated after 2 μL of pure phase TCE were delivered into the center of each of two intact cores. Permanganate transport was observed for one month and then an extraction of the entire soil core was made to determine the extent of TCE degradation. This research demonstrated that permanganate can migrate by diffusion and yield reactive zones that can be predicted based on the properties of the LPM and the oxidant source. Under the experimental conditions examined, permanganate had little effect on the LPM’s pore structure or continuity, and appreciable soil organic matter remained even after 40–60 days of exposure to the oxidant. MnO2 solids, an oxidation by-product, were observed in the LPM, but not at levels sufficient to cause pore filling or alter the apparent matrix tortuosity, even when TCE was present. During diffusive transport of permanganate, TCE in the silty clay LPM was degraded by 97%.     

Treatment of TCE-Contaminated Groundwater Using Fenton-Like Oxidation Activated with Basic Oxygen Furnace Slag

The industrial solvent trichloroethylene (TCE) is among the ubiquitous chlorinated organic compounds found in groundwater contamination. The objective of this study was to evaluate the potential of applying basic oxygen furnace (BOF) slag as the catalyst to enhance the Fenton-like oxidation to remediate TCE-contaminated groundwater. Results indicate that TCE oxidation via the Fenton-like process can be enhanced with the addition of BOF slag. Results from the X-ray powder diffraction analysis reveal that the major iron type of BOF slag/quartz sand media was iron oxyhydroxide (α-Fe2O3). Approximately 81% of TCE removal was observed (with initial TCE concentration of approximately 5?mg?L?1), with the addition of 1,000?mg?L?1 of H2O2 and 10?g?L?1 of BOF slag. Results also show that TCE concentrations dropped from 5 to 1.1?mg?L?1, and chloride concentrations increased from 0 to 2.7?mg?L?1 after 60 min of reaction with the presence of H2O2 and BOF slag. This indicates that the depletion of TCE corresponded with the oxidation reactions and release of chloride ions very well in this study. Results demonstrate that the BOF slag can be used to supply catalysts continuously, and it can be installed in a permeable barrier system to enhance the Fenton-like process in situ.     

Zero-Valent Iron: Impact of Anions Present during Synthesis on Subsequent Nanoparticle Reactivity

Zero-valent iron particles are an effective remediation technology for ground water contaminated with halogenated organic compounds. In particular, nanoscale zero-valent iron is a promising material for remediation because of its high specific surface area, which results in faster rate constants and more effective use of the iron. An aspect of iron nanoparticle reactivity that has not been explored is the impact of anions present during iron metal nanoparticle synthesis. Solutions containing chloride, phosphate, sulfate, and nitrate anions and ferric ions were used to generate iron oxide nanoparticles. The resulting materials were dialyzed to remove dissolved by-products and then dried and reduced by hydrogen gas at high temperature. The reactivity of the resulting zero-valent iron nanoparticles was quantified by monitoring the kinetics as well as products of carbon tetrachloride reduction, and significant differences in reactivity and chloroform yield were observed. The reactivity of nanoparticles prepared in the presence of sulfate and phosphate demonstrated the highest reactivity and chloroform yield. Furthermore, substantial variations in the solid-state products of oxidation (magnetite, iron sulfide, goethite, etc.) were also observed.     

Enhanced Dissolution of Trichloroethene: Effect of Carbohydrate Addition and Fermentation Processes

Remediation of source areas is challenging because lingering contaminants are often present as nonaqueous phase liquid (NAPL) and sorbed mass, and therefore difficult to remove via biodegradation or other commonly used remedial methods. Experimental results indicate that enhanced dissolution of a model NAPL, trichloroethene (TCE), can occur through the addition and/or subsequent fermentation of a dilute molasses solution. Enhanced mass transfer occurs by two mechanisms, depending upon whether the molasses solution is fresh or has fermented. The addition of fresh molasses worked to increase TCE solubility (>200%), thereby increasing mass transfer from the NAPL phase. Mixing TCE NAPL with a fermented molasses solution, however, increased TCE mass flux via the formation of a NAPL/aqueous phase emulsion. In addition, fermented liquid may have also decreased the soil partitioning coefficient (Kd) of TCE, indicating that enhanced transfer of sorbed mass to the aqueous phase could also occur in the presence of fermented molasses. These results provide guidance on how remedial systems may be optimized to increase NAPL and sorbed-mass dissolution and are therefore important, particularly when bioremediation is used to polish residual source zones.     

Remediation of Contaminated Soils with PCBs Using an Integrated Treatment: Desorption and Oxidation

During most of the past century, large quantities of substances were produced and utilized that subsequently proved harmful. This is the case with polychlorinated biphenyls (PCBs) which only became prohibited by law in the 1970s. As a result of their physicochemical properties, these substances are now present everywhere, although they are mainly found in soils, since they are hydrophobic in character. The present study evaluates an innovatory treatment for the remediation ex situ of soils contaminated by PCBs. This treatment consists of a first stage of desorption using a surfactant agent, followed by a second stage of oxidation with the object of transforming the PCBs into innocuous substances through successive oxidations using the photo-Fenton process. The results obtained (87% remediation in the desorption and 100% in the oxidation stages) show this new treatment to be a highly effective alternative, which does not generate dangerous residues of any type.     

Treatment of Fuel-Oil Contaminated Soils by Biodegradable Surfactant Washing Followed by Fenton-Like Oxidation

Among petroleum-hydrocarbon pollutants, fuel-oil is more difficult to treat compared to gasoline and diesel fuel. The objectives of this bench-scale study were to: (1) develop a two-stage remedial system consisting of surfactant washing followed by Fenton-like oxidation process to remediate fuel-oil contaminated soils; (2) evaluate the effects of residual surfactant and soil organic matter (SOM) on the efficiency of Fenton-like oxidation; (3) evaluate the effect of potassium dihydrogen phosphate (KH2PO4) addition on the stability of H2O2 and oxidation efficiency; and (4) evaluate the possible oxidation products after the oxidation process. In the surfactant washing stage, biodegradable surfactant, Simple Green (SG) (50?g?L?1), was applied to flush fuel-oil contaminated soils with initial total petroleum-hydrocarbons (TPHs) concentration of 50,000?mg?kg?1. Results show that approximately 90% of TPH could be removed after washing with 45 pore volumes (PVs) of SG followed by 25 PVs of deionized water, while the soil TPH concentration dropped from 50,000 to 4,950?mg?kg?1. In the Fenton-like oxidation stage with initial soil TPH concentration was approximately 4,950?mg?kg?1, TPH removal efficiency can be significantly increased with increased H2O2 concentrations. Results also reveal that residual SG and SOM would compete with TPH for oxidants and cause the decrease in oxidation efficiency. An “oxidation-sorption-desorption-oxidation” scheme for soil TPH was observed in this experiment due to the initial sorption of TPH on SOM. Results show that an addition of 2.2 mM of KH2PO4 could increase the stability and half-life of H2O2, but caused the decrease in TPH removal efficiency. The oxidation potential of Fenton-like process was not capable of completely oxidizing fuel-oil to nontoxic end products. The observed by-products after oxidation process contained carboxyl groups with molecular weights similar to their parent compounds. Results from this study indicate that the two-stage remedial system is a promising technology for fuel-oil contaminated soil treatment.     

Retention and Distribution of 1-Naphthol and Naphthol Polymerization Products on Surface Soils

Sorption and extractability of naphthol and naphthol polymerization products (NPP) were evaluated in two surface soils. NPP were generated by the addition of horseradish peroxidase and H2O2 to naphthol solutions in contact with the surface soils. While NPP retention on the forest soil was lower compared to the parent naphthol, no difference in sorption of naphthol and NPP was observed in the agricultural soil. The agricultural soil retained more naphthol and NPP than the forest soil. The NPP sorption behavior noted in this study was in contrast to that of phenol polymerization products observed by other researchers. The presence of phenol and 2,4-dichlorophenol as cosolutes had no significant impact on naphthol or NPP retention on the two soils, and naphthol was more easily extracted from both soils whenever phenol was present as a cosolute. Characterization of the naphthol polymerization products using reverse-phase high-pressure liquid chromatography and octanol-water partitioning indicated that significant fractions of the water-soluble and insoluble NPP were comprised of oligomers that were more polar than the parent 1-naphthol. This decrease in polarity upon polymerization is believed to have been responsible for the NPP retention and binding behavior observed in this study.     

Fate of Polybrominated Diphenyl Ethers, Nonylphenol, and Estrogenic Activity during Managed Infiltration of Wastewater Effluent

About a billion cubic meters of wastewater effluent are artificially recharged annually in the United States for maintenance of groundwater levels and prevention of seawater intrusion. There is concern that trace contaminants, including various endocrine disrupting compounds (EDCs), are not completely removed during infiltration, leading to deterioration of groundwater quality. In this work, we investigate the mechanisms and efficiency of EDC removal at the Sweetwater Recharge Facility, which is used to recharge secondary effluent from the Roger Road Wastewater Treatment Plant in Tucson, Ariz. Material was collected from the top meter of sediments in two infiltration basins and analyzed for extractable nonylphenol (NP), polybrominated diphenyl ethers (PBDE) and total estrogenic activity. The basins differed significantly in length of service (7 versus 15 years). Nevertheless, profiles of extractable contaminants and estrogenic activity were similar in the two basins. Results suggest that hydrophobic determinants of estrogenic activity are efficiently retained in surface sediments during soil-aquifer treatment. However, measurable levels of PBDEs, NP, and estrogenic activity are present in infiltrate that reaches the local unconfined aquifer at ～ 40?m below land surface.     

Advanced Oxidation of Diuron by Photo-Fenton Treatment as a Function of Operating Parameters

Advanced oxidation of diuron in aqueous solution by photo-Fenton treatment was investigated by batch experiments. Effects of operating parameters, namely, the concentrations of pesticide (diuron), hydrogen peroxide (H2O2), and ferrous ion [Fe (II)] on oxidation of diuron were investigated by using Box-Behnken statistical experiment design and the response surface methodology. Diuron oxidation by photo-Fenton treatment was evaluated by determining the total organic carbon (TOC), diuron, and adsorbable organic halogen (AOX) removals. Concentration ranges of the reagents resulting in the highest level of diuron oxidation were determined. Diuron removal increased with increasing H2O2 and Fe (II) concentrations, up to a certain level. H2O2 concentration had a more profound effect than diuron and Fe (II) on removal of diuron, TOC, and AOX from the aqueous solution. Complete (100%) disappearance of diuron was achieved after a 15?min reaction period. However, 85% of diuron was mineralized after 240?min, indicating a low level of intermediate formation. Optimal H2O2/Fe (II)/diuron ratio resulting in maximum diuron (100%), TOC (85%), and AOX (100%) removals was found to be 267/36/25?(mg?L?1).     

Investigations of Pile Foundations in Brownfields

“Brownfields” are real estate properties with subsurface or surface contamination. The redevelopment of Brownfields is required to clean, improve, and protect the environment. Pile foundations are often used in Brownfields and other contaminated site situations to support structures. Regulators are concerned about the environmental safety of pile foundations in Brownfields sites, since piling in Brownfields may lead to transport of contaminants from the contaminated region to underground aquifers. This investigation is an extension of previous research programs on pile foundations in Brownfields or contaminated sites conducted at the University of New Orleans. The purpose of the overall investigation is to evaluate the potential for contaminant transport due to pile foundations in Brownfields. The current paper summarizes the research carried out to ascertain the potential for contaminant transport from concrete piles of different shape, depth of penetration, and method of installation. The results of bench scale model tests and numerical studies are presented. Under full penetration conditions, the square shaped and circular cast-in-place piles were found to have a higher potential for contaminant transport than circular driven piles. There is a low potential for contaminant transport in the case of piles penetrating less than 95% of an aquitard. Selected results from a previous program on wooden and steel piles are summarized for comparison.     

Iron-Activated Persulfate Oxidation of an Azo Dye in Model Wastewater: Influence of Iron Activator Type on Process Optimization

The study explores the potential of iron-activated persulfate oxidation of an azo dye in model wastewater. The influence of the type of iron activator on process efficiency was investigated by using ferrous and zero valent iron. The Box-Behnken experimental design and response surface methodology were applied for the modeling of the Fe2+/S2O82- and Fe0/S2O82- processes. The combined effect of three important process parameters was investigated and presented by the means of the quadratic polynomial model. The statistical analysis of model performance was evaluated by ANOVA. The optimal process conditions giving the maximal mineralization for both processes were determined: pH 4.81, [Fe2+] = 1.64??mM, and [S2O82-] = 84.87??mM predicting 35.14% mineralization and pH 5.52; [Fe0] = 4.27??mM and [S2O82-] = 138.43mM predicting 54.38% mineralization by the Fe2+/S2O82- and Fe0/S2O82- processes, respectively. The predicted values of dye mineralization obtained by model equations were in good agreement with the experimental values. The type of iron activator was demonstrated to significantly influence both process efficiency and optimal conditions.     

Prediction of Heavy Metals Mobility and Bioavailability in Contaminated Soil Using Sequential Extraction and Biosensors

Several chemical and biological methods have been developed in the last decade to evaluate heavy metals mobility and bioavailability in contaminated soils. In this study, two methods, Biomet sensors and chemical sequential extraction [potentially bioavailable assessment sequential extraction (PBASE) method], were used to predict heavy metals bioavailability in the surface and heavy metals mobility in the subsurface of smelter-contaminated soils, respectively. The heavy metals considered (arsenic, copper, iron, lead, and zinc) were those detected in a previous sampling campaign performed in the contaminated area. Biomet biosensor results indicated that 15–25% of Cu and Zn were bioavailable for plants and animals uptake in the soil surface, whereas higher values were obtained for As and Pb (>60%). In the soil subsurface, iron was identified as the less mobile element, followed by As and Pb, since they were mainly present in the nonsoluble fractions of PBASE method. In contrast, Cu and Zn showed similar distribution between the soluble and nonsoluble fractions. Therefore, PBASE and Biomet are useful and complementary methods which supply different information about heavy metals occurrence in contaminated soils: the first method indicates their potential mobility, whereas the second one shows their potential bioavailability for biota.     

Characterization of Methane Flux and Oxidation at a Solid Waste Landfill

Methane emissions were measured at several locations at a typical solid waste facility using a static chamber technique. At the entire facility, methane flux varied from ?13.6?to?1,755?g?m?2?day?1. The flux data had an arithmetic mean value of 71.3?g?m?2?day?1 and a geometric mean value of 18.6?g?m?2?day?1. At this site, methane emission was generally lower on the side slopes relative to the flat areas of the landfill. The spatial variability of methane flux was characterized by point kriging and inverse distance weighing (IDW) in an intensive study of a 61×61-m area. The geospatial means in this area obtained by both methods were almost identical (20.9 versus 20.8?g?m?2?day?1). These geospatial means for the area were also similar to the arithmetic mean (24.5?g?m?2?day?1), but 3.4 times the geometric mean (6.5?g?m?2?day?1). Methane oxidation was evaluated at the surface of the landfill and at several depths within the cover soil using stable isotope techniques. The δ?13C of CH4 averaged ?55.4% in the anoxic zone. Methane collected in chambers and in surficial soil probes exhibited more 13C enriched values, ranging from ?55.4 to ?34.5%, due to the preferential uptake of 12CH4 by methanotrophic bacteria. Methane oxidation at the landfill averaged 22% and occurred in the upper 70?cm of the landfill cover soil. Oxidation occurred in all tested locations of the landfill and for all ages of buried waste.     

Chemistry of Modified Fenton’s Reagent (Catalyzed H2O2 Propagations–CHP) for In Situ Soil and Groundwater Remediation

The use of modified Fenton’s reagent, or catalyzed H2O2 propagations (CHP), has become increasingly popular for the in situ and ex situ treatment of surface soils and the in situ remediation of the subsurface. The process is based on the catalyzed decomposition of hydrogen peroxide by soluble iron, iron chelates, or iron minerals to generate the strong oxidant hydroxyl radical as well as other reactive oxygen species. Some of these species function as reductants and nucleophiles and may be responsible for the enhanced treatment of sorbed and nonaqueous phase liquid (NAPL) contaminants that is sometimes observed in the field. This paper serves as a review of the process chemistry of CHP; the goal is to provide researchers and practitioners with fundamental concepts that will aid in applying the CHP process to soil and groundwater contamination. Although the importance of well placement and the method of reagent injection must be considered in CHP remediation, understanding and promoting the most effective process chemistry is essential to successful soil and groundwater remediation.     

Subsurface Radioactive Contaminant Transport Modeling Using Particle and Kalman Filter Schemes

Contamination of groundwater by radioactive contaminants can be harmful to the environment. Various prediction models have been adopted to simulate the state of contaminants in the subsurface. Conventional numerical models are simplified by approximation and the model parameters are assumed to be constant, thereby introducing error to the prediction results. Particle and Kalman filters are used in this research to simulate the radioactive contaminant cobalt-57 transport in a subsurface environment by using a two-dimensional advection-dispersion model. A radioactive contaminant concentration was predicted spatially and temporally within boundary conditions. The errors in the prediction results were assessed by using the root-mean-square-error (RMSE) equation. The results show that the Kalman filter performs better than the particle filter when the prediction model is linear. Furthermore, the results from filters are closer to the true value in comparison with the numerical solution, and the filters are capable of reducing the RMSE of the numerical solution by approximately 80%.     

Assessment of Fossil Fuel Fly Ash Formulations in the Immobilization of Hazardous Wastes

In this work, a simple and inexpensive method is introduced for the immobilization of the hazardous elements Cd, Pb, and Fe from their aqueous solutions in compressed fossil fuel fly ash formulations, as candidates for waste forms. The molded formulations were prepared by initially mixing the hazardous waste solutions with the fossil fuel fly ash material at a constant ratio (17%). Then the resulting pastes were pressed at the appropriate pressure using a manual hydraulic press. The compressed formulations revealed good water resistance, compression strength, and radiation resistance. Leachability investigations of the molded matrices were performed in terms of the accelerated leach test, the toxicity characteristic leaching procedure (TCLP), and long-term leach tests. The TCLP results obtained for Cd and Pb were well below their TCLP limits. On the other hand, the accelerated and long-term leach tests showed a similar behavior. The properties of the compressed formulations revealed their high performance as an alternative for waste forms as indicated by their durability, compression strength, and leachability. The low leachability of Cd, Pb, and Fe from the compressed fly ash formulations could be attributed to a dual mechanism of microencapsulation and/or chemical fixation.     

Cyclodextrin-Enhanced Electrokinetic Remediation of Soils Contaminated with 2,4-Dinitrotoluene

The removal of 2,4-dinitrotoluene (2,4-DNT), a munitions waste constituent and an industrial intermediate, from contaminated soils was evaluated using enhanced electrokinetic (EK) remediation. Two model soils were spiked with 480?mg of 2,4-DNT/kg of dry soil for the EK experiments. The spiked soils were kaolin, a low-buffering clayey soil, and glacial till, a high-buffering silty soil. The glacial till was obtained from a field site and contained 2.8% organic matter. Deionized (DI) water and cyclodextrin solutions were used as the EK purging solutions. Cyclodextrin was selected as a nonhazardous solubility enhancer for enhancing the desorption and removal of 2,4-DNT from soils in EK remediation. Two aqueous solutions of hydroxypropyl β-cyclodextrin (HPCD) at concentrations of 1 and 2% were selected for kaolin and glacial till, respectively, based on results for batch extraction of 2,4-DNT from the same soils. During the EK experiments, greater current and electro-osmotic flow were observed for HPCD solutions than for DI water. After the completion of the EK experiments, the soils in the EK cell were extruded and the residual 2,4-DNT in the soils was determined. Less 2,4-DNT remained in the kaolin soil (up to 94% transformed) than in the glacial till soil (20% transformed) due to strong retention of 2,4-DNT by the soil organic matter in glacial till. For kaolin, less 2,4-DNT remained in the soil using HPCD solutions than using DI water. For glacial till, comparable levels of 2,4-DNT remained in the soil for both EK solutions. Since no 2,4-DNT was detected in the effluents from the EK cells, the decrease in 2,4-DNT concentration in the kaolin and glacial till soils was attributed to electrochemical transformation of 2,4-DNT to other species.