Effect of sequestration on PAH degradability with Fenton's reagent: roles of total organic carbon, humin, and soil porosity

Effect of H(2)SO(4) and HCl in the anode purging solution for the electrokinetic-Fenton remediation of soil contaminated with phenanthrene

The Electrokinetic-Fenton (EK-Fenton) process is a powerful technology to remediate organic-contaminated soil. The behavior of salts and acids introduced for the pH control has significant influence on the H(2)O(2) stabilization and destruction of organic contaminants. In this study, the effects of the type and concentration of acids, which were introduced at the anode, were investigated for the treatment of clayey soil contaminated with phenanthrene. In experiments with H(2)SO(4) as the anode solution, H(2)O(2) concentration in the anode reservoir decreased due to reaction between reduced species of sulfate and H(2)O(2), as time elapsed. By contrast, HCl as an electrolyte in the anode reservoir did not decrease the H(2)O(2) concentration in the anode reservoir. The reaction between the reduced species of sulfate and H(2)O(2) hindered the stabilization of H(2)O(2) in the soil and anode reservoir. In experiments with HCl for pH control, Cl(.), and Cl(2)(. -), which could be generated with mineral catalyzed Fenton-like reaction, did not significantly hinder H(2)O(2) stabilization. H(2)O(2) transportation with electro-osmotic flow and mineral catalyzed Fenton-like reaction on the soil surface resulted in the simultaneous transport and degradation of phenanthrene, which are dependent of the advancement rate of the acid front and electro-osmotic flow toward the cathode according to HCl and H(2)SO(4) concentrations in the anode purging solution.

Oxidation of PAHs in a simplified system using peroxy-acid and glass beads: Identification of oxidizing species

Polycyclic aromatic hydrocarbons (PAHs) are organic contaminants of concern due to their ubiquity, persistence in the natural environment and adverse health effects. Numerous studies have looked into the removal and treatment of these contaminants, with mixed results. High molecular weight PAHs have been particularly problematic due to their hydrophobicity and high affinity for organics, resulting in mass transfer limitations for even the fastest advanced oxidation processes (AOPs). The peroxy-acid process has been used to successfully treat PAH contaminated matrices. Experiments were conducted on benzo[a]pyrene contaminated glass beads in order to elucidate the reaction mechanisms responsible for the effectiveness of this process. For the first time peracetic acid (PAA) was identified as the important oxidant in this reaction. Different v/v/v ratios of hydrogen peroxide/acetic acid/DI water were studied which illustrated the importance of reaction ratio on oxidant concentration and rate of formation. Approximately 60% degradation of benzo[a]pyrene was achieved in 24 hours with 1.7% PAA. Observations of the reaction kinetics suggest that the slow desorption/dissolution of benzo[a]pyrene limits the efficiency of the peroxy-acid process. Modifications of the reaction setup supported this observation as treatment efficiencies increased with reactive surface area, and an increase in system agitation. These limitations were also overcome by increasing the concentration of PAA delivered to the contaminated matrix. Greater than 80% degradation of benzo[a]pyrene was achieved in 24 hours with approximately 9.2% PAA.

Phenanthrene and pyrene oxidation in contaminated soils using Fenton's reagent

Fenton's reagent has shown its applicability to oxidizing these biorefractory organic contaminants. The purpose of this contribution was to investigate the influence of operating parameters on the process efficiency for soil highly contaminated by PAHs. Five variables were selected: pH, reaction time, UV irradiation, hydrogen peroxide concentration and Fe (II) amendment. Their effects on the oxidation of (i) phenanthrene and on (ii) phenanthrene and pyrene present in freshly contaminated soil samples were studied through batch reactor experiments following factorial designs. For phenanthrene oxidation run with a soil contaminated at 700 mg kg(-1), one set of variables enabled us to reach a residual concentration lower than 40 mg kg(-1) (Dutch legislation threshold). The most important factor was the reaction time, followed at a certain distance by UV irradiation, Fe (II), H(2)O(2) concentration and pH, this last variable being the least significant. The possibility of operating without pH adjustment is of importance in the treatment at the field scale. This shows the feasibility of photo-Fenton-like oxidation for the treatment of soil highly contaminated with PAH and the relative importance of the process variables.

Bioaccumulation of hexachlorobenzene in Eisenia foetida at different aging stages

The impacts of contact time on the extractability, the availability of hexachlorobenzene (HCB) in different soils (paddy soil, red soil, and fluvo-aquic soil) and bioaccumulation in earthworm Eisenia foetida were investigated under controlled conditions in laboratory. Results indicated that the aging rate of HCB displaying a biphasic character in different soils: a rapid aging in the first 60 d followed by a slow aging in the next 120 d incubation time. Moreover, most of extractable HCB (about 90%) decline occurred in the first 60 d after HCB was spiked into the soils. The aging rate of HCB in the paddy soil was higher than that in the fluvo-aquic soil or the red soil. The amount of HCB accumulated in the earthworms and its accumulative ability, expressed as a bioaccumulation factor (BAF), declined as the aging time increased from 1 to 180 d. Although the extractable HCB decreased with increasing residence time in soil, much of HCB could still be accumulated by earthworms (457.6-984.3 ng/g) through bioaccumulation, which poses a potential risk to soil ecological safety.

Application of advanced oxidation processes and electrooxidation for the remediation of river sediments contaminated by PAHs

This study was performed to assess and compare the effectiveness of electrochemical oxidation and chemical oxidation with hydrogen peroxide and modified Fenton's reagent for the remediation of sorbed polycyclic aromatic hydrocarbons (PAHs) in river sediments. The initial total PAH concentration in the sediment samples ranged from about 1032.8 mg/kg(DW) to 2816.4 mg/kg(DW) and a 90% degradation was required to meet the remediation goals. Several tests were performed at laboratory scale, the removal efficiency being evaluated in terms of contaminant removal and of ecotoxicity. The chemical oxidation tests resulted in about 95% total PAH degradation, when a sufficient oxidant dose was used (i.e. about 50-100 mmol of H2O2 per 30 g sediment samples), but proved to increase the ecotoxitity of the treated sediments significantly. Electrooxidation showed degradation efficiencies above 90%, with a negligible residual toxic effect, after 4-week treatments at constant voltage gradients of 1-2 V/cm. This technique seems to be effectively applicable either for the in situ or for the ex situ recovery of the target sediments.

Effect of humic substances on the Fenton treatment of wastewater at acidic and neutral pH

This paper describes results of treatability studies of the effect of humic substances (humate, HS, at the concentration 500-5000 mg l-1) on the Fenton (Fe2+/H2O2) treatment of industrial wastewater at pH 3.5 and 7.0. Without humate, the removal of all contaminants was significantly higher at pH 3.5 than at pH 7. At pH 7.0, the removal of all compounds in the presence of HS (3000 mg l-1) was comparable to that at pH 3.5 without HS. At pH 3.5, humate had no effect on the removal of arsenic, thiocyanate and cyanide, but the removal of all organic compounds (phenol, 2,4-dimethylphenol, benzene, toluene, o-xylene, m- & p-xylene and dichloromethane) was significantly inhibited. Mechanisms of the processes are discussed. It is suggested that, in the presence of HS, acidification of the treated wastewater may not only be unnecessary but it can even hinder the degradation of organic pollutants.

Influence of pyrene combination state in soils on its treatment efficiency by Fenton oxidation

Interactions of hydrophobic organic compounds (HOCs) with soil organic matter (SOM) determine their combination state in soils, and therefore strongly influence their mobility, bioavailability, and chemical reactivity. Contact time (aging) of an HOC in soil also strongly influences its combination state and environmental fate. We studied Fenton oxidation of pyrene in three different soils to reveal the influences of SOM, contact time, and combination state on the efficiency of vigorous chemical reactions. Pyrene degradation efficiency depended strongly on the dose of oxidant (H(2)O(2)) and catalyst (Fe(2+)); the greatest degradation was achieved at an oxidant to catalyst molar ratio of 10:1. Pyrene degradation differed among the three soils, ranging from 65.4% to 88.9%. Pyrene degradation efficiency decreased with increasing SOM content, and the aromatic carbon content in SOM was the key parameter. We hypothesize that pyrene molecules that combine with the compact net structure of aromatic SOM are less accessible to Fenton oxidation. Furthermore, pyrene degradation efficiency decreased considerably after aged for 30 days, but further aging to 60 and 180 days did not significantly change degradation efficiency. The Fenton oxidation efficiency of pyrene in both unaged and aged soils was greater than the corresponding desorption rate during the same period, perhaps because Fenton reaction can make pyrene more accessible to the oxidant through the enhancement of HOCs' desorption by generating reductant species or by destroying SOM through oxidation.

Remediation of phenanthrene from contaminated kaolinite by electroremediation-Fenton technology

Polycyclic aromatic hydrocarbons (PAHs) cause a high environmental impact when released into the environment. The objective of this study was to evaluate the capacity to decontaminate polluted soils with phenanthrene as a model PAH using a combination of two technologies: electrokinetic remediation and Fenton process. Kaolinite was used as a model sample that was artificially polluted at the laboratory at an initial concentration of phenanthrene of 500 mg kg(-1) of dried kaolinite. The standard electrokinetic process resulted in negligible removal of phenanthrene from the kaolinite sample. Faster and more efficient degradation of this compound can be promoted by introduction of a strong oxidant into the soil such as hydroxyl radicals. For this reason, the Fenton reactions have been induced in several experiments in which H(2)O(2) (10%) was used as flushing solution, and kaolinite polluted with iron was used. When anode and cathode chambers were filled with H(2)O(2) (10%), the kaolinite pH is maintained at an acid value around 3.5 without pH control and an overall removal and destruction efficiency of phenanthrene of 99% was obtained in 14 days by applying a voltage gradient of 3 V cm(-1). Therefore, it is evident that a combined technology of electrokinetic remediation and Fenton reaction is capable of simultaneously removing and degrading of PAHs in polluted model samples with kaolinite.

Effect of modified Fenton treatment on the thermal behavior of contaminated harbor sediments

This study presents the results of experimental Fenton-like treatments conducted on marine sediment slurries (2g sediment vs. 20 ml liquid). The sediment was collected in a harbor situated in a high density industrial area, characterized by a great hydrocarbon C>12 and PAHs contamination. The investigated parameters were: the H(2)O(2) dose, the reagent's pH and the effect of a phosphate salt and ferrous iron addition. To evaluate sediment's characteristics COD, particle size, thermogravimetric and differential thermal analyses were performed under N(2) and O(2) atmosphere while dissolved organic carbon and COD analyses were performed on the filtrate. Results indicate that the treatment was able to change the organic matter to a less hydrophobic state, to destroy part of the organic carbon (up to 78% decrease of the 200-400 degrees C labile organic matter), to lower the COD of the sediment (60% COD removal maximum) and to increase the cumulated distribution undersize. In addition as the treated sediment showed easier-to-handle characteristics, reduced caking and lower aggregation capacity, the modified Fenton treatment could also be considered a pre-treatment of a successive thermal treatment.

Effect of microbial activity, soil water content and added copper on the temporal distribution patterns of HCB and DDT among different soil organic matter fractions

Temporal changes in the distribution of exogenous HCB and DDT among different soil organic matter fractions were studied under sterile and non-sterile conditions, different soil water contents, and different concentrations of added Cu(2+). The residence time was 311days. Soil organic matter was fractionated into fulvic acid (FA), humic acid (HA), bound-humic acid (BHA), lipid, and insoluble residue (IR) fractions by a methyl isobutyl ketone (MIBK) method. Results revealed that there is a mass transfer tendency of DDT and HCB from FA, HA and BHA to IR and lipid fractions with increasing residence time. Microbial activity accelerated the mass transfer, while the addition of Cu(2+) slowed it down. The HCB and DDT transfer rate decreased as the soil moisture increased from 1.9% to 60%, but increased when soil moisture increased further to 90%. A two-compartment first order kinetic model was used to describe the mass transfer from FA, HA and BHA.

Temporal change in the distribution patterns of hexachlorobenzene and dichlorodiphenyltrichloroethane among various soil organic matter fractions

Residence time-dependent distribution patterns of hexachlorobenzene (HCB) and dichlorodiphenyltrichloroethane (DDT) among different soil organic matter fractions of three Chinese soils were investigated. Soil organic matter (SOM) was fractionated into fulvic acid (FA), humic acid (HA), bound-humic acid (BHA), lipid, and insoluble residue (IR) fractions using methyl isobutyl ketone (MIBK) method. Results revealed that as the residence time prolonged, the amounts of HCB and DDT in the FA, HA and BHA fractions decreased, while those in the lipid and IR fractions increased. One- and two-compartment first order, and one- and two-parameter pore-diffusion kinetic models were used to describe the mobility of HCB and DDT from the FA, HA and BHA fractions. The results suggest that excellent agreements were achieved between the experimental data and fits to the two-compartment first order kinetic model (R2>0.97). The transfer rates of HCB and DDT followed the order FA>HA>BHA.

Degradation of polycyclic aromatic hydrocarbons (PAHs) in contaminated soils by Fenton's reagent: a multivariate evaluation of the importance of soil characteristics and PAH properties

In this study, we investigated how the chemical degradability of polycyclic aromatic hydrocarbons (PAHs) in aged soil samples from various contaminated sites is influenced by soil characteristics and by PAH physico-chemical properties. The results were evaluated using the multivariate statistical tool, partial least squares projections to latent structures (PLS). The PAH-contaminated soil samples were characterised (by pH, conductivity, organic matter content, oxide content, particle size, specific surface area, and the time elapsed since the contamination events, i.e. age), and subjected to relatively mild, slurry-phase Fenton's reaction conditions. In general, low molecular weight PAHs were degraded to a greater extent than large, highly hydrophobic variants. Anthracene, benzo(a)pyrene, and pyrene were more susceptible to degradation than other, structurally similar, PAHs; an effect attributed to the known susceptibility of these compounds to reactions with hydroxyl radicals. The presence of organic matter and the specific surface area of the soil were clearly negatively correlated with the degradation of bi- and tri-cyclic PAHs, whereas the amount of degraded organic matter correlated positively with the degradation of PAHs with five or six fused rings. This was explained by enhanced availability of the larger PAHs, which were released from the organic matter as it degraded. Our study shows that sorption of PAHs is influenced by a combination of soil characteristics and physico-chemical properties of individual PAHs. Multivariate statistical tools have great potential for assessing the relative importance of these parameters.

Influence of Fenton oxidation on soil organic matter and its sorption and desorption of pyrene

The influences of Fenton oxidation on the content and composition of soil organic matter (SOM) and the consequent change of its sorption and desorption of pyrene were investigated using three soil samples. The results showed that both the content and the composition of the SOM changed, with total SOM content decreasing. The content of humic acid (HA) was reduced, while the content of humin did not change significantly, however the content of fulvic acid (FA) had a tendency to increase. Correlation analysis of soil-water distribution coefficient (K(d)) and different parts of the SOM reveals that humin and HA are the key factors controlling the sorption of pyrene. Organic carbon normalized K(d) (K(OC)) varied to different extents after Fenton oxidation due to the change of SOM composition. The reduction of K(OC) is significant in Soils 1 and 2 where large part of HA was reduced to FA, whose sorption ability is low. The change of K(OC) by oxidation in Soil 3 is not so significant due to that the percentage of humin and HA in Soil 3 did not change greatly after oxidation. Desorption was hysteretic in all cases, and humin percentage was found to be the key factor on the extent of desorption hystersis. Oxidation made desorption more hysteretic due to the elevated proportion of humin.

Remediating polluted soils

This review focuses on treatment-based remediation of soils and the acquisition of data to support and monitor this remediation. Only in the last two decades has significant progress been made in regulating for soil pollution, with a parallel development of methodologies for soil assessment and remediation. However, soil complexity remains a problem for pollutant measurements relevant to environmental risk and informative to the design or evaluation of remediation technologies. Understanding the distribution of pollutants between different soil phases and the kinetics of transfer between these pools is fundamental to prediction for these processes; further progress is needed to characterise less accessible pollutant pools and to develop guidelines for their analysis. Available remediation options include physical, chemical and biological treatments, and these options offer potential technical solutions to most soil pollution. However, selecting the most appropriate approach requires detailed information on how pollutants interact with soil physio-chemical properties. Only general information is available as to the effectiveness of specific treatment systems for particular soil type-pollutant combinations. Given the high degree of heterogeneity in physio-chemical characteristics and pollutant distribution of affected soils, prediction of treatment timescales and levels of residual contamination remains a problem. On sites with a range of organic and inorganic pollutants present, combinations of different treatment approaches may offer the best prospect for effective remediation. Further work is needed to provide evidence that residual contamination does not pose significant risk and to evaluate effects of treatments on general soil function in relation to this contamination.

Experimental in situ chemical peroxidation of atrazine in contaminated soil

Lab-scale experiments of in situ chemical oxidation (ISCO), were performed on soil contaminated with 100 mg kg(-1) of atrazine (CIET). The oxidant used was hydrogen peroxide catalysed by naturally occurring minerals or by soluble Fe(II) sulphate, added in aqueous solution. The oxidation conditions were: CIET:H2O2=1:1100, 2 PV or 3 PV reaction volume, Fe(II):H2O2=0, 1:22, 1:11. Stabilized (with KH2PO4 at a concentration of 16 g l(-1)) or non-stabilized hydrogen peroxide was used. The pH of the reagents was adjusted to pH=1 with sulphuric acid, or was not altered. Results showed that the addition of soluble Fe(II) increased the temperature of the soil slurry and the use of stabilized hydrogen peroxide resulted in a lower heat generation. The treatment reduced the COD of the soil of about 40%, pH was lowered and natural organic matter became less hydrophobic. The highest atrazine conversion (89%) was obtained in the conditions: 3 PV, Fe(II):H2O2=1:11 with stabilized hydrogen peroxide added in two steps. The stabilizer only increased H2O2 life-time significantly when soluble Fe(II) was added. Results indicate as preferential degradation pathway of atrazine in soil dechlorination instead of dealkylation.

Removal of sorbed polycyclic aromatic hydrocarbons from soil, sludge and sediment samples using the Fenton's reagent process

The use of the Fenton's reagent process has been investigated for the remediation of environmental matrices contaminated by polycyclic aromatic hydrocarbons (PAHs). Laboratory experiments were first conducted in aqueous solutions, to study the kinetics of oxidation and adsorption of PAHs. Benzo[a]pyrene was more rapidly degraded than adsorbed, while only partial oxidation of fluoranthene occurred. In the case of benzo[b]fluoranthene, its adsorption prevented its oxidation. Besides competition effects between PAHs were found, with slower oxidation of mixtures as compared to single PAH solutions. Apparition of some by-products was observed, and a di-hydroxylated derivative of benzo[a]pyrene could be identified under our conditions. Consequently, application to solid environmental matrices (soil, sludge and sediment samples) was performed using large amounts of reagents. The efficiency of the Fenton treatment was dependent on the matrix characteristics (such as its organic carbon content) and the PAH availability (correlated to the date and level of contamination). However, no pH adjustment was required, as well as no iron addition due to the presence of iron oxides in the solid matrices, suggesting the potential application of Fenton-like treatment for the remediation of PAH-contaminated environmental solids.

"Humic coverage index" as a determining factor governing strain-specific hydrocarbon availability to contaminant-degrading bacteria in soils

We report development of a novel parameter for quantifying the amount of humic and fulvic acids per unit surface area in a particular soil. This quantity, the "humic coverage index" (HCI), provides a measurement of the relative spatial extents and/or thicknesses of the humic/fulvic overlayers in different soils, and, therefore, can be used in modeling various soils' behavior in sequestration processes in which humic materials are involved. HCI is herein applied to modeling biodegradation of aromatic and aliphatic hydrocarbons (phenanthrene, pyrene, and hexadecane) by several bacterial strains. Results indicate that, for the cases studies here, contaminant biodegradation is highest at a particular HCI and decreases if the coverage density of humic material is lower or higher than this optimum value. The HCI value at which maximal degradation was observed varied across different strains (indicating strain-specific differences in ability to degrade contaminants sorbed to humic materials) and, to a lesser extent, across different contaminants. The HCI concept is also demonstrated to be useful in explaining soil-, strain-, and contaminant-specific variations in the ability of fulvic acid supplementation to enhance contaminant biodegradation. Finally, we show that, in general, strains which are comparatively better at degrading contaminants in high-HCI soils also show enhanced contaminant mineralization in vitro in the presence of humic acids, such as when hydrocarbons are adsorbed onto these materials.