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The efficacy of two oxidant systems, iron-activated hydrogen peroxide (HO) and iron-activated hydrogen peroxide coupled with persulfate (SO ), was investigated for treatment of two chlorinated organic compounds, trichloroethene (TCE) and 1,2-dichloroethane (DCA). Batch tests were conducted at multiple temperatures (10-50 °C) to investigate degradation kinetics and reaction thermodynamics. The influence of an inorganic salt, dihydrogen phosphate ion (HPO ), on oxidative degradation was also examined. The degradation of TCE was promoted in both systems, with greater degradation observed for higher temperatures. The inhibition effect of HPO on the degradation of TCE increased with increasing temperature for the iron-activated HO system but decreased for the iron-activated hydrogen peroxide-persulfate system. DCA degradation was limited in the iron-activated hydrogen peroxide system. Conversely, significant DCA degradation (87% in 48 h at 20 °C) occurred in the iron-activated hydrogen peroxide-persulfate system, indicating the crucial role of sulfate radical (SO ∙) from persulfate on the oxidative degradation of DCA. The activation energy values varied from 37.7 to 72.9 kJ/mol, depending on the different reactants. Overall, the binary hydrogen peroxide-persulfate oxidant system exhibited better performance than hydrogen peroxide alone for TCE and DCA degradation. [ABSTRACT FROM AUTHOR]

Petroleum hydrocarbon, a complex mixture including aliphatic and aromatic hydrocarbons, is known to have negative effects on the environment. We determined the effectiveness of persulfate (PS) (5% w/ w) activated using 1% ( w/ w) of various types of soil minerals, goethite (α-FeOOH), hematite (FeO), magnetite (FeO), maghemite (γ- FeO), manganese oxide (MnO), and zeolite (clinoptilolite) to treat petroleum hydrocarbon-contaminated soil. Total petroleum hydrocarbon (TPH) was 4200 ± 124 mg kg. The TPH removal efficiency was in the order: FeO > MnO > γ-FeO > FeO > α-FeOOH > clinoptilolite. When the PS dosage and the moisture content of the soil increased, the degradation rate ( k ) of TPH removal increased; on the other hand, lowering the pH increased the k of TPH removal. The PS oxidation of TPH was optimized using response surface methodology (RSM). The interactive effects of three factors, namely, persulfate dosage ( X ), pH ( X ), and soil moisture content ( X ), were investigated. The optimum removal of TPH by PS oxidation activated using 1% ( w/ w) magnetite was obtained at 5.5% ( w/ w) PS and 85% ( w/ w) moisture content at an initial pH of 4.5. However, the soil treated by PS showed a negative effect on soil health. The germination of mung bean ( Vigna radiata (L.) R. Wilczek) and the CO release for the treated soil were low, indicating that toxicity had occurred in the treated soil. To restore the treated soil, adding a soil amendment, like CaCO, fly ash, or crop residue, was able to improve plant growth and soil microbial activity. [ABSTRACT FROM AUTHOR]

In situ chemical oxidation using persulfate is one alternative to remediate polycyclic aromatic hydrocarbon-contaminated soil; however, oxidation can lead to the formation of toxic and persistent by-products, and treatment efficiency can be dependent on environmental conditions. Temperature and soil matrix properties can dictate reaction rates and pathways, promoting oxidant activation or scavenging the free radicals generated. This research investigated the ability of persulfate to degrade anthracene in tropical environmental conditions. Batch tests were conducted for various persulfate systems (naturally and chelated-iron-activated), with an Oxisol contaminated with anthracene. Electron paramagnetic resonance (EPR) was used to identify free radicals formed. Naturally activated persulfate degraded more than 96% of the anthracene and its by-product anthraquinone after 90 days, considered more toxic and persistent, while the chelated-iron-activated persulfate system used was able to remove 70% of the anthracene. EPR measurements showed the coexistence of SO and OH radicals. Sulfate radicals were formed by thermal activation at ambient temperatures (mean of 23.7 °C), and OH was formed by propagation reactions and hydrolysis in acidic conditions that lead to peroxide formation. In the naturally activated system, anthracene degradation was observed and SO radicals were abundant, indicating that this treatment system can be effective in a typical tropical soil environment. [ABSTRACT FROM AUTHOR]

Recently, persulfate (PS) has been applied to the oxidation of organic contaminants in wastewater, groundwater, and soil. However, PS requires activation by UV light, heat, transition metal, or pH control to be useful. In particular, transition metals are able to rapidly activate PS to sulfate radical. However, it is difficult to control the concentration of transition metal solution in an environmental setting. In this study, the potential of an electrochemical reaction using an iron anode to activate PS was investigated with phenol as a model contaminant. Based on Faraday's law, Fe(II) generated by the electrochemical reaction was regularly supplied to the solution to activate PS to sulfate radical. The activation of PS was influenced by current intensity; however, excess Fe(II) decreased the oxidation rate of phenol because anodic oxidation-generated Fe(II) also scavenged sulfate radical. However, the electrochemical reaction using the iron anode could be readily controlled to supply an optimal amount of Fe(II) for activation of PS. Therefore, it is expected that this electrochemical process using an iron anode could be useful for the effective removal of phenol. [ABSTRACT FROM AUTHOR]

Persulfate use as a chemical oxidant for remediation of contaminated sites has increased due to its higher in situ persistence and reactivity with environmentally relevant contaminants. The interaction of persulfate with soil materials can significantly influence treatment efficiency by either promoting activation or by decreasing its persistence. In this investigation, the interaction between persulfate and three soils (two highly weathered and clayey Oxisols, and a sandy Psamment soil) found in tropical environments was evaluated. A series of batch tests were conducted using a high (14 g L) and low (1 g L) persulfate concentration. Additional persulfate mass was added after 120 days into low persulfate concentration systems. Persulfate degradation generally followed a first-order kinetic model; however, the reaction rate coefficients varied with initial concentration and with the addition of persulfate at 120 days. A kinetic model that accounts for the presence of a finite mass of oxidizable material was shown to capture all experimental conditions. In all systems, the pH decreased significantly, causing favorable conditions for the dissolution of clay minerals such as kaolinite, as supported by mineralogical analyses. This dissolution resulted in an increase in exchangeable aluminum and iron, as well as conversion of iron associated with amorphous oxides to crystalline oxides. The increased availability of these species resulted in accelerated persulfate degradation. Based on the data set assembled, a conceptual model was developed that represents the interaction between persulfate and soils that have clay minerals containing iron that are susceptible to dissolution. [ABSTRACT FROM AUTHOR]

An electrochemically activated persulfate (EC/PS) system was proposed for the degradation of herbicide diuron in this study. In the EC/PS system, the ferrous ions (Fe) produced from iron electrode can activate persulfate to generate sulfate radical (SO ) as well as hydroxyl radical (OH). The results showed that the degradation of diuron was significantly enhanced in the EC/PS system, compared to electrocoagulation, persulfate, and Fe/PS process. Both of SO and OH contributed to the degradation of diuron in the EC/PS system according to the radical scavenging studies. The pseudo first-order rate constants of diuron increased with increasing the applied currents and dosages of persulfate. pH affected the degradation of diuron indirectly through the speciation of iron and resulted in higher removal efficiency in acidic condition than in alkaline condition. Chloride, carbonate, and bicarbonate in real water inhibited the degradation of diuron dramatically through consuming SO and OH and abided by the order of CO >HCO >Cl. This study demonstrates that the EC/PS system is a novel, efficient, promising, and environmental-friendly method to treat diuron contamination. [ABSTRACT FROM AUTHOR]

Inorganic arsenic occurs mainly in As(III) and As(V) states in water environment, but arsenite is more toxic and difficult to remove than arsenate by usual adsorption processes. To achieve the in situ oxidation of As(III) and simultaneous removal of both As(III) and As(V) in water, a novel-layered double hydroxide (Mg-Fe-SO-LDH) with the intercalation of persulfate has been designed and synthesized by a calcination-reconstruction method. The arsenic adsorption performances and removal mechanism with the Mg-Fe-SO-LDH material were studied. The experimental result showed that, since the strong oxidation ability of the exchangeable persulfate ions from the LDH, the As(III) species in water were almost completely oxidized to the As(V) state and simultaneously adsorbed onto the Mg-Fe-SO-LDH. It was found that the maximum adsorption capacity for As(III) and As(V) in single-pollutant system was 75.00 and 75.63 mg·g, respectively. When the adsorbent dosage was 0.5 g·L for a mixed As(III) and As(V) solution, the batch experiment showed that the residual arsenic concentration can be reduced from 1 mg·L to lower than the limit value of drinking water standard recommended by WHO. It indicated that the synthesized Mg-Fe-SO-LDH is a potential attractive adsorbent for simultaneous removal of As(III) and As(V) in water. [ABSTRACT FROM AUTHOR]

Advanced oxidation of bisphenol A (BPA) in aqueous system by O/NaSO was investigated, the degradation of BPA was affected by ozone concentration, persulfate dosages, initial pH, and BPA concentration. Experimental results indicated that the degradation of BPA was proved to follow the pseudo-first order kinetics model and was enhanced with the increase of O concentration and the decrease of initial BPA concentration. pH played a significant role in the BPA removal especially under the alkaline condition. Free radical species in the O/NaSO system were identified by using tertiary butyl alcohol (TBA) and ethanol (ETOH) as two probes, the results found that the major free radical was SO · at acidic condition (pH = 3), and the concentration of ·OH increased with the pH increased. Eight products were detected during the reaction according to liquid chromatograph-mass spectrometry analysis. Most of the intermediates contained quinonoid derivatives, carboxylic acid, and the relevant mechanism for BPA degradation by O/NaSO system were proposed. [ABSTRACT FROM AUTHOR]

This study proposes an improved activation for hydrogen peroxide and persulfate using Fe-modified diatomite (MD) to favorably lead the reaction to generate hydroxyl and sulfate radicals to degrade the contaminants phenanthrene and anthracene. Diatomite was modified by impregnating it with a mixture of ferrous (Fe) and ferric (Fe) ions in the form of precipitated iron oxides and hydroxides. The raw and synthesized materials were characterized by powder X-ray diffraction (XRD), X-ray fluorescence (XRF), particle size by laser diffraction, chemical microanalysis of the elements by energy-dispersive X-ray, and scanning electron microscopy (SEM). Batch experiments were performed to compare the new activator material (modified diatomite) with traditional methods of activation for these oxidants and to statistically study the optimum ratio between the amount of this material and the concentration of one oxidant to the degradation of the contaminants phenanthrene and anthracene. The characterization results showed that the materials are amorphous and that the Fe ion concentration was 4.78 and 17.65 % for the raw and modified diatomites, respectively. This result shows a significant increase in the amount of iron ions after synthesis. Comparing the traditional activation method with the modified diatomite, the results of batch experiments showed that the synthesized material presents significant catalytic activity for the oxidation of these contaminants, using sodium persulfate and hydrogen peroxide as oxidants. The analysis of the variables results showed that the concentration of the oxidant has higher significance than the amount of the catalyst. [ABSTRACT FROM AUTHOR]

The present work studies the remediation of a B20 (20 % biodiesel, 80 % diesel) biodiesel blend-contaminated soil (1,000 mg kg) with persulfate activated by iron. Three different sources of iron (Fe(II)), granular zerovalent iron (gZVI), and a slurry of nanoparticles of zerovalent iron (nZVI), without pH adjustment were tested. Besides, the effect of the addition of chelating agents, such as trisodium citrate (SC), or citric acid (CiA), has been also studied. SC promotes pH under near-neutral conditions and reaction takes place at low rate at these experimental conditions. On the other hand, the use of CiA leads to an acidic pH and chelating agent is oxidized at higher rate than total petroleum hydrocarbons (TPH). Therefore, CiA addition does not seem to produce any improvement on the removal efficiency of TPH. Regarding the three different sources of iron used as activators, Fe(II), gZVI and nZVI, in absence of chelating agent, under acidic pH and by adding the same amount of iron, the highest TPH conversion was obtained with ZVI (about 60 %), while a conversion of about 40 % was obtained with the addition of Fe(II). The maximum TPH conversion value was achieved in shorter time using nZVI. Concerning the removal efficiency of each fraction of biodiesel abated, fatty acid methyl esters (FAME) were by far the easiest to oxidize, achieving 100 % of conversion, either by using Fe(II) or nZVI activated persulfate. [ABSTRACT FROM AUTHOR]

In view of the fatal illnesses caused by methylene blue (MB) which is contained in the dye wastewater, the present study focused on the use of natural sunlight in heterogeneous photocatalysis to decolorize and degrade MB. The present study also investigated the effects of enhancers (hydrogen peroxide and persulfate ion) and inhibitors (chloride and carbonate ions) on photodecolorization of MB. Pseudo-first-order rate constants for each studied effect were determined through Langmuir-Hinshelwood model. The recommended conditions to photodecolorize 60 ppm of MB under natural sunlight were 1.0 g/L of titanium dioxide nanopowder at initial pH 10.5 in order to achieve 85.3 % decolorization (rate constant of 10.8 × 10 min). The addition of 4,080 ppm of hydrogen peroxide and persulfate ion significantly enhanced the decolorization efficiency up to 96.6 and 99.3 %, respectively (rate constants of 66.2 and 91.0 × 10 min, respectively). However, the addition of 2,000 ppm of chloride and carbonate ions reduced the decolorization efficiency of MB to 74.7 and 70.2 %, respectively (rate constants of 7.8 and 7.3 × 10 min, respectively). The present study implied that it was possible to use natural sunlight as a light source for photocatalytic treatment of dye in tropical countries like Malaysia. [ABSTRACT FROM AUTHOR]

This work evaluated surfactant-enhanced in situ chemical oxidation (S-ISCO) in a hydrocarbon-contaminated soil. Surfactants and efficacy of oxidant activation as well as the treatability of contaminated soil were assessed. The surfactant VeruSOL-3 with a critical micelle concentration (CMC) of 5.5 g/L was selected. Based on the results, activated oxidations by sodium persulphate and hydrogen peroxide were able to effectively destroy target organic compounds in emulsion and soil. The destruction of total petroleum hydrocarbon (TPH) in emulsion was completed in 14 days and polycyclic aromatic hydrocarbons (PAHs) in excess of 96 %. Green nanoiron was much more active than other activators in emulsion. The data also indicates that oxidation using activators was much less pronounced in soil matrices. However, it is expected that given sufficient dose and treatment time, a higher destruction rate in the contaminated soil can be achieved. The study showed that the remediation of target organic contaminants (TPH, PAH) in soil by S-ISCO using activated sodium persulphate is feasible. [ABSTRACT FROM AUTHOR]

Recently, metal nanoparticles have attracted attention as promising peroxygen activators for the rapid and effective remediation of organic contaminants. In this work, a one-dimensional physical model experiment was designed to investigate the mobility of the metal nanoparticles in porous media and the potential use of metal nanoparticles as peroxygen activators for in situ treatment of source zones. We found that our synthesized nano-Pd–Fe 0 particles were mobile in a non-geological porous medium and relatively immobile in a geological porous medium. In addition, we observed that iron-based bimetallic nanoparticles were able to remain in suspension in an ideal aqueous system much longer (>6 weeks) than iron-based monometallic nanoparticles (<1 h). To overcome the nano-Pd–Fe 0 particle delivery issue in geological porous media, an activation zone approach was adopted. Nano-Pd–Fe 0 particles were injected in order to create a zone to activate persulfate for the treatment of a trichloroethylene source zone. Trichloroethylene mass destruction was only 9 % higher in the nano-Pd–Fe 0 activated persulfate system compared to the non-activated persulfate system as revealed by a short-duration chloride concentration spike in the effluent. In addition, the nano-Pd–Fe 0 activation zone was rapidly deactivated after being exposed to persulfate as visually observed by a color change, indicating that the longevity of the activation zone is limited. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the removal of both polycyclic aromatic hydrocarbons (PAHs) and heavy metals from field-contaminated sediments by activated persulfate oxidation. Various chemicals, including hydroxypropyl-β-cyclodextrin (HPCD), S, S-ethylenediaminedisuccinic acid (EDDS), tetrasodium pyrophosphate (NaPO), and hydrochloric acid (HCl), were applied individually before or after activated persulfate oxidation to enhance the co-removal of both types of pollutants. It was found that the organic removal efficiency was not significantly enhanced by increasing the concentration of HPCD from 2.5 to 5.0 mM. The removal efficiency of heavy metals was not improved even at an excess amount of EDDS after activated persulfate oxidation. However, the addition of EDDS acted as the Fe carrier for activated persulfate oxidation. In addition, no significant enhancement of heavy metal removal was observed by increasing the concentrations of NaPO and HCl from 0.01 to 0.1 M after activated persulfate oxidation. However, comparing 0.1 M HCl with 0.1 M NaPO, HCl was shown to be more effective in promoting the removal of organic pollutants. With further adjustments on the experimental conditions, the highest removal amount of metals and PAHs was achieved by adding 2 M of HCl with 3 days mixing, followed by Fe-activated persulfate oxidation (PS/Fe molar ratio at 4:1) for further 6 h mixing. The removal efficiency of low and high molecular weight PAHs was about 70 and 20 %, respectively, while the removal efficiency of metals was 70, 100, 40, 65, 65, 80, and 100 % for Cr, Cu, Hg, Mn, Ni, Pb, and Zn, respectively. [ABSTRACT FROM AUTHOR]

A laboratory study was conducted to assess the feasibility of remediating diesel-contaminated soils using sodium persulfate (SPS) oxidation under an alkaline pH. Lime (CaO) and sodium hydroxide (NaOH) were used as the alkaline sources, and various factors, including temperature, reaction time and concentration level, were investigated. Moreover, the combined usage of hydrogen peroxide (HP) and SPS in the presence or absence of NaOH was also studied. It was found that lime hydration resulted in rapid increases in pH (>12) and temperature (75 °C maximum) at a CaO/HO mass ratio of 3/20. In the NaOH or CaO/SPS system, the maximum diesel degradation achieved was approximately 30 %. It was observed that using a larger amount of alkaline increased SPS decomposition and had almost no effect on diesel degradation. Limited solubilization of contaminants may have inhibited the effectiveness of alkaline-activated persulfate oxidation during the aqueous phase and hence resulted in incomplete diesel degradation. The highest rate of diesel degradation (i.e., 56 % in 7 days) was achieved using the dual oxidation system, in which a HP/SPS molar ratio of 3.3/0.5 was used. An aggressive oxidation process, coupled with HP, may enhance desorption of diesel from soils and allow oxidation to occur during the aqueous phase. [ABSTRACT FROM AUTHOR]

Single-walled carbon nanotubes, both before (SWNTs) and after treatment (t-SWNTs) with acidified ammonium persulfate, were successfully used to adsorb bisphenol A (BPA) and 17β-estradiol (E2) from aqueous systems. The surface characteristics of the SWNTs and t-SWNTs were analyzed by measuring their surface charge and by imaging their morphological properties through transmission electron microscopy. The extent of defects on the SWNT scaffold generated through acid etching was analyzed by Raman spectroscopy. A total of 19.4, 15.4, and 14.3 mg/g of BPA was adsorbed on SWNTs, while a total of 8.0, 6.4, and 5.1 mg/g was adsorbed on t-SWNTs with a 72-h contact time at 280, 295, and 315 K, respectively. A significantly high fraction of E2 (27.2 mg/g) was absorbed by both SWNTs and t-SWNTs, as compared to BPA. The adsorption kinetics was analyzed using a pseudo-second-order model. Sorption experiments showed that t-SWNTs adsorbed less than half as much BPA as SWNTs, but their E2 adsorption was similar. The sorption mechanism was investigated by performing molecular-level calculations. Adsorption energies calculated using density functional theory show preferential sorption of E2 to SWNTs and graphene (−26.2 kcal/mol on SWNT and −34.1 kcal/mol on graphene) compared to BPA (−17.1 kcal/mol on SWNT and −22.5 kcal/mol on graphene), which were consistent with the experimental findings. Thus, ab initio calculations can mechanistically explain the adsorption differences of BPA and E2 on SWNTs. [ABSTRACT FROM AUTHOR]

The effectiveness of persulfate oxidation for the destruction of tetrachlorobiphenyl a representative polychlorobiphenyl (PCB), in spiked subsurface soils was evaluated in this study. Kaolin and glacial till soils were selected as representative low permeability soils; both soils were spiked with 50 mg PCB per dry kilogram of soil. Activation of persulfate oxidation was necessary to achieve effective destruction of PCBs in soils. As persulfate oxidation activators, temperature and high pH were used in order to maximize PCB destruction. In addition, the effect of oxidant dose and reaction time was investigated. The optimal dose for persulfate was found to be 30% for maximum oxidation. The persulfate activation with temperature of 45°C was superior to persulfate activation with high pH (pH 12), where higher PCB destructions were observed for kaolin and glacial till soils. PCB destruction increased with reaction time, where maximum degradation was achieved after 7 days. The highest PCB destruction was achieved with temperature activation at 45°C using a dosage of 30% persulfate at pH 12 for kaolin and glacial till soils after 7 days. [ABSTRACT FROM AUTHOR]

The oxidation of para-nitrochlorobenzene (pNCB) by persulfate (PS) activated with zero-valent iron (Fe0) was investigated through a series of batch experiments. The pNCB reduction ratio increased with the decrease of the initial solution pH. It is found that temperature and Fe0 dosage could also influence the pNCB removal. Under the conditions of initial Fe0 dosage 0.8 mmol/g, initial pH of 6.6, and 25 °C, 66.3% of pNCB was reduced in 6 h. The pNCB was slightly degraded in the presence of PS alone. When PS was dosed after 2 h of Fe0 reduction, significantly higher pNCB removal (94.1%) and mineralization (36.4%) were obtained relative to the case of simultaneous dosing of Fe0 and PS (85.3% removal, 22.6% mineralization). This indicates that the reduction product of pNCB was more easily oxidized by PS than pNCB, suggesting that converting the nitro groups of pNCB to amino groups prior to oxidation can enhance their oxidation. These results suggest that a sequential Fe0 reduction-PS oxidation process may be an effective strategy to promote pNCB decomposition in contaminated soil. [ABSTRACT FROM AUTHOR]

In this study, the performance of oxidation with actived persulfate (PS) by graphene oxide-TiO2 nanosheet (GO-TiO2) was investigated for diclofenac (DCF) removal, an anti-inflammatory analgesic being widely used in human health care and veterinary treatment. GO-TiO2 containing oxygen functional groups is employed as an activator for the activation of PS used as the oxidizing agent. Modeling and optimization of the process were performed by central composite design (CCD) as a response surface methodology (RSM). The effects of various factors, including PS concentration, GO-TiO2 amount, initial pH of DCF solution, and reaction time on DCF oxidation, were evaluated. When the estimated values of the full quadratic model obtained with CCD were compared with the actual experimental results, a strong agreement was obtained with an R2 value of 0.9553. Besides, the model consistency was verified by analysis of variance (ANOVA) with a value of 20.17 of F value and P value of less than 0.05. After the optimization run, maximum DCF removal of 93.06% occurred with contact time of 14 min, pH of 5.54, PS concentration of 10 g/L, and 0.1 g of GO-TiO2 as optimal variable values. [ABSTRACT FROM AUTHOR]