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    Biodegradation of 2,4-dinitrotoluene (DNT) by Arthrobacter sp K1 isolated from a crude oil contaminated soil
    (BMC, 2015) Kuce, Pinar; Coral, Gokhan; Kantar, Cetin
    Laboratory experiments were performed to characterize and identify 2,4-dinitrotoluene (DNT)-degrading bacterial strains isolated from crude oil contaminated soil from a landfill dump site of a petroleum refinery in Mersin, Turkey. Fluorescent in situ hybridization (FISH) with dntAa probes encoding 2,4-DNT dioxygenase was used to detect 2,4-DNT-degrading bacteria. The direct FISH analysis of soil samples collected from a petroleum refinery showed very weak signals. Therefore, a selective enrichment culture technique using 2,4-DNT as the sole carbon source was then used to isolate DNT degrading bacteria. Following the culture enrichment procedure, the hybridization signals improved significantly in the isolated bacterial strains. Based on 16S rRNA sequences, the bacteria isolated from the soil samples were identified as Arthrobacter sp. Results from the batch biodegradation experiments indicate that the biodegradation rates of 2,4-DNT with this strain were highly dependent on environmental conditions such as pH and temperature, with optimum conditions obtained at 30 A degrees C and pH similar to 7. A first-order kinetic model was able to accurately describe 2,4-DNT degradation rates under different environmental conditions (e.g., pH). The ability of Arthrobacter sp. for degrading 2,4-DNT was found to be plasmid-mediated through curing experiments. The size of the plasmid involved, referred to as pArK1, was estimated to be about 8.1 kb.
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    Comparison of different chelating agents to enhance reductive Cr(VI) removal by pyrite treatment procedure
    (Pergamon-Elsevier Science Ltd, 2015) Kantar, Cetin; Ari, Cihan; Keskin, Selda
    New technologies involving in-situ chemical hexavalent chromium [Cr(VI)] reduction to trivalent chromium [Cr(III)] with natural Fe(II)-containing minerals can offer viable solutions to the treatment of wastewater and subsurface systems contaminated with Cr(VI). Here, the effects of five different chelating agents including citrate, EDTA, oxalate, tartrate and salicylate on reductive Cr(VI) removal from aqueous systems by pyrite were investigated in batch reactors. The Cr(VI) removal was highly dependent on the type of ligand used and chemical conditions (e.g., ligand concentration). While salicylate and EDTA had no or little effect on Cr(VI) removal, the ligands including citrate, tartrate and oxalate significantly enhanced Cr(VI) removal at pH < 7 relative to non-ligand systems. In general, the efficiency of organic ligands on Cr(VI) removal decreased in the order: citrate >= oxalate tartrate approximate to EDTA > salicylate approximate to non-ligand system. Organic ligands enhanced Cr(VI) removal by 1) removing surface oxide layer via the formation of soluble Fe-Cr-ligand complexes, and 2) enhancing the reductive iron redox cycling for the regeneration of new surface sites. While citrate, oxalate and tartrate eliminated the formation of surface Cr (III) Fe(III)-oxides, the surface phase Cr (III) species was observed in the presence of EDTA and salicylate indicating that Cr(III) complexed with EDTA and salicylate sorbed or precipitated onto pyrite surface, thereby blocking the access of Cr-4(2-) to pyrite surface. The binding of Fe(III) with the disulfide reactive sites (equivalent to Fe-S-S-Fe(III)) was essential for the regeneration of new surface sites through pyrite oxidation. Although Fe(III)-S species was detected at the pyrite surface in the presence of citrate, oxalate and tartrate, Fe(III) complexed with EDTA and salicylate did not strongly interact with the disulfide reactive sites due to the formation of non-sorbing Fe(III)-ligand complexes. The absence of surface Fe(III)-S species indicated that no new reactive sites were generated through Fe redox cycling in the presence of salicylate and EDTA. (C) 2015 Elsevier Ltd. All rights reserved.
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    Coupling Pyrite-Fenton Process with Aerobic Biodegradation for the Treatment of 2-Chlorophenol
    (Springer International Publishing Ag, 2020) Kayan, Iremsu; Oz, Nilgun Ayman; Kantar, Cetin
    This study investigates the performance of a sequential pyrite-Fenton and biological process for the treatment of 2-chlorophenol (2-CP) containing wastewater using pyrite-Fenton process as a pretreatment stage. Pyrite was tested as a catalyst material in Fenton reaction due to its low cost and high abundance in the environment. All experiments were run in batch mode. The biodegradation experiments were performed under aerobic conditions using glucose as the co-substrate with untreated or Fenton-pretreated 2-CP. Despite the 100% removal of 2-CP in batch pyrite-Fenton reactors, the total organic carbon (TOC) removal only approached 70%, implying the transformation of 2-CP into some chemically stable intermediate reaction by products during pyrite-Fenton oxidation. In systems with no pyrite-Fenton pretreatment, a combined effect of biotic and abiotic processes including biological degradation, sorption, and volatilization played a significant role on 2-CP removal. The pyrite-Fenton pretreatment of 2-CP significantly improved the performance of aerobic biological reactor relative to system with no pyrite-Fenton pretreatment by (1) reducing the toxicity of 2-CP on aerobic microbial cells and (2) enhancing cell growth. Overall, this study shows that pyrite-Fenton pretreatment coupled with aerobic biological degradation could provide a cost-effective solution for the treatment of wastewater containing low-biodegradable toxic compounds such as chlorophenols.
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    Cr(VI) removal from aqueous systems using pyrite as the reducing agent: Batch, spectroscopic and column experiments
    (Elsevier Science Bv, 2015) Kantar, Cetin; Ari, Cihan; Keskin, Selda; Dogaroglu, Zeynep Gorkem; Karadeniz, Aykut; Alten, Akin
    Laboratory batch and column experiments, in conjunction with geochemical calculations and spectroscopic analysis, were performed to better understand reaction mechanisms and kinetics associated with Cr(VI) removal from aqueous systems using pyrite as the reactive material under both static and dynamic flow conditions similar to those observed in in situ permeable reactive barriers (PRBs). The X-ray photoelectron spectroscopy (XPS) and geochemical calculations suggest that the Cr(VI) removal by pyrite occurred due to the reduction of Cr(VI) to Cr(III), coupled with the oxidation of Fe(II) to Fe(III) and S-2(2-) to SO42- at the pyrite surface. Zeta potential measurements indicate that although the pyrite surface was negatively charged under a wide pH range in the absence of Cr(VI), it behaved more like a metal oxide surface with the surface potential shifting from positive to negative values at pH values >pH 6 in the presence of Cr(VI). Batch experiments show that increasing solution pH led to a significant decrease in Cr(VI) removal. The decrease in Cr(VI) removal at high Cr(VI) concentrations and pH values can be explained through the precipitation of sparingly soluble Cr(OH)(3(s)), Fe(OH)(3(s)) and Fe(III)-Cr(III) (oxy) hydroxides onto pyrite surface which may, then, lead to surface passivation for further Cr(VI) reduction. Batch results also suggest that the reaction kinetics follow a first order model with rate constants decreasing with increasing solution pH, indicating proton consumption during Cr(VI) reducdon by pyrite. Column experiments indicate that nearly 100% of total Fe in the column effluent was in the form of Fe(II) species with a [[SO42-]/[Fe2+]] stoichiometric ratio of 2.04, indicating that the reduction of Cr(VI) by pyrite produced about 2 mol of sulfate per mole of Fe (II) release under excess surface sites relative to Cr(VI) concentration. Column experiments provide further evidence on the accumulation of oxidation products which consequently led to a significant pressure build up in pyrite packed columns over time. (C) 2015 Elsevier B.V. All rights reserved.
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    Diclofenac removal by pyrite-Fenton process: Performance in batch and fixed-bed continuous flow systems
    (Elsevier Science Bv, 2019) Oral, Ozlem; Kantar, Cetin
    This study provides experimental results from batch and column studies to investigate diclofenac degradation by pyrite-Fenton process under variable chemical conditions (e.g., pyrite loading). Batch experiments show that diclofenac removal increased with increasing hydrogen peroxide and pyrite concentration. On the other hand, the addition of organic chelating agents such as citrate had an adverse effect on diclofenac removal by pyrite-Fenton process in batch systems due to scavenging effect of these agents for hydroxyl radicals. Batch results showed a direct correlation between the rate of diclofenac degradation and the rate of iron dissolution from pyrite, suggesting that diclofenac removal by pyrite-Fenton process was mainly controlled by solution phase hydroxyl radical attack on aromatic structure. Column experiments show that the effluent diclofenac concentration initially reached a peak value, and then sharply decreased to zero at higher pore volumes. The initial diclofenac breakthrough coincided well with the highest Fe(II) concentration observed in the breakthrough curve, implying that the generation of excess Fe(II) had a detrimental effect on removal efficiency due to scavenging effect of excess Fe(II) for hydroxyl radicals. The column system continued to function with 100% diclofenac removal efficiency when the effluent Fe(II) concentration decreased to a level at which the scavenging effect was minimized. (C) 2019 Elsevier B.V. All rights reserved.
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    Effect of Chromium and Organic Acids on Microbial Growth and Exopolymeric Substance Production by Pseudomonas Bacteria
    (Wiley-Blackwell, 2014) Dogan, Nazime Mercan; Kantar, Cetin; Dogan, Goksel
    Natural organic acids are capable of stimulating microbial chromium(VI) reduction, but little information is available about their behavior on microbial growth, exopolymeric substance (EPS) production, and subsequent microbial Cr(VI) reduction. Here, laboratory batch experiments were conducted to determine the effects of different natural organic acids (galacturonic, glucuronic, citric, and alginic acid) on microbial EPS production and the growth rates of four different naturally occurring soil bacteria (Pseudomonas putida P18, P. aeruginosa P16, P. fluorescens ATCC 55241, and P. stutzeri P40) as a function of pH and time in solutions containing toxic metal ions such as Cr(III) and Cr(VI). While the addition of Cr(VI) led to a negative impact on microbial growth in all strains studied, Cr(VI) significantly enhanced EPS release from cells due to extreme cell lysis. Organic acids diminished the toxic effects of Cr(VI) on cells, and thus significantly increased microbial cell growth and the EPS yield. The addition of Cr(III) with Cr(VI), on the other hand, led to a significant decrease in microbial cell growth rates relative to the systems containing only Cr(VI). This toxic effect decreased significantly in the presence of organic acids, and thus the EPS yield increased due to the formation of less toxic Cr(III)-EPS species. The overall results indicate that while the accumulation of free Cr(III) ion in aqueous phase during microbial Cr(VI) reduction may have an adverse influence on microbial cell growth, the EPS released by bacteria may bind with free Cr(III) ion in solution, and thus increase the cell growth rate due to the removal of toxic products of microbial reduction.
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    Effect of exopolymeric substances on the kinetics of sorption and desorption of trivalent chromium in soil
    (Springer International Publishing Ag, 2014) Kantar, Cetin; Demir, Aydeniz; Koleli, Nurcan
    Laboratory batch sorption-desorption and column experiments were performed to better understand the effects of microbial exopolymeric substances (EPS) on Cr(III) sorption/desorption rates in the soil-water system. The experiments were carried out in two different modes: one mode (sorption) in which Cr(III) and EPS were applied simultaneously, and the other (desorption) included the sequential application of Cr(III) and EPS to the soil-water system. The batch sorption and desorption experiments showed that, while chromium(III) desorption was significantly enhanced in the presence of EPS relative to non-EPS-containing systems, the desorption rates were much smaller than the sorption rates, and the fraction dissolved by EPS accounted for only a small portion of the total chromium initially sorbed onto soil minerals. Similarly, the column experiments suggested that, while the microbial EPS led to an increase in Cr dissolution relative to non-EPS-containing systems, only a small portion of the total chromium initially added to the soil was mobilised. The differences observed in Cr sorption and desorption rates can be explained through the very low solubility and strong interactions of chromium species with soil minerals as well as the mass transfer effects associated with low diffusion rates. The overall results suggest that, while microbial EPS may play an important role in microbial Cr(VI) treatment in sub-surface systems due to the formation of soluble Cr-EPS complexes, the extent and degree of Cr mobilisation are highly dependent on the type of initial Cr sorption. (C) 2013 Institute of Chemistry, Slovak Academy of Sciences
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    Effect of organic ligands on oxidative degradation of chlorophenolic compounds (CP) with modified-Fenton process using pyrite as the catalyst
    (Amer Chemical Soc, 2018) Kantar, Cetin; Oral, Ozlem; Oz, Nilgun
    [Anstract Not Available]
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    Effect of pH-buffering on Cr(VI) reduction with pyrite in the presence of various organic acids: Continuous-flow experiments
    (Elsevier Science Sa, 2016) Kantar, Cetin; Bulbul, Muhammet Samet
    The effects of pH and pH buffering on catalytic hexavalent chromium (Cr(VI)) reduction by pyrite were investigated in a series of column experiments. The experiments show a strong dependence of Cr(VI) removal by pyrite on solution pH, with Cr(VI) removal decreasing with increasing solution pH. While organic buffers e.g., (acetic acid/acetate) showed higher Cr(VI) removal by pyrite under acidic conditions (e.g., pH 4) relative to unbuffered systems, the addition of an organic buffer (MOPS) decreased Cr(VI) removal by pyrite at pH 8 relative to systems buffered with an inorganic buffer (bicarbonate). Similarly, in systems buffered with acetate buffer at pH 4, organic acids (e.g., citrate and tartrate) significantly improved Cr(VI) removal by pyrite due to removal of surface oxidation products (e.g., Fe(OH)(3(s))). Unlike acidic conditions, organic acids such as citrate and EDTA adversely affected Cr(VI) removal under alkaline pH conditions relative to systems containing 0.01 M MOPS buffer only. This inhibitory effect observed under alkaline pH conditions may be explained through competitive adsorption of organic buffers (MOPS) and acids (citrate, EDTA) onto pyrite surface, which, not only, modified pyrite surface properties, but also, blocked access of Cr(VI) to pyrite surface. Overall, it is clear that while pH buffering under acidic conditions may significantly improve the process efficiency of pyrite-based Cr(VI) treatment, it may have adverse effects on process efficiency under alkaline conditions (e.g., pH 8) since organic buffers (e.g., MOPS) and acids (e.g., EDTA) may directly interact with pyrite surface, and change its surface properties. (C) 2015 Elsevier B.V. All rights reserved.
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    Effect of pyrite on the treatment of chlorophenolic compounds with zero-valent iron-Fenton process under uncontrolled pH conditions: reaction mechanism and biodegradability
    (Springer, 2024) Oral, Ozlem; Kantar, Cetin; Yildiz, Ilker
    This current study explored the effect of pyrite on the treatment of chlorophenolic compounds (CP) by Fenton process with micron-sized zero-valent iron (ZVI) as the catalyst. The experiments were conducted in batch reactors with 100 mg L?1 CP, 0–0.02 M H2O2, and variable pyrite and ZVI doses (0–1 g L?1). Our findings show that while the reactor with 1 g L?1 ZVI as the only catalyst achieved only 10% CP removal efficiency due to rapid ZVI surface passivation and ZVI particle aggregation, the CP removal efficiency increased with increasing pyrite dose and reached 100% within couple of minutes in reactors with 0.8 g L?1 pyrite and 0.2 g L?1 ZVI. The CP removal was mainly driven by the oxidative treatment of CPs with some strong radicals such as hydroxyl radicals (•OH) while the adsorption onto the catalyst surface was only responsible for 10 to 25% of CP removals, depending on the type of CP studied. The positive impact of pyrite on CP removal by the ZVI/H2O2 system could be attributed to the ability of pyrite to (1) create an acidic environment for optimum Fenton process, (2) provide support material for ZVI to minimize ZVI particle agglomeration, and (3) stimulate iron redox cycling for improved surface site generation. Following oxidative Fenton treatment, the degradation intermediate products of CPs, including some aromatic compounds (benzoquinone, hydroquinone, etc.) and organic acids (e.g., acetic acid), became more biodegradable in comparison to their mother compounds. Overall, the treatment systems with a mixture of ZVI and pyrite as catalyst materials could offer a suitable cost-effective technology for the treatment of wastewater containing biologically non- or low-degradable toxic compounds such as chlorophenols. © The Author(s) 2024.
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    Effects of low molecular weight organic acids and Cr(VI) on Fe/Cr solubility and electrophoretic properties of pyrite
    (Amer Chemical Soc, 2013) Kantar, Cetin; Ari, Cihan; Karadeniz, Aykut
    [Anstract Not Available]
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    Effects of water hardness and humic substances on Cr(VI) removal from aqueous systems using pyrite as the reducing agent
    (Amer Chemical Soc, 2015) Kantar, Cetin; Bulbul, Muhammet
    [Anstract Not Available]
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    Heavy Metal Accumulation in Serpentine Flora of Mersin-Findikpinari (Turkey) - Role of Ethylenediamine Tetraacetic Acid in Facilitating Extraction of Nickel
    (Academic Press Ltd-Elsevier Science Ltd, 2015) Koleli, Nurcan; Demir, Aydeniz; Kantar, Cetin; Atag, Gunsu Altindisli; Kusvuran, Kadir; Binzet, Riza
    [Anstract Not Available]
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    Ligand enhanced pharmaceutical wastewater treatment with Fenton process using pyrite as the catalyst: Column experiments
    (Pergamon-Elsevier Science Ltd, 2019) Kantar, Cetin; Oral, Ozlem; Oz, Nilgun Ayman
    Advanced oxidation processes offer practical and cost effective solutions for the treatment of poorly biodegradable industrial wastewaters. Here, column experiments were performed to understand the role of a complexing agent, citrate, on Fenton-treatment of an actual pharmaceutical wastewater with pyrite as the catalyst under dynamic flow conditions. Our results suggest that the pharmaceutical wastewater treatment with Fenton reaction using pyrite as the catalyst was mainly regulated by the extent of Fe dissolution from pyrite, which, in turn, resulted in formation of hydroxyl radicals in solution. The Fenton treatment efficiency was much lower in the absence of citrate compared to citric acid containing systems due to clogging of column pores with oxidized Fe species. On the other hand, the addition of citrate to wastewater significantly improved Fenton process efficacy, and prolonged the lifecycle of pyrite-packed columns depending on solution pH. Low pH values were favorable for better Fenton efficiency in systems containing citrate due to combined effect of proton and ligand promoted dissolution and mobilization of oxidized Fe species. (C) 2019 Elsevier Ltd. All rights reserved.
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    Methylene blue treatment with zero-valent iron/pyrite/H2O2 system under static and continuous flow conditions: Reaction mechanism and toxicity evaluation
    (Elsevier Science Inc, 2024) Oral, Ozlem; Arslan, Sevki; Dogan, Nazime Mercan; Yildiz, Ilker; Kantar, Cetin; Abdelsalam, Amine Hafis; Kuzucu, Volkan
    Laboratory batch and continuous flow studies, coupled with surface and toxicity analysis, were performed to evaluate methylene blue treatment by heterogeneous Fenton process using zero-valent iron (ZVI) and pyrite as co-catalyst. The use of pyrite in batch reactors significantly enhanced methylene blue treatment by the ZVI/H2O2 system because of improved iron redox cycling. The continuous-flow experiments revealed that the reactor performance increased in the order of: ZVI/H2O2 < pyrite/H2O2 < ZVI/pyrite/H2O2 under dynamic flow conditions. The methylene blue treatment by the ternary ZVI/pyrite/H2O2 system was described by an initial degradation of methylene blue with *OH radicals, followed by the adsorption and/or co-precipitation of degradation intermediates with some spherical particles. The surface analysis showed that these spherical particles formed, even at pH less than 4. The genotoxicity and cytotoxicity tests performed on mouse embryonic fibroblast (3 T3-L1) and human embryonic kidney (HEK293) cell lines showed that the Fenton treatment of methylene blue using the ZVI/pyrite/H2O2 system resulted in the formation of degradation species with much lower toxicity levels relative to methylene blue. Moreover, the Fenton degradation species of methylene blue significantly enhanced the metabolic activity of several bacterial strains, including E. coli ATCC 8739 and P. aeruginosa PAO1.
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    Oxidative degradation of chlorophenolic compounds with pyrite-Fenton process
    (Elsevier Sci Ltd, 2019) Kantar, Cetin; Oral, Ozlem; Urken, Ozge; Oz, Nilgun Ayman; Keskin, Selda
    Batch experiments, in conjunction with chromatographic and spectroscopic measurements, were performed to comparatively investigate the degradation of various chlorophenolic (CP) compounds (e.g., 2-CP, 4-CP, 2,3-DCP, 2,4-DCP, 2,4,6-TCP, 2,3,4,6-TeCP) by a modified Fenton process using pyrite as the catalyst The batch results show that the CP removal by pyrite-Fenton process was highly dependent on chemical conditions (e.g., pH, CP and pyrite concentration), CP type, number and location of chlorine atoms on the aromatic ring. With the exception of 2,3,4,6-TeCP and 2,3-DCP, the CP removal decreased with increasing the number of chlorine constituents. While the main mechanism responsible for monochlorophenol removal (e.g., 2-CP and 4-CP) was the hydroxyl radical attack on aromatic rings, the CP removal for multichlorophenolic compounds (e.g., 2,3,4,6-TeCP) was driven by both: (1) hydroxyl radical attack on aromatic rings by both solution and surface-bound hydroxyl radicals and (2) adsorption onto pyrite surface sites. The adsorption affinity increased with increasing the number of Cl atoms on the aromatic ring due to enhanced hydrophobic effect. The TOC removal was not 100% complete for all CPs investigated due to formation of chemically less degradable chlorinated intermediate organic compounds as well as low molecular weight organic acids such as formic and acetic acid. Spectroscopic measurements with SEM-EDS, zeta potential and XPS provided evidence for the partial oxidation of pyrite surface Fe(II) and disulfide groups under acidic conditions. (C) 2019 Elsevier Ltd. All rights reserved.
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    Reductive Immobilization of Chromium in Soils Containing Heterogeneous Fe-Bearing Minerals
    (Taylor & Francis Inc, 2016) Dogaroglu, Zeynep Gorkem; Kantar, Cetin
    Cr(VI) immobilization in systems containing Fe-bearing soil minerals was studied in batch and column systems. Batch experiments showed that water chemistry such as solution pH and Cr(VI) concentration had a pronounced impact on Cr(VI) removal by Fe-bearing soil minerals. Acidic conditions were observed to be more favorable for enhanced Cr(VI) removal. The dependence of Cr(VI) removal on Cr(VI) concentration indicated that there were limited numbers of surface sites on Fe-bearing minerals responsible for Cr(VI) removal. A complexing agent, citrate, significantly enhanced both Cr(VI) removal and total Fe-dissolution from the mineral surfaces relative to non-citrate containing systems, and the iron drm, implying that Cr(VI) removal occurred mainly on mineral surfaces, andissolved from the mineral surfaces was in Fe(III) oxidation fo the surface Fe(II) sites played an active role in Cr(VI) reduction. The results from column experiments showed that the accumulation of surface precipitates resulted in clogging of pore spaces, thereby creating preferential flow paths within the column. However, the addition of citrate significantly prevented the accumulation of surface precipitates due to the formation of highly soluble Fe-citrate complexes. SEM images revealed that the precipitates accumulated in the column had sponge-like shapes. The energy-dispersive spectroscopy analysis provided further evidence that the surface precipitates formed also contained Cr species as well as Fe. Overall it is clear that Fe-bearing minerals may serve as an effective reducing agent for in-situ reductive immobilization of hexavalent chromium in subsurface systems.
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    Role of citric acid on reduction and immobilization of chromium (VI) by pyrite under variable chemical conditions
    (Amer Chemical Soc, 2013) Kantar, Cetin; Karadeniz, Aykut; Ari, Cihan; Dogaroglu, Zeynep G.; Keskin, Selda
    [Anstract Not Available]
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    Role of complexing agents on oxidative degradation of chlorophenolic compounds by pyrite-Fenton process: Batch and column experiments
    (Elsevier Science Bv, 2019) Kantar, Cetin; Oral, Ozlem; Urken, Ozge; Oz, Nilgun Ayman
    This study involves batch reactor and fixed-bed continuous flow experiments to determine the effects of complexing agents (e.g., tartrate and citrate) on the treatment of chlorophenolic (CP) compounds using heterogeneous Fenton system with pyrite mineral as the iron source. While the addition of organic ligands to the batch systems adversely affected CP removal, organic ligands had a beneficial effect on CP removal in column systems. Although the ligands extended the life span of pyrite-packed columns by removing surface oxidation products through the formation of soluble Fe-ligand complexes, the ligands competed against CPs for hydroxyl radicals (HO*). The competitive effect was much higher in batch systems since pyrite loading was very low in order to generate sufficient hydroxyl radicals. On the other hand, at much higher pyrite loading of column experiments, the H* radicals generated during Fenton process were sufficient to overcome the competitive effect exerted by organic ligands. In spite of much higher Fe solubility in the presence of citrate, citrate was less effective in enhancing CP removal in column systems compared to tartrate since the competitive effect caused by citrate for HO* radicals was more than that exerted by tartrate.