Chemosphere 131 (2015) 157–163
Contents lists available at ScienceDirect
Chemosphere journal homepage: www.elsevier.com/locate/chemosphere
Electroremediation of PCB contaminated soil combined with iron nanoparticles: Effect of the soil type Helena I. Gomes a,b,c,⇑, Celia Dias-Ferreira b, Lisbeth M. Ottosen c, Alexandra B. Ribeiro a a CENSE – Center for Environmental and Sustainability Research, Departamento de Ciências e Engenharia do Ambiente, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal b CERNAS – Research Center for Natural Resources, Environment and Society, Escola Superior Agraria de Coimbra, Instituto Politecnico de Coimbra, Bencanta, 3045-601 Coimbra, Portugal c Department of Civil Engineering, Technical University of Denmark, Brovej, Building 118, DK 2800 Kgs. Lyngby, Denmark
h i g h l i g h t s The type of soil strongly influences PCB removal effectiveness. pH and soil buffer capacity are relevant for electro-nano remediation. Higher PCB removal were obtained in the two-compartment cell. Better iron distribution in the suspended soil increases PCB reduction.
a r t i c l e
i n f o
Article history: Received 25 June 2014 Received in revised form 16 February 2015 Accepted 4 March 2015 Available online 1 April 2015 Handling Editor: X. Cao Keywords: Electroremediation nZVI Polychlorinated biphenyls PCB Contaminated soil
a b s t r a c t Polychlorinated biphenyls (PCB) are carcinogenic and persistent organic pollutants that accumulate in soils and sediments. Currently, there is no cost-effective and sustainable remediation technology for these contaminants. In this work, a new combination of electrodialytic remediation and zero valent iron particles in a two-compartment cell is tested and compared to a more conventional combination of electrokinetic remediation and nZVI in a three-compartment cell. In the new two-compartment cell, the soil is suspended and stirred simultaneously with the addition of zero valent iron nanoparticles. Remediation experiments are made with two different historically PCB contaminated soils, which differ in both soil composition and contamination source. Soil 1 is a mix of soils with spills of transformer oils, while Soil 2 is a superficial soil from a decommissioned school where PCB were used as windows sealants. Saponin, a natural surfactant, was also tested to increase the PCB desorption from soils and enhance dechlorination. Remediation of Soil 1 (with highest pH, carbonate content, organic matter and PCB concentrations) obtained the maximum 83% and 60% PCB removal with the two-compartment and the three-compartment cell, respectively. The highest removal with Soil 2 were 58% and 45%, in the twocompartment and the three-compartment cell, respectively, in the experiments without direct current. The pH of the soil suspension in the two-compartment treatment appears to be a determining factor for the PCB dechlorination, and this cell allowed a uniform distribution of the nanoparticles in the soil, while there was iron accumulation in the injection reservoir in the three-compartment cell. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction Electrokinetic (EKR) and electrodialytic (EDR) remediation are reliable technologies, successfully used, both at laboratorial and ⇑ Corresponding author at: CENSE – Center for Environmental and Sustainability Research, Departamento de Ciências e Engenharia do Ambiente, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal. Tel.: +351 212948300. E-mail address: [email protected] (H.I. Gomes). http://dx.doi.org/10.1016/j.chemosphere.2015.03.007 0045-6535/Ó 2015 Elsevier Ltd. All rights reserved.
pilot scale, for the removal of organic and inorganic contaminants from different matrices, like soils, sediments, mine tailings, wastes and ashes (Ribeiro et al., 2000, 2005, 2011; Ferreira et al., 2005; Ribeiro and Rodríguez-Maroto, 2006; Ottosen et al., 2006, 2008, 2009). In both methods, a low level direct current is responsible for the transport of contaminants through different mechanisms (electroosmosis, electromigration and electrophoresis), and additionally induces electrochemical reactions (electrolysis and electrodeposition) (Acar and Alshawabkeh, 1993). The use of electrokinetics in soil has evolved to include distinct enhancement
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techniques and the combination with other technologies (Gomes et al., 2012). Common problems in EKR remediation, such as the nonlinear and transient geochemical changes in the soil, were coped by treating a suspension of soils with uniform stirring in electrodialytic remediation, which allowed increasing the remediation rate (Jensen et al., 2007; Sun et al., 2012; Ottosen et al., 2013). A two-compartment electrodialytic setup recently developed at the Technical University of Denmark (Ottosen et al., 2013) is a step forward, showing additional advantages like a direct acidification of the matrix without strong acids, and it is not necessary to dispose the anolyte. Polychlorinated biphenyls (PCB) were classified as persistent organic pollutants (POP) by the United Nations Stockholm Convention. There is a need to find cost effective and more sustainable remediation alternatives for PCB-contaminated soils and sediments (Gomes et al., 2013). Zero valent iron nanoparticles (nZVI) were used with success for PCB dechlorination in aqueous solutions (Wang and Zhang, 1997; Lowry and Johnson, 2004; He et al., 2010), but revealed limited results in soils so far (Varanasi et al., 2007; Chen et al., 2014). Pd/Fe bimetallic nanoparticles, when combined with EKR, resulted in only 20% PCB removal after 14 days with historically contaminated soil (Fan et al., 2013). Very recently, the new two-compartment cell was successfully used for POP in conjunction with nZVI. This combination enabled a 83% PCB removal in just 5 days, which is much higher than the reported 27% removal in 10 d as the best result so far with EKR/nZVI (Gomes et al., 2015). The effects of soil composition on electroremediation are described in several studies. Especially the soil buffer capacity and the carbonate content, which can neutralize the acid front generated at the anode, is an important soil parameter, as the acidification aids many of the remediation processes (Reddy et al., 1997; Ottosen et al., 2001; Reddy and Saichek, 2003; Kim et al., 2006; Ouhadi et al., 2010; Mena et al., 2011; Cameselle and Reddy, 2012). Soil texture is also relevant for electroremediation (Mena et al., 2011; Sun et al., 2012) and nZVI transport in EKR/ nZVI (Yang and Chang, 2011; Gomes et al., 2013), as the soil particles distribution and their charge affect the transport mechanisms. The soil cation exchange capacity is also important, as it allows the soil to immobilize significant quantities of heavy metal ions (Lageman and Pool, 2009). The organic matter content can strongly influence the sorption/desorption of contaminants and it was also shown to affect the electroosmotic properties and ionic modification of soils (Asadi et al., 2009). In the present work, two electroremediation techniques, EKR and EDR, are compared experimentally for remediation of two different historically PCB contaminated soils. The differences between the techniques other than the design of the reactor are the use of ion-selective membranes for EDR while EKR uses passive membranes. In both setups the remediation was enhanced with a surfactant (saponin) and nZVI, as suggested beneficial in Gomes et al. (2015). The main objective was to assess the influence of soil composition on these enhanced electroremediation techniques.
2. Materials and methods 2.1. Chemicals and solvents PCB standards were analytical grade, obtained from Fluka, Sigma–Aldrich (PCB28, 52, 101, 138, 153, 180 and 209) and Ultrascientific (PCB30; PCB65 and PCB204). The solvents hexane and acetone were Pestinorm (VWR BDH Prolabo). Saponin (GPR Rectapur) was the lab grade surfactant used to enhance PCB desorption. Hydrochloric (37.6%), nitric (65%) and sulfuric (95–07%) acids were tracemetal. Anhydrous Na2SO4, KMnO4, NaCl, and silica
gel (silicic acid) were lab grade. Silica gel was cleaned up before use according to the USEPA method 3630C. The water was deionized with a Milli-Q plus system from Millipore (Bedford, MA, USA). A nZVI slurry-stabilized suspension (NANOFER 25S, NANO IRON, s.r.o., Rajhrad, Czeck Republic) was used in the experiments (Table S1, Supplementary Information). 2.2. Soil characterization Two different soils, historically contaminated with PCB, were used for the experiments. Soil 1 was provided by a hazardous waste operator in Portugal and is a mixture of contaminated soils from industrial sites with transformers oils spills. Soil 2 is a surface soil sampled in a decommissioned school in Hovedstaden (Capital Region of Denmark), and the PCB resulted from the weathering of the windows joint sealants used in 1955–1977 (Jensen, 2009). The soil characterization methods used were described in Jensen et al. (2007). The initial soils were analyzed for Al, As, Cd, Cr, Cu, Fe, Ni, Pb, Zn using Inductively Coupled Plasma-Atomic Emission Spectrometer (ICP) on an Agilent ICP-OES Varian 720-ES equipment. Soil texture was determined by laser diffraction with a Malvern Mastersizer 2000. The soil was homogenized, air dried and sieved, and only the particles with size
Contents lists available at ScienceDirect
Chemosphere journal homepage: www.elsevier.com/locate/chemosphere
Electroremediation of PCB contaminated soil combined with iron nanoparticles: Effect of the soil type Helena I. Gomes a,b,c,⇑, Celia Dias-Ferreira b, Lisbeth M. Ottosen c, Alexandra B. Ribeiro a a CENSE – Center for Environmental and Sustainability Research, Departamento de Ciências e Engenharia do Ambiente, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal b CERNAS – Research Center for Natural Resources, Environment and Society, Escola Superior Agraria de Coimbra, Instituto Politecnico de Coimbra, Bencanta, 3045-601 Coimbra, Portugal c Department of Civil Engineering, Technical University of Denmark, Brovej, Building 118, DK 2800 Kgs. Lyngby, Denmark
h i g h l i g h t s The type of soil strongly influences PCB removal effectiveness. pH and soil buffer capacity are relevant for electro-nano remediation. Higher PCB removal were obtained in the two-compartment cell. Better iron distribution in the suspended soil increases PCB reduction.
a r t i c l e
i n f o
Article history: Received 25 June 2014 Received in revised form 16 February 2015 Accepted 4 March 2015 Available online 1 April 2015 Handling Editor: X. Cao Keywords: Electroremediation nZVI Polychlorinated biphenyls PCB Contaminated soil
a b s t r a c t Polychlorinated biphenyls (PCB) are carcinogenic and persistent organic pollutants that accumulate in soils and sediments. Currently, there is no cost-effective and sustainable remediation technology for these contaminants. In this work, a new combination of electrodialytic remediation and zero valent iron particles in a two-compartment cell is tested and compared to a more conventional combination of electrokinetic remediation and nZVI in a three-compartment cell. In the new two-compartment cell, the soil is suspended and stirred simultaneously with the addition of zero valent iron nanoparticles. Remediation experiments are made with two different historically PCB contaminated soils, which differ in both soil composition and contamination source. Soil 1 is a mix of soils with spills of transformer oils, while Soil 2 is a superficial soil from a decommissioned school where PCB were used as windows sealants. Saponin, a natural surfactant, was also tested to increase the PCB desorption from soils and enhance dechlorination. Remediation of Soil 1 (with highest pH, carbonate content, organic matter and PCB concentrations) obtained the maximum 83% and 60% PCB removal with the two-compartment and the three-compartment cell, respectively. The highest removal with Soil 2 were 58% and 45%, in the twocompartment and the three-compartment cell, respectively, in the experiments without direct current. The pH of the soil suspension in the two-compartment treatment appears to be a determining factor for the PCB dechlorination, and this cell allowed a uniform distribution of the nanoparticles in the soil, while there was iron accumulation in the injection reservoir in the three-compartment cell. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction Electrokinetic (EKR) and electrodialytic (EDR) remediation are reliable technologies, successfully used, both at laboratorial and ⇑ Corresponding author at: CENSE – Center for Environmental and Sustainability Research, Departamento de Ciências e Engenharia do Ambiente, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal. Tel.: +351 212948300. E-mail address: [email protected] (H.I. Gomes). http://dx.doi.org/10.1016/j.chemosphere.2015.03.007 0045-6535/Ó 2015 Elsevier Ltd. All rights reserved.
pilot scale, for the removal of organic and inorganic contaminants from different matrices, like soils, sediments, mine tailings, wastes and ashes (Ribeiro et al., 2000, 2005, 2011; Ferreira et al., 2005; Ribeiro and Rodríguez-Maroto, 2006; Ottosen et al., 2006, 2008, 2009). In both methods, a low level direct current is responsible for the transport of contaminants through different mechanisms (electroosmosis, electromigration and electrophoresis), and additionally induces electrochemical reactions (electrolysis and electrodeposition) (Acar and Alshawabkeh, 1993). The use of electrokinetics in soil has evolved to include distinct enhancement
158
H.I. Gomes et al. / Chemosphere 131 (2015) 157–163
techniques and the combination with other technologies (Gomes et al., 2012). Common problems in EKR remediation, such as the nonlinear and transient geochemical changes in the soil, were coped by treating a suspension of soils with uniform stirring in electrodialytic remediation, which allowed increasing the remediation rate (Jensen et al., 2007; Sun et al., 2012; Ottosen et al., 2013). A two-compartment electrodialytic setup recently developed at the Technical University of Denmark (Ottosen et al., 2013) is a step forward, showing additional advantages like a direct acidification of the matrix without strong acids, and it is not necessary to dispose the anolyte. Polychlorinated biphenyls (PCB) were classified as persistent organic pollutants (POP) by the United Nations Stockholm Convention. There is a need to find cost effective and more sustainable remediation alternatives for PCB-contaminated soils and sediments (Gomes et al., 2013). Zero valent iron nanoparticles (nZVI) were used with success for PCB dechlorination in aqueous solutions (Wang and Zhang, 1997; Lowry and Johnson, 2004; He et al., 2010), but revealed limited results in soils so far (Varanasi et al., 2007; Chen et al., 2014). Pd/Fe bimetallic nanoparticles, when combined with EKR, resulted in only 20% PCB removal after 14 days with historically contaminated soil (Fan et al., 2013). Very recently, the new two-compartment cell was successfully used for POP in conjunction with nZVI. This combination enabled a 83% PCB removal in just 5 days, which is much higher than the reported 27% removal in 10 d as the best result so far with EKR/nZVI (Gomes et al., 2015). The effects of soil composition on electroremediation are described in several studies. Especially the soil buffer capacity and the carbonate content, which can neutralize the acid front generated at the anode, is an important soil parameter, as the acidification aids many of the remediation processes (Reddy et al., 1997; Ottosen et al., 2001; Reddy and Saichek, 2003; Kim et al., 2006; Ouhadi et al., 2010; Mena et al., 2011; Cameselle and Reddy, 2012). Soil texture is also relevant for electroremediation (Mena et al., 2011; Sun et al., 2012) and nZVI transport in EKR/ nZVI (Yang and Chang, 2011; Gomes et al., 2013), as the soil particles distribution and their charge affect the transport mechanisms. The soil cation exchange capacity is also important, as it allows the soil to immobilize significant quantities of heavy metal ions (Lageman and Pool, 2009). The organic matter content can strongly influence the sorption/desorption of contaminants and it was also shown to affect the electroosmotic properties and ionic modification of soils (Asadi et al., 2009). In the present work, two electroremediation techniques, EKR and EDR, are compared experimentally for remediation of two different historically PCB contaminated soils. The differences between the techniques other than the design of the reactor are the use of ion-selective membranes for EDR while EKR uses passive membranes. In both setups the remediation was enhanced with a surfactant (saponin) and nZVI, as suggested beneficial in Gomes et al. (2015). The main objective was to assess the influence of soil composition on these enhanced electroremediation techniques.
2. Materials and methods 2.1. Chemicals and solvents PCB standards were analytical grade, obtained from Fluka, Sigma–Aldrich (PCB28, 52, 101, 138, 153, 180 and 209) and Ultrascientific (PCB30; PCB65 and PCB204). The solvents hexane and acetone were Pestinorm (VWR BDH Prolabo). Saponin (GPR Rectapur) was the lab grade surfactant used to enhance PCB desorption. Hydrochloric (37.6%), nitric (65%) and sulfuric (95–07%) acids were tracemetal. Anhydrous Na2SO4, KMnO4, NaCl, and silica
gel (silicic acid) were lab grade. Silica gel was cleaned up before use according to the USEPA method 3630C. The water was deionized with a Milli-Q plus system from Millipore (Bedford, MA, USA). A nZVI slurry-stabilized suspension (NANOFER 25S, NANO IRON, s.r.o., Rajhrad, Czeck Republic) was used in the experiments (Table S1, Supplementary Information). 2.2. Soil characterization Two different soils, historically contaminated with PCB, were used for the experiments. Soil 1 was provided by a hazardous waste operator in Portugal and is a mixture of contaminated soils from industrial sites with transformers oils spills. Soil 2 is a surface soil sampled in a decommissioned school in Hovedstaden (Capital Region of Denmark), and the PCB resulted from the weathering of the windows joint sealants used in 1955–1977 (Jensen, 2009). The soil characterization methods used were described in Jensen et al. (2007). The initial soils were analyzed for Al, As, Cd, Cr, Cu, Fe, Ni, Pb, Zn using Inductively Coupled Plasma-Atomic Emission Spectrometer (ICP) on an Agilent ICP-OES Varian 720-ES equipment. Soil texture was determined by laser diffraction with a Malvern Mastersizer 2000. The soil was homogenized, air dried and sieved, and only the particles with size
