Chemosphere 150 (2016) 63e70
Contents lists available at ScienceDirect
Chemosphere journal homepage: www.elsevier.com/locate/chemosphere
The influences of dissolved organic matter and surfactant on the desorption of Cu and Zn from road-deposited sediment Jin Zhang a, *, Pei Hua b, **, Peter Krebs a a b
€t Dresden, 01062 Dresden, Germany Institute of Urban Water Management, Technische Universita €t Dresden, 01062 Dresden, Germany Chair of Water Supply Engineering, Institute of Urban Water Management, Technische Universita
h i g h l i g h t s Rainwater solutions significantly enhanced the leaching amounts of Cu and Zn. DOM enhanced the desorption of Cu from RDS at the neutral pH. DOM in sewers had adverse effect on the mobilization of Zn. SDS slightly increased the release of Cu from RDS. SDS suppressed the release of Zn from RDS.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 13 August 2015 Received in revised form 14 January 2016 Accepted 2 February 2016 Available online xxx
This study showcases the desorption behaviours of copper (Cu) and zinc (Zn) in road-deposited sediment (RDS). Batch tests were conducted to investigate the influences of rainwater, major wastewater constituents of dissolved organic matter (DOM) and surfactant on the metals leaching from RDS. Results show that the rainwater solutions considerably enhanced the total amounts of Cu (319 ± 46% of the total leaching amount by blank solutions) and Zn (617 ± 130%) released from RDS compared with blank solutions. DOM enhanced the leaching of Cu from RDS at a neutral pH. By contrast, DOM had an adverse effect on the mobilization of Zn. In the absence of DOM, a higher concentration of sodium dodecyl sulfonate (SDS) slightly increased the release of Cu from RDS than a lower concentration of SDS. However, the existence of SDS suppressed the release of Zn from RDS. © 2016 Elsevier Ltd. All rights reserved.
Handling Editor: Martine Leermakers Keywords: Desorption Dissolved organic matter Heavy metals Integrated stormwater management Road-deposited sediment Surfactant
1. Introduction The deteriorated stormwater runoff is a leading source of pollutants causing water quality impairment related to human activities in ocean shoreline, estuaries, rivers, lakes and so on (Sartor and Boyd, 1972; Strassler et al., 1999; Loganathan et al., 2013). A considerable literature confirms the importance of road-deposited sediment (RDS) adsorbed pollutants in contribution to the pollution load of stormwater runoff (Sartor and Boyd, 1972; Revitt and
* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (J. Zhang), [email protected] (P. Hua). http://dx.doi.org/10.1016/j.chemosphere.2016.02.015 0045-6535/© 2016 Elsevier Ltd. All rights reserved.
Ellis, 1980; Zhao et al., 2011; Loganathan et al., 2013). RDS, also known as road dust, street dust, surface particle, and roadside sediment, often contains elevated concentrations of pollutants (Loganathan et al., 2013; Zhang et al., 2015a, 2015c). These pollutants have been regarded as major pollutants to receiving waters transported by runoff directly and/or through sewers indirectly (Sartor and Boyd, 1972; Loganathan et al., 2013; Zhao et al., 2014). Among such pollutants, heavy metals are of concern due to their high potential toxicity of various biological forms (Sartor and Boyd, 1972; Zheng et al., 2012; Zhang et al., 2015a). Some of them are toxic even if their concentrations are very low and their toxicity increases with the accumulation in environments (Bradl, 2004; Dhanakumar et al., 2013). In terms of stormwater pollution, the potential risk of RDS adsorbed metals, with respect to the mobility
64
J. Zhang et al. / Chemosphere 150 (2016) 63e70
and ecotoxicological significance, is determined by their solideliquid partitioning rather than the total mass of metals per unit mass of dry solid (Dijkstra et al., 2004; Zheng et al., 2012). During the wet weather period, rainfall leaches and flushes the RDS on urban watershed. Certain content of the RDS adsorbed metals dissolves in runoff as free or complexed species (Revitt and Ellis, 1980). The release of metal cations to the liquid phase and thereafter the susceptibility for transport processes, depends on their solution speciation and their affinity for binding the reactive surfaces in the RDS and solution matrixes (Dijkstra et al., 2004; Zhang et al., 2015a). Copper (Cu) and zinc (Zn) are included in the priority pollutant list, which have special significance to water quality (EPA, 2014). In terms of the primary source contributors to the metal contents in RDS, Cu was identified as auto brake pad erosion; Zn was significant attributed to tire debris (Loganathan et al., 2013; Zhang et al., 2015b). Therefore, both of them are typical anthropogenic pollutants (Loganathan et al., 2013; Zhang et al., 2015a). In Germany, urban stormwater runoff has been regarded as the largest pathwayrelated emission of Cu and Zn to receiving waters (Hillenbrand et al., 2005). In terms of the integrated stormwater management, Zhang et al. (2015a) determined the chemical fractionation of Cu and Zn in RDS. Results indicates that the exchangeable components of Cu and Zn in RDS could be considered as a reasonable approximation of the easily mobilized and bio-logically available contents to aquatic environment. In their work, however, a systematic or dynamic desorption research of metal from RDS into liquid solution was not performed. Therefore, to better understand the potential adverse influence of RDS adsorbed metals on stormwater quality and assist the source oriented stormwater pollution management, it is essential to study the desorption dynamics of metals release from RDS. Concerning the desorption issue, organic compounds have been regarded as one of the most important solution parameters affecting the leaching of heavy metals from solid phase in the research matrix of soil sciences (Shi et al., 2005). The mechanisms involved in the binding of metals with organic compounds include adsorption, complexation and chelation (Ferraz and Lourençlo, 2000). In terms of RDS transported by the stormwater runoff, e.g. in a drainage area served by a combined sewer system, runoff is mixed with sewage (wastewater) containing dissolved organic matters (DOM) which has potential to form complex with metals. Therefore, the organic compounds are expected to influence the bio-availability and mobility of metals released from RDS to receiving waters through combined sewer overflows (CSOs). Although, there have been extensive studies of the influence of organic compounds on the heavy metals release from soils (Ferraz and Lourençlo, 2000; Ashworth and Alloway, 2004), less attention was paid to the influence of DOM in sewers on the leaching of metals from RDS. Additionally, surfactants also known as surface active agents are important incorporative organic compounds in various detergents, which are released in high quantities from households and industries into sewer systems, and are thus a major wastewater ndez Cirelli et al., 2008). Surfactant enhanced constituent (Ferna remediation (SER) has been proposed as a promising technology for the remediation of solubilize hydrophobic organic compounds, e.g. polycyclic aromatic hydrocarbons, polychlorinated biphenyls, etc, contaminated soils (Mulligan et al., 2001; Ramamurthy et al., 2008). More recently, it has been shown that surfactants can be used to enhance metals removal via surfactant-associated complexation and ionic exchange (Mulligan et al., 2001; Mao et al., 2015). Explicitly, Ramamurthy et al. (2008) reported that surfactants with an additional of complexing agent EDTA (ethylenediaminetetraacetic acid) can improve the desorption of Cu and Zn from an
artificially contaminated sandy soil (Ramamurthy et al., 2008). Several works have shown that the biologically produced surfactants, surfactin, rhamnolipids and sophorolipids are able to remove Cu and Zn from the hydrocarbon contaminated soil (Mulligan et al., 1999; Mulligan et al., 2001; Singh and Cameotra, 2004). However, comparably less or no studies were conducted on the function of surfactant on the metal leaching from RDS. Accordingly, this study intends to provide an in-depth understanding on the leaching dynamics of RDS adsorbed heavy metals for a stormwater pollution aspect. The detailed focuses are to (i) determine the desorption dynamics of metals from RDS to rainwater, and (ii) assess the influences of major wastewater constituents of DOM and surfactant on the desorption dynamics of metals. 2. Mentmaterials and methods 2.1. Initial characterisation of road-deposited sediment The sampling campaign was performed in April 2014. Wet and dry vacuuming methods are the prevailing methods of RDS collection. However, both of them have their own disadvantages. More explicit, increasing concern has been addressed to the wet vacuuming method due to its water filtration system which could potentially dissolve certain content of metals (Zhang and Krebs, 2013). Then, due to the pad filtration system used by the dry vacuuming method, the fine particles would not be trapped by this pad filter and result in a systematic drawback (Herngren et al., 2006). Both of them have potential adverse effects on the redistribution of the particle size fractions. Therefore, a traditional hand sweeping method with a nylon broom and a plastic dustpan were employed for the RDS collection (Charlesworth et al., 2003). This traditional hand sweeping method is able to preserve as much as possible the initial properties (physical and chemical) and structural integrity of the RDS in order to increase the reliability of the information gained by further experimental analyses. The RDS samples were collected from an asphalt traffic road (St. Petersburger Str., average daily traffic: 12600 vehicle/day, % of heavy traffic: 3e4) in the city centre of Dresden (51020 5500 N, 13 440 2900 E), located in the state of Saxony, Germany. The sampling site was selected due to the elevated RDS adsorbed pollutants levels according to the previous study (Zhang et al., 2015a, 2015c). The largest portion of the sediments was assembled near roadside curb areas (Sartor and Boyd, 1972). Therefore, the enclosed sampling plot was situated next to the roadside curb areas. RDS samples were collected over a curb length of about 30 m. Bulk RDS samples were further fractionated into sub-samples and dry-sieved using stainless-steel sieves (Retsch GmbH, Germany) with mesh sizes of 630 mm, 200 mm, and 63 mm in sequence. The particles passing through the 63 mm sieve were filtered by a 0.45 mm (classification diameter between soluble and particle) cellulose nitrite filter (Sartorius, Germany). The particle size dependent samples were homogenized by shaking thoroughly. The gravel-sized materials, plant roots, and leaves were removed during the sieving process. The fractionated RDS samples were labelled, sealed and refrigerated at 4 C in preparation for analysis. 2.2. Synthesis of rainwater To avoid external factors interfering with the desorption process, synthetic rainwater solutions were prepared. The rainwater formula was adapted from Davis et al. (2001) and are given in Table 1. After preparation, the pH of the solutions were 4.78 ± 0.02. The pH value was within the rage of rainwater pH data in central Germany (4.2e6.5 with a mean value of 4.7) (Schumann and Ernst, 1993), and the historical pH data of rainwater in the present city
J. Zhang et al. / Chemosphere 150 (2016) 63e70
65
Table 1 The characteristics of extraction solution and size fraction of the applied RDS. Solution
Composition Formula
Concentration
Blank
Distilled water
e
Rainwater
NaCl HNO3 H2SO4 Glucose Amide Cellulose Meat extract Glucose Amide Cellulose Meat extract CH3(CH2)11OSO3Na CH3(CH2)11OSO3Na
1.35 mg/L 1.13 mg/L 1.76 mg/L 35 mg/L 114 mg/L 34 mg/L 298 mg/L 175 mg/L 570 mg/L 170 mg/L 1490 mg/L 10 mg/L 2.36 g/L
DOM I
DOM II
Surfactant I Surfactant II
(mean value of 4.5) (Mrose, 1966). 2.3. Synthesis of dissolved organic matter Synthetic DOM solutions in different concentrations were prepared and were regarded as principle components in a combined sewer flow. DOM in the combined sewer flow, i.e. wastewater, were synthesized as a mixture of different organic compounds. The organic compounds formulas were adapted from Moreira et al. (2008) and are given in Table 1. The mixture of organic compounds was sterilized (121 C for 15 min) to maintain its characteristics. Accordingly, the synthetic DOM mixtures in different concentrations were optionally termed as DOM I and II. The DOM concentration was determined in the forms of chemical oxygen demand (COD) and total organic carbon (TOC). DOM I: The COD and TOC values of DOM I were determined as 376 and 110 mg/L respectively, which represents a low concentration of raw municipal wastewater with minor contributions of industrial wastewater as catalogued by Henze et al. (2002). DOM II: It contained five time higher concentrations for each organic components. The COD and TOC values of DOM II were 1880 and 550 mg/L respectively, which represents a high concentration of raw municipal wastewater with minor contributions of industrial wastewater as catalogued by Henze et al. (2002).
Buffer
pH
RDS
NaCl K2HPO4 KH2PO4 CH3COOHe CH3COONa
6.86 ± 0.02
NaCl K2HPO4 KH2PO4
6.96 ± 0.02
Contents lists available at ScienceDirect
Chemosphere journal homepage: www.elsevier.com/locate/chemosphere
The influences of dissolved organic matter and surfactant on the desorption of Cu and Zn from road-deposited sediment Jin Zhang a, *, Pei Hua b, **, Peter Krebs a a b
€t Dresden, 01062 Dresden, Germany Institute of Urban Water Management, Technische Universita €t Dresden, 01062 Dresden, Germany Chair of Water Supply Engineering, Institute of Urban Water Management, Technische Universita
h i g h l i g h t s Rainwater solutions significantly enhanced the leaching amounts of Cu and Zn. DOM enhanced the desorption of Cu from RDS at the neutral pH. DOM in sewers had adverse effect on the mobilization of Zn. SDS slightly increased the release of Cu from RDS. SDS suppressed the release of Zn from RDS.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 13 August 2015 Received in revised form 14 January 2016 Accepted 2 February 2016 Available online xxx
This study showcases the desorption behaviours of copper (Cu) and zinc (Zn) in road-deposited sediment (RDS). Batch tests were conducted to investigate the influences of rainwater, major wastewater constituents of dissolved organic matter (DOM) and surfactant on the metals leaching from RDS. Results show that the rainwater solutions considerably enhanced the total amounts of Cu (319 ± 46% of the total leaching amount by blank solutions) and Zn (617 ± 130%) released from RDS compared with blank solutions. DOM enhanced the leaching of Cu from RDS at a neutral pH. By contrast, DOM had an adverse effect on the mobilization of Zn. In the absence of DOM, a higher concentration of sodium dodecyl sulfonate (SDS) slightly increased the release of Cu from RDS than a lower concentration of SDS. However, the existence of SDS suppressed the release of Zn from RDS. © 2016 Elsevier Ltd. All rights reserved.
Handling Editor: Martine Leermakers Keywords: Desorption Dissolved organic matter Heavy metals Integrated stormwater management Road-deposited sediment Surfactant
1. Introduction The deteriorated stormwater runoff is a leading source of pollutants causing water quality impairment related to human activities in ocean shoreline, estuaries, rivers, lakes and so on (Sartor and Boyd, 1972; Strassler et al., 1999; Loganathan et al., 2013). A considerable literature confirms the importance of road-deposited sediment (RDS) adsorbed pollutants in contribution to the pollution load of stormwater runoff (Sartor and Boyd, 1972; Revitt and
* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (J. Zhang), [email protected] (P. Hua). http://dx.doi.org/10.1016/j.chemosphere.2016.02.015 0045-6535/© 2016 Elsevier Ltd. All rights reserved.
Ellis, 1980; Zhao et al., 2011; Loganathan et al., 2013). RDS, also known as road dust, street dust, surface particle, and roadside sediment, often contains elevated concentrations of pollutants (Loganathan et al., 2013; Zhang et al., 2015a, 2015c). These pollutants have been regarded as major pollutants to receiving waters transported by runoff directly and/or through sewers indirectly (Sartor and Boyd, 1972; Loganathan et al., 2013; Zhao et al., 2014). Among such pollutants, heavy metals are of concern due to their high potential toxicity of various biological forms (Sartor and Boyd, 1972; Zheng et al., 2012; Zhang et al., 2015a). Some of them are toxic even if their concentrations are very low and their toxicity increases with the accumulation in environments (Bradl, 2004; Dhanakumar et al., 2013). In terms of stormwater pollution, the potential risk of RDS adsorbed metals, with respect to the mobility
64
J. Zhang et al. / Chemosphere 150 (2016) 63e70
and ecotoxicological significance, is determined by their solideliquid partitioning rather than the total mass of metals per unit mass of dry solid (Dijkstra et al., 2004; Zheng et al., 2012). During the wet weather period, rainfall leaches and flushes the RDS on urban watershed. Certain content of the RDS adsorbed metals dissolves in runoff as free or complexed species (Revitt and Ellis, 1980). The release of metal cations to the liquid phase and thereafter the susceptibility for transport processes, depends on their solution speciation and their affinity for binding the reactive surfaces in the RDS and solution matrixes (Dijkstra et al., 2004; Zhang et al., 2015a). Copper (Cu) and zinc (Zn) are included in the priority pollutant list, which have special significance to water quality (EPA, 2014). In terms of the primary source contributors to the metal contents in RDS, Cu was identified as auto brake pad erosion; Zn was significant attributed to tire debris (Loganathan et al., 2013; Zhang et al., 2015b). Therefore, both of them are typical anthropogenic pollutants (Loganathan et al., 2013; Zhang et al., 2015a). In Germany, urban stormwater runoff has been regarded as the largest pathwayrelated emission of Cu and Zn to receiving waters (Hillenbrand et al., 2005). In terms of the integrated stormwater management, Zhang et al. (2015a) determined the chemical fractionation of Cu and Zn in RDS. Results indicates that the exchangeable components of Cu and Zn in RDS could be considered as a reasonable approximation of the easily mobilized and bio-logically available contents to aquatic environment. In their work, however, a systematic or dynamic desorption research of metal from RDS into liquid solution was not performed. Therefore, to better understand the potential adverse influence of RDS adsorbed metals on stormwater quality and assist the source oriented stormwater pollution management, it is essential to study the desorption dynamics of metals release from RDS. Concerning the desorption issue, organic compounds have been regarded as one of the most important solution parameters affecting the leaching of heavy metals from solid phase in the research matrix of soil sciences (Shi et al., 2005). The mechanisms involved in the binding of metals with organic compounds include adsorption, complexation and chelation (Ferraz and Lourençlo, 2000). In terms of RDS transported by the stormwater runoff, e.g. in a drainage area served by a combined sewer system, runoff is mixed with sewage (wastewater) containing dissolved organic matters (DOM) which has potential to form complex with metals. Therefore, the organic compounds are expected to influence the bio-availability and mobility of metals released from RDS to receiving waters through combined sewer overflows (CSOs). Although, there have been extensive studies of the influence of organic compounds on the heavy metals release from soils (Ferraz and Lourençlo, 2000; Ashworth and Alloway, 2004), less attention was paid to the influence of DOM in sewers on the leaching of metals from RDS. Additionally, surfactants also known as surface active agents are important incorporative organic compounds in various detergents, which are released in high quantities from households and industries into sewer systems, and are thus a major wastewater ndez Cirelli et al., 2008). Surfactant enhanced constituent (Ferna remediation (SER) has been proposed as a promising technology for the remediation of solubilize hydrophobic organic compounds, e.g. polycyclic aromatic hydrocarbons, polychlorinated biphenyls, etc, contaminated soils (Mulligan et al., 2001; Ramamurthy et al., 2008). More recently, it has been shown that surfactants can be used to enhance metals removal via surfactant-associated complexation and ionic exchange (Mulligan et al., 2001; Mao et al., 2015). Explicitly, Ramamurthy et al. (2008) reported that surfactants with an additional of complexing agent EDTA (ethylenediaminetetraacetic acid) can improve the desorption of Cu and Zn from an
artificially contaminated sandy soil (Ramamurthy et al., 2008). Several works have shown that the biologically produced surfactants, surfactin, rhamnolipids and sophorolipids are able to remove Cu and Zn from the hydrocarbon contaminated soil (Mulligan et al., 1999; Mulligan et al., 2001; Singh and Cameotra, 2004). However, comparably less or no studies were conducted on the function of surfactant on the metal leaching from RDS. Accordingly, this study intends to provide an in-depth understanding on the leaching dynamics of RDS adsorbed heavy metals for a stormwater pollution aspect. The detailed focuses are to (i) determine the desorption dynamics of metals from RDS to rainwater, and (ii) assess the influences of major wastewater constituents of DOM and surfactant on the desorption dynamics of metals. 2. Mentmaterials and methods 2.1. Initial characterisation of road-deposited sediment The sampling campaign was performed in April 2014. Wet and dry vacuuming methods are the prevailing methods of RDS collection. However, both of them have their own disadvantages. More explicit, increasing concern has been addressed to the wet vacuuming method due to its water filtration system which could potentially dissolve certain content of metals (Zhang and Krebs, 2013). Then, due to the pad filtration system used by the dry vacuuming method, the fine particles would not be trapped by this pad filter and result in a systematic drawback (Herngren et al., 2006). Both of them have potential adverse effects on the redistribution of the particle size fractions. Therefore, a traditional hand sweeping method with a nylon broom and a plastic dustpan were employed for the RDS collection (Charlesworth et al., 2003). This traditional hand sweeping method is able to preserve as much as possible the initial properties (physical and chemical) and structural integrity of the RDS in order to increase the reliability of the information gained by further experimental analyses. The RDS samples were collected from an asphalt traffic road (St. Petersburger Str., average daily traffic: 12600 vehicle/day, % of heavy traffic: 3e4) in the city centre of Dresden (51020 5500 N, 13 440 2900 E), located in the state of Saxony, Germany. The sampling site was selected due to the elevated RDS adsorbed pollutants levels according to the previous study (Zhang et al., 2015a, 2015c). The largest portion of the sediments was assembled near roadside curb areas (Sartor and Boyd, 1972). Therefore, the enclosed sampling plot was situated next to the roadside curb areas. RDS samples were collected over a curb length of about 30 m. Bulk RDS samples were further fractionated into sub-samples and dry-sieved using stainless-steel sieves (Retsch GmbH, Germany) with mesh sizes of 630 mm, 200 mm, and 63 mm in sequence. The particles passing through the 63 mm sieve were filtered by a 0.45 mm (classification diameter between soluble and particle) cellulose nitrite filter (Sartorius, Germany). The particle size dependent samples were homogenized by shaking thoroughly. The gravel-sized materials, plant roots, and leaves were removed during the sieving process. The fractionated RDS samples were labelled, sealed and refrigerated at 4 C in preparation for analysis. 2.2. Synthesis of rainwater To avoid external factors interfering with the desorption process, synthetic rainwater solutions were prepared. The rainwater formula was adapted from Davis et al. (2001) and are given in Table 1. After preparation, the pH of the solutions were 4.78 ± 0.02. The pH value was within the rage of rainwater pH data in central Germany (4.2e6.5 with a mean value of 4.7) (Schumann and Ernst, 1993), and the historical pH data of rainwater in the present city
J. Zhang et al. / Chemosphere 150 (2016) 63e70
65
Table 1 The characteristics of extraction solution and size fraction of the applied RDS. Solution
Composition Formula
Concentration
Blank
Distilled water
e
Rainwater
NaCl HNO3 H2SO4 Glucose Amide Cellulose Meat extract Glucose Amide Cellulose Meat extract CH3(CH2)11OSO3Na CH3(CH2)11OSO3Na
1.35 mg/L 1.13 mg/L 1.76 mg/L 35 mg/L 114 mg/L 34 mg/L 298 mg/L 175 mg/L 570 mg/L 170 mg/L 1490 mg/L 10 mg/L 2.36 g/L
DOM I
DOM II
Surfactant I Surfactant II
(mean value of 4.5) (Mrose, 1966). 2.3. Synthesis of dissolved organic matter Synthetic DOM solutions in different concentrations were prepared and were regarded as principle components in a combined sewer flow. DOM in the combined sewer flow, i.e. wastewater, were synthesized as a mixture of different organic compounds. The organic compounds formulas were adapted from Moreira et al. (2008) and are given in Table 1. The mixture of organic compounds was sterilized (121 C for 15 min) to maintain its characteristics. Accordingly, the synthetic DOM mixtures in different concentrations were optionally termed as DOM I and II. The DOM concentration was determined in the forms of chemical oxygen demand (COD) and total organic carbon (TOC). DOM I: The COD and TOC values of DOM I were determined as 376 and 110 mg/L respectively, which represents a low concentration of raw municipal wastewater with minor contributions of industrial wastewater as catalogued by Henze et al. (2002). DOM II: It contained five time higher concentrations for each organic components. The COD and TOC values of DOM II were 1880 and 550 mg/L respectively, which represents a high concentration of raw municipal wastewater with minor contributions of industrial wastewater as catalogued by Henze et al. (2002).
Buffer
pH
RDS
NaCl K2HPO4 KH2PO4 CH3COOHe CH3COONa
6.86 ± 0.02
NaCl K2HPO4 KH2PO4
6.96 ± 0.02
