Chemosphere 144 (2016) 816e826
Contents lists available at ScienceDirect
Chemosphere journal homepage: www.elsevier.com/locate/chemosphere
Photodegradation of dissolved organic matter in ice under solar irradiation Shuang Xue*, Chao Wang, Zhaohong Zhang, Youtao Song**, Qiang Liu School of Environmental Science, Liaoning University, Shenyang 110036, China
h i g h l i g h t s Naturally occurring DOM was more photoreactive than wastewater-derived DOM in ice. The photodegradation rates of UV-254 and THMFP were higher than DOC in ice. The photodegradation rates of DOM in ice were negatively correlated to DOC level. 3þ and Fe2þ accelerated the photodegradation of DOM in ice. NO 3 , NO2 , Fe Cl and Cu2þ inhibited the photodegradation of DOM in ice.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 11 June 2015 Received in revised form 12 September 2015 Accepted 14 September 2015 Available online xxx
The photodegradation behavior of dissolved organic matter (DOM) with different origins in ice under solar irradiation was investigated. Exposure to sunlight at 2.7 105 J m2 resulted in dissolved organic carbon (DOC) reductions of 22.1e36.5% in ice. The naturally occurring DOM had higher photodegradation potentials than the wastewater-derived DOM in ice. Ultraviolet (UV)-absorbing compounds in DOM, regardless of DOM origin, had much higher photodegradation potentials than gross DOC in ice. The susceptibility of UV-absorbing compounds with natural origin to sunlight exposure in ice was higher than those derived from wastewater. Trihalomethane (THM) precursors were more susceptible to photochemical reactions than gross DOC and haloacetic acid (HAA) precursors in ice. THM precursors in naturally occurring DOM were more photoreactive than those in wastewater-derived DOM in ice, while the photoreactivity of HAA precursors in ice was independent of DOM origin. In ice, the photoreactivity of humic-like fluorescent materials, regardless of DOM origin, was higher than that of gross DOC and protein-like fluorescent materials. DOC reductions caused by sunlight irradiation were found to be negatively correlated to DOC levels, and positively correlated to the aromaticity of DOM. The photodegradation of both wastewater-derived and naturally occurring DOM in ice was significantly facilitated at both acid and alkaline pH, as compared to neutral pH. The photodegradation of DOM in ice, regardless of the origin, was facilitated by nitrate ion ðNO3 Þ, nitrite ion ðNO2 Þ, ferric ion (Fe3þ) and ferrous ion (Fe2þ), and on the other hand, was inhibited by chloridion ion (Cl) and copper ion (Cu2þ). © 2015 Elsevier Ltd. All rights reserved.
Keywords: Dissolved organic matter Photodegradation Ice Sunlight irradiation
1. Introduction Dissolved organic matter (DOM) is the largest pool of reduced C and plays important roles in a variety of biogeochemical processes and ecosystem function in aquatic environments by transporting organic carbon, absorbing ultraviolet (UV)eradiation, interacting
* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (S. Xue), [email protected] (Y. Song). http://dx.doi.org/10.1016/j.chemosphere.2015.09.059 0045-6535/© 2015 Elsevier Ltd. All rights reserved.
with trace metals and anthropogenic organic compounds, and by supplying carbon and nutrient sources to aquatic organisms (Nguyen et al., 2013; Yang et al., 2013). DOM concentration, composition, and chemistry in aquatic environments are highly variable and depend on DOM sources, land use/cover, hydrology, water chemistries, and microbial and/or photochemical trans, 2003; Nguyen et al., formations of the DOM (Leenheer and Croue 2013). Treated wastewater is commonly discharged into rivers, lakes, estuaries and oceans and thus can be an important source of DOM in the receiving waters (Yang et al., 2014). The structural
S. Xue et al. / Chemosphere 144 (2016) 816e826
characteristics of wastewater-derived DOM differed from the naturally occurring DOM found in surface water having negligible anthropogenic impacts, e.g., wastewater-derived DOM is less aromatic and less reactive with chlorine than naturally occurring DOM (Sirivedhin and Gray, 2005; Meng et al., 2013). Since wastewaterderived DOM tends to have much higher dissolved organic carbon (DOC) concentrations than most surface water, wastewater effluent discharge to a surface water significantly influences the quantity and quality of DOM in the receiving waters (Sirivedhin and Gray, 2005). Therefore, the investigation of characteristics and behavior of wastewater-derived DOM is vital for an understanding of the global carbon cycle and determining the fate and transport of such substances in receiving waters (Yang et al., 2014). Because DOM molecules are very photoreactive, photodegradation is an important mechanism for the transformation of DOM in rivers, lakes and oceans (Meng et al., 2013). Numerous studies have focused on the photodegradation of DOM or some components of DOM in aqueous media (Carvalho et al., 2008; Zhang et al., 2009; Benner and Kaiser, 2011; Rajca and Bodzek, 2013; Yang et al., 2014). However, to the authors' knowledge no research has been undertaken to examine the photodegradation of DOM in ice. The ordinary chemical and biological reactions are prohibited in the ice because of the low temperature and the good transparence of ice makes the photochemical reactions possible which is little affected by the temperature (Kang et al., 2009a,b). Therefore, the photochemistry of DOM in ice may play an important role in the fate of DOM when present in cold environments. Because of the complex composition of wastewater-derived DOM and its strong potential to form reactive oxygen species, the photochemical transformation of wastewater-derived DOM is more complex than that of naturally occurring DOM (Lee et al., 2013). Yang et al. (2014) observed some photodegradation behavior of wastewater-derived DOM in water different than that of naturally occurring DOM. They believed that current knowledge concerning the photodegradation of naturally occurring DOM cannot be extrapolated for the understanding of wastewater-derived DOM photodegradation (Yang et al., 2014). However, the photodegradation behavior of wastewater-derived DOM and/or naturally occurring DOM in ice still remains unclear. The investigation of photodegradation behavior of DOM with different origins in ice would not only help in the understanding of the photochemistry of DOM in ice but also be of great significance to the understanding of carbon biogeochemistry in cold environments. The objectives of this study are, therefore, to investigate the photodegradation of wastewater-derived and naturally occurring DOM, as well as DOM in urbanized rivers which are generally derived from both natural sources and wastewater, in ice under solar irradiation. The sunlight-induced changes in spectroscopic characteristics and chlorine reactivity of DOM in ice were evaluated and the impact of various parameters (the concentration and characteristics of DOM, pH, inorganic anions and cations) on the photodegradation of DOM in ice was determined. 2. Materials and methods 2.1. Sample collection and preservation Surface water samples containing naturally occurring DOM were collected from Dahuofang Resevior (DR) and the upper reaches of the Hunhe River (UHR). The Hunhe River is located in Liaoning Province, China, with a length of 415 km, a drainage area of 11,481 km2 and a mean annual runoff of 30.52 millions m3. The Hunhe River runs through the cities of Fushun, Shunyang, Liaoyang, Haicheng, Yingkou before it flows into the Bohai Sea. The sampling point set at UHR is located at Qingyuan Manchu Autonomous
817
County Dasuhe Village Shahezi Community 13 km from the Hunhe river headstream. The section between the Hunhe river headstream and the sampling point is sparsely populated without man-made pollution. The DR reservoir is located at the midstream of the Hunhe River, 68 km northeast of Shenyang. With a surface area of 110 km2 and a maximum depth of 34 m, its maximum water capacity is of 21.87 millions m3. The DR reservoir is fed mainly by the Hunhe River, the Suzihe River, and the Shehe River with the mean annual inflow of 5.55, 5.09, and 0.84 millions m3, respectively. The DR reservoir is the main source of drinking water production for the population of Shenyang and Fushun. DR and UHR were categorized as water samples that had minimal anthropogenic (e.g., wastewater) impact. Secondary effluents were taken from the North Wastewater Treatment Plant (NWTP) and the Shenshuiwan Wastewater Treatment Plant (SWTP) that receive municipal wastewater of the city of Shenyang (mixed household and industrial origin) and discharge into the Hunhe River. Both plants have an average treatment capacity of 200,000 m3 d1. NWTP and SWTP use traditional activated sludge treatment and suspended carrier activated sludge process prior to discharge, respectively. Urban river water samples were collected from the lower reaches of the Hunhe River (LHR) and the Xinkaihe River (XR) in Shenyang. Shenyang is the largest city in Northeast China, with an urban population of more than 8 million. The sampling point set at LHR is located at Shenyang-Dalian railway bridge deck section 7.5 km from Shenyang southern sewage system discharge outlet. At the upstream of the sampling point, the Hunhe River approximately receives sewage of 490,000 tons from Shenyang southern sewage system discharge outlet per day accounting for 38.7% of the total volume of sewage discharge of Shenyang city. XR is a human-made irrigation canal located at the north of Shenyang city dug in 1914 whose water source comes from the Hunhe River. In addition to the function of urban landscape river, XR also has the function of countryside irrigation, groundwater feed and urban flood control and drainage. XR is the largest inland river in Shenyang, with a length of 27.7 km and a width of 15e25 m. The XR flow is made up freshwater from the Hunhe River as well as treated and/or untreated domestic wastewater. XR receives sewage of 85,700 tons from Shenyang northern sewage system per day accounting for 6.6% of the total volume of sewage discharge of Shenyang city. The sampling point set at XR is located at Tawan Bridge about 5 km from the West Route pumping station discharge outlet. Therefore, the LHR and XR water samples were categorized as having significant anthropogenic impact. Water samples were carefully collected and transferred to the laboratory in an ice cooler. All sampled surface waters and wastewaters were directly filtered under vacuum by using pre-rinsed cellulose nitrate membrane filters of 0.45 mm pore size as soon as they were carried back to the laboratory. The filtered samples were stored in glass bottles in the dark at 4 C. Selected water quality parameters of the DR, UHR, LHR, XR water samples, as well as NWTP and SWTP secondary effluents (NSE and SSE), which are relevant for the photodegradation studies, are given in Table 1. Note that in all used water samples iron and copper was below the limit of detection (
Contents lists available at ScienceDirect
Chemosphere journal homepage: www.elsevier.com/locate/chemosphere
Photodegradation of dissolved organic matter in ice under solar irradiation Shuang Xue*, Chao Wang, Zhaohong Zhang, Youtao Song**, Qiang Liu School of Environmental Science, Liaoning University, Shenyang 110036, China
h i g h l i g h t s Naturally occurring DOM was more photoreactive than wastewater-derived DOM in ice. The photodegradation rates of UV-254 and THMFP were higher than DOC in ice. The photodegradation rates of DOM in ice were negatively correlated to DOC level. 3þ and Fe2þ accelerated the photodegradation of DOM in ice. NO 3 , NO2 , Fe Cl and Cu2þ inhibited the photodegradation of DOM in ice.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 11 June 2015 Received in revised form 12 September 2015 Accepted 14 September 2015 Available online xxx
The photodegradation behavior of dissolved organic matter (DOM) with different origins in ice under solar irradiation was investigated. Exposure to sunlight at 2.7 105 J m2 resulted in dissolved organic carbon (DOC) reductions of 22.1e36.5% in ice. The naturally occurring DOM had higher photodegradation potentials than the wastewater-derived DOM in ice. Ultraviolet (UV)-absorbing compounds in DOM, regardless of DOM origin, had much higher photodegradation potentials than gross DOC in ice. The susceptibility of UV-absorbing compounds with natural origin to sunlight exposure in ice was higher than those derived from wastewater. Trihalomethane (THM) precursors were more susceptible to photochemical reactions than gross DOC and haloacetic acid (HAA) precursors in ice. THM precursors in naturally occurring DOM were more photoreactive than those in wastewater-derived DOM in ice, while the photoreactivity of HAA precursors in ice was independent of DOM origin. In ice, the photoreactivity of humic-like fluorescent materials, regardless of DOM origin, was higher than that of gross DOC and protein-like fluorescent materials. DOC reductions caused by sunlight irradiation were found to be negatively correlated to DOC levels, and positively correlated to the aromaticity of DOM. The photodegradation of both wastewater-derived and naturally occurring DOM in ice was significantly facilitated at both acid and alkaline pH, as compared to neutral pH. The photodegradation of DOM in ice, regardless of the origin, was facilitated by nitrate ion ðNO3 Þ, nitrite ion ðNO2 Þ, ferric ion (Fe3þ) and ferrous ion (Fe2þ), and on the other hand, was inhibited by chloridion ion (Cl) and copper ion (Cu2þ). © 2015 Elsevier Ltd. All rights reserved.
Keywords: Dissolved organic matter Photodegradation Ice Sunlight irradiation
1. Introduction Dissolved organic matter (DOM) is the largest pool of reduced C and plays important roles in a variety of biogeochemical processes and ecosystem function in aquatic environments by transporting organic carbon, absorbing ultraviolet (UV)eradiation, interacting
* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (S. Xue), [email protected] (Y. Song). http://dx.doi.org/10.1016/j.chemosphere.2015.09.059 0045-6535/© 2015 Elsevier Ltd. All rights reserved.
with trace metals and anthropogenic organic compounds, and by supplying carbon and nutrient sources to aquatic organisms (Nguyen et al., 2013; Yang et al., 2013). DOM concentration, composition, and chemistry in aquatic environments are highly variable and depend on DOM sources, land use/cover, hydrology, water chemistries, and microbial and/or photochemical trans, 2003; Nguyen et al., formations of the DOM (Leenheer and Croue 2013). Treated wastewater is commonly discharged into rivers, lakes, estuaries and oceans and thus can be an important source of DOM in the receiving waters (Yang et al., 2014). The structural
S. Xue et al. / Chemosphere 144 (2016) 816e826
characteristics of wastewater-derived DOM differed from the naturally occurring DOM found in surface water having negligible anthropogenic impacts, e.g., wastewater-derived DOM is less aromatic and less reactive with chlorine than naturally occurring DOM (Sirivedhin and Gray, 2005; Meng et al., 2013). Since wastewaterderived DOM tends to have much higher dissolved organic carbon (DOC) concentrations than most surface water, wastewater effluent discharge to a surface water significantly influences the quantity and quality of DOM in the receiving waters (Sirivedhin and Gray, 2005). Therefore, the investigation of characteristics and behavior of wastewater-derived DOM is vital for an understanding of the global carbon cycle and determining the fate and transport of such substances in receiving waters (Yang et al., 2014). Because DOM molecules are very photoreactive, photodegradation is an important mechanism for the transformation of DOM in rivers, lakes and oceans (Meng et al., 2013). Numerous studies have focused on the photodegradation of DOM or some components of DOM in aqueous media (Carvalho et al., 2008; Zhang et al., 2009; Benner and Kaiser, 2011; Rajca and Bodzek, 2013; Yang et al., 2014). However, to the authors' knowledge no research has been undertaken to examine the photodegradation of DOM in ice. The ordinary chemical and biological reactions are prohibited in the ice because of the low temperature and the good transparence of ice makes the photochemical reactions possible which is little affected by the temperature (Kang et al., 2009a,b). Therefore, the photochemistry of DOM in ice may play an important role in the fate of DOM when present in cold environments. Because of the complex composition of wastewater-derived DOM and its strong potential to form reactive oxygen species, the photochemical transformation of wastewater-derived DOM is more complex than that of naturally occurring DOM (Lee et al., 2013). Yang et al. (2014) observed some photodegradation behavior of wastewater-derived DOM in water different than that of naturally occurring DOM. They believed that current knowledge concerning the photodegradation of naturally occurring DOM cannot be extrapolated for the understanding of wastewater-derived DOM photodegradation (Yang et al., 2014). However, the photodegradation behavior of wastewater-derived DOM and/or naturally occurring DOM in ice still remains unclear. The investigation of photodegradation behavior of DOM with different origins in ice would not only help in the understanding of the photochemistry of DOM in ice but also be of great significance to the understanding of carbon biogeochemistry in cold environments. The objectives of this study are, therefore, to investigate the photodegradation of wastewater-derived and naturally occurring DOM, as well as DOM in urbanized rivers which are generally derived from both natural sources and wastewater, in ice under solar irradiation. The sunlight-induced changes in spectroscopic characteristics and chlorine reactivity of DOM in ice were evaluated and the impact of various parameters (the concentration and characteristics of DOM, pH, inorganic anions and cations) on the photodegradation of DOM in ice was determined. 2. Materials and methods 2.1. Sample collection and preservation Surface water samples containing naturally occurring DOM were collected from Dahuofang Resevior (DR) and the upper reaches of the Hunhe River (UHR). The Hunhe River is located in Liaoning Province, China, with a length of 415 km, a drainage area of 11,481 km2 and a mean annual runoff of 30.52 millions m3. The Hunhe River runs through the cities of Fushun, Shunyang, Liaoyang, Haicheng, Yingkou before it flows into the Bohai Sea. The sampling point set at UHR is located at Qingyuan Manchu Autonomous
817
County Dasuhe Village Shahezi Community 13 km from the Hunhe river headstream. The section between the Hunhe river headstream and the sampling point is sparsely populated without man-made pollution. The DR reservoir is located at the midstream of the Hunhe River, 68 km northeast of Shenyang. With a surface area of 110 km2 and a maximum depth of 34 m, its maximum water capacity is of 21.87 millions m3. The DR reservoir is fed mainly by the Hunhe River, the Suzihe River, and the Shehe River with the mean annual inflow of 5.55, 5.09, and 0.84 millions m3, respectively. The DR reservoir is the main source of drinking water production for the population of Shenyang and Fushun. DR and UHR were categorized as water samples that had minimal anthropogenic (e.g., wastewater) impact. Secondary effluents were taken from the North Wastewater Treatment Plant (NWTP) and the Shenshuiwan Wastewater Treatment Plant (SWTP) that receive municipal wastewater of the city of Shenyang (mixed household and industrial origin) and discharge into the Hunhe River. Both plants have an average treatment capacity of 200,000 m3 d1. NWTP and SWTP use traditional activated sludge treatment and suspended carrier activated sludge process prior to discharge, respectively. Urban river water samples were collected from the lower reaches of the Hunhe River (LHR) and the Xinkaihe River (XR) in Shenyang. Shenyang is the largest city in Northeast China, with an urban population of more than 8 million. The sampling point set at LHR is located at Shenyang-Dalian railway bridge deck section 7.5 km from Shenyang southern sewage system discharge outlet. At the upstream of the sampling point, the Hunhe River approximately receives sewage of 490,000 tons from Shenyang southern sewage system discharge outlet per day accounting for 38.7% of the total volume of sewage discharge of Shenyang city. XR is a human-made irrigation canal located at the north of Shenyang city dug in 1914 whose water source comes from the Hunhe River. In addition to the function of urban landscape river, XR also has the function of countryside irrigation, groundwater feed and urban flood control and drainage. XR is the largest inland river in Shenyang, with a length of 27.7 km and a width of 15e25 m. The XR flow is made up freshwater from the Hunhe River as well as treated and/or untreated domestic wastewater. XR receives sewage of 85,700 tons from Shenyang northern sewage system per day accounting for 6.6% of the total volume of sewage discharge of Shenyang city. The sampling point set at XR is located at Tawan Bridge about 5 km from the West Route pumping station discharge outlet. Therefore, the LHR and XR water samples were categorized as having significant anthropogenic impact. Water samples were carefully collected and transferred to the laboratory in an ice cooler. All sampled surface waters and wastewaters were directly filtered under vacuum by using pre-rinsed cellulose nitrate membrane filters of 0.45 mm pore size as soon as they were carried back to the laboratory. The filtered samples were stored in glass bottles in the dark at 4 C. Selected water quality parameters of the DR, UHR, LHR, XR water samples, as well as NWTP and SWTP secondary effluents (NSE and SSE), which are relevant for the photodegradation studies, are given in Table 1. Note that in all used water samples iron and copper was below the limit of detection (
