Sorption and transport of sulfamethazine in agricultural soils amended with invasive-plant-derived biochar

Journal of Environmental Management 141 (2014) 95e103

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Sorption and transport of sulfamethazine in agricultural soils amended with invasive-plant-derived biochar Meththika Vithanage a, b, Anushka Upamali Rajapaksha a, b, Xiangyu Tang c, Sören Thiele-Bruhn d, Kye Hoon Kim e, Sung-Eun Lee f, Yong Sik Ok a, g, * a

Korea Biochar Research Center and Department of Biological Environment, Kangwon National University, Chuncheon, Republic of Korea Chemical and Environmental Systems Modeling Research Group, Institute of Fundamental Studies, Kandy, Sri Lanka Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, Chengdu, China d Department of Soil Science, University of Trier, Trier, Germany e Department of Environmental Horticulture, The University of Seoul, Seoul, Republic of Korea f School of Applied Biosciences, Kyungpook National University, Daegu, Republic of Korea g Department of Renewable Resources, University of Alberta, Edmonton, Canada b c

a r t i c l e i n f o

a b s t r a c t

Article history: Received 6 July 2013 Received in revised form 6 February 2014 Accepted 27 February 2014 Available online

Sulfonamides (SAs) are one of the most frequently used antibiotics in the veterinary industry, showing high mobility in soils. Objectives of this research were to determine the sorption, distribution coefficients and involvement of different ionic forms of sulfamethazine (SMZ), a representative SAs, and to evaluate the transport of SMZ in biochar treated soils. Biochars were produced from an invasive plant, burcucumber (Sicyos angulatus L.), under slow pyrolysis conditions at peak temperatures of 300
C (biochar300) and 700
C (biochar-700), respectively. The abilities of the biochars to retain SMZ in loamy sand and sandy loam soils were examined under different pHs and SMZ loadings. Soil column experiments were performed with and without biochars addition. Results showed that biochar-700 had a high degree of SMZ retention, with resultant decreased pH in both soils. Modeled effective sorption coefficients (KD,eff) values indicated that the observed high SMZ retention at pH 3 could be attributed to the p-p electron donoreacceptor interaction and electrostatic cation exchange, whereas at pH 5 and 7, cation exchange was the main mechanisms responsible. There was no temporal retardation of SMZ in biochar treated soil as compared to the untreated soil. However, biochar-700 treatment achieved up to 89% and 82% increase in the SMZ retention in sandy loam and loamy sand soils, respectively. The overall results demonstrated that burcucumber biochar produced at higher temperature was effective in reducing the mobility of SMZ in the studied soils. Ó 2014 Elsevier Ltd. All rights reserved.

Keywords: Black carbon Charcoal Emerging contaminants Pharmaceuticals Biosorption Soil organic matter

1. Introduction Pharmaceutical residues, which are recognized as emerging contaminants, are frequently detected in treated wastewater, surface water, and groundwater worldwide (Hu et al., 2010). Sulfonamides (SAs) are one of the most frequently used antibiotic classes in the veterinary industry (Kwon et al., 2011). They are reported to be the second most frequently used group of antibiotics in France, Germany, and the United Kingdom, accounting for 11e23% of the total veterinary antibiotic usage (Thiele-Bruhn, 2003), and in the

* Corresponding author. Korea Biochar Research Center and Department of Biological Environment, Kangwon National University, Chuncheon, Republic of Korea. Tel.: þ82 33 250 6443. E-mail addresses: [email protected], [email protected] (Y.S. Ok). http://dx.doi.org/10.1016/j.jenvman.2014.02.030 0301-4797/Ó 2014 Elsevier Ltd. All rights reserved.

U.S., SAs are the fourth largest group of antibacterials used (AHI, 2002). Hence, SAs may be detected in most environmental samples (Hu et al., 2010) as it has been ubiquitously found in the high ng/L (sometimes reaching 10,000 ng/L) range in discharges from Wastewater Treatment Plants (WWTP), and in the low ng/L (<100 ng/L) range in rivers and groundwater (Kim et al., 2011). Among different SAs in the veterinary industry, sulfamethazine (SMZ) is the most commonly used drug, and thus is frequently detected in the environment due to its high mobility and low sorptivity (Haller et al., 2002). Sulfonamides (SAs) are characterized by relatively unreactive soil surface interactions, and hence, show a high mobility in soils (Kim et al., 2011, 2010b; Thiele-Bruhn, 2003). Recent studies have reported that the sorption of SMZ depends strongly on soil pH, organic matter content, clay content, cation exchange capacity and ionic strength (Gao and Pedersen, 2005; Haham et al., 2012; Kahle

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and Stamm, 2007; Thiele-Bruhn et al., 2004). The high polarity, low octanolewater distribution coefficients (Kow), low chelating ability and high water solubility of SMZ, all contribute to its low affinity to soils (Thiele-Bruhn et al., 2004). Many studies have been conducted recently to determine the fate of SMZ in different soils (Kim et al., 2010a; Kurwadkar et al., 2007; Thiele-Bruhn et al., 2004). Because of low affinity of SMZ to soil mineral particles, it is important to find an effective soil amendment for the management of SMZcontaminated soil and water. Due to its heavy usage, it has been found in manure, effluent from wastewater treatment plants (WWTPs) as well as leachate from animal burial sites (Ok et al., 2011). Therefore, once released into the soil environment, SMZ may be leached into groundwater and flow with water (Ok et al., 2011). Sulfamethazine has been found in groundwater samples in many places, including Korea, Germany, China, Spain, Taiwan and the U.S., at concentrations up to 0.67 mg/L (Kim et al., 2011). The presence of SMZ such as other sulfonamides in the environment may lead to the development and spread of antibiotic resistant bacteria (Heuer et al., 2011). It may also result in increased phytotoxicity to plants, however, only a few studies have been conducted with this regard (Dolliver et al., 2007). Biochar, which is derived from the thermal decomposition of carbon-rich biomass, is being widely used in agriculture as a soil amendment as it can effectively increase soil fertility and create a carbon sink to mitigate environmental pollution of many compounds which are associated with global warming (Awad et al., 2012). Biochar has been found to be an effective adsorbent for various contaminants. A number of investigations have revealed the potential of biochar as a low-cost adsorbent for the control of pollutant migration in soils, applicable to both organic and inorganic pollutants (Ahmad et al., 2012a; Tsang et al., 2007). However, among the different species of pollutants studied previously, only a few have focused on the removal of pharmaceuticals by soil, particularly using biochar under different pH values and pollutant loadings (Yao et al., 2012). Since biochars can be produced from many kinds of feedstock, invasive plant species could be a potentially effective kind, and the collection and utilization of such materials have additional ecosystem benefits. Burcucumber (Sicyos angulatus L.) is a widespread invasive species in Korea, and it has been regarded as one of the most invasive species (Kil et al., 2006). This plant has harmful impacts on not only agriculture but also the natural ecosystems. Due to its severe threat to the country’s rich biodiversity, the Korea Ministry of Environment has adopted a series of regulations for its control, and also called for contributions of the general public to eliminate the plant (Ahmad et al., 2014). In this light, our study intends to make use of the burcucumber biomass as a feedstock to produce biochars. The overarching objective of this work was to understand the adsorption and transport behavior of SMZ in biochar-amended and untreated soils attempting to reduce contaminant leaching from wastewater used for soil irrigation, manure applied soils or animal burial sites. The specific objectives were to: (1) determine the sorption and distribution coefficients of SMZ in the simulated biochar-amended soil environment; (2) determine the involvement of different ionic forms of SMZ in sorption; and (3) determine the effects of the texture of biocharamended soil on transport of SMZ. 2. Material and methods 2.1. Soil samples, biochar and chemicals The two soils were collected from agricultural fields in Bonghwa-gun, Gyeongsangbuk-do Province and Jeongseon-gun, Gangwon Province, Korea. The soils were sieved through a 2-mm

mesh, dried in an oven overnight and then sealed in a container prior to use. The physico-chemical characteristics of the two experimental soils were tested based on standard methods. Burcucumber plants were collected and firstly dried in the sun for one week and later in a fan-forced oven at 60
C for 24 h. The dried shoots were then crushed and ground to <1.0-mm particle size. The biomass was pyrolyzed at both 300 and 700
C in a muffle furnace (N11/H Nabertherm, Germany) under a limited air supply. To achieve slow pyrolysis, biomass was heated to the peak temperature (i.e., 300 or 700
C) at a rate of 7
C min1, and a holding time of 2 h was applied for peak temperature to complete the carbonization of biomass. The produced burcucumber biochars after pyrolysis were kept inside the furnace overnight till completely cooled. The biochar products were then crushed and sieved <2-mm. SMZ was purchased from Fluka Analytical Ltd. (USA). Other chemicals were all analytical reagents and supplied by Sigma Aldrich (USA). 2.2. Soil and biochar characterization Soil pH and electrical conductivity (EC) were determined in a 1:5 (w/v) soil/deionized-water suspension. Soil organic matter was determined using the loss on-ignition method (Sparks, 1996). Extraction with 1 M ammonium acetate (NH4OAc), buffered at pH 7.0, followed by analysis by ICP-OES was used for the determination of exchangeable cations (Ahmad et al., 2012). The standard textural classification was based on the guide from the U.S. Department of Agriculture, Soils and Agricultural Engineering (USDA). The results of soil characterization are presented in Table 1. To test properties of biochars including moisture, mobile matter, ash and resident matter contents, proximate analysis was conducted in duplicate following American Society for Testing and Materials (ASTM) method D5142. Moisture of biochars was measured by heating the samples at 105
C for 24 h without closing the lids. The dehydrated samples kept in covered crucibles were then heated in a furnace at 450
C for 1 h to determine the mobile matter. Subsequently, the ash contents were measured after heating in open crucibles at 750
C for 1 h. After the determination of moisture, ash and mobile matter, resident carbon was calculated based on the weight difference (Ahmad et al., 2013). The elemental composition (C, H, N, S and O) of biochars was then determined on the dry basis by an elemental analyzer (Flash EA 1112 series, CE Instruments, UK). Scanning electron microscopic (SEM) analysis was conducted for both the original biomass and the produced biochars. 2.3. Batch sorption experiments and TCLP extraction Batch adsorption experiments were conducted to understand the effects of pH, reaction time and SMZ loading on adsorption of SMZ by soils with and without biochar amendment. The initial pH values ranged from 3 to 9 and were kept constant using phosphate and acetate buffers (10 mM) in 50 g/L soil suspension spiked with 10 mg/L SMZ and 2 wt.% biochar at room temperature (25
C) in order to observe the effect of pH. The mixtures were shaken at 100 rpm in an incubator shaker for 24 h. Adsorption isotherm experiments were conducted at initial pH of 5.0. Following equilibration, the pH was measured, and samples were centrifuged at 4000 rpm for 15 min, and were then filtered through 0.45 mm PVDF disposable filters (Whatman, UK) and collected in Agilent amber vials prior to HPLC analysis. To determine the SMZ sorption capacity, isotherm experiments were conducted at pH 5 in 50 g/L soils using a series of SMZ concentrations ranging from 2.5 to 50 mg/L. The soils were air dried and used for toxicity characteristic leaching procedure (TCLP) extraction (USEPA, 1990). This extraction

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Table 1 Selected physical and chemical properties of soils used in the study. Silt

Clay

pH

Electrical conductivity dS/m

cmolc/kg

————————%————————

Soil S1 Soil S2

5.95 6.38

24.3 35.9

2.07 2.34

84.1 64.1

a

Cation exchange capacity

Sand

Soil sample

6.2 26.1

9.7 9.8

USDA class

Total N

Avail. P2O5

Soil organic C

ee%ee

eemg/kgee

——————g/kg——————

Loamy sand Sandy loam

0.02 0.11

23 579

4.33 29.4

Soil organic mattera

7.46 50.8

Determined by loss on ignition.

has been used to determine the mobility and the bioavailability of both inorganic and organic contaminants in soils. One gram of samples was placed into 20 mL TCLP fluid. Extraction liquid was prepared by adding 5.7 mL glacial acetic acid and 63.7 mL 1 N NaOH into deionized water containing volumetric flask, mixed well and volume-up to 1000 mL. The pH of the TCLP solution was measured. The solids from batch and column experiments were treated as 1:20 w/v and shaken for 18 h at room temperature. A high performance liquid chromatography (HPLC) system (SCL-10A, Shimadzu, Tokyo, Japan) equipped with an auto-sampler (SIL-10AD, Shimadzu) and UV-VIS detector (SPD-10A, Shimadzu) was used for SMZ analysis in batch equilibrium solutions and TCLP extracts. A reverse-phase Sunfire C18 column (4.6 mm  250 mm; Waters, Bedford, MA, USA) was employed in a column oven (CTO-10AS, Shimadzu) serving as stationary phase and HPLC grade water and formic acid (99.9:0.1 vv1) and HPLC grade acetonitrile and formic acid (99.9:0.1 vv1) were delivered as mobile phase at 0.5 mL min1 (in a gradient program). The injection volume was 20 mL. Calibration was done with SMZ standards in concentrations of up to 10 mg/L. Limits of detection and limits of quantification were 0.05 mg/L.

2.4. Determination of solid-water distribution coefficients of ionic SMZ species The effective sorption coefficients (KD,eff) and individual KD values for cationic, anionic and zwitterionic SMZ species in soilbiochars were calculated. First, the mass fractions of three SMZ species were calculated as function of pH and pKa values as shown in Eqs (1)e(3) (Kurwadkar et al., 2007).

a0 ¼

1 1 þ 10ðpHpK1 Þ þ 10ð2pHpK1 pK2 Þ

(1)

a1 ¼

1 1 þ 10ðpK1 pHÞ þ 10ðpHpK2 Þ

(2)

1 1 þ 10ðpK2 pHÞ þ 10ðpK1 þpK2 2pHÞ

(3)

a2 ¼

Where, pK1 and pK2 are constants being 2.07 and 7.49 respectively; a0 , a1 and a2 represent fractions of cationic, anionic and neutral species, respectively (Qiang and Adams, 2004). Individual sorption coefficients for different ionic forms of SMZ were determined by solving the speciation model (Eq. (4)) using the observed KD values as weighted averages using MS Excel 2007 (Microsoft) (Kurwadkar et al., 2007).

KD;eff ¼ KD0 a0 þ KD1 a1 þ KD2 a2

(4)

Where KD0, KD1 and KD2 represent individualKD values for cationic, anionic and neutral SMZ species, respectively.

2.5. Data modeling Effective adsorption at a given pH in batch experiments was modeled using different equations, i.e. the non-linear Langmuir, Freundlich and Hill isotherm, and the linear Henry isotherm, calculating KD for the initial linear section of the isotherm, respectively. The isotherm models and related parameters are as follows: Freundlich isotherm

qads ¼ KF Cen

(5)

Langmuir isotherm

qads ¼

qm KL Ce 1 þ KL Ce

(6)

Where Ce is equilibrium concentration, qads is adsorption of SMZ per kg of soil (mg/kg), qm is the Langmuir constant associated with maximum adsorption capacity (mg/kg), and KL is the Langmuir equilibrium constant (L/mol), KF ((mg/kg)/(mol/L)n) and n are Freundlich constants, a measure of non-linearity related to adsorption capacity and adsorption intensity. Hill isotherm. Most of the organic contaminant sorption processes with organic sorbate surfaces have been described by cooperative sorption mechanisms, which is represented by the Hill isotherm equation (Eq. (7)) (Sposito, 1984).

Q e ¼ Q max ðKCe Þn



1 þ ðKCe Þn




(7)

Where Qmax is maximum sorption capacity, K is the Hill constant and n is the empirical parameter, which varies with the degree of heterogeneity. In the second approach used to analyze the sorption results, the model of the initial linear part of the plotted isotherm is based on:

qads ¼ Kd Ce

(8)

Kd is the sorption coefficient (L/kg). It should be noted that in the case of low SMZ concentrations, adsorption site saturation will not occur that may result in linear isotherm. Thus, depending on the abundance of surface adsorption sites and the adsorbate molecules, either a nonlinear or a linear model may be appropriate for modeling the empirical results. 2.6. Soil column experiments The soil columns were constructed in acrylic cylinders (6.0 cm  2.8 cm ID) with the bottom of the columns covered with a nylon mesh to prevent soil loss. Soils with or without BC amendment was wet-packed into the column. Three types of soil columns, in duplicate, were used: (1) soil 1 amended with 2% biochar-700 (w/w), (2) soil 2 amended with 2% biochar-700 (w/w), and (3) 2 controls with no biochar. Biochar was added as a top dressing in the

1.68 1.05 0.38 3.26 5.24 4.78 6.12 6.00 2.48 46.81 20.39 14.66 43.37 68.37 78.07 16.82 31.24 54.29 6.49 13.61 8.13 66.54 52.30 34.71 10.16 2.86 2.87 a

Moisture and ash free.

e 50.07 29.66 8.45 10.54 12.56 Biomass Biochar-300 Biochar-700

H/C N H Moisture

Mobile matter

Resident matter

Ash

O C Yield

------------------------------------------------------------------------------------ % -----------------------------------------------------------------------------------1:5

The results of the ultimate and proximate analyses for burcucumber feedstock and biochars produced at 300 and 700
C are shown in Table 2. It can be seen that the biochars have higher ash contents than their precursor, and as compared to many other reported biochars, burcucumber-derived biochar had less resident matter with relatively higher mobile matter (Ahmad et al., 2012a; Uchimiya et al., 2010). The presence of high content of mobile matter has inconsistent impacts on the soils e given that a higher amount of mobile matter indicates more organic materials supply to soil microorganisms and thus improve soil quality, whereas such biochar itself may decompose faster and thus decrease C sink potential as compared to those with high resident matter. In comparison, the pH of the biochar produced at 700
C (pH 12.56 for biochar-700) was much higher than that of biochar-300 (pH 10.54), which may be due to the residual accumulation of alkali salts from the organic matrix (Shinogi and Kanri, 2003) and the loss of acidic functional groups. Scanning electron microscope images (SEM) showed morphological changes/differences between biomass and biochars, and between biochars produced at different temperatures (Fig. 1). The occurrence and development of channels, macro- and micropores were well observed in the case of biochar700 (Fig. 1c). Molar ratios of elements were calculated to estimate the aromaticity (H/C) and polarity (O/C) of the biochars (Uchimiya et al., 2010). The reduction of O at higher temperature resulted from the removal of various acidic functional groups, making the biochars surface more basic for biochar-700 (Ahmad et al., 2012a).

Ultimate analysisa

3.2. Characteristics of biochars

Proximate analysis

Soil samples were analyzed for selected physical and chemical characteristics (Table 1). Soil S1 and soil S2 were categorized as loamy sand (84.1% sand and 6.2% silt) and sandy loam (64.1% sand and 26.1% silt), respectively. Both soils were slightly acidic. Contrasting differences were observed between two soils for available P2O5, total N and for soil organic carbon (Table 1). Soil organic carbon content of the soil S2 (29.4 g/kg) is about 7 times higher than the soil S1.

pH

3.1. Soil properties

Table 2 Proximate and ultimate analyses of burcucumber biomass and the derived biochars produced at 300
C (biochar-300) and 700
C (biochar-700).

3. Results and discussion

O/C

column. Porosity of the columns was 50e52%, and the pore volume was 18e20 mL. About three pore-volumes of deionized water (i.e., 60 mL) were first fed in gravity steady flow to saturate and precondition the column. Columns were then covered with aluminum foil to prevent any photodegradation of SMZ. The initial SMZ concentration used in this study was 10 mg/L. A peristaltic pump (Watson, Marlow) was used to pump SMZ solution into the columns at a flow rate of 0.25 mL/min. Sample filtration and HPLC analysis was done as described above. A total of 5 pore volumes of SMZ solution was injected into the soil column during the initial set up, and the subsequent leaching experiment was conducted with 12 pore volumes of artificial rainwater so as to represent a moderate precipitation rate of 18 mm/h (He et al., 2001). Artificial rainwater was prepared by adding a number of salts into de-ionized water (He et al., 2001). The system pH was not controlled by buffers during the column experiments but was determined at various time intervals. All the column experiments were conducted in duplicate, and the averaged values are reported. Following each column leaching experiment, soil columns were divided into three subsamples for subsequent extraction by the toxicity characteristic leaching procedure (TCLP) (Tsang et al., 2013).

0.81 0.22 0.14

M. Vithanage et al. / Journal of Environmental Management 141 (2014) 95e103

Sample

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M. Vithanage et al. / Journal of Environmental Management 141 (2014) 95e103

99

Fig. 1. Scanning electron microscopic images of burcucumber biomass (a), and the derived biochars produced at 300
C (biochar-300) (b) and 700
C (biochar-700) (c).

Table 3 Sorption coefficients for cationic, zwitterionic and anionic forms of SMZ determined from batch-type sorption experiments.

3.10e9.02 3.03e9.16

KD,eff

KD0

pH 5

--------------------------------- L/kg ---------------------------------

31.49 23.54

390.239 281.539

Noticeably, lower H/C and O/C molar ratios were obtained in biochars produced at higher temperature (Table 2). The high H/C ratio, as in the case of biomass in our study, indicates the direct bonding between C and polarized hydrogen from OH groups (Knicker et al., 2005). The reduction of the H/C ratio with increasing temperature is attributed to enhanced carbonization and increased aromaticity, whereas the reduction of molar O/C ratio due to O removal may lead to increased hydrophobicity of biochar surface (Ahmad et al., 2012a). 3.3. Effects of pH on SMZ sorption and speciation Preliminary batch experiments have shown that the untreated soils and soils with biochar-300 amendment showed a limited sorption potential for SMZ, while biochar-700 addition to soils greatly enhanced the retention. In order to examine the contributions of individual SMZ species to the overall sorption, the speciesspecific equilibrium adsorption coefficients (KDþ, KD and KD0, for SMZþ, SMZ and SMZ0, respectively; Table 3) were calculated from the experimental KD values by multiple regression of the speciation model (Gao and Pedersen, 2005; Kurwadkar et al., 2007; Teixidó et al., 2011). Due to the pH dependent and rapid dissociation of SMZ, considerable changes in KD values were observed within the tested pH range (Kurwadkar et al., 2007). Fig. 2 shows the dependence of KD values on pH for biochar-700-treated soils S1 and soil S2. SMZ adsorption was largest at pH 3 and decreased with increasing aqueous pH. For soil S1, about 75% of SMZ was adsorbed at pH 3, about 50% at the pH 5e7, and only 25% when pH further increased to 9. The observed high sorption of SMZ at low pH can be attributed primarily to the cation exchange of dominant cationic species and sorption of zwitterionic species. Under neutral conditions, adsorption of zwitterionic SMZ species dominates. A major shift to anionic SMZ species occurred when pH increased above 7. Also, according to previous reports, the observed trends in buffered samples may also be applicable to unbuffered samples, as no significant differences have been observed (Gao and Pedersen, 2005). In the case of mineral surfaces, it has been observed that both the dominant SMZþ and SMZ0 species at low pH values are responsible for sorption (Gao and Pedersen, 2005). The results showed a significant correlation (a ¼ 0.01) between the experimental and simulated data for KD (Table 4). For both soils, R2 were obtained as 0.999 for linear regression. With the two species (SMZþ and SMZ0) dominating at pH 3, we hypothesize that two chemical mechanisms are involved in the adsorption and collectively

KD1

KD2

31.104 23.299

19.866 6.666

contribute to the high KD,eff values for both soils (68 L/kg for the loamy sand soil, and 50 L/kg) for the sandy loam soil. First mechanism as the electrostatic cation exchange and the second as the pp electron donoreacceptor interaction of the protonated aniline ring of the SMZ molecule with the p-electron rich graphene surface of the biochars, referred to as pþep EDA (Teixidó et al., 2011). Under neutral conditions, the distribution coefficients were similar at pH 5 and 7, indicating cation exchange was the main mechanism for the sorption of SMZ to biochar (Teixidó et al., 2011). Lastly, in the alkali region at pH 9, as anionic SMZ species prevail in the aqueous phase, low KD,eff values were observed for both biochar-700amended soils. The obtained KD1 values were significantly lower than KD0 values, while the corresponding KD2 values were the lowest of all. The high water solubility of anionic species and the lack of charged sites for anion sorption are possible reasons to explain the low KD2 values. Besides, as compared to the loamy sand soil, the sandy loam soil shows a lower sorption ability even though it contains a high amount of SOM, which may be due to the competition of DOC or with high P2O5 content in the soil for the sorption sites (Haham et al., 2012).

soil S1 + 2% biochar-700 soil S2 + 2% biochar-700 Modeled KD, effective values

70 60 -1

Soil S1 þ biochar-700 Soil S2 þ biochar-700

pH range

KD,effective, L Kg

Soil texture

50 40 30 20 10 0 3

4

5

6

7

8

9

pH Fig. 2. Effects of pH on experimental (symbols) and modeled (solid lines) sorption coefficients for SMZ in the loamy sand soil (soil S1, squares) and the sandy loam soil (soil S2, circles) with biochar amendment.

100

M. Vithanage et al. / Journal of Environmental Management 141 (2014) 95e103

Table 4 Adsorption isotherm parameters of SMZ in soils with and without biochar amendment obtained by model fitting to the data of batch-type sorption experiments. Sample

Parameters Freundlich 1/n

KF Soil Soil Soil Soil

S1 S1 þ 2% biochar-700 S2 S2 þ 2% biochar-700

Langmuir

9.962 65.77 2.643 47.71

R

0.576 0.406 1.000 0.371

2

qm (mg kg

0.909 0.943 0.956 0.723

Hill 1

)

215.68 314.62 129.37 259.91

2

KL 4.39 1.51 1.72 1.43

   

10 101 102 101

R

Qmax (mg kg

0.957 0.992 0.986 0.829

e 297.89 e 188.45

Several models, including Freundlich and Langmuir isotherms, were fitted to the experimental data (Fig. 3) and the corresponding adsorption isotherm model parameters and maximum adsorption densities are listed in Table 4. According to the obtained R2 values, best fittings were achieved using Hill isotherm model (Fig. 4). Freundlich model was also adequate with R2 values in the range of w0.7e0.9. The value of 1/n in the Freundlich isotherm model describes the deviation from linearity (Jung et al., 2011). In this study, the 1/n values of 2% biochar-700treated soils were as low as 0.41 and 0.37 for soil S1 and soil S2, respectively, suggesting that biochar-700 addition could be an effective amendment for low initial SMZ concentrations. As the exponent of the Freundlich model relates to the degree of heterogeneity of the adsorption sites (i.e., a value of 1/n deviates from 1 indicates a greater heterogeneity) (Srivastava et al., 2006), high degree of heterogeneity was observed for biochar-added soils in this study. The adsorptive capacities (qm) were obtained from the Langmuir modeling, with the values in the order of soil S1 þ biochar700 (314.62 mg kg1) > soil S2 þ biochar-700 (259.91 mg kg1) > soil S1 (215.68 mg kg1) > soil S2 (129.37 mg kg1), indicating the higher adsorption ability of soils treated with biochar-700. In the case of organic pollutants adsorption, cooperative interactions may occur between the surface and sorbent and the sorption pattern, corresponding to an S-curve (Giles et al., 1974). In our study, such cooperative sorption was indicated by the fitting results using Hill model (Fig. 3). The adsorption isotherms of SMZ treated with biochar700 were best described by the Hill model, resulting in R2 values of 0.993 and 0.959 for soil S1 þ 2% biochar-700 and soil S2 þ 2% biochar-700 soils, respectively. Hill fitting results indicate that the adsorbed SMZ molecules probably tend to be

(a)

(b) soil S1 soil S1 + 2% biochar-700

300

soil S2 soil S2 + 2% biochar-700

200

200

(mg kg )

250

K

n

R

KD

R2

e 0.172 e 0.201

e 1.11 e 2.84

e 0.993 e 0.959

3.666 32.39 2.243 17.46

0.873 0.957 0.933 0.823

soil S2 soil S2 + 2% biochar-700

150 100

q

q

100

soil S1 soil S1 + 2% biochar-700

300

250

150

)

2

packed in rows or clusters on the biochar surfaces (Kinniburgh, 1986). The coefficient n of the Hill model is a quantitative measure of the degree of cooperativity where cooperativity is defined as positive when n > 1 (Luo and Andrade, 1998), thus sorption of the biochar-treated soils in this study was proved to be a corporative sorption process as indicated by the values of n above 1 (Table 4). In a different way, sorption competition with phosphate which suppresses SMZ sorption until SMZ concentration exceeds a certain threshold also postulated. Adsorption concentrations of untreated and biochar-treated soils are plotted as function of equilibrium concentration of SMZ in Fig. 4, with corresponding values of model parameters compiled in Table 4. Only subtle chemical loss if any was observed in the control samples. Batch isotherm experiments were conducted at pH 5 without buffer addition. For linear modeling, the coefficients were calculated using the initial part of the isotherm at low SMZ concentration, where “n” in Eq. (5) was kept as 1 (Kurwadkar et al., 2007). The highest KD value of 32.39 was observed for 2% biochar-700-treated soil S1, whereas the lowest of 2.24 was reported for the untreated soil S2, as can be seen in Fig. 3 and Table 4. The KD values obtained in this study are similar to those values reported in literature (Kurwadkar et al., 2007). Both unamended soils showed a very limited retention ability for SMZ, while the loamy sand soil (soil S1) showed a relatively higher sorption capacity than the sandy loam soil (soil S2), which may be due to the high organic matter content in the latter. DOC has been known to have a strong negative correlation with the pH of the media (Ishikawa et al., 2006), and therefore, given high OC content, DOC may be released to the soil solution under acidic pH conditions (Ahmad et al., 2012b). DOC may then compete with the antibiotics or other trace-level contaminants for the sorption sites, leading to reduced SMZ sorption ability of the soil (Lertpaitoonpan et al., 2009).

3.4. Partition coefficients and isotherms

(mg kg )

2

Linear 1

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Fig. 3. Fittings of Langmuir (a) and Freundlich (b) model (lines) to the experimental data for the untreated soils (solid symbols) and the soils treated with 2% biochar-700 (cross symbols).

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Fig. 4. Non-linear (Hill and Freundlich) and linear modeling of adsorption isotherms for (a) the loamy sand soil (soil S1) and (b) sandy loam soil (soil S2) amended with 2% biochar700. Symbols represent experimental data and lines represent modeled results.

3.5. Transport potential As shown in Fig. 5, the two soils showed only a slight difference in SMZ transport through the columns. Distilled water was used to wash the column in the beginning; thereafter SMZ was injected and then leached with artificial rainwater. A portion of each and every sample was tested for pH and the pH of the rainwater was 4.32. In agreement with the results in batch sorption experiments, the SMZ retention in the soil columns was very low. The mass of SMZ retained in the untreated soils was calculated to be 0.19 mg and 0.16 mg for the sandy loam soil (soil S2) and the loamy sand soil (soil S1), respectively equaling 80% and 83% release of the initially applied mass. This indicates a high transport potential of SMZ in natural soil environments. Similarly, application of biochar-300 did not lead to reduction in the transport of SMZ considerably within the soil columns, resulting in 77% and 79% of SMZ leaching out of the columns packed with soil S2 and soil S1, respectively. In contrast, application of 2% biochar-700 demonstrated a remarkable effect on SMZ transport potential as indicated by the observed

Distilled water

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5-fold lower SMZ concentrations in leachate from the biochar-700treated soils than that from the unamended soils. SMZ was detected in the leachate for all column experiments showing a continuous decrease in the SMZ concentration after running one pore volume of artificial rainwater through the soil column. The maximum C/C0 (outflow SMZ concentration to inflow SMZ concentration ratio) of SMZ for the unamended soils was much higher than that for biochar-amended soils. It should be noted that the results of column experiments are somewhat different from the batch experiments. The highest sorption of SMZ was reported for soil S1 treated with biochar-700 in the batch experiments, while for column study, this was found for the biochar-700-treated soil S2. No obvious difference in the SMZ adsorption was observed during column experiments for the two untreated soils. Since batch adsorption experiments were conducted basically at pH 5 while column experiments were done at varying pH in the range of 7.5e9, the observed difference may be attributed to the changes of soil pH caused by the addition of relatively high pH biochar materials to the soil matrix in the absence of buffers. Although the mechanisms involved in the binding of SAs to different adsorbent surfaces are still unclear, it has been shown recently that, at alkaline pH, SAs can form strong H bonding between amine functionalities and H acceptor moieties of OC, biochar or mineral matrix (Haham et al., 2012; Teixidó et al., 2011). SMZ is known to have 6H bond acceptors and 3H bond donor moieties (Schwarz et al., 2012). Because the sandy loam soil (soil S2) is rich in organic carbon (OC) (Table 1), interactions of the H acceptor moieties of OC with ionic SMZ species may be principally responsible for the soil’s relatively higher adsorption ability.

3.6. TCLP extraction data

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Pore volume Fig. 5. Concentrations of SMZ leached through soil columns with and without biochars. Closed symbols represent the untreated soils, open symbols represent biochar300-treated soils, and crossed symbols represent biochar-700-treated soils. Squares represent loamy sand soil (soil S1) and circles represent the sandy loam soil (soil S2).

Experiments were conducted for both isotherm and column studies. As shown in Fig. 6, the extraction percentage of SMZ was highest in the sandy loam soil compared to the loamy sand in both treatments. The results agree with the finding in the adsorption isotherm experiment. Soil DOC may play dual roles in the SMZ sorption process as it may compete with SMZ for sorption sites and/ or may adsorb SMZ (Haham et al., 2012; Lertpaitoonpan et al., 2009). However, sorption of neutral SMZ onto organic carbon is known to be a weak process that involves physical bonding through van der Waals interaction, hence, bonded compounds would be leached again sometime after adsorption or can be extracted easily, whereas sorption of ionic species and especially to the soil mineral

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Fig. 6. Differences in TCLP extracted percentage of adsorbed SMZ concentration in the two experimental soils with and without biochar amendment. Soil S1 and soil S2 represent loamy sand soil and sandy loam soil, respectively.

matrix is through substantially stronger ion exchange processes (Haham et al., 2012). This may explain the reduced SMZ sorption and high TCLP extraction efficiency (30e40%) in the sandy loam soil (soil S2). No considerable change in pH was observed even in column experiments after biochar application. Leachate pH was 0.5 in with and without biochar. However, pHs of the soil columns were wpH 5 where the sorption is favored due to the zwitterionic behavior of SMZ. The addition of 2% biochar-700 significantly reduced the TCLP extracted amount of SMZ by about 50% (Fig. 6). The results also showed that with biochar-700 addition, the maximum extractable amount of adsorbed SMZ was decreased to around 22%. On the other hand, at low SMZ initial concentrations of 5 and 10 mg/L, the extracted amount remained low, with the maximum extractable amounts being <8%. This is in agreement with the corporative and multilayer-sorption observed in the adsorption isotherm study. Therefore, addition of biochar-700 enhanced SMZ adsorption and thus reduced the availability of the chemical in the aqueous phase of soils and to the plants.

4. Conclusions Retention and transport of antibiotic SMZ in the biocharamended soil was explored by batch and column experiments, regarding the characteristics of the experimental soils and biochars, the different forms of the target pollutant SMZ and the biochar sorbent application rate. The invasive-plant-derived biochars were characterized as highly aromatic and carbonized with low H/C and O/C ratios and demonstrated a high potential for SMZ sorption. The two untreated soils used in this study showed very limited sorption ability and soils with biochar-300 amendment brought about only a slight improvement. However, the application of biochar-700 showed an obvious enhancement in the sorption of SMZ. The results of the sorption edge experiments and species-specific modeling demonstrated that the pH of the media greatly affected the speciation of SMZ, and would thereby influence the fate and transport of the SMZ. Interestingly, the sandy loam soil with a high organic carbon content showed lower retention ability for SMZ as compared to the loamy sand soil, which is likely due to the competition of soil DOC for the sorption sites. The adsorption isotherm modeling data indicate that the adsorbed SMZ molecules tend to be packed in rows or clusters on the biochar surfaces, which implies a corporative sorption. At pH 5, the maximum sorption

density was observed for biochar-700-treated soils that were about 2 times higher than that under higher pH conditions. Overall, a remarkable enhancement in the SMZ retention was observed by the addition of 2 wt.% burcucumber-derived biochars produced at high temperature pyrolysis, especially under acidic environmental conditions. Acknowledgments This work is fully supported by the Korea Ministry of Environment as Geo-Advanced Innovative Action Project (G112-000560004-0). Instrumental analyses were supported by the Korea Basic Science Institute, the Environmental Research Institute and the Central Laboratory of Kangwon National University, Korea. The Ministry of Technology and Research in Sri Lanka partially supported the first author. References AHI, 2002. Animal Antibiotics. Animal Health Institute. Available from: http://www. ahi.org/. Ahmad, M., Lee, S.S., Dou, X., Mohan, D., Sung, J.K., Yang, J.E., Ok, Y.S., 2012a. Effects of pyrolysis temperature on soybean stover- and peanut shell-derived biochar properties and TCE adsorption in water. Bioresour. Technol. 118, 536e544. Ahmad, M., Lee, S.S., Rajapaksha, A.U., Vithanage, M., Zhang, M., Cho, J.S., Lee, S.-E., Ok, Y.S., 2013. Trichloroethylene adsorption by pine needle biochars produced at various pyrolysis temperatures. Bioresour. Technol. 143, 615e622. Ahmad, M., Moon, D.H., Lim, K.J., Shope, C.L., Lee, S.S., Usman, A.R.A., Kim, K.R., Park, J.H., Hur, S.O., Yang, J.E., Ok, Y.S., 2012b. An assessment of the utilization of waste resources for the immobilization of Pb and Cu in the soil from a Korean military shooting range. Environ. Earth Sci. 67, 1023e1031. Ahmad, M., Moon, D.H., Vithanage, M., Koutsospyros, A., Lee, S.S., Yang, J.E., Lee, S.E., Jeon, C., Ok, Y.S., 2014. Production and use of biochar from buffalo-weed (Ambrosia trifida L.) for trichloroethylene removal from water. J. Chem. Technol. Biotechnol. 89, 150e157. Awad, Y.M., Blagodatskaya, E., Ok, Y.S., Kuzyakov, Y., 2012. Effects of polyacrylamide, biopolymer and biochar on decomposition of soil organic matter and plant residues as determined by 14C and enzyme activities. Eur. J. Soil. Biol. 48, 1e10. Dolliver, H., Kumar, K., Gupta, S., 2007. Sulfamethazine uptake by plants from manure-amended soil. J. Environ. Qual. 36, 1224e1230. Gao, J., Pedersen, J.A., 2005. Adsorption of sulfonamide antimicrobial agents to clay minerals. Environ. Sci. Technol. 39, 9509e9516. Giles, C.H., D’Silva, A.P., Easton, I.A., 1974. A general treatment and classification of the solute adsorption isotherm part. II. Experimental interpretation. J. Colloid Interface Sci. 47, 766e778. Haham, H., Oren, A., Chefetz, B., 2012. Insight into the role of dissolved organic matter in sorption of sulfapyridine by semiarid soils. Environ. Sci. Technol. 46, 11870e11877. Haller, M.Y., Müller, S.R., McArdell, C.S., Alder, A.C., Suter, M.J.F., 2002. Quantification of veterinary antibiotics (sulfonamides and trimethoprim) in animal manure by liquid chromatographyemass spectrometry. J. Chromatogr. A 952, 111e120.

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