Research Article Cite This: ACS Sustainable Chem. Eng. 2019, 7, 9928−9936
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Proper Mode of Using Rice Straw Biochar To Treat Cd-Contaminated Irrigation Water in Mining Regions Based on a Multiyear in Situ Experiment Qiuwen Chen,*,†,‡,∥ Jianwei Dong,†,‡,∥ Qitao Yi,‡ Xiaoli Liu,§ Jianyun Zhang,*,† and Zhaoxia Zeng⊥
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†
State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Nanjing Hydraulic Research Institute, Nanjing 210029, China ‡ Center for Eco-Environmental Research, Nanjing Hydraulic Research Institute, No. 34 Hujuguan, Nanjing 210029, China § College of Resources & Environment, Hunan Agricultural University, No. 1 Nongda Road, Changsha 410128, China ⊥ Institute of Subtropical Agriculture, Chinese Academy of Sciences, No. 644 Yuanda second Road, Changsha 410125, China S Supporting Information *
ABSTRACT: Biochar has been widely used for immobilizing heavy metals in soils due to its favorable sorption capacity. Previous investigations on heavy metal immobilization in waters by biochar are conducted in laboratory. Knowledge about the long-term effects of in situ biochar application on water bodies contaminated by heavy metals remains scarce. In this research, biochar was derived from cadmium (Cd)-accumulated rice straw. A 35-d laboratory simulation and a three-year field enclosure experiment were carried out to assess the impacts of biochar application on Cd behavior in a water−sediment system of a historically Cd-contaminated irrigation pond. Results indicated that the pH of sediment and overlying water increased with biochar addition in both the lab and field experiments. The rice-straw biochar transformed the Cd in sediments from the exchangeable to residual fraction, because biochar addition increased the pH values and organic matter contents in sediment, leading to the sorption, sequestration, and passivation of Cd by sediment. The Cd concentration in overlying water decreased with the increase in biochar addition, and it continuously decreased with repeated annual application. Overall, for long-term effects of biochar addition on soluble Cd concentrations, the repeated annual addition of 2% biochar exhibited better performance than the repeated annual addition of 1% biochar and one-time addition of 6% biochar. This study provided a proper mode of utilizing rice-straw biochar to treat Cd-contaminated irrigation water in mining regions. KEYWORDS: Cd contamination, Irrigation pond, Overlying water, Sediment, Biochar
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INTRODUCTION Heavy metals released from anthropogenic activities (e.g., mineral exploitation and waste release) have contaminated many water bodies worldwide,1,2 giving rise to a hot issue of heavy metal contamination in water-sediment systems. In the aquatic environment, heavy metals are often preferentially associated with surface sediments, and cannot be removed effectively by biodegradation. Once sediment resuspension occurs, heavy metals can enter the overlying water, further impacting local water quality and ecological safety.1−3 Therefore, in situ remediation of sediment polluted by heavy metals is essential. © 2019 American Chemical Society
Sewage or wastewater is often used for irrigation because it contains valuable nutrients and organic matter for plants. However, sewage irrigation also worsens the quality of farmland due to possible heavy metal contamination.4 Of particular concern, water ponds in mining areas, which contain heavy metals, are frequently used for irrigation purposes.5,6 Bansal7 reported higher concentrations of cadmium (Cd) in soil under sewage irrigation than fields irrigated by underground water. In Received: February 6, 2019 Revised: April 29, 2019 Published: May 13, 2019 9928
DOI: 10.1021/acssuschemeng.9b00761 ACS Sustainable Chem. Eng. 2019, 7, 9928−9936
Research Article
ACS Sustainable Chemistry & Engineering
Figure 1. Study site and view of the studied irrigation pond (Cd concentrations in field rice in each city were obtained from Williams et al.21).
China, almost 20% of total cultivated lands are Cd-tainted.8 Therefore, the long-term effects of sewage irrigation on heavy metal concentrations in soil, plants, and even groundwater should be assessed due to the potential impact on ecological and human health.9 Thus, how to reduce dissolved heavy metals in irrigation water is an urgent issue. Being a useful biomass pyrolysis product, crop straw biochar has been considered as a type of renewable bioenergy, avoiding the loss of a valuable resource and environmental pollution.10,11 It is also an environment-friendly functional material used for water and soil remediation. It is a well-known heavy metal modifier due to its favorable immobilization properties (e.g., microporous structure, high pH, and cation exchange capacity (CEC)).10 Biochar has a strong adsorption affinity for heavy metals and can influence speciation and bioaccumulation of heavy metals in polluted soils.12,13 Previous studies have indicated that the addition of biochar can be beneficial for carbon sequestration and heavy metal immobilization in soils due to its highly resistant properties.14,15 However, few studies have investigated the effects of biochar surface addition on Cd behavior in overlying water and surface sediment in static water bodies (e.g., reservoir/lakes/ponds) used for irrigation but contaminated by heavy metals. Several researchers have investigated the remediation effects of biochar on contaminated soils. For example, the short-term application of biochar showed a reduction in rice grain Cd content of 90%.16 Cao et al.17 found that dairy-manure biochar was effective in immobilizing both atrazine and lead (Pb) and effectiveness was enhanced with the increase in incubation time and biochar rates. Beesley and Marmiroli18 reported that the addition of biochar significantly decreased the arsenic (As) and copper (Cu) concentrations in the porewater of soils. These studies highlight the potential of biochar as an unique amendment for immobilization of both heavy metal and organic contaminants in contaminated soils. On the basis of lab simulations, some researchers have studied the removal and immobilization of heavy metals in aqueous solution by biochar.11,19,20 Although the sorption properties of biochar in soils and aqueous solutions are well-known, insight on biochar− metal interactions in water−sediment systems remains elusive. In particular, the long-term effect of biochar application on heavy metals in real aquatic environments is little reported but deserves insightful investigation. In this study, an irrigation pond in a mining area was selected to study the mechanisms of Cd immobilization by biochar through lab simulation and in situ field container experiments.
We hypothesized that application of biochar could reduce Cd concentration in water and increase Cd immobilization in surface sediment of irrigation ponds, the same as it functions in agricultural soils. As the biochar was derived from Cd-polluted rice straw, this study provides a novel way to deal with polluted rice straw and contaminated water bodies simultaneously.
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MATERIALS AND METHODS
Study Site. The selected irrigation pond (N27°50′1.3″, E113°02′8.4″) was located in the typical industrial city of Zhuzhou in the Hunan Province of China (Figure 1). The area is identified as “Demonstration Zone for Comprehensive Treatment of Heavy Metal Pollution” because of the high average Cd concentration of 0.99 mg· kg−1 in field rice,21 which is about five times of the national food limits for Cd (0.2 mg·kg−1).22 The pond was severely contaminated by both waste discharge from a small electroplating factory, which was closed in 2007, and metal-bearing atmospheric deposition originating from adjacent Pb and Zn smelting plants. The mean exchangeable and total Cd concentrations in the 0−15 cm surface sediment of the pond were 2.75 ± (0.91) and 21.9 ± (2.37) mg·kg−1, respectively (Table 1). The
Table 1. Properties of Rice Straw Biochar Derived at 500 °C, Straw Feedstock, and Sediment straw feedstock pH yield (%) ash content (%) CEC (cmol·kg−1) total Cd (mg·kg−1) exchangeable Cd (mg·kg−1) organic matter (g·kg−1) C (%) N (%) H (%) O (%) K (mg·g−1) P (mg·g−1)
0.471
biochar (RBC500) 10.5 41.2 9.97 36.1 ± 1.96 0.78 ± 0.38 0.083 ± 0.01
sediment (0−15 cm) 7.28
21.9 ± 2.37 2.75 ± 0.91 21.8
37.5 0.88 18.8 3.09 47.7 0.69
mean soluble Cd concentration in the overlying water reached 13.1 ± (4.01) μg·L−1, significantly higher than the irrigation water standard of 5.0 μg·L−1.23 The mean pH values of the overlying water and surface sediment were 6.62 ± (0.39) and 7.28 ± (0.53), respectively. According to the results reported by Zhao et al.,24 the irrigation water with a concentration of 13.1 μg·L−1 contributed approximately 78% of Cd inputs to the double-rice cropping systems in Southern China. 9929
DOI: 10.1021/acssuschemeng.9b00761 ACS Sustainable Chem. Eng. 2019, 7, 9928−9936
Research Article
ACS Sustainable Chemistry & Engineering Table 2. Biochar Treatments at Different Concentrations and Amounts in Laboratory and Field Experiments field experiment (%)
total addition amount (%)
treatment
biochar addition rate (%)
lab simulation (%)
2014
2015
2016
lab simulation
field experiment
CK B1 B2 B6
0 1 2 6
0 1 2 6
0 1 2 6
0 1 2 0
0 1 2 0
0 1 2 6
0 3 6 6
Therefore, removal of Cd from the polluted irrigation water has great practical significance. Biochar Preparation. Rice straw from Cd-contaminated paddy fields in the study area was collected, chipped, and pyrolyzed under oxygen-limited conditions in a pyrolysis muffle furnace reactor in the laboratory. The temperature of the pyrolysis process was slowly and continuously increased from 25 °C at steps of 10 °C per min to 500 °C. The ash content was measured according to the standard method for wood-based-activated carbon of China (GB/T 12496.3−1999). The protonation and charge distribution of the biochar surface were analyzed using pH and zeta potential measurements, as described in Jin et al.25 These measurements were conducted in triplicate. Scanning electron microscope (SEM) imaging analysis was conducted using a HITACHI S4800 SEM (Tokyo, Japan) to observe the morphological properties of the biochar (Figure S1). Elemental (C, H, N, and O) analysis was performed using an elemental analyzer (Vario ELIII, Elementar, Germany). Biochar derived from rice straw has a high pH value of 10.5 and CEC of 36.1 cmol·kg−1 (Table 1), indicating a strong buffer capacity to acidic environments.26 The characteristics of biochar obtained in this study were consistent with those derived from crop straw obtained previously.27−29 The mean Cd content in the biochar (0.78 ± 0.38 mg·kg−1) was much less than the Cd level (21.9 ± 2.37 mg· kg−1) in the surface sediment of the studied pond. Compared to the sorption capacity of Cd (28 mg·kg−1) by this biochar, the Cd sequestration of the biochar during preparation was negligible. Simulation Experiment of Cd Immobilization in Laboratory. Prior to field application, simulation experiments were conducted in the lab to test the effectiveness of biochar on immobilizing Cd. The surface sediment in the selected irrigation pond was collected by a stainlesssteel grab sampler in July 2013. The wet sediment was packed into a series of beakers (0.4 m diameter ×0.5 m height) to a depth of 15 cm. Overlying water collected from the same irrigation pond was then added to the beakers to a depth of 15 cm. The water-sediment systems were stabilized over 10 d to reach equilibrium. According to Kumpiene et al.30 and Liu et al.,31 the addition of 0.2−4% biochar can improve soil quality effectively. In this study, biochar with a total amount of ∼1.7 kg was applied across the water surface at concentration doses of 1, 2, and 6% (w biochar/w 0−15 cm sediment), expressed as treatments B1, B2, and B6, respectively (Table 2). In addition, a control group (CK) was established without the addition of biochar. Biochar was added to the beakers through uniform surface application with a sieve (the same diameter with beakers) and was added once for each treatment. Overlying water samples in the beakers were collected using a syringe and needle on days 1, 7, 14, 21, 28, and 35 after biochar addition. Each sample was filtered through a 0.45-μm nylon membrane and then acidified to pH 1−2 using HNO3 for further analysis. Final experimental sediments were collected with a stainless-steel grab sampler on the last day to determine Cd concentrations and their different fractions. Enclosure Experiment of Cd Immobilization in Field. The in situ field experiment was carried out from 2014 to 2016 to further test and verify the long-term effects of biochar on Cd immobilization in both overlying water and surface sediment. A field container was constructed with a PVC column (Φ 60 cm). The volume of the surface water in the container was ∼0.4 m3. The container was inserted into sediment to a depth of 30 cm and extended above the water surface to a height of 50 cm. There was no exchange of surface water between the container and outside. A stainless-steel tube was wedged on either side of the container to provide support. Biochar was added annually according to the B1 and B2 treatments in mid-March, and once according to the B6 treatment in mid-March of 2014 (Table 2). The
total addition amount of biochar was approximately 5.4 kg. All the prepared biochar was collected together and homogenized fully with a stir bar in a vat. Biochar was evenly distributed with sieves (Φ 60 cm) through stirring and oscillating. The water/sorbent ratio (g·L−1) ranged from 1.0−6.0, which was consistent with the common ratios (1−10 g· L−1) of others.20,32 After biochar addition, the surface water samples from the field containers were collected to a depth of 20 cm with 0.5 L polyethylene plastic bottles in the middle of each month from March to December 2014−2016. The pH values of the water samples were measured on site using a pH meter (PHS3C). The sediment samples in the containers were collected carefully in mid-December in 2014−2016 using an improved gravity columnar sediment sampler (Φ 60 mm). All samples were transported to the laboratory and stored at 4 °C before analysis. Samples collected in each year were analyzed immediately after taking. Analysis of Cd in Overlying Water and Sediment. Porewater samples (50 mL) were collected at 5 cm below the surface sediment with a soil moisture sampler and then filtered through 0.45-μm syringedriven filters. Preweighed 0.45-μm cellulose acetate membranes were used to filter the overlying water samples. Each filtered water sample was transferred into a 50-ml centrifuge tube and then acidified immediately using HNO3 (1:1 V/V) to pH ≤ 2.0. The dissolved heavy metal concentrations in the water phases were determined by a graphite furnace atomic absorption spectrometer (GFAAS) (GTA120, Varian, USA). To determine Cd concentrations in sediment, the sediment samples were ground homogeneously and sieved though a 100-mesh sieve. The samples (1 g) were then added to Teflon beakers with 2 mL of HF, 3 mL of HClO4, and 3 mL of HNO3. After 30 min, the samples were processed using a microwave digestion system (DigiBlock EHD36, China). An atomic absorption spectrophotometer (TAS-990, Beijing Puxi Instrument Factory, Beijing, China) was used to measure Cd concentrations. Different fractions of Cd in the sediment samples (0.50 g) were analyzed by applying the sequential extraction procedures proposed by Tessier et al.33 Consequently, five Cd fractions were identified through five sequential extraction steps, including the exchangeable (F1, readily active and bioavailable), carbonate-bound (F2), bound to Fe−Mn oxide (F3), bound to organic matters (F4), and the residual (F5, not active or bioavailable for plants and microorganisms) fractions, as detailed in Table S1. The soluble Cd in the overlying water collected from both the lab-scale and field experiments and the solutions of each fraction in sediment were analyzed using flame atomic absorption spectroscopy (GTA120, Varian, USA). Quality Assurance/Quality Control. The detection limit for GFAAS was 1 μg·L−1 for Cd. The coefficient of determination for the standard curve was higher than 0.99. National standard reference samples (sediment GBW07403) were used for quality control of sediment samples, and the results coincided well with the reference values, with standard deviations of 0.05). The pH in sediment increased in B2 in 2015 when 2% biochar was added a second time; whereas the pH increased in B1 in 2016 when 1% biochar was added a third time (Figure 4). It is worth noting, that the effectiveness of treatment B6 gradually decreased without the repeated addition of biochar (Figure 3b). Interesting, the Cd concentration in the overlying water in all biochar addition treatments showed less fluctuation than that in the control. 9932
DOI: 10.1021/acssuschemeng.9b00761 ACS Sustainable Chem. Eng. 2019, 7, 9928−9936
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ACS Sustainable Chemistry & Engineering
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DISCUSSION Impact of Biochar on Soluble Cd in Overlying Water. Previous research has reported on the sorption of organic contaminants and heavy metals in soils by biochar.17,19,34,35 Bian et al.36 reported that biochar can significantly reduce extractable Cd in contaminated paddy fields. To date, the removal efficiency and mechanism of heavy metals by biochar in real water bodies are little known, as most relevant studies conducted in aqueous solutions are based on laboratory simulations (e.g., pot experiments).11,12,19,37 However, it is important to understand the long-term effectiveness of metal stabilization by biochar in real water bodies to determine practical applications of this remediation technology.38 In this study, a long-term biochar application experiment on contaminated irrigation ponds was conducted, with the long-term effects of biochar addition on Cd pollution in the ponds then investigated. As shown in Figures 2a and 3b, all three treatments (1, 2, and 6% biochar addition) reduced the soluble Cd concentrations in the overlying water with a linear downtrend in both the lab simulation and field experiment. Sorption of Cd on biochar was accompanied by the release of Ca2+, Mg2+, K+, and Na+ into the overlying water.32 Ion strength did have influences on Cd sorption, and the Cd reduction in overlying water was mainly attributed to ion exchange, especially Ca2+ and Mg2+.39 However, the total Cd sorption amount was usually larger than the increase of these cations in the overlying water, indicating that, in addition to ion exchange, other processes (e.g., electrostatic attraction and surface complexation) also affect the Cd sorption. The zeta potential of biochar was negative and ranged from −37 to −44 mV when pH values ranged from 6.5 to 7.5, which might promote stronger electrostatic interaction between biochar and Cd ion. In the lab simulation, the soluble Cd concentration in the overlying water decreased with the increase in biochar amount. It seemed that a higher addition amount of biochar would be better in the short term from our lab simulation result. However, according to the results obtained in the long term field experiment, a similar pattern to the lab simulation was found only during the first year of application (Figure 3b). During the second- and third-year applications, biochar was added again in the B1 and B2 treatments, and the soluble Cd concentrations in the overlying water decreased significantly. The soluble Cd concentrations in B2 during second- and third-year applications were comparable to and lower than the Cd concentrations in B6, respectively (Figure S2). For example, the soluble Cd concentration in B2 decreased significantly from 7.09 (average of the first-year application) to 3.94 μg·L−1 (average of the second-year application) to 2.92 μg·L−1 (average of the thirdyear application). During the second- and third-year applications, the soluble Cd concentration in B2 was the lowest among the three treatments (Figure S2). Thus, repeated addition of 2% biochar each year performed better than the one-time addition of 6% biochar. The accumulation of Cd in crops is positively related to Cd concentration in irrigation water;10,40 therefore, the removal of Cd from polluted irrigation water has received growing attention. Application of biochar combined with organic fertilizer is a typical method for soil remediation.41 In this study, we suggested a new approach to remove Cd from farmland. The surface application of biochar in irrigation water in the laboratory and field experiments effectively decreased the concentration of soluble Cd in the overlying water (Figures 2a and 3b), suggesting that Cd in the overlying water could be
sorbed by biochar particles, which subsequently settled in the irrigation pond. This indicated that, in addition to the immense and sustainable potential of enhancing soil carbon sequestration, rice straw-derived biochar could be used to effectively mitigate Cd-contaminated irrigation water. Mechanisms of Biochar Effects on pH Values and Cd Speciation in Sediment. Bioavailable Cd in sediment includes soluble Cd in porewater and the bioavailable (exchangeable and carbonate-bound) fraction of sediment. The addition of biochar significantly reduced soluble Cd in sediment porewater (Figure S4). Furthermore, the percentage of bioavailable Cd in sediment decreased with the increase of biochar addition, as shown in Figure 6. However, there was no significant difference in total Cd concentrations of sediment among the three-year application for all treatments (P > 0.05). This result indicated that biochar derived from rice straw transformed the exchangeable Cd fraction into residual forms in the sediment of the heavily contaminated irrigation pond. Unlike the sorption of organic contaminants by biochar, the mechanisms of biochar interaction with heavy metals include ion exchange, (co)precipitation, and electrostatic attraction.37,39 The properties of soil/sediment changed after biochar addition. The application of biochar can increase the CEC and pH of soil/sediment as well as their negative surface charge.10 The reduction in Cd activity and mobility can be partially attributed to the increase in pH values in soil/sediment,43 leading to the sorption of Cd by soil/sediment due to negative surface charge of sediment particles.44,45 Surface application and sedimentation of biochar can gradually increase pH in sediments, as previously reported in soils with biochar addition.46 The mobility of heavy metals in sediment was largely influenced by the pH of the sediment.36,39 In this study, the pH of the biochar was 10.5, well within the range (5.9−12.3) observed for similar biochar materials.39 Thus, the biochar used here was alkaline and therefore induced immobilization of heavy metals and mobilization of oxyanions. Results showed that the B1 treatment significantly increased the pH in sediment at the third addition (accumulative addition amount of biochar, 3%); B2 treatment significantly increased the pH in sediment at the second addition (accumulative addition amount of biochar, 4%); and treatment B6 significantly increased the pH in sediment with the single addition (6%) (Figure 4). This demonstrated that, during field application when the accumulative biochar amount reached 3% or more (≥3.0 g·L−1 of water/ sorbent ratio), treatment significantly increased the pH in sediment. The five fractions of Cd in the sediment indicated different potential for bioavailability, following the order of exchangeable (F1) > carbonate (F2) > Fe/Mn oxide (F3) > organic (F4) > residual (F5). Fractions of heavy metals changed with environmental factors, which had important implications for the in situ immobilization of Cd3. Biochar addition significantly improved the stabilization of Cd by transforming the exchangeable fraction into the residual fraction (Figure 6) with the increase in sediment pH (Figure 4). The addition of biochar also increased the content of organic matter in sediment, leading to passivation and sequestration of Cd in sediment. The similar results were also found by Walker et al.42 Moreover, the effects of Cd stabilization were enhanced by increasing biochar addition through annually repeated patterns. Treatment of rice straw from farmland polluted by heavy metals in mining areas is a challenging issue, as the direct tillage of contaminated straw into farmland may increase the ecological risk of releasing bioavailable forms of heavy metals.47 This study provided insight 9933
DOI: 10.1021/acssuschemeng.9b00761 ACS Sustainable Chem. Eng. 2019, 7, 9928−9936
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ACS Sustainable Chemistry & Engineering
amount of biochar but also with the application mode. Biochar addition should be precisely designed to maximize the reduction in Cd bioavailability in irrigation ponds for sustainable application.
into reusing and recycling rice straw to control the ecological risks of heavy metal pollution from irrigation in mining areas, which offered a proper mode for treating rice straw and irrigation water systems contaminated by heavy metals. Influencing Mechanisms of Biochar on Cd in Water− Sediment Systems. The partitioning coefficient (KP, L·kg1−) of Cd between overlying water and sediment phases in field application could be expressed as KP = CSx−i/CWx−i× 1000, where CSx−i is the annual average Cd concentration in the sediment (μg· g−1); CWi is the annual average Cd concentration in the overlying water (μg·L−1); and x − i is the ith addition of biochar in treatment x (x = B1, B2, or B6). There were no significant differences in the KP values in the control during the three years (Figure S5), indicating that Cd in this static water body reached apparent equilibrium. Cd is nonbiodegradable and persistent in the environment.26 In the control, Cd only existed in the overlying water and sediment phases; whereas Cd in B1, B2, and B6 existed in three phases, i.e., overlying water, sediment, and biochar. In this study, the sorption capacity of sediment for Cd (∼22 mg/kg) was higher than the measured sorption capacity of biochar for Cd (6−29 mg/kg) for all treatments. Once the biochar was added to these systems, the balance was disturbed, and redistribution of Cd occurred in the overlying water, sediment, and biochar. Ion-exchange followed by surface complexation is proposed as the dominant mechanism responsible for Cd immobilization by biochar derived from rice-straw. In this study, half of Cd in biochar were in the residual form (Figure S6); thus, the adsorbed-Cd by biochar was stabilized further during the aging of biochar. Biochar has a high sorption capacity for soluble Cd in water;37 thus, the KP values increased with the increase in biochar addition (Figure S5). For treatment B6, one-time biochar addition at a large concentration (6%) reduced the Cd concentration in the overlying water immediately and dramatically. Although reduction of Cd adsorption by biochar was not found during the aging of biochar in treatment B6 within three-year application, the Cd concentration in the overlying water increased slightly from 2014 to 2016 (Figure 3b). The deposited biochar formed a new “layer” upon the surface sediment; thus, the transport trend of Cd from sediment to the overlying water was partially blocked by this new biochar “layer”. However, this blocking was weakened due to the slow aging of biochar during the threeyear application. Therefore, the exchangeable Cd contents in sediment increased from 0.99 mg·kg−1 during the first year to 1.57 mg·kg−1 during the third year (Figure 6). As shown in Table 2, the accumulative total biochar amount after the second addition in B2 was 4%, which was lower than that (6%) for treatment B6. However, the KP value of the former was higher than that of the latter, consistent with the slightly lower Cd concentration in overlying water after the second addition of biochar in B2 (Figure 3b). The sorption sites on biochar particles in B6 may be covered by each other due to the high density of biochar particles at one-time addition. Thus, the biochar absorption efficiency for treatment B6 was lower than that for treatment B2 after the second addition of biochar. The second addition of biochar in B2 could still adsorb Cd from the overlying water based on the new equilibrium among the three phases (overlying water, sediment, and biochar) after the first addition. Therefore, the repeated addition of 2% biochar each year performed better than the one-time addition of 6% biochar. Thus, this study demonstrated that the influence of biochar on heavy metal bioavailability varied not only with application
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ASSOCIATED CONTENT
* Supporting Information S
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.9b00761.
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Sequential extraction procedures for Cd speciation used in this study; SEM image of the rice-straw biochar; Cd concentrations in overlying water with different amounts of biochar addition in field application; Cd concentrations in sediment for all treatments in field application; variations in soluble Cd concentrations in sediment porewater in treatment B2 for field application; partition coefficients of Cd between sediment and overlying water under different amounts of biochar addition in field application, log KP values of Cd during the first-year (2014), second-year (2015), and third-year (2016) biochar application in situ; different fractions of Cd in biochar (PDF)
AUTHOR INFORMATION
Corresponding Authors
*Tel./Fax: +86 25 85829765; E-mail:
[email protected]. *Tel./Fax: +86 25 85828007; E-mail:
[email protected]. ORCID
Qiuwen Chen: 0000-0003-0905-7591 Qitao Yi: 0000-0001-9145-3459 Author Contributions ∥
Q.C. and J.D. contributed equally to this work.
Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported by the Natural Science Foundation of China (91547206, 51425902, and 51409101), the Innovation Cluster Fund of Jiangsu province, and the Innovation Cluster Fund of Nanjing Hydraulic Research Institute. We are grateful to Dr. Christine Watts for proofreading the English.
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REFERENCES
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DOI: 10.1021/acssuschemeng.9b00761 ACS Sustainable Chem. Eng. 2019, 7, 9928−9936
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DOI: 10.1021/acssuschemeng.9b00761 ACS Sustainable Chem. Eng. 2019, 7, 9928−9936
