- Email: [email protected]
Adsorption of copper(II) and lead(II) from seawater using hydrothermal biochar derived from Enteromorpha
Marine Pollution Bulletin 149 (2019) 110586
Contents lists available at ScienceDirect
Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul
Adsorption of copper(II) and lead(II) from seawater using hydrothermal biochar derived from Enteromorpha
T
Wenchao Yanga, Zhaowei Wangb, , Shuang Songb, Jianbo Hana, Hong Chena, Xiaomeng Wanga, Ruijun Suna, Jiayi Chenga ⁎
a b
Key Laboratory of Coastal Ecology and Environment of State Oceanic Administration, National Marine Environmental Monitoring Center, Dalian 116023, China College of Environmental Science and Engineering, Dalian Maritime University, Dalian 116026, China
ARTICLE INFO
ABSTRACT
Keywords: Biochar Heavy metals Seawater Adsorption model Enteromorpha
The objective of this research was to evaluate the capacity of Enteromorpha derived biochar to adsorb heavy metals from seawater. The biochar characteristics were determined, and isothermal and kinetic data were obtained using batch experiments. Copper [Cu(II)] and lead [Pb(II)] adsorption by the biochar was favored by high pH conditions, while elevated salinity had a relatively weak negative effect on adsorption. The Langmuir isotherm and adsorption kinetics pattern enabled interpretation of the equilibrium and kinetics of Cu(II) and Pb(II) removal by the biochar. The maximum removal rates of Cu(II) and Pb(II) by the biochar in 60 min were estimated to be 91% and 54%, respectively. A model describing the adsorption processes was developed to predict the efficiency of heavy metal removal by the biochar. The outcomes of the present study indicate that Enteromorpha derived biochar could be an effective and environmentally friendly adsorbent for removing heavy metals from marine environments.
1. Introduction Pollution of marine systems by heavy metals has become an environmental problem worldwide, and it is one of the most important issues being monitored in marine environments (Zhang et al., 2017). Heavy metals have high level of toxicity, and persistence capacity possessing potential for biomagnification, bioaccumulation and incorporation into the food chain after reaching a certain limit in the ocean (Salam et al., 2019). Contamination by Cu(II) and Pb(II) are of particular concern because these metals are causing increasingly environmental deterioration, and have detrimental effects on living things in the ocean (Harvey et al., 2016). Consequently, approaches to address this problem are developed by related departments, including stringent environmental regulations that require the removal of heavy metal compounds from seawater and sediments. Conventional methods and technologies that have been used for the removal of heavy metals include precipitation and membrane filtration (Fu and Wang, 2011), but the most effective method for heavy metal removal has been proven to be adsorption (Demirbas, 2008). Macroalgal blooms are also a serious environmental problem in coastal ecosystems around the world (Lapointe et al., 2018). Since 2007, masses of free-floating green algae have accumulated in the
⁎
Yellow Sea (China) during summer, with Enteromorpha being prominent in most green tides (Harun-Al-Rashid and Yang, 2018). Despite the many difficulties because of the different carbohydrate composition of seaweeds compared with terrestrial biomass, macroalgae are attracting increasing attention as a promising biomass resource for energy production (Subhadra and Edwards, 2010). Hydrothermal liquefaction is a thermochemical process that is used widely to produce liquid fuel (termed bio-oil) from a variety of biomass materials (Guo et al., 2015). One of substantial byproducts of the hydrothermal liquefaction processes is biochar (Yang et al., 2014), which is a solid residue having a high carbon content. Like activated carbon, the biochar can be used as an adsorbent and for removing pollutants from water (Qian et al., 2015). Capping remediation with biochar to control the migration and diffusion of pollutants from the contaminated dredged materials in seafloor has also broader applications (Zhu et al., 2019). No doubt biochar is an environmentally benign adsorbent. A recent study indicated that biochar derived from red macroalga Porphyra tenera is a highly effective adsorbent for copper in aqueous solutions (Park et al., 2016). However, there is still a paucity of data showing the universal applicability of biochar in removing heavy metals, especially in marine environments. It is also unclear whether marine algal biochar vary in their capacity to remove heavy metals from aqueous solution.
Corresponding author at: College of Environmental Sciences and Engineering (room 307), Dalian Maritime University, 1 Linghai Road, Dalian 116026, China. E-mail address: [email protected] (Z. Wang).
https://doi.org/10.1016/j.marpolbul.2019.110586 Received 11 March 2019; Received in revised form 4 September 2019; Accepted 7 September 2019 Available online 26 September 2019 0025-326X/ © 2019 Elsevier Ltd. All rights reserved.
Marine Pollution Bulletin 149 (2019) 110586
W. Yang, et al.
The over-arching objective of this study was to use Enteromorpha derived biochar as an effective adsorbent to remove heavy metals from seawater. Batch experiments were used to investigate heavy metal adsorption onto Enteromorpha derived biochar. In particular, the present work aimed to investigate: 1) the effects of seawater salinity and pH on the adsorption of Cu(II) and Pb(II) by Enteromorpha derived biochar; 2) the adsorption equilibrium and kinetics for Enteromorpha derived biochar; and 3) to develop a model to improve understanding and quantitative analysis of the processes of adsorption of heavy metals onto Enteromorpha derived biochar.
biochar, salinity, pH, and contact time were varied systematically, as summarized in Table 1. The seawater pH was adjusted by hydrochloric acid. Pure water mixed with seawater in different proportions to produce salinity gradient. All experiments were carried out at room temperature in triplicates to improve the statistic confidence of the experimental data and the individual data were used to plot adsorption kinetics and isotherms. Blank experimental controls without biochar or heavy metals in solution were also included. The data collected were analyzed statistically using SPSS software (version 17). A P < 0.05 was considered to be statistically significant and the variability in the data was expressed as the standard deviation.
2. Material and methods
2.4. Data processing and adsorption models
2.1. Biochar production
The Cu(II) and Pb(II) concentrations in the filtrates were determined using ICP–OES. The rates of removal of heavy metals by the biochar were calculated based on Eq. (1). The heavy metal adsorption capacity (Qe, mg/kg) was defined as the ratio of the amount of heavy metal adsorbed and the biochar concentration (Eq. (2)).
The biochar used in this study was produced from hydrothermal liquefaction of Enteromorpha as a byproduct. Enteromorpha samples were collected from the Zhanqiao area in Qingdao, China. The samples were dried, pulverized, and sieved to provide particles < 2 mm in size. The liquefaction process was performed in a stainless steel autoclave, equipped with an electrically heated furnace, a magnetic stirrer, and a temperature controller (Yang et al., 2014). In a typical run, 30 g Enteromorpha powder and 80 mL distilled water were placed in the autoclave, and the reaction was initiated by heating the autoclave following purging with nitrogen for 2 min. The liquefaction process occurred over 40 min at a temperature of 250 °C. After liquefaction, the liquid products were separated by filtration, with solid residue (biochar) as the byproduct. The obtained biochar was extracted with dichloromethane, and washed sequentially with acid and distilled water to neutral pH (Note that this process may be repeated 3–5 times), and dried at 80 °C.
Removal rate (%) = Qe =
C0
Cd C0
× 100%
(1)
C0 Cd × 103 [Biochar ]
(2)
where, C0 (mg/L) is the initial heavy metal concentration, Cd (mg/L) is the equilibrium concentration of the non-adsorbed heavy metal, and [Biochar] (g/L) is the concentration of Enteromorpha derived biochar in the solution. Adsorption isotherms in this study were determined using the Langmuir, Freundlich and Henry models (Allen et al., 2003). Langmuir isotherm equation:
2.2. Characterization
Q0 × Cd A + Cd
The structure and morphology of Enteromorpha derived biochar were investigated using scanning electron microscopy (Oxford Instruments, FEI Quanta Inspect S). The functional groups present on the surface of the biochar were analyzed using Fourier transform infrared (FT-IR) spectroscopy over a range of 400–4000 cm−1 (Thermo Fisher, Nicolet 6700). The elemental composition of the biochar was determined using a Thermo Flash 2000 CHNO elemental analyzer. The specific surface area of the biochar was determined using a Quantachrome Autosorb1 surface area analyzer. pH and salinity were measured by a portable multi-parameter analyzer (Multi 3620).
Qe =
2.3. Sample preparation and batch experiments
Q = Kp × Cd
Adsorption of Cu(II) and Pb(II) by the biochar was conducted with batch experiments. All reagents used in the experiments were of guaranteed grade. The batch adsorption experiments were carried out in 60 mL plastic centrifuge tubes (PEs), to which a specified amount of Enteromorpha derived biochar and 40 mL of heavy metal solution containing Cu(II) and Pb(II) were added. The initial concentration of each metal in the solution was adjusted to be 1 mg/L. The mixtures were shaken in a reciprocating shaker for the pre-set time, and filtered immediately through 0.45 μm pore size membranes. The quantity of
where, Kp is the Henry distribution coefficient.
(3)
0
where, Q is the maximum sorption capacity and A is the constant that related to free energy of adsorption. Freundlich isotherm equation: (4)
Q = Kp × Cdn
where, Kf is the Freundlich constant related to sorption capacity and n is the empirical parameter varied with the degree of heterogeneity of adsorbing sites. Henry isotherm equation: (5)
3. Results and discussion 3.1. Biochar characterization The yields of biochar obtained from hydrothermal liquefaction of Enteromorpha were approximately 20.5%, confirming it is a major byproduct of the hydrothermal liquefaction process to produce liquid fuel
Table 1 Adsorption experiment conditions. Experiments
Initial heavy metal concentration (mg/L)
Biochar dose (g/L)
Contact time (min)
pH
Salinity
Effect Effect Effect Effect Effect
1 0.2, 0.5, 0.8, 1, 2, 3, 5, 8 1 1 1
1, 2, 5, 10, 20, 30, 50 30 30 30 30
30 30 0, 5, 10, 15, 30, 60 30 30
8.1 8.1 8.1 2.3, 4.5, 6.2, 8.1 8.1
35 35 35 35 0, 10, 20, 35
of of of of of
biochar dose initial heavy metal concentration contact time pH salinity
2
Marine Pollution Bulletin 149 (2019) 110586
W. Yang, et al.
3.2.1. Effect of salinity Salinity played an important role in the removal of heavy metals by Enteromorpha derived biochar because seawater acted as a cationic intermediary (Khelifa et al., 2005). The removal rates were 94% for Cu(II) and 69% for Pb(II) in a freshwater solution, whereas they were slightly lower with increasing salinity, reaching 90% for Cu(II) and 55% for Pb (II) at a salinity of 35 (Fig. 2a). In laboratory studies, Di Natale et al. (2007) showed that an increase in solution salinity led to a significant decrease in chromium (Cr) adsorption onto a granular activated carbon. Jiang et al. (2016) also reported that increasing salinity decreased Cu (II) and Zn(II) adsorption by pine and jarrah derived biochars. A decrease in adsorption with increasing salinity can be attributed to the ionic solution conditions: ionic solutions such as seawater have high concentrations of Na+, K+, and Ca2+, a competition between those ions and heavy metals may have occurred. Elevated concentrations of Na+, K+, and Ca2+ ions could prevent heavy metals reaching the adsorption sites because of repulsive forces (Villaescusa et al., 2004).
Table 2 Basic features of the biochar derived from Enteromorpha. Surface area (m2/g)
Content composition (wt%)
Biochar
C (%)
H (%)
N (%)
O (%)
70.2
4.5
2.2
23.1
29.7, N2
(Yang et al., 2014). The basic characteristics of the biochar are listed in Table 2. The predominant elements of Enteromorpha derived biochar were carbon (70.2%) and oxygen (23.1%). The surface area of the biochar was 29.7 m2/g, which is similar to that of biochar obtained from farmyard manure (Tan et al., 2015; Batool et al., 2017). The SEM image and pre-adsorption FTIR spectrum of the biochar are shown in Fig. 1. Obviously, the biochar was porous, with numerous holes forming a honeycomb structure, suggesting a high potential to adsorb heavy metal ions from aqueous media. In addition, the internal structure of biochar also possesses a number of irregular spherical structure (Fig. 1a). The peaks in the FTIR spectra of the biochar near to 3400 cm−1 and 2900 cm−1 indicated the OeH and CeH stretching, thus confirming the existence of the hydrogen bonded functional groups. Meanwhile, the hydroxyl group was also detected besides carbonyl group stretching based on the peaks located at 1600 cm−1. The small peak at 1000 cm−1 was ascribed to the carboxyl groups in the biochar (Fig. 1b).
3.2.2. Effect of pH pH is an important parameter in heavy metal adsorption studies, as it affects the degree of ionization and speciation of metal ions in solution (Aksu and İşoğlu, 2005). The effect of pH on Cu(II) and Pb(II) removal by Enteromorpha derived biochar was investigated for a pH range of 2.3 to 8.1 (Fig. 2b). The adsorption of Cu(II) and Pb(II) increased with increasing pH, the removal rates at pH 2.3 were 19% for Cu(II) and 11% for Pb(II), while the removal rates were 90% for Cu(II) and 55% for Pb(II) at pH 8.1. An explanation for the poor heavy metal removal at low pH is that under these conditions the solution contains high concentrations of H+ ions, which characteristically have high mobility and compete with the metal ions for the active sites on the adsorbents (Pellera et al., 2012). As the solution pH increases, the zeta potential of the biochar becomes more negative, which is favorable for cation adsorption (Jiang et al., 2016).
3.2. Significant factors governing the adsorption of Cu(II) and Pb(II) onto biochar: Solution salinity and pH Changes in seawater salinity and pH are most likely to occur in marine environments, and earlier studies have indicated that solution salinity and pH are important parameters affecting the adsorption behavior of heavy metals (Aksu and Balibek, 2007; Zou et al., 2016). However, there are very limited research data available at the present on the effect of salinity and pH on heavy metal adsorption by biochar. A better understanding of how those factors affect the removal of heavy metals by Enteromorpha derived biochar is needed as part of considering its potential uses. Fig. 2 shows the quantity of Cu(II) and Pb(II) removed by Enteromorpha derived biochar as a function of the solution salinity and pH.
3.3. Adsorption isotherms and kinetics The adsorption isotherm helps understanding of the interactions between heavy metals and the Enteromorpha derived biochar. Fig. 3 shows adsorption curves for the biochar as a function of the equilibrium concentration of heavy metals in solution. At lower concentrations, the removal rate of heavy metals increased markedly with increasing the concentration. However, the removal rate approached a constant value
Fig. 1. SEM image (a) and FTIR spectrum (b) of the biochar derived from Enteromorpha. 3
Marine Pollution Bulletin 149 (2019) 110586
W. Yang, et al.
Table 3 Constants for the Langmuir, Freundlich and Henry isotherms for Cu(II) and Pb (II) adsorption by Enteromorpha derived biochar (Experimental conditions: Biochar dose 30 g/L, Contact time 30 min, pH 8.1, and Salinity 35). Langmuir Q Cu(II) Pb(II)
0
254 98
Freundlich 2
Henry 2
A
r
Kf
n
r
Kp
r2
0.6 2.3
0.99 0.99
143 28
0.5 0.6
0.93 0.95
88 11
0.80 0.87
Fig. 4. Kinetics of adsorption of Cu(II) and Pb(II) onto Enteromorpha derived biochar.
with the Langmuir model. Consequently, it was assumed that adsorption mainly occurs in monolayers, or through a fixed number of identical and energetically equivalent sites on the surface. The adsorption capacity of Enteromorpha derived biochar was 254 mg/kg for Cu(II) and 98 mg/kg for Pb(II) (Table 3), which is comparable to those reported for biochar derived from other biomass materials (Park et al., 2016). Fig. 4 shows the rate of heavy metal removals by Enteromorpha derived biochar as a function of the contact time (0 to 60 min). As anticipated, the adsorption kinetics showed an initial increase in the rate with time, but the rate plateaued as equilibrium was reached. The best curve fit to the experimental data showed that variations in the removal rate with contact time could be described by Eq. (6) (Sun et al., 2014):
Fig. 2. Rates of removal of Cu(II) and Pb(II) by Enteromorpha derived biochar as functions of solution salinity and pH.
at higher concentrations. The parameters and correlation coefficients (r2) are shown in Table 3. Better fits were obtained using the Langmuir model than the Freundlich or Henry models, suggesting that the mechanism of heavy metal adsorption onto biochar was more consistent
Removalrate (%) =
Rmax 1+e
t t0 b
(6)
where, Rmax is the maximum heavy metal removal rate by biochar, t is the contact time (min), t0 is the critical time when the removal rate is 50% of Rmax and when the removal rate reached its maximum, and b is a parameter that controls the shape of the curve. The maximum Cu(II) removal rate reached 91% within 60 min and the maximum rate of Table 4 Fitting parameters for the equations describing the kinetics of Cu(II) and Pb(II) adsorption onto Enteromorpha derived biochar.
Cu(II) Pb(II)
Fig. 3. Isotherms for Cu(II) and Pb(II) adsorption onto Enteromorpha derived biochar. The line is the fitted line based on the Langmuir adsorption isotherm. 4
r2
Rmax (%)
t0 (min)
b
0.94 0.97
91 54
7 11
8 9
Marine Pollution Bulletin 149 (2019) 110586
W. Yang, et al.
equilibrium concentration of the non-adsorbed heavy metals in solution, then the mass balance describing the adsorption equilibrium (Eq. (8)) was: (8)
C0 = Cd + Cp
Eqs. (1), (7), and (8) can be rearranged to enable calculation of the removal rate of heavy metals at varying biochar concentrations according to Eq. (9):
Removal rate (%) =
increase of the adsorption occurred at 7 min. For Pb(II) the maximum removal rate was 54% within 60 min, and the maximum increase in the rate of the reaction occurred at 11 min (Table 4). Our results are consistent with those of Ofomaja (2010), who reported that the adsorption kinetics for heavy metals depended greatly on the physical and/or chemical characteristics of the biochar. The initially high removal rate was attributed to the presence of bare active sites on the surface of the biochar. As available sites become occupied by heavy metals, the system will tend to reach an equilibrium between adsorption and desorption processes (Bhaumik et al., 2016). 3.4. Model for adsorption of Cu(II) and Pb(II) by Enteromorpha derived biochar The relationship between the heavy metal removal rate and the biochar concentration in aqueous solution was of interest because the two factors appeared to be related (Fig. 5). The adsorption of heavy metals onto biochar has been reported to be enhanced by increasing the amount of biochar in solution, because of the increased concentration of adsorption sites (Li et al., 2017). Adsorption is an important heavy metal scavenging process. The occurrence of such a relationship suggests that solute-particulate interactions may play a dominant role in controlling the concentrations of heavy metals. The partitioning of heavy metals between solid and solution phases is often described by a conditional parameter, in terms of an empirical distribution coefficient (Kd, units L·g−1), which is defined as (Alloway, 1990):
C0 Cd Cd × [Biochar ]
(9)
Based on our hypothesis, Eq. (9) provides a model for estimation of the heavy metal removal rate as a function of the biochar concentration. Using this equation, five curves were generated with Kd values ranging from 0.02 to 1 L·g−1 (Fig. 5, dashed lines). Fig. 5 shows that the Cu(II) and Pb(II) data fall well in the zone defined by the Kd values of 0.5 and 0.02 to 0.05 L·g−1, respectively. To a certain circumstance, our results suggested a quasi-equilibrium distribution of heavy metals between the dissolved and adsorbed phases under the role of biochar, and we can conclude that the reactions determining adsorption onto biochar were likely to be a significant factor in controlling the removal of heavy metals from the water column. Fig. 5 also reveals that Kd values decreased with increasing biochar concentrations, consistent with the “particle concentration effect” (O'Connor and Connolly, 1980), this is linked to the particle concentration, composition, and the characteristics of the adsorbent and solution. There are limitations associated with this model: 1) We assumed that the adsorption reaction was completely reversible and an equilibrium reaction, which is unrealistic; 2) we did not take into consideration other effects, such as temperature and salinity, which could significantly change the removal behavior and 3) Kd is an empirical and conditional parameter, and the data used here may overestimate in reality circumstance. Despite some deficiencies in the model, the trend in Fig. 5 suggests our model did provide a method for predicting the removal of heavy metals by the biochar in seawaters, and this could be a potential approach to describing heavy metal adsorption onto biochar in an aquatic system.
Fig. 5. Adsorption model for the removal of Cu(II) and Pb(II) by Enteromorpha derived biochar. Note: The dashed lines represent the model results computed using Eq. (9), with Kd values from 0.02 to 1 L·g−1.
Kd =
K d [Biochar ] 1 + K d [Biochar ]
4. Conclusions The present work focused on treatment of seawater contaminated with heavy metals using an environmentally benign biochar derived from Enteromorpha. The Cu(II) and Pb(II) adsorption was significantly affected by the biochar dose, pH, contact time, and salinity. The adsorption isotherm fitted well to the Langmuir isotherm model, whereas the kinetics of adsorption of Cu(II) and Pb(II) onto the biochar was best represented by a 3-parameter sigmoidal kinetic model. The heavy metal adsorption capacity of the biochar was approximately 254 mg/kg for Cu (II) and 98 mg/kg for Pb(II) in typical marine environments. The results showed that Enteromorpha derived biochar may be an effective and benign heavy metal adsorbent, and a useful value-adding byproduct.
(7)
where, (C0 − Cd) is the concentration of heavy metals adsorbed onto biochar (mg/L). The value of Kd is highly sensitive to adsorbent type and concentration, and varies over a large range (Abo-Farha et al., 2009; Muya et al., 2016; Park et al., 2016). It can be derived by Eq. (7) or from empirical model calculations. The Kd could be used to address the solute-particulate balance in the exchange of metal species in aqueous systems (Yantasee et al., 2007). Heavy metals adsorbed onto the biochar are assumed to be part of the particulate phase, while the non-adsorbed heavy metals in solution were taken to be the dissolved phase. We assumed that the heavy metals in the aqueous solution were scavenged only through the adsorption process, and as the biochar provided limited surface sites for adsorption, the adsorption reaction would reach equilibrium. If C0 was defined as the initial concentration of heavy metals in the water column, Cp was the concentration of heavy metals adsorbed onto biochar at equilibrium, and Cd was the
Acknowledgements The authors are grateful to colleagues at the College of Dalian Maritime University for their help with the test work. This work was supported by the National Natural Science Foundation of China (41806128, 51879019), and the Fundamental Research Funds for the Central Universities (3132018179). References Abo-Farha, S.A., Abdel-Aal, A.Y., Ashour, I.A., Garamon, S.E., 2009. Removal of some heavy metal cations by synthetic resin purolite C100. J. Hazard. Mater. 169 (1–3), 190–194. Aksu, Z., Balibek, E., 2007. Chromium (VI) biosorption by dried Rhizopus arrhizus: effect of salt (NaCl) concentration on equilibrium and kinetic parameters. J. Hazard. Mater.
5
Marine Pollution Bulletin 149 (2019) 110586
W. Yang, et al. 145 (1–2), 210–220. Aksu, Z., İşoğlu, I.A., 2005. Removal of copper (II) ions from aqueous solution by biosorption onto agricultural waste sugar beet pulp. Process Biochem. 40 (9), 3031–3044. Allen, S.J., Gan, Q., Matthews, R., Johnson, P.A., 2003. Comparison of optimised isotherm models for basic dye adsorption by kudzu. Bioresour. Technol. 88 (2), 143–152. Alloway, B.J., 1990. Soil processes and the behavior of metals. In: Heavy Metals in Soils, pp. 7–27. Batool, S., Idrees, M., Hussain, Q., Kong, J., 2017. Adsorption of copper (II) by using derived-farmyard and poultry manure biochars: efficiency and mechanism. Chem. Phys. Lett. 689, 190–198. Bhaumik, M., Agarwal, S., Gupta, V.K., Maity, A., 2016. Enhanced removal of Cr (VI) from aqueous solutions using polypyrrole wrapped oxidized MWCNTs nanocomposites adsorbent. J Colloid Interf Sci 470, 257–267. Demirbas, A., 2008. Heavy metal adsorption onto agro-based waste materials: a review. J. Hazard. Mater. 157 (2–3), 220–229. Di Natale, F., Lancia, A., Molino, A., Musmarra, D., 2007. Removal of chromium ions form aqueous solutions by adsorption on activated carbon and char. J. Hazard. Mater. 145 (3), 381–390. Fu, F., Wang, Q., 2011. Removal of heavy metal ions from wastewaters: a review. J. Environ. Manag. 92 (3), 407–418. Guo, Y., Yeh, T., Song, W., Xu, D., Wang, S., 2015. A review of bio-oil production from hydrothermal liquefaction of algae. Renew. Sust. Energ. Rev. 48, 776–790. Harun-Al-Rashid, A., Yang, C.S., 2018. Hourly variation of green tide in the Yellow Sea during summer 2015 and 2016 using Geostationary Ocean Color Imager data. Int. J. Remote Sens. 39 (13), 4402–4415. Harvey, P.J., Handley, H.K., Taylor, M.P., 2016. Widespread copper and lead contamination of household drinking water, New South Wales, Australia. Environ. Res. 151, 275–285. Jiang, S., Huang, L., Nguyen, T.A., Ok, Y.S., Rudolph, V., Yang, H., Zhang, D., 2016. Copper and zinc adsorption by softwood and hardwood biochars under elevated sulphate-induced salinity and acidic pH conditions. Chemosphere 142, 64–71. Khelifa, A., Hill, P.S., Stoffyn-Egli, P., Lee, K., 2005. Effects of salinity and clay composition on oil-clay aggregations. Mar. Environ. Res. 59 (3), 235–254. Lapointe, B.E., Burkholder, J.M., Van Alstyne, K.L., 2018. Harmful macroalgal blooms in a changing world: causes, impacts, and management. In: Harmful Algal Blooms: A Compendium Desk Reference, pp. 515–560. Li, B., Yang, L., Wang, C.Q., Zhang, Q.P., Liu, Q.C., Li, Y.D., Xiao, R., 2017. Adsorption of Cd (II) from aqueous solutions by rape straw biochar derived from different modification processes. Chemosphere 175, 332–340. Muya, F.N., Sunday, C.E., Baker, P., Iwuoha, E., 2016. Environmental remediation of heavy metal ions from aqueous solution through hydrogel adsorption: a critical
review. Water Sc Technol 73 (5), 983–992. O’Connor, D.J., Connolly, J.P., 1980. The effect of concentration of adsorbing solids on the partition coefficient. Water Res. 14 (10), 1517–1523. Ofomaja, A.E., 2010. Intraparticle diffusion process for lead (II) biosorption onto mansonia wood sawdust. Bioresour. Technol. 101 (15), 5868–5876. Park, S.H., Cho, H.J., Ryu, C., Park, Y.K., 2016. Removal of copper (II) in aqueous solution using pyrolytic biochars derived from red macroalga Porphyra tenera. J. Ind. Eng. Chem. 36, 314–319. Pellera, F.M., Giannis, A., Kalderis, D., Anastasiadou, K., Stegmann, R., Wang, J.Y., Gidarakos, E., 2012. Adsorption of Cu(II) ions from aqueous solutions on biochars prepared from agricultural by-products. J. Environ. Manag. 96 (1), 35–42. Qian, K., Kumar, A., Zhang, H., Bellmer, D., Huhnke, R., 2015. Recent advances in utilization of biochar. Renew. Sust. Energ. Rev. 42, 1055–1064. Salam, M.A., Paul, S.C., Noor, S.N.B.M., Siddiqua, S.A., Aka, T.D., Wahab, R., Aweng, E.R., 2019. Contamination profile of heavy metals in marine fish and shellfish. Glo J Environ Sci Manag 5 (2), 225–236. Subhadra, B., Edwards, M., 2010. An integrated renewable energy park approach for algal biofuel production in United States. Energ Policy 38 (9), 4897–4902. Sun, J., Khelifa, A., Zhao, C.C., Zhao, D.F., Wang, Z.D., 2014. Laboratory investigation of oil–suspended particulate matter aggregation under different mixing conditions. Sci. Total Environ. 473, 742–749. Tan, X., Liu, Y., Zeng, G., Wang, X., Hu, X., Gu, Y., Yang, Z., 2015. Application of biochar for the removal of pollutants from aqueous solutions. Chemosphere 125, 70–85. Villaescusa, I., Fiol, N., Martı́nez, M., Miralles, N., Poch, J., Serarols, J., 2004. Removal of copper and nickel ions from aqueous solutions by grape stalks wastes. Water Res. 38 (4), 992–1002. Yang, W.C., Li, X.G., Liu, S.S., Feng, L.J., 2014. Direct hydrothermal liquefaction of undried macroalgae Enteromorpha prolifera using acid catalysts. Energ Convers Manage 87, 938–945. Yantasee, W., Warner, C.L., Sangvanich, T., Addleman, R.S., Carter, T.G., Wiacek, R.J., Fryxell, G.E., Timchalk, C., Warner, M.G., 2007. Removal of heavy metals from aqueous systems with thiol functionalized superparamagnetic nanoparticles. Environ Sci Technol 41 (14), 5114–5119. Zhang, Y., Chu, C., Li, T., Xu, S., Liu, L., Ju, M., 2017. A water quality management strategy for regionally protected water through health risk assessment and spatial distribution of heavy metal pollution in 3 marine reserves. Sci. Total Environ. 599, 721–731. Zhu, Y.Y., Tang, W.Z., Jin, X., Shan, B.Q., 2019. Using biochar capping to reduce nitrogen release from sediments in eutrophic lakes. Sci. Total Environ. 646, 93–104. Zou, Y.D., Wang, X.X., Khan, A., Wang, P.Y., Liu, Y.H., Alsaedi, A., Hayat, T., Wang, X.K., 2016. Environmental remediation and application of nanoscale zero-valent iron and its composites for the removal of heavy metal ions: a review. Environ Sci Technol 50 (14), 7290–7304.
6
Contents lists available at ScienceDirect
Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul
Adsorption of copper(II) and lead(II) from seawater using hydrothermal biochar derived from Enteromorpha
T
Wenchao Yanga, Zhaowei Wangb, , Shuang Songb, Jianbo Hana, Hong Chena, Xiaomeng Wanga, Ruijun Suna, Jiayi Chenga ⁎
a b
Key Laboratory of Coastal Ecology and Environment of State Oceanic Administration, National Marine Environmental Monitoring Center, Dalian 116023, China College of Environmental Science and Engineering, Dalian Maritime University, Dalian 116026, China
ARTICLE INFO
ABSTRACT
Keywords: Biochar Heavy metals Seawater Adsorption model Enteromorpha
The objective of this research was to evaluate the capacity of Enteromorpha derived biochar to adsorb heavy metals from seawater. The biochar characteristics were determined, and isothermal and kinetic data were obtained using batch experiments. Copper [Cu(II)] and lead [Pb(II)] adsorption by the biochar was favored by high pH conditions, while elevated salinity had a relatively weak negative effect on adsorption. The Langmuir isotherm and adsorption kinetics pattern enabled interpretation of the equilibrium and kinetics of Cu(II) and Pb(II) removal by the biochar. The maximum removal rates of Cu(II) and Pb(II) by the biochar in 60 min were estimated to be 91% and 54%, respectively. A model describing the adsorption processes was developed to predict the efficiency of heavy metal removal by the biochar. The outcomes of the present study indicate that Enteromorpha derived biochar could be an effective and environmentally friendly adsorbent for removing heavy metals from marine environments.
1. Introduction Pollution of marine systems by heavy metals has become an environmental problem worldwide, and it is one of the most important issues being monitored in marine environments (Zhang et al., 2017). Heavy metals have high level of toxicity, and persistence capacity possessing potential for biomagnification, bioaccumulation and incorporation into the food chain after reaching a certain limit in the ocean (Salam et al., 2019). Contamination by Cu(II) and Pb(II) are of particular concern because these metals are causing increasingly environmental deterioration, and have detrimental effects on living things in the ocean (Harvey et al., 2016). Consequently, approaches to address this problem are developed by related departments, including stringent environmental regulations that require the removal of heavy metal compounds from seawater and sediments. Conventional methods and technologies that have been used for the removal of heavy metals include precipitation and membrane filtration (Fu and Wang, 2011), but the most effective method for heavy metal removal has been proven to be adsorption (Demirbas, 2008). Macroalgal blooms are also a serious environmental problem in coastal ecosystems around the world (Lapointe et al., 2018). Since 2007, masses of free-floating green algae have accumulated in the
⁎
Yellow Sea (China) during summer, with Enteromorpha being prominent in most green tides (Harun-Al-Rashid and Yang, 2018). Despite the many difficulties because of the different carbohydrate composition of seaweeds compared with terrestrial biomass, macroalgae are attracting increasing attention as a promising biomass resource for energy production (Subhadra and Edwards, 2010). Hydrothermal liquefaction is a thermochemical process that is used widely to produce liquid fuel (termed bio-oil) from a variety of biomass materials (Guo et al., 2015). One of substantial byproducts of the hydrothermal liquefaction processes is biochar (Yang et al., 2014), which is a solid residue having a high carbon content. Like activated carbon, the biochar can be used as an adsorbent and for removing pollutants from water (Qian et al., 2015). Capping remediation with biochar to control the migration and diffusion of pollutants from the contaminated dredged materials in seafloor has also broader applications (Zhu et al., 2019). No doubt biochar is an environmentally benign adsorbent. A recent study indicated that biochar derived from red macroalga Porphyra tenera is a highly effective adsorbent for copper in aqueous solutions (Park et al., 2016). However, there is still a paucity of data showing the universal applicability of biochar in removing heavy metals, especially in marine environments. It is also unclear whether marine algal biochar vary in their capacity to remove heavy metals from aqueous solution.
Corresponding author at: College of Environmental Sciences and Engineering (room 307), Dalian Maritime University, 1 Linghai Road, Dalian 116026, China. E-mail address: [email protected] (Z. Wang).
https://doi.org/10.1016/j.marpolbul.2019.110586 Received 11 March 2019; Received in revised form 4 September 2019; Accepted 7 September 2019 Available online 26 September 2019 0025-326X/ © 2019 Elsevier Ltd. All rights reserved.
Marine Pollution Bulletin 149 (2019) 110586
W. Yang, et al.
The over-arching objective of this study was to use Enteromorpha derived biochar as an effective adsorbent to remove heavy metals from seawater. Batch experiments were used to investigate heavy metal adsorption onto Enteromorpha derived biochar. In particular, the present work aimed to investigate: 1) the effects of seawater salinity and pH on the adsorption of Cu(II) and Pb(II) by Enteromorpha derived biochar; 2) the adsorption equilibrium and kinetics for Enteromorpha derived biochar; and 3) to develop a model to improve understanding and quantitative analysis of the processes of adsorption of heavy metals onto Enteromorpha derived biochar.
biochar, salinity, pH, and contact time were varied systematically, as summarized in Table 1. The seawater pH was adjusted by hydrochloric acid. Pure water mixed with seawater in different proportions to produce salinity gradient. All experiments were carried out at room temperature in triplicates to improve the statistic confidence of the experimental data and the individual data were used to plot adsorption kinetics and isotherms. Blank experimental controls without biochar or heavy metals in solution were also included. The data collected were analyzed statistically using SPSS software (version 17). A P < 0.05 was considered to be statistically significant and the variability in the data was expressed as the standard deviation.
2. Material and methods
2.4. Data processing and adsorption models
2.1. Biochar production
The Cu(II) and Pb(II) concentrations in the filtrates were determined using ICP–OES. The rates of removal of heavy metals by the biochar were calculated based on Eq. (1). The heavy metal adsorption capacity (Qe, mg/kg) was defined as the ratio of the amount of heavy metal adsorbed and the biochar concentration (Eq. (2)).
The biochar used in this study was produced from hydrothermal liquefaction of Enteromorpha as a byproduct. Enteromorpha samples were collected from the Zhanqiao area in Qingdao, China. The samples were dried, pulverized, and sieved to provide particles < 2 mm in size. The liquefaction process was performed in a stainless steel autoclave, equipped with an electrically heated furnace, a magnetic stirrer, and a temperature controller (Yang et al., 2014). In a typical run, 30 g Enteromorpha powder and 80 mL distilled water were placed in the autoclave, and the reaction was initiated by heating the autoclave following purging with nitrogen for 2 min. The liquefaction process occurred over 40 min at a temperature of 250 °C. After liquefaction, the liquid products were separated by filtration, with solid residue (biochar) as the byproduct. The obtained biochar was extracted with dichloromethane, and washed sequentially with acid and distilled water to neutral pH (Note that this process may be repeated 3–5 times), and dried at 80 °C.
Removal rate (%) = Qe =
C0
Cd C0
× 100%
(1)
C0 Cd × 103 [Biochar ]
(2)
where, C0 (mg/L) is the initial heavy metal concentration, Cd (mg/L) is the equilibrium concentration of the non-adsorbed heavy metal, and [Biochar] (g/L) is the concentration of Enteromorpha derived biochar in the solution. Adsorption isotherms in this study were determined using the Langmuir, Freundlich and Henry models (Allen et al., 2003). Langmuir isotherm equation:
2.2. Characterization
Q0 × Cd A + Cd
The structure and morphology of Enteromorpha derived biochar were investigated using scanning electron microscopy (Oxford Instruments, FEI Quanta Inspect S). The functional groups present on the surface of the biochar were analyzed using Fourier transform infrared (FT-IR) spectroscopy over a range of 400–4000 cm−1 (Thermo Fisher, Nicolet 6700). The elemental composition of the biochar was determined using a Thermo Flash 2000 CHNO elemental analyzer. The specific surface area of the biochar was determined using a Quantachrome Autosorb1 surface area analyzer. pH and salinity were measured by a portable multi-parameter analyzer (Multi 3620).
Qe =
2.3. Sample preparation and batch experiments
Q = Kp × Cd
Adsorption of Cu(II) and Pb(II) by the biochar was conducted with batch experiments. All reagents used in the experiments were of guaranteed grade. The batch adsorption experiments were carried out in 60 mL plastic centrifuge tubes (PEs), to which a specified amount of Enteromorpha derived biochar and 40 mL of heavy metal solution containing Cu(II) and Pb(II) were added. The initial concentration of each metal in the solution was adjusted to be 1 mg/L. The mixtures were shaken in a reciprocating shaker for the pre-set time, and filtered immediately through 0.45 μm pore size membranes. The quantity of
where, Kp is the Henry distribution coefficient.
(3)
0
where, Q is the maximum sorption capacity and A is the constant that related to free energy of adsorption. Freundlich isotherm equation: (4)
Q = Kp × Cdn
where, Kf is the Freundlich constant related to sorption capacity and n is the empirical parameter varied with the degree of heterogeneity of adsorbing sites. Henry isotherm equation: (5)
3. Results and discussion 3.1. Biochar characterization The yields of biochar obtained from hydrothermal liquefaction of Enteromorpha were approximately 20.5%, confirming it is a major byproduct of the hydrothermal liquefaction process to produce liquid fuel
Table 1 Adsorption experiment conditions. Experiments
Initial heavy metal concentration (mg/L)
Biochar dose (g/L)
Contact time (min)
pH
Salinity
Effect Effect Effect Effect Effect
1 0.2, 0.5, 0.8, 1, 2, 3, 5, 8 1 1 1
1, 2, 5, 10, 20, 30, 50 30 30 30 30
30 30 0, 5, 10, 15, 30, 60 30 30
8.1 8.1 8.1 2.3, 4.5, 6.2, 8.1 8.1
35 35 35 35 0, 10, 20, 35
of of of of of
biochar dose initial heavy metal concentration contact time pH salinity
2
Marine Pollution Bulletin 149 (2019) 110586
W. Yang, et al.
3.2.1. Effect of salinity Salinity played an important role in the removal of heavy metals by Enteromorpha derived biochar because seawater acted as a cationic intermediary (Khelifa et al., 2005). The removal rates were 94% for Cu(II) and 69% for Pb(II) in a freshwater solution, whereas they were slightly lower with increasing salinity, reaching 90% for Cu(II) and 55% for Pb (II) at a salinity of 35 (Fig. 2a). In laboratory studies, Di Natale et al. (2007) showed that an increase in solution salinity led to a significant decrease in chromium (Cr) adsorption onto a granular activated carbon. Jiang et al. (2016) also reported that increasing salinity decreased Cu (II) and Zn(II) adsorption by pine and jarrah derived biochars. A decrease in adsorption with increasing salinity can be attributed to the ionic solution conditions: ionic solutions such as seawater have high concentrations of Na+, K+, and Ca2+, a competition between those ions and heavy metals may have occurred. Elevated concentrations of Na+, K+, and Ca2+ ions could prevent heavy metals reaching the adsorption sites because of repulsive forces (Villaescusa et al., 2004).
Table 2 Basic features of the biochar derived from Enteromorpha. Surface area (m2/g)
Content composition (wt%)
Biochar
C (%)
H (%)
N (%)
O (%)
70.2
4.5
2.2
23.1
29.7, N2
(Yang et al., 2014). The basic characteristics of the biochar are listed in Table 2. The predominant elements of Enteromorpha derived biochar were carbon (70.2%) and oxygen (23.1%). The surface area of the biochar was 29.7 m2/g, which is similar to that of biochar obtained from farmyard manure (Tan et al., 2015; Batool et al., 2017). The SEM image and pre-adsorption FTIR spectrum of the biochar are shown in Fig. 1. Obviously, the biochar was porous, with numerous holes forming a honeycomb structure, suggesting a high potential to adsorb heavy metal ions from aqueous media. In addition, the internal structure of biochar also possesses a number of irregular spherical structure (Fig. 1a). The peaks in the FTIR spectra of the biochar near to 3400 cm−1 and 2900 cm−1 indicated the OeH and CeH stretching, thus confirming the existence of the hydrogen bonded functional groups. Meanwhile, the hydroxyl group was also detected besides carbonyl group stretching based on the peaks located at 1600 cm−1. The small peak at 1000 cm−1 was ascribed to the carboxyl groups in the biochar (Fig. 1b).
3.2.2. Effect of pH pH is an important parameter in heavy metal adsorption studies, as it affects the degree of ionization and speciation of metal ions in solution (Aksu and İşoğlu, 2005). The effect of pH on Cu(II) and Pb(II) removal by Enteromorpha derived biochar was investigated for a pH range of 2.3 to 8.1 (Fig. 2b). The adsorption of Cu(II) and Pb(II) increased with increasing pH, the removal rates at pH 2.3 were 19% for Cu(II) and 11% for Pb(II), while the removal rates were 90% for Cu(II) and 55% for Pb(II) at pH 8.1. An explanation for the poor heavy metal removal at low pH is that under these conditions the solution contains high concentrations of H+ ions, which characteristically have high mobility and compete with the metal ions for the active sites on the adsorbents (Pellera et al., 2012). As the solution pH increases, the zeta potential of the biochar becomes more negative, which is favorable for cation adsorption (Jiang et al., 2016).
3.2. Significant factors governing the adsorption of Cu(II) and Pb(II) onto biochar: Solution salinity and pH Changes in seawater salinity and pH are most likely to occur in marine environments, and earlier studies have indicated that solution salinity and pH are important parameters affecting the adsorption behavior of heavy metals (Aksu and Balibek, 2007; Zou et al., 2016). However, there are very limited research data available at the present on the effect of salinity and pH on heavy metal adsorption by biochar. A better understanding of how those factors affect the removal of heavy metals by Enteromorpha derived biochar is needed as part of considering its potential uses. Fig. 2 shows the quantity of Cu(II) and Pb(II) removed by Enteromorpha derived biochar as a function of the solution salinity and pH.
3.3. Adsorption isotherms and kinetics The adsorption isotherm helps understanding of the interactions between heavy metals and the Enteromorpha derived biochar. Fig. 3 shows adsorption curves for the biochar as a function of the equilibrium concentration of heavy metals in solution. At lower concentrations, the removal rate of heavy metals increased markedly with increasing the concentration. However, the removal rate approached a constant value
Fig. 1. SEM image (a) and FTIR spectrum (b) of the biochar derived from Enteromorpha. 3
Marine Pollution Bulletin 149 (2019) 110586
W. Yang, et al.
Table 3 Constants for the Langmuir, Freundlich and Henry isotherms for Cu(II) and Pb (II) adsorption by Enteromorpha derived biochar (Experimental conditions: Biochar dose 30 g/L, Contact time 30 min, pH 8.1, and Salinity 35). Langmuir Q Cu(II) Pb(II)
0
254 98
Freundlich 2
Henry 2
A
r
Kf
n
r
Kp
r2
0.6 2.3
0.99 0.99
143 28
0.5 0.6
0.93 0.95
88 11
0.80 0.87
Fig. 4. Kinetics of adsorption of Cu(II) and Pb(II) onto Enteromorpha derived biochar.
with the Langmuir model. Consequently, it was assumed that adsorption mainly occurs in monolayers, or through a fixed number of identical and energetically equivalent sites on the surface. The adsorption capacity of Enteromorpha derived biochar was 254 mg/kg for Cu(II) and 98 mg/kg for Pb(II) (Table 3), which is comparable to those reported for biochar derived from other biomass materials (Park et al., 2016). Fig. 4 shows the rate of heavy metal removals by Enteromorpha derived biochar as a function of the contact time (0 to 60 min). As anticipated, the adsorption kinetics showed an initial increase in the rate with time, but the rate plateaued as equilibrium was reached. The best curve fit to the experimental data showed that variations in the removal rate with contact time could be described by Eq. (6) (Sun et al., 2014):
Fig. 2. Rates of removal of Cu(II) and Pb(II) by Enteromorpha derived biochar as functions of solution salinity and pH.
at higher concentrations. The parameters and correlation coefficients (r2) are shown in Table 3. Better fits were obtained using the Langmuir model than the Freundlich or Henry models, suggesting that the mechanism of heavy metal adsorption onto biochar was more consistent
Removalrate (%) =
Rmax 1+e
t t0 b
(6)
where, Rmax is the maximum heavy metal removal rate by biochar, t is the contact time (min), t0 is the critical time when the removal rate is 50% of Rmax and when the removal rate reached its maximum, and b is a parameter that controls the shape of the curve. The maximum Cu(II) removal rate reached 91% within 60 min and the maximum rate of Table 4 Fitting parameters for the equations describing the kinetics of Cu(II) and Pb(II) adsorption onto Enteromorpha derived biochar.
Cu(II) Pb(II)
Fig. 3. Isotherms for Cu(II) and Pb(II) adsorption onto Enteromorpha derived biochar. The line is the fitted line based on the Langmuir adsorption isotherm. 4
r2
Rmax (%)
t0 (min)
b
0.94 0.97
91 54
7 11
8 9
Marine Pollution Bulletin 149 (2019) 110586
W. Yang, et al.
equilibrium concentration of the non-adsorbed heavy metals in solution, then the mass balance describing the adsorption equilibrium (Eq. (8)) was: (8)
C0 = Cd + Cp
Eqs. (1), (7), and (8) can be rearranged to enable calculation of the removal rate of heavy metals at varying biochar concentrations according to Eq. (9):
Removal rate (%) =
increase of the adsorption occurred at 7 min. For Pb(II) the maximum removal rate was 54% within 60 min, and the maximum increase in the rate of the reaction occurred at 11 min (Table 4). Our results are consistent with those of Ofomaja (2010), who reported that the adsorption kinetics for heavy metals depended greatly on the physical and/or chemical characteristics of the biochar. The initially high removal rate was attributed to the presence of bare active sites on the surface of the biochar. As available sites become occupied by heavy metals, the system will tend to reach an equilibrium between adsorption and desorption processes (Bhaumik et al., 2016). 3.4. Model for adsorption of Cu(II) and Pb(II) by Enteromorpha derived biochar The relationship between the heavy metal removal rate and the biochar concentration in aqueous solution was of interest because the two factors appeared to be related (Fig. 5). The adsorption of heavy metals onto biochar has been reported to be enhanced by increasing the amount of biochar in solution, because of the increased concentration of adsorption sites (Li et al., 2017). Adsorption is an important heavy metal scavenging process. The occurrence of such a relationship suggests that solute-particulate interactions may play a dominant role in controlling the concentrations of heavy metals. The partitioning of heavy metals between solid and solution phases is often described by a conditional parameter, in terms of an empirical distribution coefficient (Kd, units L·g−1), which is defined as (Alloway, 1990):
C0 Cd Cd × [Biochar ]
(9)
Based on our hypothesis, Eq. (9) provides a model for estimation of the heavy metal removal rate as a function of the biochar concentration. Using this equation, five curves were generated with Kd values ranging from 0.02 to 1 L·g−1 (Fig. 5, dashed lines). Fig. 5 shows that the Cu(II) and Pb(II) data fall well in the zone defined by the Kd values of 0.5 and 0.02 to 0.05 L·g−1, respectively. To a certain circumstance, our results suggested a quasi-equilibrium distribution of heavy metals between the dissolved and adsorbed phases under the role of biochar, and we can conclude that the reactions determining adsorption onto biochar were likely to be a significant factor in controlling the removal of heavy metals from the water column. Fig. 5 also reveals that Kd values decreased with increasing biochar concentrations, consistent with the “particle concentration effect” (O'Connor and Connolly, 1980), this is linked to the particle concentration, composition, and the characteristics of the adsorbent and solution. There are limitations associated with this model: 1) We assumed that the adsorption reaction was completely reversible and an equilibrium reaction, which is unrealistic; 2) we did not take into consideration other effects, such as temperature and salinity, which could significantly change the removal behavior and 3) Kd is an empirical and conditional parameter, and the data used here may overestimate in reality circumstance. Despite some deficiencies in the model, the trend in Fig. 5 suggests our model did provide a method for predicting the removal of heavy metals by the biochar in seawaters, and this could be a potential approach to describing heavy metal adsorption onto biochar in an aquatic system.
Fig. 5. Adsorption model for the removal of Cu(II) and Pb(II) by Enteromorpha derived biochar. Note: The dashed lines represent the model results computed using Eq. (9), with Kd values from 0.02 to 1 L·g−1.
Kd =
K d [Biochar ] 1 + K d [Biochar ]
4. Conclusions The present work focused on treatment of seawater contaminated with heavy metals using an environmentally benign biochar derived from Enteromorpha. The Cu(II) and Pb(II) adsorption was significantly affected by the biochar dose, pH, contact time, and salinity. The adsorption isotherm fitted well to the Langmuir isotherm model, whereas the kinetics of adsorption of Cu(II) and Pb(II) onto the biochar was best represented by a 3-parameter sigmoidal kinetic model. The heavy metal adsorption capacity of the biochar was approximately 254 mg/kg for Cu (II) and 98 mg/kg for Pb(II) in typical marine environments. The results showed that Enteromorpha derived biochar may be an effective and benign heavy metal adsorbent, and a useful value-adding byproduct.
(7)
where, (C0 − Cd) is the concentration of heavy metals adsorbed onto biochar (mg/L). The value of Kd is highly sensitive to adsorbent type and concentration, and varies over a large range (Abo-Farha et al., 2009; Muya et al., 2016; Park et al., 2016). It can be derived by Eq. (7) or from empirical model calculations. The Kd could be used to address the solute-particulate balance in the exchange of metal species in aqueous systems (Yantasee et al., 2007). Heavy metals adsorbed onto the biochar are assumed to be part of the particulate phase, while the non-adsorbed heavy metals in solution were taken to be the dissolved phase. We assumed that the heavy metals in the aqueous solution were scavenged only through the adsorption process, and as the biochar provided limited surface sites for adsorption, the adsorption reaction would reach equilibrium. If C0 was defined as the initial concentration of heavy metals in the water column, Cp was the concentration of heavy metals adsorbed onto biochar at equilibrium, and Cd was the
Acknowledgements The authors are grateful to colleagues at the College of Dalian Maritime University for their help with the test work. This work was supported by the National Natural Science Foundation of China (41806128, 51879019), and the Fundamental Research Funds for the Central Universities (3132018179). References Abo-Farha, S.A., Abdel-Aal, A.Y., Ashour, I.A., Garamon, S.E., 2009. Removal of some heavy metal cations by synthetic resin purolite C100. J. Hazard. Mater. 169 (1–3), 190–194. Aksu, Z., Balibek, E., 2007. Chromium (VI) biosorption by dried Rhizopus arrhizus: effect of salt (NaCl) concentration on equilibrium and kinetic parameters. J. Hazard. Mater.
5
Marine Pollution Bulletin 149 (2019) 110586
W. Yang, et al. 145 (1–2), 210–220. Aksu, Z., İşoğlu, I.A., 2005. Removal of copper (II) ions from aqueous solution by biosorption onto agricultural waste sugar beet pulp. Process Biochem. 40 (9), 3031–3044. Allen, S.J., Gan, Q., Matthews, R., Johnson, P.A., 2003. Comparison of optimised isotherm models for basic dye adsorption by kudzu. Bioresour. Technol. 88 (2), 143–152. Alloway, B.J., 1990. Soil processes and the behavior of metals. In: Heavy Metals in Soils, pp. 7–27. Batool, S., Idrees, M., Hussain, Q., Kong, J., 2017. Adsorption of copper (II) by using derived-farmyard and poultry manure biochars: efficiency and mechanism. Chem. Phys. Lett. 689, 190–198. Bhaumik, M., Agarwal, S., Gupta, V.K., Maity, A., 2016. Enhanced removal of Cr (VI) from aqueous solutions using polypyrrole wrapped oxidized MWCNTs nanocomposites adsorbent. J Colloid Interf Sci 470, 257–267. Demirbas, A., 2008. Heavy metal adsorption onto agro-based waste materials: a review. J. Hazard. Mater. 157 (2–3), 220–229. Di Natale, F., Lancia, A., Molino, A., Musmarra, D., 2007. Removal of chromium ions form aqueous solutions by adsorption on activated carbon and char. J. Hazard. Mater. 145 (3), 381–390. Fu, F., Wang, Q., 2011. Removal of heavy metal ions from wastewaters: a review. J. Environ. Manag. 92 (3), 407–418. Guo, Y., Yeh, T., Song, W., Xu, D., Wang, S., 2015. A review of bio-oil production from hydrothermal liquefaction of algae. Renew. Sust. Energ. Rev. 48, 776–790. Harun-Al-Rashid, A., Yang, C.S., 2018. Hourly variation of green tide in the Yellow Sea during summer 2015 and 2016 using Geostationary Ocean Color Imager data. Int. J. Remote Sens. 39 (13), 4402–4415. Harvey, P.J., Handley, H.K., Taylor, M.P., 2016. Widespread copper and lead contamination of household drinking water, New South Wales, Australia. Environ. Res. 151, 275–285. Jiang, S., Huang, L., Nguyen, T.A., Ok, Y.S., Rudolph, V., Yang, H., Zhang, D., 2016. Copper and zinc adsorption by softwood and hardwood biochars under elevated sulphate-induced salinity and acidic pH conditions. Chemosphere 142, 64–71. Khelifa, A., Hill, P.S., Stoffyn-Egli, P., Lee, K., 2005. Effects of salinity and clay composition on oil-clay aggregations. Mar. Environ. Res. 59 (3), 235–254. Lapointe, B.E., Burkholder, J.M., Van Alstyne, K.L., 2018. Harmful macroalgal blooms in a changing world: causes, impacts, and management. In: Harmful Algal Blooms: A Compendium Desk Reference, pp. 515–560. Li, B., Yang, L., Wang, C.Q., Zhang, Q.P., Liu, Q.C., Li, Y.D., Xiao, R., 2017. Adsorption of Cd (II) from aqueous solutions by rape straw biochar derived from different modification processes. Chemosphere 175, 332–340. Muya, F.N., Sunday, C.E., Baker, P., Iwuoha, E., 2016. Environmental remediation of heavy metal ions from aqueous solution through hydrogel adsorption: a critical
review. Water Sc Technol 73 (5), 983–992. O’Connor, D.J., Connolly, J.P., 1980. The effect of concentration of adsorbing solids on the partition coefficient. Water Res. 14 (10), 1517–1523. Ofomaja, A.E., 2010. Intraparticle diffusion process for lead (II) biosorption onto mansonia wood sawdust. Bioresour. Technol. 101 (15), 5868–5876. Park, S.H., Cho, H.J., Ryu, C., Park, Y.K., 2016. Removal of copper (II) in aqueous solution using pyrolytic biochars derived from red macroalga Porphyra tenera. J. Ind. Eng. Chem. 36, 314–319. Pellera, F.M., Giannis, A., Kalderis, D., Anastasiadou, K., Stegmann, R., Wang, J.Y., Gidarakos, E., 2012. Adsorption of Cu(II) ions from aqueous solutions on biochars prepared from agricultural by-products. J. Environ. Manag. 96 (1), 35–42. Qian, K., Kumar, A., Zhang, H., Bellmer, D., Huhnke, R., 2015. Recent advances in utilization of biochar. Renew. Sust. Energ. Rev. 42, 1055–1064. Salam, M.A., Paul, S.C., Noor, S.N.B.M., Siddiqua, S.A., Aka, T.D., Wahab, R., Aweng, E.R., 2019. Contamination profile of heavy metals in marine fish and shellfish. Glo J Environ Sci Manag 5 (2), 225–236. Subhadra, B., Edwards, M., 2010. An integrated renewable energy park approach for algal biofuel production in United States. Energ Policy 38 (9), 4897–4902. Sun, J., Khelifa, A., Zhao, C.C., Zhao, D.F., Wang, Z.D., 2014. Laboratory investigation of oil–suspended particulate matter aggregation under different mixing conditions. Sci. Total Environ. 473, 742–749. Tan, X., Liu, Y., Zeng, G., Wang, X., Hu, X., Gu, Y., Yang, Z., 2015. Application of biochar for the removal of pollutants from aqueous solutions. Chemosphere 125, 70–85. Villaescusa, I., Fiol, N., Martı́nez, M., Miralles, N., Poch, J., Serarols, J., 2004. Removal of copper and nickel ions from aqueous solutions by grape stalks wastes. Water Res. 38 (4), 992–1002. Yang, W.C., Li, X.G., Liu, S.S., Feng, L.J., 2014. Direct hydrothermal liquefaction of undried macroalgae Enteromorpha prolifera using acid catalysts. Energ Convers Manage 87, 938–945. Yantasee, W., Warner, C.L., Sangvanich, T., Addleman, R.S., Carter, T.G., Wiacek, R.J., Fryxell, G.E., Timchalk, C., Warner, M.G., 2007. Removal of heavy metals from aqueous systems with thiol functionalized superparamagnetic nanoparticles. Environ Sci Technol 41 (14), 5114–5119. Zhang, Y., Chu, C., Li, T., Xu, S., Liu, L., Ju, M., 2017. A water quality management strategy for regionally protected water through health risk assessment and spatial distribution of heavy metal pollution in 3 marine reserves. Sci. Total Environ. 599, 721–731. Zhu, Y.Y., Tang, W.Z., Jin, X., Shan, B.Q., 2019. Using biochar capping to reduce nitrogen release from sediments in eutrophic lakes. Sci. Total Environ. 646, 93–104. Zou, Y.D., Wang, X.X., Khan, A., Wang, P.Y., Liu, Y.H., Alsaedi, A., Hayat, T., Wang, X.K., 2016. Environmental remediation and application of nanoscale zero-valent iron and its composites for the removal of heavy metal ions: a review. Environ Sci Technol 50 (14), 7290–7304.
6