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leaf for fast and efficient removal of diclofenac
Journal Pre-proof Production of biochar from waste sludge/leaf for fast and efficient removal of diclofenac
Hao Zhang, Yao-Jen Tu, Yan-Ping Duan, Jin Liu, Weidi Zhi, Yu Tang, Li-Shan Xiao, Liang Meng PII:
S0167-7322(19)34552-0
DOI:
https://doi.org/10.1016/j.molliq.2019.112193
Reference:
MOLLIQ 112193
To appear in:
Journal of Molecular Liquids
Received date:
13 August 2019
Revised date:
20 November 2019
Accepted date:
21 November 2019
Please cite this article as: H. Zhang, Y.-J. Tu, Y.-P. Duan, et al., Production of biochar from waste sludge/leaf for fast and efficient removal of diclofenac, Journal of Molecular Liquids(2018), https://doi.org/10.1016/j.molliq.2019.112193
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© 2018 Published by Elsevier.
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Production of Biochar from Waste Sludge/Leaf for Fast and Efficient Removal of Diclofenac
Hao Zhanga, Yao-Jen Tua,b*, Yan-Ping Duana,b,
Pr
a
e-
pr
oo
f
Jin Liua, Weidi Zhia, Yu Tanga, Li-Shan Xiaoa,b, Liang Menga,b
School of Environmental and Geographical Sciences, Shanghai Normal University,
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No. 100, Guilin Rd., Shanghai 200234, China b
Jo u
200234, China
rn
Institute of Urban Study, Shanghai Normal University, No. 100, Guilin Rd., Shanghai
Corresponding author: Yao-Jen Tu TEL: +86-13661920584 E-mail: [email protected] 1
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Abstract Sludge and leaf are two kinds of typical solid wastes with huge production. How to effectively treat sludge/leaf thus becomes a hot issue and needs to be solved at present. This study aims to develop the resource recycling technology in converting waste sludge/leaf to biochar material for diclofenac (DFC) removal. Through the
f
orthogonal test design, the effects of pyrolysis temperature, sludge/leaf ratio, and
oo
pyrolysis time were systematically investigated. Under the conditions of pyrolysis
pr
temperature 200oC, sludge/leaf ratio 1:3, and pyrolysis time 1 h, the optimized
e-
biochar was simply produced where the key indicators iodine value and biochar yield
Pr
reached 287.81 mg/g and 85.15%, respectively. Adsorption results revealed that DFC was rapidly and efficiently adsorbed by the recycled sludge/leaf biochar at the
al
conditions of 25oC, initial DFC concentration of 10 mg/L, solution volume of 8 mL,
rn
and biochar dosage of 0.005 g. With the maximum adsorption capacity of 877 mg/g,
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the DFC adsorption process was described well by pseudo-second order kinetics and Temkin isotherm model. Furthermore, after activation by 9% HCl solution, the specific surface area of the biochar increased from 3.30 to 4.17 m2/g, indicating that activated biochar had more sites for DFC adsorption. That was also confirmed by SEM images which showed more porous and rough characteristics on the surface structure of biochar. The data displayed a green environmental technique in converting waste sludge/leaf to useful biochar adsorbent for rapid and efficient DFC removal. Keywords: Waste sludge, waste leaf, recycling, biochar, diclofenac 2
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1. Introduction The compositions of industrial and domestic sludge contain variety of harmful heavy metals, organic compounds, and pathogenic microorganisms. Without appropriate treatment, sludge will pose great harm to human life and the natural environment[1]. Up to 2017, China has already built 4063 sewage treatment plants and
f
the treatment capacity can reach 178 million m3/d with municipal sludge produced in
oo
30-40 million tons/year (80% moisture content). The estimated municipal sludge may
pr
approach 60-90 million tons/year by 2020[2]; hence the treatment and disposal of
e-
sludge has become one of the hot issues that need to be solved urgently. At present,
Pr
the treatment and disposal of sludge include landfill, incineration, aerobic compost, land use, building materials use and other aspects. Among mentioned above, landfill,
al
incineration, aerobic compost plus land use, natural dry comprehensive utilization,
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open air stacking, and overseas transportation individually account for 60-65%, 2-3%,
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10-15%, 3-6%, 2%, and 15%, respectively. Generally speaking, sludge landfill, outdoor stacking and outward transport are disposed casually[3]; therefore, the secondary pollution will be inevitably occurred and bring far greater harm than wastewater discharge. The living environment would thus become worse and the ecological system may become difficult to remediate[4]. City green-clustered landscapes generate a huge amount of leaves which are easy to collect. However ecological circulation mechanism is suspended once these leaves were taken to a landfill. Beyond that, leaves mixed with garbage, not conducive to urban garbage reduction, will generate more disposal problems[5]. Traditional leaves 3
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treatment methods include incineration, landfill, etc. However, in terms of the environmental impact, the aforementioned simple treatment methods may not only cause serious pollution to the environment but also result in the waste of leaves resources[6].
Many
previous
literatures
focused
on
sludge
properties
of
biodegradation[7], fermentation[8], biogas production[9], and adsorption[10]. Only few
f
reports were discussed on their properties of biochar production. So the cotonier
oo
leaves were selected as one of the original materials for preparation of biochar in this
pr
study. Currently, the comprehensive utilization of the fallen leaves are the preparation
e-
of feed and composting, etc[11]. However, these methods have not been widely used in
Pr
city. Therefore, it is necessary to explore a reasonable and effective treatment of fallen leaves.
al
Generally speaking, biochar is a carbon-rich and porous solid produced from
rn
biomass via pyrolysis in the absence of oxygen[12]. The International Biochar
Jo u
Initiative (IBI) standardized its definition as “a solid material obtained from the thermochemical conversion of biomass in an oxygen-limited environment”[13]. With a well-developed pore structure, very large surface area, high stability, and exceptional adsorption properties, biochar has great potential in the application of many fields [14]. Currently, some scholars have studied the preparation of biochar by pyrolysis of straw, chestnut shell, chicken manure, pineapple waste, and pomelo peel[15-19]. However, few studies focused on the pyrolysis of biomass in mixing of waste sludge and leaves. Besides, very rare work was found in investigating biochar’s adsorption behavior of Pharmaceuticals and Personal Care Products (PPCPs). If these waste sludge/leaves 4
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can be converted to a useful material, not only the problem that waste sludge and leaves has nowhere to go is solved, but the useful biochar material is also produced. Besides, it can further help us to evaluate the prospect of homemade biochar as an adsorption material in the application of removal emerging contaminants. It should be addressed that PPCPs is the general term of a new class of organic pollutants, including all kinds of antibiotic, diet pills, hypnotics, steroid, cosmetics,
oo
f
hair dye and fungicide etc, which are closely associated with people’s daily lives[20].
pr
In 1999, this concept has been first published in《Environmental Health Perspectives》
e-
and put forward by Daughton and Ternes[21]. Owing to the strong of bioactive, bioaccumulation, and durability characteristic of PPCPs, the human health and
Pr
ecological risk are difficult to be estimated if they are in the long-term exposure[22]. It
al
should be known that there is no unique technology designed for PPCPs removal in
rn
conventional sewage treatment plants. This is the reason why PPCPs cannot be
Jo u
removed efficiently by the current urban sewage treatment plants[23]. Thus how to effectively treat PPCPs has gradually begun a hot issue all over the world. Among
all
PPCPs,
diclofenac
(DFC)
is
regarded
as
non-steroidal
anti-inflammatory drugs which is widely used in analgesic, arthritis drug, and medicines to treat rheumatism[24,25]. It has been reported that about 65% DFC is expelled from urine in the form of hydroxy metabolites after oral administration[26]. When DFC enters into the environment, it is difficult to be biodegraded and transformed by microorganisms. Consequently, the aquatic ecosystems and human health would be potentially threatened because of the living organisms’ accumulation 5
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and amplification of DFC from food chain. In addition, it should be emphasized that the aqueous DFC cannot be effectively removed from traditional wastewater treatment technology. It is hence necessary to find a simple, costless, and effective way to remove DFC from water systems. A series of batch experiments were performed to evaluate the capability of the produced biochar for aqueous DFC
f
removal. The key parameters (pyrolysis temperature, pyrolysis time, sludge/leaf ratio)
oo
for preparation biochar were investigated in detail. Further kinetics and isotherms of
pr
adsorption of DFC on produced biochar were also systematically discussed. The
Pr
for DFC removal from water system.
e-
information obtained implied great potential for developing a cost-effective biochar
2. Material and methods
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2.1 Preparation and activation of biochar from waste sludge/leaves
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The raw sludge, with 65% moisture content, was collected from a sludge drying
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plant in China. After drying process, the sludge was crushed by soil grinding machine (XDB050304, Beijing new landmark soil equipment) and then sieved through 100-mesh screen cloth. The waste leaves were collected from cotonier during autumn and winter season at the university campus of Shanghai, China. The waste leaves were ultrasonic washed firstly, then crushed by soil grinding machine and sieved through 100-mesh screen cloth. The pretreated sludge and leaf powders were placed in the crucibles. After covered by excessive nitrogen, they were put in the box-type muffle furnace. The reaction temperature was set to 200-500oC at a rate of 6oC per minute. The resource 6
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recycled biochar was then produced after 1-5 h pyrolysis. The optimum preparation parameters of biochar were evaluated by iodine value (GB/T 12496.8-2015) and biochar yield. The steps for determination of iodine value can be briefly described as follows. Put 0.5 g sample into a 250 mL corked conical flask and add 10 mL 5% of hydrochloric acid accurately into the flask. The sample was heated to boiling point on
f
an electric furnace for (30±2) seconds. After cooling to room temperature, 50 mL
oo
iodine standard solution was added to the flask. Plug the bottle cap immediately and
pr
oscillate the flask for 15 minutes. Filtrate it quickly into the dry beaker. 10 mL filtrate
e-
was then absorbed into a 250 mL wide-mouth conical flask which contains 100 mL
Pr
distilled water. Finally, the standard solution of sodium thiosulfate was then used for titration. The iodine value of biochar was calculated according to the volume of
al
sodium thiosulfate consumed. With the activation time of 24 h, the four reagents
rn
hydrochloric acid, phosphoric acid, sulfuric acid, and hydrogen peroxide at different
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concentration were employed to activate the produced biochar. After activation, the biochar was dried in an electric thermostatic air drying box. The DFC adsorption efficiency and cost of produced biochar were taken into consideration for determining the optimum activator and the activation method. Additionally, to understand the effect of activation to the biochar for DFC adsorption, various concentrations of hydrochloric acid (HCl 9, 18, and 36%), phosphoric acid (H3PO4 21 and 43%), sulfuric acid (H2SO4 25 and 45%), and hydrogen peroxide (H2O2 10 and 20%) were applied to activate the produced biochar. The activated biochars were then examined for their DFC adsorption efficiency. 7
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2.2 Batch adsorption Orthogonal experiment was applied to investigate the optimum preparation conditions of biochar. Pyrolysis temperature, sludge/leaf ratio and pyrolysis time were used as the three factors where each factor includes four levels. The pyrolysis temperature is set to 200, 300, 400, and 500oC, sludge/leaf ratio is set to 0 (leaf), 1:3,
f
1:1, 3:1, and pyrolysis time is set to 1 h, 2 h, 3 h, 5 h.
oo
Weigh 0.05 g samples of unactivated biochar, activated biochar and commercial
pr
activated carbon (named as U-BC, A-BC, C-AC, respectively). Then U-BC, A-BC,
e-
C-AC were put into 15 mL plastic centrifuge tube with 10 mg/L DFC solution of 8 mL. The batch kinetic adsorption was performed under the conditions of 45 rpm,
Pr
25oC, adsorbent dosage 0.05 g, and volume 8 mL. The sample collection time was
al
designed at the gradient from 1 to 240 min where each time point has three parallel
rn
experiments. The supernatant was taken out and the DFC residual concentration was
Jo u
determined by high performance liquid chromatography (HPLC). The adsorption kinetic characteristics were investigated by fitting pseudo-first order and pseudo-second order kinetic equations. The adsorption capacity calculation equation, pseudo-first order kinetic equation, pseudo-second order kinetic equation can be expressed as Eqs. (1)-(3). Adsorption capacity calculation equation: （C - C ）*V Qe t e m
(1)
pseudo-first order kinetic equation: ln（Qe-Qt）=lnQe-k1t
(2) 8
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pseudo-second order kinetic equation: t 1 t 2 Qt k 2 Q e 2 Qe 2
(3)
In Eqs. 1-3, where Qe is the adsorption capacity at equilibrium time, mg/g; Qt is the adsorption capacity at t time, mg/g; K1 is the pseudo-first order rate constant, 1/min; K2 is pseudo-second order rate constant, g/(mg·min).
oo
f
The isothermal adsorption experiments were conducted similarly as batch kinetic experiment. Under the conditions of 45 rpm, 25oC, adsorbent dosage 0.005 g, and
pr
volume 8 mL, DFC initial concentration 10 to 500 mg/L, the supernatant was taken at
e-
the equilibrium time and the residual concentration was determined by HPLC. To
Pr
study the adsorption isotherm process of DFC solution onto biochar, Langmuir, Freundlich, Temkin isotherm models (Eqs. 4-6, respectively) were examined for their
al
abilities to accurately describe the adsorption process. The Langmuir model is an
rn
ideal model, which assumes that the solution is an ideal solution and the surface is a
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single molecular layer adsorption process. The Freundlich model is an empirical model, which is generally used to describe the process of surface adsorption as single layer or multi-layer adsorption. It is generally believed that in Freundlich model when 1/n is less than 0.5, adsorbents are easy to be adsorbed. When 1/n is larger than 2, it is difficult to be adsorbed[27]. Temkin model mainly describes the chemical adsorption process dominated by electrostatic adsorption[28]. The mathematical expressions of the three models are as follows: Langmuir isotherm equation
9
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Ce 1 1 Ce qe QmaxK L Qmax
Freundlich isotherm equation 1
(5)
qe K f C e n
Temkin isotherm equation qe
RT RT ln K T ln Ce bT bT
(6)
f
Where Qe is the adsorption capacity at equilibrium time, mg/g; KL is Langmuir
oo
constant, L/mg; Qmax is the maximum adsorption capacity, mg/g; Kf is Freundlich
pr
constant, L/mg; 1/n is the heterogeneity of the sorption sites and an indicator of
e-
isotherm nonlinearity; KT is the equilibrium binding constant, L/mg; bT is the Temkin
Pr
isotherm constant.
2.3 Characterization of the produced biochar
al
The surface functional group distribution of biochar samples was analyzed by
rn
FTIR (Nicolet iS5, Thermo Fisher Scientific) which can accurately analyze the
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changes of functional groups on the surface of biochar materials caused by surface modification and adsorption. The KBr pellet method was adopted here for the produced biochar. The detection wavelength range is from 400-4000 cm-1 at the scanning step size to 1 cm-1. Specific surface area, pore volume, and pore diameter were obtained from BET instrument (ASAP2390 series, McMuratick). The BET equation is based on the theory of multilayer adsorption, and the material is closer to the actual adsorption process; therefore the results are more accurate. In this experiment, the sample was vacuum dried for 2 h at 300oC for removing moisture and miscellaneous gases. Under the condition of 196.15oC, liquid nitrogen was used for 10
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adsorption and desorption experiments and for analyzing surface area and pore size distribution of materials. Surface micro-characteristics of prepared adsorbent were investigated by scanning electron microscope (S-4800, Hitachi), which can observe the microstructure of sludge/leaf and biochar before and after activation. In this experiment, the samples were placed on the electrical tape, sprayed with gold and
f
then placed under SEM for observation and photography.
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3. Results and discussion
pr
3.1 Optimum parameters for producing biochar
e-
As can be seen in Fig. 1, with the increase of temperature (200 to 500oC),
Pr
biochar yield decreased from 85.15 to 29.71% where iodine values increased from 287.81 mg/g to 324.53 mg/g. During the preparation of biochar, pyrolysis temperature
al
is an important factor affecting the physical and chemical properties of biochar. With
rn
the increase of temperature, the degree of carbonization of biochar would increase.
Jo u
The number of micropores would increase correspondingly which would lead to the increase of iodine value[29]. Generally, the yield of biochar decreases with the increase of temperature while the carbon content, ash content, specific surface area and porosity of biochar increase with the increase of temperature[30-32]. Hossia et al. also found that the yield of biochar would change with the change of temperature which can be concluded in the trend of the higher the temperature, the lower the biochar yield[33]. The temperature 200oC was then selected as the optimum temperature for biochar preparation owing to the consideration of biochar yield, iodine value, and preparation cost. 11
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Fig. 2 showed the influence of sludge and leaf ratio on biochar preparation. As indicated here, with the increase of the leaf content in the sludge/leaf ratio, both iodine value and biochar yield increase and then decrease. When the sludge/leaf ratio is 1:3, the iodine value of biochar reaches 287.81 mg/g, and the yield reached 85.15%. Considering that this phenomenon is caused by the difference in composition between
f
sludge and leaf, the volatile content of sludge is relatively low. Xiang et al. used the
oo
co-pyrolysis of sludge and bagasse to prepare biochar and found that increasing the
pr
amount of bagasse can improve the iodine value of biochar [34]. Adding bagasse can
e-
improve the carbon content in activated sludge, further increasing the carbon amount
Pr
in pyrolysis of biochar. Hence the adsorption performance is improved accordingly. Contrarily, Zhou et al. used the co-pyrolysis of sludge and straw to prepare biological
al
activated carbon. When the amount of straw increased, the carbon content of biochar
rn
increased, but the adsorption property reduced[35]. This may be due to the change of
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pore structure in biochar. Therefore, it can be concluded that the ratio of sludge and leaf is a key parameter for biochar’s adsorption performance, but the effect can be positive or negative.
Fig. 3 displayed the influence of pyrolysis time on biochar preparation. As can be seen in Fig. 3, the iodine value decreased from 287.81 to 234.61 mg/g, and the biochar yield decreased from 85.15 to 71.33% when the pyrolysis time increased from 1 to 5 h. Tay et al. has used co-pyrolysis method for biochar preparation using sludge and coconut shell. They observed that the biochar yield would change with the pyrolysis time. Increasing pyrolysis time may increase the pore structure of biochar, 12
Journal Pre-proof however, the pore structure would not increase beyond a certain pyrolysis time[36]. In our case, the maximum iodine value and biochar yield were observed at 1 h pyrolysis time. It is speculated that after the broken and screened pretreatment, the particle size of sludge and leaves is small enough for the fast reaction of pyrolysis. This is consistent with the result found by Fan et al.[37]. The summarized and detailed
f
orthogonal experimental design and data were displayed in Table 1.
oo
To sum up, the optimum biochar preparation condition can be concluded as:
pr
pyrolysis temperature 200oC, sludge/leaf ratio 1:3, and pyrolysis time 1 h. Under this
e-
condition, the maximum iodine value and biochar yield reached 287.81 mg/g and
Pr
85.15%, respectively.
Table 2 demonstrated the comparison of DFC adsorption efficiency by various
al
activation reagents. The data shown in Table 2 obviously tell us that activation can
rn
improve the characteristic of biochar, further facilitating materials’ DFC adsorption
Jo u
efficiency. After 12 h adsorption, 100% DFC can be removed from solutions using biochars activated by HCl (9, 18, and 36%), H3PO4 (21 and 43%), and H2SO4 (25 and 45%). Compared to unactivated biochar (58.4% DFC adsorption efficiency), these activated biochars own more adsorptive site in removing DFC from water. Take the economic costs and test security into consideration, 9% HCl was chosen as the most adequate activator to activate the biochar. 3.2 Adsorption kinetics Fig. 4 illustrated the comparison of adsorption capacity between A-BC, U-BC, and C-AC. Evidently, all three adsorbents can reach adsorption equilibrium under the 13
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conditions of DFC concentration 10 mg/L, volume 8 mL, adsorbent dose 0.05 g, and contact time 240 min. It should be noticed that A-BC possesses the fastest adsorption rate among the three adsorbents. The adsorption efficiency of A-BC can reach 89.51% in 10 min while the adsorption efficiency of C-AC and U-BC only can reach 12.24% and 70.07% in 10 min. Lonappan use pine wood and pig manure to manufacture biochar for DFC removal[38]. The results displayed that under the conditions of DFC
oo
f
concentration 2 mg/L, pH 6.5, adsorbent dose 0.1 g, temperature 25±1oC, pine
pr
biochar reached equilibrium after 4.5 h and pig manure biochar reached equilibrium
e-
after 5 h. Compared to pine biochar and pig manure biochar, the equilibrium time of
Pr
the A-BC is much shorter which would cut the cost when it was applied in practice. Pseudo-first order and pseudo-second order kinetic equations of A-BC were
al
shown in Fig. 5. As can be seen in Fig. 5, the R2 of pseudo-first order kinetic and
rn
pseudo-second order kinetic equation is 0.9782 and 0.9999, respectively, implying
Jo u
that pseudo-second order model owns better fit than pseudo-first order model for simulating the kinetic process. Since the pseudo-second order equation includes external liquid film diffusion, surface adsorption, and internal particle diffusion, etc. Thus, the adsorption mechanism of DFC on sludge/leaf biochar can be more comprehensively reflected by pseudo-second order model[39]. 3.3 Adsorption isotherm Fig. 6 shows the adsorption isotherm curve of DFC solution onto sludge/leaf biochar. Evidently, the used three isothermal adsorption equations (Langmuir, Freundlich, and Temkin) can fit well the adsorption process. The Temkin isotherm 14
Journal Pre-proof owns high R2 value (0.9732), implying that electrostatic adsorption is an important mechanism for the interaction between sludge/leaf biochar and DFC. Furthermore, the parameter 1/n shown in Freundlich equation can reflect the feasibility of adsorption. The result indicated that the 1/n value of DFC adsorbed by sludge/leaf biochar was 0.508, indicating that this temperature (25oC) is conducive to adsorption. Table 3 listed DFC adsorption isotherm parameters on various materials biochar,
oo
f
ferrite magnets and other materials[38, 40-43]. The result revealed that among these
pr
materials, the adsorption capacity of A-BC can reach 877 mg/g by using Langmuir
e-
model, further implying that the produced biochar has great potential in DFC removal
Pr
from water system.
3.4 Characterization of sludge/leaf biochar
al
Table 4 summarized the specific surface area, pore diameter, and pore volume of
rn
U-BC, A-BC, and DFC-A-BC. It can be found that the specific surface area of biochar
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increased from 3.2999 to 4.1741 m2/g after activation. However, after adsorption of DFC, the specific surface area of the adsorbent (DFC-A-BC) decreased to 0.0880 m2/g. The pore diameter increased from 6.7365 to 11.6928 nm after activation, while it decreased to 11.3034 nm after DFC adsorption. In addition, the pore volume rose from 0.00313 to 0.00372 cm3/g after the activation of biochar while it decreased to 0.00017 cm3/g after DFC adsorption. The result further implied that activation is favorable to the release of the pore. The specific surface area and pore volume of biochar would increase by the released pores, which also improved their DFC adsorption performance. 15
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SEM images of sludge (S), leaf (L), U-BC and A-BC were displayed in Fig. 7. Obviously, the structure of sludge is relatively dense, but the pore structure is relatively dispersed (Fig. 7a). The structure of leaf surface presented a terrier state (Fig. 7b), indicating that the main components were cellulose and hemicellulose. More pore structure and coarse surface were observed in the produced biochar (Fig.
f
7c), implying that biochar has the potential to be an adsorbent. After activation, the
pr
increasing surface pores and the rough surface.
oo
biochar can be regarded as a porous carbon adsorption material owing to the
e-
FTIR spectra of sludge (S), leaf (L), U-BC and A-BC were shown in Fig. 8. It can be found that the peak of its spectrum mainly vibrated around 3152 cm-1 (C-H
Pr
stretching), 2853 cm-1 (aliphatic C−H group), 1620 cm-1 (C=O stretching), 1385 cm-1
al
(Aromatic C=C stretching), 1041 cm-1 (C-O-H stretching), but it has some offset. For
rn
instance, C=O stretching of sludge vibrated from 1649 cm to 1620 cm-1. The peak of
Jo u
sludge and leaf vibrating at 1724 cm-1 (Esters C=O stretching) was disappeared due to pyrolysis. After the activation of biochar, a new peak can be seen at 2335 cm-1 (Aliphatic C≡O stretching). It can be seen that the compounds of protein, seters, aliphatic, and cellulose were decomposed gradually during the preparation of biochar while the aromaticity of the produced biochar was increased[44]. 4. Conclusion (1) A resource recycling technology in converting waste sludge/leaf to biochar material was established in this study. Besides, these biochar can be used as a fast and effective adsorbent for DFC removal from water system. 16
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(2) The optimal conditions for preparing biochar from sludge and leaf were pyrolysis temperature of 200oC, sludge/leaf ratio of 1:3, and pyrolysis time of 1 h. Under the optimal conditions, the iodine value and yield of biochar reached 287.81 mg/g and 85.15%, respectively. (3) The specific surface area of activated sludge/leaf biochar increased from 3.30 to
oo
to the improvement of DFC adsorption performance.
f
4.17 m2/g and the adsorption rate accelerated, indicating that activation was beneficial
pr
(4) The DFC adsorption onto sludge/leaf biochar conformed to pseudo-second order
e-
kinetics model (R2 is 0.9999), implying that chemical reaction/chemical adsorption
Pr
could be interpreted as the main process of adsorption. (5) After activation, the adsorption capacity of biochar can be significantly enhanced.
al
With the maximum adsorption capacity of 877 mg/g, the DFC adsorption process can
Jo u
rn
be described well by Langmuir, Freundlich, and Temkin isotherms.
Acknowledgments
This research is sponsored by National Major Program Social Science Fund of China (17ZDA058), Ministry of Science and Technology National Key Research and Development Program (2016YFC0502706), Shanghai Natural Science Foundation (17ZR1420700), and National Natural Science Foundation of China (41601514, 41971257, 41730642, 41877425).
17
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13. Standardized product definition and product testing guidelines for biochar that is used in soil. International Biochar Initiative, April 2012. 14. Y.X. Liu, S. Yao, Y.Y. Wang, H.H. Lu, K.B. Satinder, S.M. Yang, Bio- and hydrochars from rice straw and pig manure: Inter-comparison, Bioresour. Technol. 235 (2017) 332-337. 15. C. Liang, Y. Hu, M. Ji, W. Sang, D. Li, Adsorptive characteristics of rice straw biochar on composite heavy metals Cd2+ and Pb2+ in soil (in Chinese), Res. Environ. Sci. 1 (2019) 1-12. 16. K.M. Jiang, C.G. Cheng, M. Ran, Y.G. Lu, Q.L. Wu, Preparation of a biochar 19
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with a high calorific value from chestnut shells, New. Carbon. Mater. 33 (2018) 183-187. 17. J.G. Yu, X.W. Zhang, D. Wang, P. Li, Adsorption of methyl orange dye onto biochar adsorbent prepared from chicken manure, Water Sci. Technol. 77 (2018) 1303-1312.
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18. K. Napat, R. Patrick, E.U. Apiluck, Characterization of activated biochar
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prepared from pineapple waste for metal catalyst support, Suran. J. Sci. Technol.
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19. X.Y. Song, G.X. Pan, Y.W. Bai, F Liang, J.J. Xing, J. Gao, F.N. Shi,
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Preparation and electrochemical properties of biochar from pyrolysis of pomelo peel via different methods, Fuller. Nanotub. Car. N. 5 (2019) 453-458.
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sewage treatment plant of northwest Spain, Water Sci. Technol. 52 (2005) 29-35. 21. C.G. Daughton, T.A. Ternes, Pharmaceuticals and personal care products in the environment: agents of subtle change? J. Nation. Inst. Environ. Health. Sci. 107 (1999) 907-938. 22. M.L. Wu, Research status and removal of pharmaceuticals and personal care products in urban water environment (in Chinese), Water Purifica. Technol. S1 (2018) 230-234. 23. H.D. Zhou, X. Huang, X.H. Wen, Progress of the studies on occurrence and fate of new emerging micro-pollutants-PPCPs in municipal wastewaters (in Chinese), 20
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J. Environ. Eng. 12 (2007) 1-9. 24. J.L. Liu, M.H. Wong, Pharmaceuticals and personal care products (PPCPs): A review on environmental contamination in China, Environ. Int. 59 (2013) 208-224. 25. Q. Bu, B. Wang, J. Huang, Pharmaceuticals and personal care products in the
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aquatic environment in China: A review, J. Hazard. Mater. 262 (2013) 189-211.
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26. Y. Zhang, S.U. Geißen, C. Gal, Carbamazepine and diclofenac: Removal in
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wastewater treatment plants and occurrence in water bodies, Chemosphere 73
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(2008) 1-11.
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27. L. Shi, G. Zhang, D. Wei, Preparation and utilization of anaerobic granular sludge-based biochar for the adsorption of methylene blue from aqueous solution,
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J. Mol. Liq. 198 (2014) 334-340.
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28. M. Ahmad, S.S. Lee, A.U. Rajapaksha, Trichloroethylene adsorption by pine
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needle biochars produced at various pyrolysis temperatures, Bioresour. Technol. 143 (2013) 615-622.
29. Z.P. Wang, H.N. Zhu, W.L. Xing, Q. Song, X.Q. Shu, Y.X. Zhang, Optimization of using co-pyrolysis of sludge and straw of prepare and adsorption of Cr(VI) (in Chinese), Environ. Eng. 37 (2019) 138-143. 30. D.M. Wang, R.X. Xu, D.X. Qin, Influence of final hydrothermal carbonization temperatures on the yields and characteristics of sludge biochars, Ecol. Environ. Sci. 21 (2012) 1775-1780. 31. Y. Luo, L.X. Zhao, H.B. Meng, X. Xiang, X.R. Zhao, G.T. Li, Q.M. Lin, 21
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Physio-chemical characterization of biochars pyrolyzed from miscanthus under two different temperatures, Trans. CSAE. 29 (2013) 208-217. 32. F.F. Hu, P.W. He, Phosphate adsorption in wastewater by bio-carbon prepared from pyrolysis of chicken manure at different temperature, Hubei. Agric. Sci. 53 (2014) 1774-1785.
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33. M.K. Hossain, V.K. Strezov, Y. Chan, A. Ziolkowski, P.F. Nelson, Influence of
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pyrolysis temperature on production and nutrient properties of wastewater sludge
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biochar, J. Environ. Manage. 92 (2010) 223-228.
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34. G.L. Xiang, Z.N. Yu, Y. Chen, Optimizing the preparation of sugarcane
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bagasse-sludge compositional activated carbon by response surface methodology (in Chinese), J. Environ. Eng. 8 (2014) 5475-5482.
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35. P. Zhou, L. Gu, S. Rao, Y. Huang, H. Yuan, N. Zhu, Preparation of sludge-straw
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based actived carbon and its adsorption for 1-diazo-2-naphtol-4-sulfonic acid (in
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Chinese), Environ. Chem. 32 (2013) 106-111. 36. J.H. Tay, X.G. Chen, S. Jeyaseelan, Optimising the preparation of activated carbon from digested sewage sludge and coconut husk, Chemosphere 44 (2001) 45-51. 37. S.S. Fan, H. Li, H. Zhang, X. Lu, Z.W. Yang, Application of response surface methodology for the optimization of biochar preparation derived from sludge and tea residue (in Chinese), J. Environ. Eng. 11 (2017) 1778-1786. 38. L. Lonappan, T. Rouissi, B.S. Kaur, M.S. Verma, Y. Rao, An insight into the adsorption of diclofenac on different biochars: Mechanisms, surface chemistry, 22
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and thermodynamics, Bioresour. Technol. 249 (2018) 386-394. 39. L. Sun, S. Wan, W. Luo, Biochars prepared from anaerobic digestion residue, palm bark, and eucalyptus for adsorption of cationic methylene blue dye: Characterization, equilibrium, and kinetic studies, Bioresour. Technol. 140 (2013) 406-413.
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40. S.S. Cao, Y.P. Duan, Y.J. Tu, Y.L. Pu, Removal of emerging contaminant
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diclofenac from water using ferrite nanoparticles (in Chinese), Environ. Chem. 37
pr
(2018) 761-768.
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41. C. Piccirillo, I.S. Moreira, R.M. Novais, A.J.S. Fernandes, R.C. Pullar, P.M.L.
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Castro, Biphasic apatite-carbon materials derived from pyrolysed fish bones for effective adsorption of persistent pollutants and heavy metals, J. Environ. Chem.
al
Eng. 5 (2017) 4884-4894.
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42. Y. Li, Utilizing low-cost natural waste for the removal of pharmaceuticals from
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water: Mechanisms, isotherms and kinetics at low concentration, J. Clean. Prod. 227 (2019) 88-97.
43. C. Jung, Competitive adsorption of selected non-steroidal anti-inflammatory drugs on activated biochars: Experimental and molecular modeling study, Chem. Eng. J. 264 (2015) 1-9. 44. S.S. Fan, J. Tang, Y. Wang, H. Li, H. Zhang, J. Tang, Z. Wang, X.D. Li, Biochar prepared from co-pyrolysis of municipal sewage sludge and tea waste for the adsorption of methylene blue from aqueous solutions: kinetics, isotherm, thermodynamic and mechanism, J. Mol. Liq. 220 (2016) 432-441. 23
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Table Captions Table 1. Orthogonal experimental design and results Table 2. Comparison of DFC adsorption efficiency by various activation reagents Table 3. DFC adsorption isotherm parameters on various materials Table 4. Specific surface area, pore diameter and pore volume of U-BC, A-BC, and
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DFC-A-BC
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Figure Captions
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Fig. 1. Influence of pyrolysis temperature on biochar preparation
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Fig. 2. Influence of sludge and leaf ratio on biochar preparation Fig. 3. Influence of pyrolysis time on biochar preparation
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Fig. 4. Comparison of adsorption capacity between activated biochar (A-BC),
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unactivated biochar (U-BC) and commercial activated carbon (C-AC)
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Fig. 5. Kinetic fits for DFC adsorption on biochar (25oC). (a) pseudo-first model, (b) pseudo-second model
Fig. 6. Linear fits of the isotherm models for DFC adsorption on biochar. (a) Langmuir, (b) Freundlich, (c) Temkin Fig. 7. SEM micrographs of (a) sludge (S), (b) leaf (L), (c) unactivated biochar (U-BC), (d) activated biochar (A-BC) Fig. 8. FITR of sludge (S), leaf (L), unactivated biochar (U-BC), activated biochar (A-BC)
24
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Author statement Hao Zhang: Methodology, Investigation, Writing- Original draft preparation. Yao-Jen Tu: Conceptualization, Methodology, Data curation, Writing- Reviewing and Editing. Yan-Ping Duan: Visualization, Investigation. Jin Liu: Investigation. Weidi Zhi: Validation. Yu Tang: Writing- Editing. Li-Shan Xiao: Data curation,
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Validation. Liang Meng: Methodology, Writing- Reviewing and Editing.
25
Journal Pre-proof Declaration of interests ■
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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□ The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
26
Journal Pre-proof Table 1. Orthogonal experimental design and results Biochar yield (%) 85.15 55.85 40.67 29.71 77.47 85.15 76.41 75.87 85.15 76.74 72.32 71.33
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Pyrolysis time (h) 1 1 1 1 1 1 1 1 1 2 3 5
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Pr
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Sludge/leaf ratio 1:3 1:3 1:3 1:3 leaf 1:3 1:1 3:1 1:3 1:3 1:3 1:3
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1 2 3 4 5 6 7 8 9 10 11 12
Pyrolysis temperature (oC) 200 300 400 500 200 200 200 200 200 200 200 200
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No.
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Iodine value (mg/g) 287.81 251.62 316.85 324.53 283.18 287.81 198.65 109.18 287.81 266.08 249.07 234.61
Journal Pre-proof Table 2. Comparison of DFC adsorption efficiency by various activation reagents DFC adsorption efficiency Equilibrium absorption (%) capacity (mg/kg) Unactivated biochar 58.4 465.10 9% HCl 100 783.31 18% HCl 100 787.67 36% HCl 100 790.81 21% H3PO4 100 788.99 43% H3PO4 100 779.81 25% H2SO4 100 785.39 45% H2SO4 100 783.12 10% H2O2 76.8 609.35 20% H2O2 77.8 609.71 Condition: biochar dosage: 0.05 g; DFC concentration: 10 mg/L; Volume of DFC solution: 8 mL.
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Activation reagents
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Journal Pre-proof Table 3. DFC adsorption isotherm parameters on various materials
Langmuir isotherm model
Materials
KL
(mg/g)
(L/mg)
0.53
1.39
R2 0.984
Kf
n
KT
bT
-3
0.939
27.63
27.00
0.924
[38]
-2
0.995
2.02
35.00
0.876
[38]
6.8×10
(L/mg)
R2
References
R2
(mg/g)
1.92
Temkin isotherm model
12.50
0.86
0.891
1.15
1.6×10
NiFe2O4
18.58
0.05
0.930
1.72
1.44
0.949
/
/
/
[40]
MnFe2O4
7.58
0.03
0.925
1.82
0.50
0.968
/
/
/
[40]
A-biochar
2.39
0.42
0.706
/
0.20
0.982
/
/
/
[41]
Biochar
7.25
0.54
0.998
3.32
0.50
0.824
/
/
/
[42]
M-algae
0.02
11.9
0.997
3.39
0.28
0.978
/
/
/
[42]
Wood
8.33
23.5
0.999
3.21
0.43
N-biochar
372
5.89
0.990
/
/
O-biochar
214
3.19
0.994
/
/
877
0.11
0.936
1.968
17.625
0.964
/
/
/
[42]
/
/
/
/
[43]
/
/
/
/
[43]
60.74
0.791
0.973
This study
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biochar
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Activated
f
BC-PM
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BC-PW
Qmax
Freundlich isotherm model
29
0.898
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Table 4. Specific surface area, pore diameter and pore volume of U-BC, A-BC, and DFC-A-BC
Samples
Pore diameter (nm) 6.7365 11.6928 11.3034
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U-BC A-BC DFC-A-BC
BET Surface Area (m2/g) 3.2999 4.1741 0.0880
30
Pore volume (cm3/g) 0.00313 0.00372 0.00017
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Highlights A green technique in converting sludge/leaf to biochar adsorbent was established.
The iodine value and biochar yield reached 287.81 mg/g and 85.15%, respectively.
Activation improved the adsorbent structure and enhanced the capacity of biochar.
Characterization analysis showed that biochar performance was obviously improved.
The biochar derived from sludge/leaf has a great potential in diclofenac removal.
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31
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure 8
Hao Zhang, Yao-Jen Tu, Yan-Ping Duan, Jin Liu, Weidi Zhi, Yu Tang, Li-Shan Xiao, Liang Meng PII:
S0167-7322(19)34552-0
DOI:
https://doi.org/10.1016/j.molliq.2019.112193
Reference:
MOLLIQ 112193
To appear in:
Journal of Molecular Liquids
Received date:
13 August 2019
Revised date:
20 November 2019
Accepted date:
21 November 2019
Please cite this article as: H. Zhang, Y.-J. Tu, Y.-P. Duan, et al., Production of biochar from waste sludge/leaf for fast and efficient removal of diclofenac, Journal of Molecular Liquids(2018), https://doi.org/10.1016/j.molliq.2019.112193
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© 2018 Published by Elsevier.
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Production of Biochar from Waste Sludge/Leaf for Fast and Efficient Removal of Diclofenac
Hao Zhanga, Yao-Jen Tua,b*, Yan-Ping Duana,b,
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a
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Jin Liua, Weidi Zhia, Yu Tanga, Li-Shan Xiaoa,b, Liang Menga,b
School of Environmental and Geographical Sciences, Shanghai Normal University,
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No. 100, Guilin Rd., Shanghai 200234, China b
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200234, China
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Institute of Urban Study, Shanghai Normal University, No. 100, Guilin Rd., Shanghai
Corresponding author: Yao-Jen Tu TEL: +86-13661920584 E-mail: [email protected] 1
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Abstract Sludge and leaf are two kinds of typical solid wastes with huge production. How to effectively treat sludge/leaf thus becomes a hot issue and needs to be solved at present. This study aims to develop the resource recycling technology in converting waste sludge/leaf to biochar material for diclofenac (DFC) removal. Through the
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orthogonal test design, the effects of pyrolysis temperature, sludge/leaf ratio, and
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pyrolysis time were systematically investigated. Under the conditions of pyrolysis
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temperature 200oC, sludge/leaf ratio 1:3, and pyrolysis time 1 h, the optimized
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biochar was simply produced where the key indicators iodine value and biochar yield
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reached 287.81 mg/g and 85.15%, respectively. Adsorption results revealed that DFC was rapidly and efficiently adsorbed by the recycled sludge/leaf biochar at the
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conditions of 25oC, initial DFC concentration of 10 mg/L, solution volume of 8 mL,
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and biochar dosage of 0.005 g. With the maximum adsorption capacity of 877 mg/g,
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the DFC adsorption process was described well by pseudo-second order kinetics and Temkin isotherm model. Furthermore, after activation by 9% HCl solution, the specific surface area of the biochar increased from 3.30 to 4.17 m2/g, indicating that activated biochar had more sites for DFC adsorption. That was also confirmed by SEM images which showed more porous and rough characteristics on the surface structure of biochar. The data displayed a green environmental technique in converting waste sludge/leaf to useful biochar adsorbent for rapid and efficient DFC removal. Keywords: Waste sludge, waste leaf, recycling, biochar, diclofenac 2
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1. Introduction The compositions of industrial and domestic sludge contain variety of harmful heavy metals, organic compounds, and pathogenic microorganisms. Without appropriate treatment, sludge will pose great harm to human life and the natural environment[1]. Up to 2017, China has already built 4063 sewage treatment plants and
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the treatment capacity can reach 178 million m3/d with municipal sludge produced in
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30-40 million tons/year (80% moisture content). The estimated municipal sludge may
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approach 60-90 million tons/year by 2020[2]; hence the treatment and disposal of
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sludge has become one of the hot issues that need to be solved urgently. At present,
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the treatment and disposal of sludge include landfill, incineration, aerobic compost, land use, building materials use and other aspects. Among mentioned above, landfill,
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incineration, aerobic compost plus land use, natural dry comprehensive utilization,
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open air stacking, and overseas transportation individually account for 60-65%, 2-3%,
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10-15%, 3-6%, 2%, and 15%, respectively. Generally speaking, sludge landfill, outdoor stacking and outward transport are disposed casually[3]; therefore, the secondary pollution will be inevitably occurred and bring far greater harm than wastewater discharge. The living environment would thus become worse and the ecological system may become difficult to remediate[4]. City green-clustered landscapes generate a huge amount of leaves which are easy to collect. However ecological circulation mechanism is suspended once these leaves were taken to a landfill. Beyond that, leaves mixed with garbage, not conducive to urban garbage reduction, will generate more disposal problems[5]. Traditional leaves 3
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treatment methods include incineration, landfill, etc. However, in terms of the environmental impact, the aforementioned simple treatment methods may not only cause serious pollution to the environment but also result in the waste of leaves resources[6].
Many
previous
literatures
focused
on
sludge
properties
of
biodegradation[7], fermentation[8], biogas production[9], and adsorption[10]. Only few
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reports were discussed on their properties of biochar production. So the cotonier
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leaves were selected as one of the original materials for preparation of biochar in this
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study. Currently, the comprehensive utilization of the fallen leaves are the preparation
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of feed and composting, etc[11]. However, these methods have not been widely used in
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city. Therefore, it is necessary to explore a reasonable and effective treatment of fallen leaves.
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Generally speaking, biochar is a carbon-rich and porous solid produced from
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biomass via pyrolysis in the absence of oxygen[12]. The International Biochar
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Initiative (IBI) standardized its definition as “a solid material obtained from the thermochemical conversion of biomass in an oxygen-limited environment”[13]. With a well-developed pore structure, very large surface area, high stability, and exceptional adsorption properties, biochar has great potential in the application of many fields [14]. Currently, some scholars have studied the preparation of biochar by pyrolysis of straw, chestnut shell, chicken manure, pineapple waste, and pomelo peel[15-19]. However, few studies focused on the pyrolysis of biomass in mixing of waste sludge and leaves. Besides, very rare work was found in investigating biochar’s adsorption behavior of Pharmaceuticals and Personal Care Products (PPCPs). If these waste sludge/leaves 4
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can be converted to a useful material, not only the problem that waste sludge and leaves has nowhere to go is solved, but the useful biochar material is also produced. Besides, it can further help us to evaluate the prospect of homemade biochar as an adsorption material in the application of removal emerging contaminants. It should be addressed that PPCPs is the general term of a new class of organic pollutants, including all kinds of antibiotic, diet pills, hypnotics, steroid, cosmetics,
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hair dye and fungicide etc, which are closely associated with people’s daily lives[20].
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In 1999, this concept has been first published in《Environmental Health Perspectives》
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and put forward by Daughton and Ternes[21]. Owing to the strong of bioactive, bioaccumulation, and durability characteristic of PPCPs, the human health and
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ecological risk are difficult to be estimated if they are in the long-term exposure[22]. It
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should be known that there is no unique technology designed for PPCPs removal in
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conventional sewage treatment plants. This is the reason why PPCPs cannot be
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removed efficiently by the current urban sewage treatment plants[23]. Thus how to effectively treat PPCPs has gradually begun a hot issue all over the world. Among
all
PPCPs,
diclofenac
(DFC)
is
regarded
as
non-steroidal
anti-inflammatory drugs which is widely used in analgesic, arthritis drug, and medicines to treat rheumatism[24,25]. It has been reported that about 65% DFC is expelled from urine in the form of hydroxy metabolites after oral administration[26]. When DFC enters into the environment, it is difficult to be biodegraded and transformed by microorganisms. Consequently, the aquatic ecosystems and human health would be potentially threatened because of the living organisms’ accumulation 5
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and amplification of DFC from food chain. In addition, it should be emphasized that the aqueous DFC cannot be effectively removed from traditional wastewater treatment technology. It is hence necessary to find a simple, costless, and effective way to remove DFC from water systems. A series of batch experiments were performed to evaluate the capability of the produced biochar for aqueous DFC
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removal. The key parameters (pyrolysis temperature, pyrolysis time, sludge/leaf ratio)
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for preparation biochar were investigated in detail. Further kinetics and isotherms of
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adsorption of DFC on produced biochar were also systematically discussed. The
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for DFC removal from water system.
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information obtained implied great potential for developing a cost-effective biochar
2. Material and methods
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2.1 Preparation and activation of biochar from waste sludge/leaves
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The raw sludge, with 65% moisture content, was collected from a sludge drying
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plant in China. After drying process, the sludge was crushed by soil grinding machine (XDB050304, Beijing new landmark soil equipment) and then sieved through 100-mesh screen cloth. The waste leaves were collected from cotonier during autumn and winter season at the university campus of Shanghai, China. The waste leaves were ultrasonic washed firstly, then crushed by soil grinding machine and sieved through 100-mesh screen cloth. The pretreated sludge and leaf powders were placed in the crucibles. After covered by excessive nitrogen, they were put in the box-type muffle furnace. The reaction temperature was set to 200-500oC at a rate of 6oC per minute. The resource 6
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recycled biochar was then produced after 1-5 h pyrolysis. The optimum preparation parameters of biochar were evaluated by iodine value (GB/T 12496.8-2015) and biochar yield. The steps for determination of iodine value can be briefly described as follows. Put 0.5 g sample into a 250 mL corked conical flask and add 10 mL 5% of hydrochloric acid accurately into the flask. The sample was heated to boiling point on
f
an electric furnace for (30±2) seconds. After cooling to room temperature, 50 mL
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iodine standard solution was added to the flask. Plug the bottle cap immediately and
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oscillate the flask for 15 minutes. Filtrate it quickly into the dry beaker. 10 mL filtrate
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was then absorbed into a 250 mL wide-mouth conical flask which contains 100 mL
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distilled water. Finally, the standard solution of sodium thiosulfate was then used for titration. The iodine value of biochar was calculated according to the volume of
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sodium thiosulfate consumed. With the activation time of 24 h, the four reagents
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hydrochloric acid, phosphoric acid, sulfuric acid, and hydrogen peroxide at different
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concentration were employed to activate the produced biochar. After activation, the biochar was dried in an electric thermostatic air drying box. The DFC adsorption efficiency and cost of produced biochar were taken into consideration for determining the optimum activator and the activation method. Additionally, to understand the effect of activation to the biochar for DFC adsorption, various concentrations of hydrochloric acid (HCl 9, 18, and 36%), phosphoric acid (H3PO4 21 and 43%), sulfuric acid (H2SO4 25 and 45%), and hydrogen peroxide (H2O2 10 and 20%) were applied to activate the produced biochar. The activated biochars were then examined for their DFC adsorption efficiency. 7
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2.2 Batch adsorption Orthogonal experiment was applied to investigate the optimum preparation conditions of biochar. Pyrolysis temperature, sludge/leaf ratio and pyrolysis time were used as the three factors where each factor includes four levels. The pyrolysis temperature is set to 200, 300, 400, and 500oC, sludge/leaf ratio is set to 0 (leaf), 1:3,
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1:1, 3:1, and pyrolysis time is set to 1 h, 2 h, 3 h, 5 h.
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Weigh 0.05 g samples of unactivated biochar, activated biochar and commercial
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activated carbon (named as U-BC, A-BC, C-AC, respectively). Then U-BC, A-BC,
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C-AC were put into 15 mL plastic centrifuge tube with 10 mg/L DFC solution of 8 mL. The batch kinetic adsorption was performed under the conditions of 45 rpm,
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25oC, adsorbent dosage 0.05 g, and volume 8 mL. The sample collection time was
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designed at the gradient from 1 to 240 min where each time point has three parallel
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experiments. The supernatant was taken out and the DFC residual concentration was
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determined by high performance liquid chromatography (HPLC). The adsorption kinetic characteristics were investigated by fitting pseudo-first order and pseudo-second order kinetic equations. The adsorption capacity calculation equation, pseudo-first order kinetic equation, pseudo-second order kinetic equation can be expressed as Eqs. (1)-(3). Adsorption capacity calculation equation: （C - C ）*V Qe t e m
(1)
pseudo-first order kinetic equation: ln（Qe-Qt）=lnQe-k1t
(2) 8
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pseudo-second order kinetic equation: t 1 t 2 Qt k 2 Q e 2 Qe 2
(3)
In Eqs. 1-3, where Qe is the adsorption capacity at equilibrium time, mg/g; Qt is the adsorption capacity at t time, mg/g; K1 is the pseudo-first order rate constant, 1/min; K2 is pseudo-second order rate constant, g/(mg·min).
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The isothermal adsorption experiments were conducted similarly as batch kinetic experiment. Under the conditions of 45 rpm, 25oC, adsorbent dosage 0.005 g, and
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volume 8 mL, DFC initial concentration 10 to 500 mg/L, the supernatant was taken at
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the equilibrium time and the residual concentration was determined by HPLC. To
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study the adsorption isotherm process of DFC solution onto biochar, Langmuir, Freundlich, Temkin isotherm models (Eqs. 4-6, respectively) were examined for their
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abilities to accurately describe the adsorption process. The Langmuir model is an
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ideal model, which assumes that the solution is an ideal solution and the surface is a
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single molecular layer adsorption process. The Freundlich model is an empirical model, which is generally used to describe the process of surface adsorption as single layer or multi-layer adsorption. It is generally believed that in Freundlich model when 1/n is less than 0.5, adsorbents are easy to be adsorbed. When 1/n is larger than 2, it is difficult to be adsorbed[27]. Temkin model mainly describes the chemical adsorption process dominated by electrostatic adsorption[28]. The mathematical expressions of the three models are as follows: Langmuir isotherm equation
9
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Ce 1 1 Ce qe QmaxK L Qmax
Freundlich isotherm equation 1
(5)
qe K f C e n
Temkin isotherm equation qe
RT RT ln K T ln Ce bT bT
(6)
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Where Qe is the adsorption capacity at equilibrium time, mg/g; KL is Langmuir
oo
constant, L/mg; Qmax is the maximum adsorption capacity, mg/g; Kf is Freundlich
pr
constant, L/mg; 1/n is the heterogeneity of the sorption sites and an indicator of
e-
isotherm nonlinearity; KT is the equilibrium binding constant, L/mg; bT is the Temkin
Pr
isotherm constant.
2.3 Characterization of the produced biochar
al
The surface functional group distribution of biochar samples was analyzed by
rn
FTIR (Nicolet iS5, Thermo Fisher Scientific) which can accurately analyze the
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changes of functional groups on the surface of biochar materials caused by surface modification and adsorption. The KBr pellet method was adopted here for the produced biochar. The detection wavelength range is from 400-4000 cm-1 at the scanning step size to 1 cm-1. Specific surface area, pore volume, and pore diameter were obtained from BET instrument (ASAP2390 series, McMuratick). The BET equation is based on the theory of multilayer adsorption, and the material is closer to the actual adsorption process; therefore the results are more accurate. In this experiment, the sample was vacuum dried for 2 h at 300oC for removing moisture and miscellaneous gases. Under the condition of 196.15oC, liquid nitrogen was used for 10
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adsorption and desorption experiments and for analyzing surface area and pore size distribution of materials. Surface micro-characteristics of prepared adsorbent were investigated by scanning electron microscope (S-4800, Hitachi), which can observe the microstructure of sludge/leaf and biochar before and after activation. In this experiment, the samples were placed on the electrical tape, sprayed with gold and
f
then placed under SEM for observation and photography.
oo
3. Results and discussion
pr
3.1 Optimum parameters for producing biochar
e-
As can be seen in Fig. 1, with the increase of temperature (200 to 500oC),
Pr
biochar yield decreased from 85.15 to 29.71% where iodine values increased from 287.81 mg/g to 324.53 mg/g. During the preparation of biochar, pyrolysis temperature
al
is an important factor affecting the physical and chemical properties of biochar. With
rn
the increase of temperature, the degree of carbonization of biochar would increase.
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The number of micropores would increase correspondingly which would lead to the increase of iodine value[29]. Generally, the yield of biochar decreases with the increase of temperature while the carbon content, ash content, specific surface area and porosity of biochar increase with the increase of temperature[30-32]. Hossia et al. also found that the yield of biochar would change with the change of temperature which can be concluded in the trend of the higher the temperature, the lower the biochar yield[33]. The temperature 200oC was then selected as the optimum temperature for biochar preparation owing to the consideration of biochar yield, iodine value, and preparation cost. 11
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Fig. 2 showed the influence of sludge and leaf ratio on biochar preparation. As indicated here, with the increase of the leaf content in the sludge/leaf ratio, both iodine value and biochar yield increase and then decrease. When the sludge/leaf ratio is 1:3, the iodine value of biochar reaches 287.81 mg/g, and the yield reached 85.15%. Considering that this phenomenon is caused by the difference in composition between
f
sludge and leaf, the volatile content of sludge is relatively low. Xiang et al. used the
oo
co-pyrolysis of sludge and bagasse to prepare biochar and found that increasing the
pr
amount of bagasse can improve the iodine value of biochar [34]. Adding bagasse can
e-
improve the carbon content in activated sludge, further increasing the carbon amount
Pr
in pyrolysis of biochar. Hence the adsorption performance is improved accordingly. Contrarily, Zhou et al. used the co-pyrolysis of sludge and straw to prepare biological
al
activated carbon. When the amount of straw increased, the carbon content of biochar
rn
increased, but the adsorption property reduced[35]. This may be due to the change of
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pore structure in biochar. Therefore, it can be concluded that the ratio of sludge and leaf is a key parameter for biochar’s adsorption performance, but the effect can be positive or negative.
Fig. 3 displayed the influence of pyrolysis time on biochar preparation. As can be seen in Fig. 3, the iodine value decreased from 287.81 to 234.61 mg/g, and the biochar yield decreased from 85.15 to 71.33% when the pyrolysis time increased from 1 to 5 h. Tay et al. has used co-pyrolysis method for biochar preparation using sludge and coconut shell. They observed that the biochar yield would change with the pyrolysis time. Increasing pyrolysis time may increase the pore structure of biochar, 12
Journal Pre-proof however, the pore structure would not increase beyond a certain pyrolysis time[36]. In our case, the maximum iodine value and biochar yield were observed at 1 h pyrolysis time. It is speculated that after the broken and screened pretreatment, the particle size of sludge and leaves is small enough for the fast reaction of pyrolysis. This is consistent with the result found by Fan et al.[37]. The summarized and detailed
f
orthogonal experimental design and data were displayed in Table 1.
oo
To sum up, the optimum biochar preparation condition can be concluded as:
pr
pyrolysis temperature 200oC, sludge/leaf ratio 1:3, and pyrolysis time 1 h. Under this
e-
condition, the maximum iodine value and biochar yield reached 287.81 mg/g and
Pr
85.15%, respectively.
Table 2 demonstrated the comparison of DFC adsorption efficiency by various
al
activation reagents. The data shown in Table 2 obviously tell us that activation can
rn
improve the characteristic of biochar, further facilitating materials’ DFC adsorption
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efficiency. After 12 h adsorption, 100% DFC can be removed from solutions using biochars activated by HCl (9, 18, and 36%), H3PO4 (21 and 43%), and H2SO4 (25 and 45%). Compared to unactivated biochar (58.4% DFC adsorption efficiency), these activated biochars own more adsorptive site in removing DFC from water. Take the economic costs and test security into consideration, 9% HCl was chosen as the most adequate activator to activate the biochar. 3.2 Adsorption kinetics Fig. 4 illustrated the comparison of adsorption capacity between A-BC, U-BC, and C-AC. Evidently, all three adsorbents can reach adsorption equilibrium under the 13
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conditions of DFC concentration 10 mg/L, volume 8 mL, adsorbent dose 0.05 g, and contact time 240 min. It should be noticed that A-BC possesses the fastest adsorption rate among the three adsorbents. The adsorption efficiency of A-BC can reach 89.51% in 10 min while the adsorption efficiency of C-AC and U-BC only can reach 12.24% and 70.07% in 10 min. Lonappan use pine wood and pig manure to manufacture biochar for DFC removal[38]. The results displayed that under the conditions of DFC
oo
f
concentration 2 mg/L, pH 6.5, adsorbent dose 0.1 g, temperature 25±1oC, pine
pr
biochar reached equilibrium after 4.5 h and pig manure biochar reached equilibrium
e-
after 5 h. Compared to pine biochar and pig manure biochar, the equilibrium time of
Pr
the A-BC is much shorter which would cut the cost when it was applied in practice. Pseudo-first order and pseudo-second order kinetic equations of A-BC were
al
shown in Fig. 5. As can be seen in Fig. 5, the R2 of pseudo-first order kinetic and
rn
pseudo-second order kinetic equation is 0.9782 and 0.9999, respectively, implying
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that pseudo-second order model owns better fit than pseudo-first order model for simulating the kinetic process. Since the pseudo-second order equation includes external liquid film diffusion, surface adsorption, and internal particle diffusion, etc. Thus, the adsorption mechanism of DFC on sludge/leaf biochar can be more comprehensively reflected by pseudo-second order model[39]. 3.3 Adsorption isotherm Fig. 6 shows the adsorption isotherm curve of DFC solution onto sludge/leaf biochar. Evidently, the used three isothermal adsorption equations (Langmuir, Freundlich, and Temkin) can fit well the adsorption process. The Temkin isotherm 14
Journal Pre-proof owns high R2 value (0.9732), implying that electrostatic adsorption is an important mechanism for the interaction between sludge/leaf biochar and DFC. Furthermore, the parameter 1/n shown in Freundlich equation can reflect the feasibility of adsorption. The result indicated that the 1/n value of DFC adsorbed by sludge/leaf biochar was 0.508, indicating that this temperature (25oC) is conducive to adsorption. Table 3 listed DFC adsorption isotherm parameters on various materials biochar,
oo
f
ferrite magnets and other materials[38, 40-43]. The result revealed that among these
pr
materials, the adsorption capacity of A-BC can reach 877 mg/g by using Langmuir
e-
model, further implying that the produced biochar has great potential in DFC removal
Pr
from water system.
3.4 Characterization of sludge/leaf biochar
al
Table 4 summarized the specific surface area, pore diameter, and pore volume of
rn
U-BC, A-BC, and DFC-A-BC. It can be found that the specific surface area of biochar
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increased from 3.2999 to 4.1741 m2/g after activation. However, after adsorption of DFC, the specific surface area of the adsorbent (DFC-A-BC) decreased to 0.0880 m2/g. The pore diameter increased from 6.7365 to 11.6928 nm after activation, while it decreased to 11.3034 nm after DFC adsorption. In addition, the pore volume rose from 0.00313 to 0.00372 cm3/g after the activation of biochar while it decreased to 0.00017 cm3/g after DFC adsorption. The result further implied that activation is favorable to the release of the pore. The specific surface area and pore volume of biochar would increase by the released pores, which also improved their DFC adsorption performance. 15
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SEM images of sludge (S), leaf (L), U-BC and A-BC were displayed in Fig. 7. Obviously, the structure of sludge is relatively dense, but the pore structure is relatively dispersed (Fig. 7a). The structure of leaf surface presented a terrier state (Fig. 7b), indicating that the main components were cellulose and hemicellulose. More pore structure and coarse surface were observed in the produced biochar (Fig.
f
7c), implying that biochar has the potential to be an adsorbent. After activation, the
pr
increasing surface pores and the rough surface.
oo
biochar can be regarded as a porous carbon adsorption material owing to the
e-
FTIR spectra of sludge (S), leaf (L), U-BC and A-BC were shown in Fig. 8. It can be found that the peak of its spectrum mainly vibrated around 3152 cm-1 (C-H
Pr
stretching), 2853 cm-1 (aliphatic C−H group), 1620 cm-1 (C=O stretching), 1385 cm-1
al
(Aromatic C=C stretching), 1041 cm-1 (C-O-H stretching), but it has some offset. For
rn
instance, C=O stretching of sludge vibrated from 1649 cm to 1620 cm-1. The peak of
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sludge and leaf vibrating at 1724 cm-1 (Esters C=O stretching) was disappeared due to pyrolysis. After the activation of biochar, a new peak can be seen at 2335 cm-1 (Aliphatic C≡O stretching). It can be seen that the compounds of protein, seters, aliphatic, and cellulose were decomposed gradually during the preparation of biochar while the aromaticity of the produced biochar was increased[44]. 4. Conclusion (1) A resource recycling technology in converting waste sludge/leaf to biochar material was established in this study. Besides, these biochar can be used as a fast and effective adsorbent for DFC removal from water system. 16
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(2) The optimal conditions for preparing biochar from sludge and leaf were pyrolysis temperature of 200oC, sludge/leaf ratio of 1:3, and pyrolysis time of 1 h. Under the optimal conditions, the iodine value and yield of biochar reached 287.81 mg/g and 85.15%, respectively. (3) The specific surface area of activated sludge/leaf biochar increased from 3.30 to
oo
to the improvement of DFC adsorption performance.
f
4.17 m2/g and the adsorption rate accelerated, indicating that activation was beneficial
pr
(4) The DFC adsorption onto sludge/leaf biochar conformed to pseudo-second order
e-
kinetics model (R2 is 0.9999), implying that chemical reaction/chemical adsorption
Pr
could be interpreted as the main process of adsorption. (5) After activation, the adsorption capacity of biochar can be significantly enhanced.
al
With the maximum adsorption capacity of 877 mg/g, the DFC adsorption process can
Jo u
rn
be described well by Langmuir, Freundlich, and Temkin isotherms.
Acknowledgments
This research is sponsored by National Major Program Social Science Fund of China (17ZDA058), Ministry of Science and Technology National Key Research and Development Program (2016YFC0502706), Shanghai Natural Science Foundation (17ZR1420700), and National Natural Science Foundation of China (41601514, 41971257, 41730642, 41877425).
17
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13. Standardized product definition and product testing guidelines for biochar that is used in soil. International Biochar Initiative, April 2012. 14. Y.X. Liu, S. Yao, Y.Y. Wang, H.H. Lu, K.B. Satinder, S.M. Yang, Bio- and hydrochars from rice straw and pig manure: Inter-comparison, Bioresour. Technol. 235 (2017) 332-337. 15. C. Liang, Y. Hu, M. Ji, W. Sang, D. Li, Adsorptive characteristics of rice straw biochar on composite heavy metals Cd2+ and Pb2+ in soil (in Chinese), Res. Environ. Sci. 1 (2019) 1-12. 16. K.M. Jiang, C.G. Cheng, M. Ran, Y.G. Lu, Q.L. Wu, Preparation of a biochar 19
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43. C. Jung, Competitive adsorption of selected non-steroidal anti-inflammatory drugs on activated biochars: Experimental and molecular modeling study, Chem. Eng. J. 264 (2015) 1-9. 44. S.S. Fan, J. Tang, Y. Wang, H. Li, H. Zhang, J. Tang, Z. Wang, X.D. Li, Biochar prepared from co-pyrolysis of municipal sewage sludge and tea waste for the adsorption of methylene blue from aqueous solutions: kinetics, isotherm, thermodynamic and mechanism, J. Mol. Liq. 220 (2016) 432-441. 23
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Table Captions Table 1. Orthogonal experimental design and results Table 2. Comparison of DFC adsorption efficiency by various activation reagents Table 3. DFC adsorption isotherm parameters on various materials Table 4. Specific surface area, pore diameter and pore volume of U-BC, A-BC, and
oo
f
DFC-A-BC
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Figure Captions
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Fig. 1. Influence of pyrolysis temperature on biochar preparation
Pr
Fig. 2. Influence of sludge and leaf ratio on biochar preparation Fig. 3. Influence of pyrolysis time on biochar preparation
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Fig. 4. Comparison of adsorption capacity between activated biochar (A-BC),
rn
unactivated biochar (U-BC) and commercial activated carbon (C-AC)
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Fig. 5. Kinetic fits for DFC adsorption on biochar (25oC). (a) pseudo-first model, (b) pseudo-second model
Fig. 6. Linear fits of the isotherm models for DFC adsorption on biochar. (a) Langmuir, (b) Freundlich, (c) Temkin Fig. 7. SEM micrographs of (a) sludge (S), (b) leaf (L), (c) unactivated biochar (U-BC), (d) activated biochar (A-BC) Fig. 8. FITR of sludge (S), leaf (L), unactivated biochar (U-BC), activated biochar (A-BC)
24
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Author statement Hao Zhang: Methodology, Investigation, Writing- Original draft preparation. Yao-Jen Tu: Conceptualization, Methodology, Data curation, Writing- Reviewing and Editing. Yan-Ping Duan: Visualization, Investigation. Jin Liu: Investigation. Weidi Zhi: Validation. Yu Tang: Writing- Editing. Li-Shan Xiao: Data curation,
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rn
al
Pr
e-
pr
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Validation. Liang Meng: Methodology, Writing- Reviewing and Editing.
25
Journal Pre-proof Declaration of interests ■
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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□ The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
26
Journal Pre-proof Table 1. Orthogonal experimental design and results Biochar yield (%) 85.15 55.85 40.67 29.71 77.47 85.15 76.41 75.87 85.15 76.74 72.32 71.33
f
Pyrolysis time (h) 1 1 1 1 1 1 1 1 1 2 3 5
al
Pr
e-
pr
oo
Sludge/leaf ratio 1:3 1:3 1:3 1:3 leaf 1:3 1:1 3:1 1:3 1:3 1:3 1:3
rn
1 2 3 4 5 6 7 8 9 10 11 12
Pyrolysis temperature (oC) 200 300 400 500 200 200 200 200 200 200 200 200
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No.
27
Iodine value (mg/g) 287.81 251.62 316.85 324.53 283.18 287.81 198.65 109.18 287.81 266.08 249.07 234.61
Journal Pre-proof Table 2. Comparison of DFC adsorption efficiency by various activation reagents DFC adsorption efficiency Equilibrium absorption (%) capacity (mg/kg) Unactivated biochar 58.4 465.10 9% HCl 100 783.31 18% HCl 100 787.67 36% HCl 100 790.81 21% H3PO4 100 788.99 43% H3PO4 100 779.81 25% H2SO4 100 785.39 45% H2SO4 100 783.12 10% H2O2 76.8 609.35 20% H2O2 77.8 609.71 Condition: biochar dosage: 0.05 g; DFC concentration: 10 mg/L; Volume of DFC solution: 8 mL.
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rn
al
Pr
e-
pr
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f
Activation reagents
28
Journal Pre-proof Table 3. DFC adsorption isotherm parameters on various materials
Langmuir isotherm model
Materials
KL
(mg/g)
(L/mg)
0.53
1.39
R2 0.984
Kf
n
KT
bT
-3
0.939
27.63
27.00
0.924
[38]
-2
0.995
2.02
35.00
0.876
[38]
6.8×10
(L/mg)
R2
References
R2
(mg/g)
1.92
Temkin isotherm model
12.50
0.86
0.891
1.15
1.6×10
NiFe2O4
18.58
0.05
0.930
1.72
1.44
0.949
/
/
/
[40]
MnFe2O4
7.58
0.03
0.925
1.82
0.50
0.968
/
/
/
[40]
A-biochar
2.39
0.42
0.706
/
0.20
0.982
/
/
/
[41]
Biochar
7.25
0.54
0.998
3.32
0.50
0.824
/
/
/
[42]
M-algae
0.02
11.9
0.997
3.39
0.28
0.978
/
/
/
[42]
Wood
8.33
23.5
0.999
3.21
0.43
N-biochar
372
5.89
0.990
/
/
O-biochar
214
3.19
0.994
/
/
877
0.11
0.936
1.968
17.625
0.964
/
/
/
[42]
/
/
/
/
[43]
/
/
/
/
[43]
60.74
0.791
0.973
This study
pr
ePr al rn
biochar
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Activated
f
BC-PM
oo
BC-PW
Qmax
Freundlich isotherm model
29
0.898
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Table 4. Specific surface area, pore diameter and pore volume of U-BC, A-BC, and DFC-A-BC
Samples
Pore diameter (nm) 6.7365 11.6928 11.3034
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al
Pr
e-
pr
oo
f
U-BC A-BC DFC-A-BC
BET Surface Area (m2/g) 3.2999 4.1741 0.0880
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Pore volume (cm3/g) 0.00313 0.00372 0.00017
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Highlights A green technique in converting sludge/leaf to biochar adsorbent was established.
The iodine value and biochar yield reached 287.81 mg/g and 85.15%, respectively.
Activation improved the adsorbent structure and enhanced the capacity of biochar.
Characterization analysis showed that biochar performance was obviously improved.
The biochar derived from sludge/leaf has a great potential in diclofenac removal.
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