Adsorption removal of tetracycline from aqueous solution by anaerobic granular sludge: equilibrium and kinetic studies
Ke Li 1, Feng Ji2, Yuanlu Liu1, Zilin Tong 1, Xinmin, Zhan 3, Zhenhu Hu 1*,
1 Department of Civil Engineering, Hefei University of Technology, Hefei 230009,
2 Feed Research Institute, Chinese Academy of Agricultural Sciences, Beijing, 100081, China 3 Department of Civil Engineering, National University of Ireland, Galway, Ireland *Corresponding author: Zhenhu Hu Department of Civil Engineering, Hefei University of Technology, Hefei, 230009 China Tel:86-551-2904144 Fax: 86-551-2902066 E-mail address: Abstract In this study, the effects of initial pH, humic acid concentration, and temperature on the removal of tetracycline by anaerobic granular sludge from aqueous solution were investigated using batch adsorption technique. The results show that the highest removal efficiency of 93% was achieved around pH 3.0. The thermodynamic analysis indicates that the adsorption process was spontaneous and endothermic process. The adsorption kinetics followed the pseudo-second order equation. The adsorption isotherms analysis indicates that Langmuir model is better fitted than Freundlich model for the description of the adsorption equilibrium and confirmed the result of thermodynamics analysis. The maximum adsorption capacities were 2.984, 4.108 and 4.618 mg g-1 at 25, 35 and 45 oC, respectively. These results are important to understand the fate and transformation of tetracycline in anaerobic granular digestion system. Keywords: Adsorption; anaerobic granular sludge; removal; tetracycline; thermodynamic analysis 1. Introduction
antibiotics for animal therapy and health
protection has increased from only 91 tons in
antibiotics have been widely used in animal
antibiotics, tetracyclines were the most
protection or as growth promoter (Sarmah et
al., 2006). In Europe, over 10,000 tons of
industry because of their broad-spectrum
(Koike et al., 2007). For example, in China,
the annual tetracycline usage was about 9413
animal husbandry (Schlusener & Bester,
2006). In the United States, according to the
10000 tons in 2003 (Hu et al., 2008; Zhang
with granular sludge was often used for the
treatment of high concentration of organic
the animal gut, resulting in about 30-90% of
the antibiotics excreting into environment as
information regarding the adsorption process
parent compounds after animal use (Sarmah
of tetracycline on anaerobic granular sludge
et al., 2006). Since antibiotics are designed
wastewater, which limits the understanding
of antibiotics behavior in the UASB reactor.
Therefore, the objective of this study was to
evaluate the sorption capacity of anaerobic
2006). The short-term effects of veterinary
antibiotics on aquatic organisms, bacteria,
kinetics of the sorption process, which will
macro-invertebrates, and plants have been
management and operation of UASB reactor
toxicity studies were undertaken at higher
treating tetracycline contaminated animal
concentrations than that in the environment
(Sarmah et al., 2006). Tetracycline residue in
the environment will induce the occurrence
2. Materials and methods
of anti-tetracycline bacteria. The diversity of
2.1 Chemical and stock solution preparation
treatment plants, lagoons and groundwater
Stock solution of tetracycline (200 mg L-1)
managements on the fate and transformation
was prepared by accurately dissolving 0.2 g
of residual tetracyclines in animal manures.
of tetracycline in 1.0 L deionized water. The
For the solid part of manures, composting
provided an effective way in reducing most
obtained by diluting the stock solution into
of the tetracyclines by the action of aerobic
microorganisms (Hu et al., 2011). For the
liquid part, anaerobic digestion is a potential
2.2 Characteristics of anaerobic granular
investigated the fate of oxytetracycline
during anaerobic digestion of manure and
province, China. The characteristics of the
obtained the half-life of oxytetracycline of
56 days, which was longer than the solid and
Anaerobic granular sludge contained 14.8%
of dry matter, in which volatile organic solid
anaerobic reactor. Alvarez et al. (2010)
was 43.9% and the left was inorganic matter
oxytetracycline onto solid matter during
Table 1 Characteristics of anaerobic granular
Upflow anaerobic sludge bioreactor (UASB)
355 nm. The retention time of tetracycline
* Note: the content of metals is based on the
3. Results and discussion
dry matter of anaerobic granular sludge.
Batch adsorption experiments were carried
removal of tetracycline. The highest removal
out in 100 mL flasks with 75 mL of working
efficiency of more than 93% was achieved
around pH 3.0. With the increase of pH from
granular sludge and determined amounts of
3.0 to 5.0, the tetracycline removal slightly
stock solution were added into flasks and
decreased to 91%, while the removal was not
obviously affected over the pH range of 6.0-
initial pH of the solution was adjusted to 6.5
9.0. The adsorption behavior at various pHs
might be affected by several parameters such
loaded flasks were sealed and shaken at an
as adsorption capacity of adsorbent, surface
charges and active sites of both tetracycline
and anaerobic granular sludge (Xu & Li,
acid concentration from 5.0 to 150.0 mg L-1
2010). For anaerobic granular sludge, the
isoelectric point is usually between 1 and 3
(Gao & Wang, 2007), while tetracycline has
sludge addition was conducted following the
three different species in the various pH
same procedure as the control. Each test was
ranges because of its functional groups, as
carried out in triplicate and the average was
described by Xu and Li (Xu & Li, 2010).
reported here. Liquid samples were collected
When solution pH is lower than isoelectrical
intervals. The collected liquid samples were
centrifuged at 10000 rpm for 10 min and the
which leads to the interaction between the
filter for the determination of residual
of tetracycline and the groups of the granular
surface, resulting in enhancing adsorption.
When the pH is higher than the isoelectrical
point, the overall surfaces of granular sludge
gradually gets negatively charged, while
liquid chromatography (HPLC) was used for
tetracycline carries a positive charge at 3.0 <
the determination of tetracycline. A SHIM-
pH < 5.6, which leads to the interaction
(Shimadzu Corporation, Japan) was used for
molecules through electrostatic forces of
separation. The mobile phase was composed
attraction. However, the electrostatic forces
gradually decreased with the increase of pH
acetonitrile and 8% methanol at pH 2.5, and
the flow rate was 0.8 mL min-1. Tetracycline
was detected by a UV detector at wavelength
decrease of tetracycline removal over a pH range of 3.0 to 5.6. Over the pH range of
6.0-9.0, the adsorption was probably due to
multiple simultaneous interactions between
acids in the solution on the adsorption of
tetracycline by anaerobic granular sludge.
The results show that low concentration of
adsorption of tetracycline into anaerobic
granular sludge. This might be due to the competition of humic acid for the surface
sites with tetracycline. However, when the concentration of humic acid increased to 10
mg L-1, the adsorption was less influenced
by the addition of the humic acids. With the further increase of humic acid concentration
from 10.0 to 150.0 mg L-1, the removal of
tetracycline from the solution shows a very
slight decrease. This phenomenon could be
explained by hydrophobic partitioning of
sludge associated humic acid and “free”
dissolved organic matter in liquid animal
adsorption capacity of anaerobic granular
aromatic macromolecules with fatty acids,
resulting in “free” humic acids increase in
aliphatic side chains (Kulshrestha et al.,
desorbed from the anaerobic granular sludge
2004). The functional groups of humic acids
interact with tetracycline and therefore
influence the mobility of tetracycline (Tolls,
granular sludge were carried out at initial tetracycline concentration of 80.0 mg L-1 and temperature of 25, 35 and 45 oC,
respectively. The adsorption process can be
such as ∆G0, ∆H0, and ∆S0, which are
Fig. 2 Effect of humic acid on the adsorption
where ∆G0, ∆H0 and ∆S0 are free energy
The values of ∆G0 were negative and
change, standard enthalpy change, standard
decreased with increasing temperature as
entropy change, respectively, Kc is the
listed in Table 2. Since negative ∆G0 at
equilibrium constant, Cs is the equilibrium
different temperatures indicates that the
concentration of tetracycline on anaerobic
adsorption process is spontaneous and the
granular sludge (mg L-1), Ce is the
shift of ∆G0 to higher negative values is
equilibrium concentration of tetracycline in
indicative of a rapid and more spontaneous
solution (mg L-1), R is the ideal gas constant
adsorption. The ∆G0 and its trend in this
(8.314 J mol-1 K-1), and T is the adsorption
tetracycline on anaerobic granular sludge
∆G0 was calculated at the initial
tetracycline concentration of 80 mg L-1. The
high temperature. This was confirmed by the
plot of lnKc against 1T-1 was carried out as
positive value of ∆H0, which revealed that
indicated in Fig. 3, in which the slope and
the adsorption of tetracycline on anaerobic
intercept obtained by a curve-fitting program
granular sludge was endothermic and likely
were used to calculate the ∆H0 and ∆S0. The
to be dominated by physical processes. The
slope of the plot equals to -∆H0/R and its
positive value of ∆S0 suggests a slight
intercept value equals to ∆S0/R. These
increase in randomness at the solid/solution
thermodynamic parameters are presented in
widely used to investigate the kinetics of
adsorption process. In this study, peudo-first order equation and pseudo-second order
equation were separately used to fit the
anaerobic granular sludge. The first order Lagergren equation is expressed as (Hu et
of tetracycline by anaerobic granular sludge.
where k1 is the rate constant of first-order
adsorption (min-1), qeq and qt are the amounts
of tetracycline adsorbed on granulars at
equilibrium and at time t (min), respectively.
A plot of log (qeq-qt) versus t is shown in
Fig. 4a. The shape of the lines indicates that
the first-order Lagergren equation didn’t fit
well to the whole range of the adsorption
process, while it was generally applicable
over the initial stage of the adsorption
3.5 Langmuir and Freundlich adsorption
equation was also applied to describe the
isotherms at various temperatures
equation is expressed as (Wang et al., 2006):
adsorbed phase on the adsorbents and that in
the solution can be analyzed by adsorption
isotherms. According to previous studies, the
where k2 is the pseudo-second order rate
constant (g mg-1 min-1). The intercept of the
plots of t/qt vs t was used to calculate the
rate constant k2. All regression coefficients
monolayer adsorption onto a surface with a
finite number of identical sites, and is
pseudo-second order equation fitted very
well to the adsorption process. As seen in
Fig. 4b, the pseudo-second order equation is
solute molecules on the adsorbent surface. It
more suitable for predicting the behavior
is given in the following (Alemayehu et al.):
where Qmax and b are Langmuir constants, in
which Qmax is maximum adsorption capacity
and b is the affinity of the binding sites, c
is the residual tetracycline concentration in
solution at equilibrium (mg L-1) and qeq is the
amount of tetracycline per unit of anaerobic
granular sludge at equilibrium (mg g-1).
max and b can be calculated from
the slope and intercept of the linear plots of
1/qeq versus 1/ceq, as shown in Fig. 5a. The
correlation coefficients (R2) were 0.983-
adsorption capacities of tetracycline by
anaerobic granular sludge at 25, 35 and 45oC
were 2.984, 4.108 and 4.618, respectively,
confirming the results of thermodynamics
Fig. 4 Linear fit at different temperature: (a) pseudo-first order rate equation and (b) pseudo-second order rate equation.
Tetracycline is one of the most often used
antibiotics in animal husbandry. The residual
tetracycline after animal use will enter into
animal wastewaters, which are further treated by anaerobic digestion system.
granular sludge system will provide useful
information on the fate and transformation of
tetracycline. Adsorption of tetracycline by
process. Although the adsorption is affected
by different kinds of parameters, batch adsorption data in this study clearly
demonstrated that tetracycline adsorption is
characteristics of anaerobic granular sludge,
environment. These findings are important to
understand the fate and transformation of
tetracycline in anaerobic granular digestion
isotherms of the adsorption of tetracycline
by anaerobic granular sludge at different
4. Conclusions
Freundlich isotherm equation is expressed as
removal efficiency of tetracycline 93% was
efficiency of tetracycline was affected by the
where Kf and nf are Freundlich constants
initial pH and the concentration of humic
acid in the solution, the temperature in the
adsorption intensity, respectively, and can be
determined from the log qeq versus log ceq, as
indicated that the adsorption process was a
Freundlich isotherm, Kf and nf were obtained
adsorption isotherms analysis shows that
respectively. The correlation coefficient (R2)
was 0.925-0.986, which was lower than that
equilibrium and confirmed the results of
Langmuir model is better fitted than the
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This research was partially supported by
the NSFC (51078122, 50808061), the NSFC-JST Joint Project (21021140001, the Special Fund of State Key Joint Laboratory of Environment Simulation and Pollution Control (10K06ESPCT), and the project-sponsored by SRF for ROCS, SEM.
Epinephrine Salts – Medicinal Nitroglycerine – P & U Listed Syringe Waste Following is a list of each state and whether or not they are consistent with the EPA’s stance on Epinephrine Salts, Medicinal Nitroglycerine and P & U Listed Used Syringe Waste. Epinephrine Salts SUMMARY: Epinephrine Salts are not a P-Listed waste. DETAILS: USEPA Memo Dated 10/07/2007. Subject: Scope
Adsorption removal of tetracycline from aqueous solution by anaerobic granular sludge: 
10000 tons in 2003 (Hu et al., 2008; Zhang
with granular sludge was often used for the
treatment of high concentration of organic
the animal gut, resulting in about 30-90% of
the antibiotics excreting into environment as
information regarding the adsorption process
parent compounds after animal use (Sarmah
of tetracycline on anaerobic granular sludge
et al., 2006). Since antibiotics are designed
wastewater, which limits the understanding
of antibiotics behavior in the UASB reactor.
Therefore, the objective of this study was to
evaluate the sorption capacity of anaerobic
2006). The short-term effects of veterinary
antibiotics on aquatic organisms, bacteria,
kinetics of the sorption process, which will
macro-invertebrates, and plants have been
management and operation of UASB reactor
toxicity studies were undertaken at higher
treating tetracycline contaminated animal
concentrations than that in the environment
(Sarmah et al., 2006). Tetracycline residue in
the environment will induce the occurrence
2. Materials and methods 
355 nm. The retention time of tetracycline
* Note: the content of metals is based on the
3. Results and discussion 
6.0-9.0, the adsorption was probably due to
multiple simultaneous interactions between
acids in the solution on the adsorption of
tetracycline by anaerobic granular sludge.
The results show that low concentration of
adsorption of tetracycline into anaerobic
granular sludge. This might be due to the competition of humic acid for the surface
sites with tetracycline. However, when the concentration of humic acid increased to 10
mg L-1, the adsorption was less influenced
by the addition of the humic acids. With the further increase of humic acid concentration
from 10.0 to 150.0 mg L-1, the removal of
tetracycline from the solution shows a very
slight decrease. This phenomenon could be
explained by hydrophobic partitioning of
sludge associated humic acid and “free”
dissolved organic matter in liquid animal
adsorption capacity of anaerobic granular
aromatic macromolecules with fatty acids,
resulting in “free” humic acids increase in
aliphatic side chains (Kulshrestha et al.,
desorbed from the anaerobic granular sludge
2004). The functional groups of humic acids
interact with tetracycline and therefore
influence the mobility of tetracycline (Tolls,
granular sludge were carried out at initial tetracycline concentration of 80.0 mg L-1 and temperature of 25, 35 and 45 oC,
respectively. The adsorption process can be
such as ∆G0, ∆H0, and ∆S0, which are
Fig. 2 Effect of humic acid on the adsorption
where ∆G0, ∆H0 and ∆S0 are free energy
The values of ∆G0 were negative and
change, standard enthalpy change, standard
decreased with increasing temperature as
entropy change, respectively, Kc is the
listed in Table 2. Since negative ∆G0 at
equilibrium constant, Cs is the equilibrium
different temperatures indicates that the
concentration of tetracycline on anaerobic
adsorption process is spontaneous and the
granular sludge (mg L-1), Ce is the
shift of ∆G0 to higher negative values is
equilibrium concentration of tetracycline in
indicative of a rapid and more spontaneous
solution (mg L-1), R is the ideal gas constant
adsorption. The ∆G0 and its trend in this
(8.314 J mol-1 K-1), and T is the adsorption
tetracycline on anaerobic granular sludge
∆G0 was calculated at the initial
tetracycline concentration of 80 mg L-1. The
high temperature. This was confirmed by the
plot of lnKc against 1T-1 was carried out as
positive value of ∆H0, which revealed that
indicated in Fig. 3, in which the slope and
the adsorption of tetracycline on anaerobic
intercept obtained by a curve-fitting program
granular sludge was endothermic and likely
were used to calculate the ∆H0 and ∆S0. The
to be dominated by physical processes. The
slope of the plot equals to -∆H0/R and its
positive value of ∆S0 suggests a slight
intercept value equals to ∆S0/R. These
increase in randomness at the solid/solution
thermodynamic parameters are presented in
widely used to investigate the kinetics of
adsorption process. In this study, peudo-first order equation and pseudo-second order
equation were separately used to fit the
anaerobic granular sludge. The first order Lagergren equation is expressed as (Hu et
of tetracycline by anaerobic granular sludge.
where k1 is the rate constant of first-order
adsorption (min-1), qeq and qt are the amounts
of tetracycline adsorbed on granulars at
equilibrium and at time t (min), respectively.
A plot of log (qeq-qt) versus t is shown in
Fig. 4a. The shape of the lines indicates that
the first-order Lagergren equation didn’t fit
well to the whole range of the adsorption
process, while it was generally applicable
over the initial stage of the adsorption
3.5 Langmuir and Freundlich adsorption
equation was also applied to describe the
isotherms at various temperatures
equation is expressed as (Wang et al., 2006):
adsorbed phase on the adsorbents and that in
the solution can be analyzed by adsorption
isotherms. According to previous studies, the
where k2 is the pseudo-second order rate
constant (g mg-1 min-1). The intercept of the
plots of t/qt vs t was used to calculate the
rate constant k2. All regression coefficients
monolayer adsorption onto a surface with a
finite number of identical sites, and is
pseudo-second order equation fitted very
well to the adsorption process. As seen in
Fig. 4b, the pseudo-second order equation is
solute molecules on the adsorbent surface. It
more suitable for predicting the behavior
is given in the following (Alemayehu et al.):
where Qmax and b are Langmuir constants, in
which Qmax is maximum adsorption capacity
and b is the affinity of the binding sites, c
is the residual tetracycline concentration in
solution at equilibrium (mg L-1) and qeq is the
amount of tetracycline per unit of anaerobic
granular sludge at equilibrium (mg g-1).
max and b can be calculated from
the slope and intercept of the linear plots of
1/qeq versus 1/ceq, as shown in Fig. 5a. The
correlation coefficients (R2) were 0.983-
adsorption capacities of tetracycline by
anaerobic granular sludge at 25, 35 and 45oC
were 2.984, 4.108 and 4.618, respectively,
confirming the results of thermodynamics
Fig. 4 Linear fit at different temperature: (a) pseudo-first order rate equation and (b) pseudo-second order rate equation.
Tetracycline is one of the most often used
antibiotics in animal husbandry. The residual
tetracycline after animal use will enter into
animal wastewaters, which are further treated by anaerobic digestion system.
granular sludge system will provide useful
information on the fate and transformation of
tetracycline. Adsorption of tetracycline by
process. Although the adsorption is affected
by different kinds of parameters, batch adsorption data in this study clearly
demonstrated that tetracycline adsorption is
characteristics of anaerobic granular sludge,
environment. These findings are important to
understand the fate and transformation of
tetracycline in anaerobic granular digestion
isotherms of the adsorption of tetracycline
by anaerobic granular sludge at different
4. Conclusions 
macro and micro-vesicular volcanic rocks
Kulshrestha P., Giese R.F., Aga D.S. (2004).
from water. Separation and Purification
Investigating the molecular interactions of
Technology, 78(1), 55-61. 
Carbon Nanotubes. Environmental Science