g) degradation of Ofloxacin, antibiotic: Synergetic effect, kinetic studies & assessment of its degraded metabolites" /> g) degradation of Ofloxacin, antibiotic: Synergetic effect, kinetic studies & assessment of its degraded metabolites" /> g) degradation of Ofloxacin, antibiotic: Synergetic effect, kinetic studies & assessment of its degraded metabolites" />
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Frontiers of Environmental Science & Engineering

Front. Environ. Sci. Eng.    2019, Vol. 13 Issue (3) : 42     https://doi.org/10.1007/s11783-019-1126-3
Statistical modeling of radiolytic (60Co g) degradation of Ofloxacin, antibiotic: Synergetic effect, kinetic studies & assessment of its degraded metabolites
G. S. Muthu Iswarya, B. Nirkayani, A. Kavithakani, V. C. Padmanaban()
Centre for Research, Department of Biotechnology, Kamaraj College of Engineering & Technology, Madurai, Tamilnadu, India
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Linear, interactive and quadratic effects of process parameters were studied.

Degradation of Ofloxacin (Ofx) was related with G value of irradiation process.

The synergistic effect of H2O2 on lower dose of g-irradiation was established.

The process follows pseudo first order with dose constant (d = 0.232 kGy1).

The impact of human activities in the past few decades has paved the way for the release of pollutants due to the improper effluent treatment. Recent studies revealed that, Ofloxacin, an antibiotic as one of the major pollutant affecting surface water and ground water. In this study, the radiolytic potential of Ofloxacin was investigated. The effects of pH, dose and concentration of Ofloxacin were analyzed using One Factor At a Time (OFAT) and the interactive effects between the parameters were studied using Face Centered Central Composite Design. The statistically optimised developed model shows 30% degradation at initial antibiotic concentration of 1mM at pH 3.0 and at 2 kGy dose of gamma ray. The process efficiency was evaluated in terms of G value and its correlation with the concentration of antibiotic was also established. The process of degradation was augmented by the addition of H2O2 (1.5 mM). The reaction kinetics for the process was evaluated, the dose rate constant and the rate of degradation for the augmented process was found to be 0.232 kGy-1 and 0.232 mM/kGy, respectively. The degraded metabolites of the radiolytic degradation of Ofloxacin were analyzed through change in pH, reduction in TOC and GC-MS spectrum.

Keywords Ofloxacin      Gamma irradiation      Face centered central composite design      Reaction kinetics      Gas Chromatography-Mass spectrum     
This article is part of themed collection: Environmental Antibiotics and Antibiotic Resistance (Xin Yu, Hui Li & Virender K. Sharma)
Corresponding Authors: V. C. Padmanaban   
Issue Date: 26 June 2019
 Cite this article:   
G. S. Muthu Iswarya,B. Nirkayani,A. Kavithakani, et al. Statistical modeling of radiolytic (60Co g) degradation of Ofloxacin, antibiotic: Synergetic effect, kinetic studies & assessment of its degraded metabolites[J]. Front. Environ. Sci. Eng., 2019, 13(3): 42.
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G. S. Muthu Iswarya
B. Nirkayani
A. Kavithakani
V. C. Padmanaban
Parameters Details & values
Class of Antibiotic Second generation- fluoroquinolone
Hydrogen Bond Donor Count 1
Hydrogen Bond Acceptor Count 8
Melting point 254°C
Solubility in water 28.3 mg/mL
Tab.1  Physical and chemical properties of Ofloxacin
Fig.1  (a)  Spectral graph of Ofx antibiotic (Untreated & treated at 0, 3 and 6 kGy), (b) Structure of Ofx.
Factor Units Low actual High actual Mean Std. Dev.
A = pH 3.00 9.00 6 2121
B = Dose of Gamma ray kGy 1 6 3.5 1.768
C = Conc. of Ofx mM 0.20 1.00 0.60 0.283
Response Units Model Transformation Mean Ratio
Y1 = Conc. of Ofx degraded mM Quadratic Base10log 0.22 8.20
Tab.2  Experimental design for radiolytic degradation of Ofloxacin (Ofx) Antibiotic by high energy gamma irradiation
Fig.2  Effect of pH and Dose of Gamma ray on radiolytic degradation of Ofloxacin (Ofx); Initial Ofx. Concentration: 0.8 mM (a); effect of concentration of Ofloxacin on radiolytic degradation of Ofloxacin (Ofx) in terms of percentage of degradation (b) and in terms of concentration of Ofx degraded (c).
Fig.3  BOX-COX Plots (a) before transformation (b) after log10 transformation.
Source Sum of
Degrees of freedom Mean
Model 1.16 9 0.13 39.71 <0.0001
A - pH 0.17 1 0.17 51.67 <0.0001
B - Dose of Gamma Ray 0.49 1 0.49 149.22 <0.0001
C - Concentration of Ofx 0.17 1 0.17 52.07 <0.0001
AB 0.074 1 0.074 22.65 0.0008
AC 0.016 1 0.016 5.01 0.0491
BC 0.056 1 0.056 17.16 0.0020
A2 0.020 1 0.020 6.07 0.0334
B2 0.051 1 0.051 15.68 0.0027
C2 0.051 1 0.051 15.66 0.0027
Residual 0.033 10 3.258E-003
Lack of fit 0.033 5 6.517E-003 3.648E+ 005 <0.0001
Pure error 8.933E-08 5 1.787E-008
Cor total 1.20 19
Tab.3  Analysis of variance (ANOVA) for the degradation of Ofx
Fig.4  Degradation of Ofloxacin; (a) A plot of the experimental vs predicted values and (b, c, d) respective normal and residual plots.
Fig.5  The contour plot (a) and the 3D response surface plot of the degradation of Ofloxacin as the function of pH and dose of gamma ray (kGy) (b). Concentration of Ofx= 0.60 mM.
Fig.6  The contour plot (a) and the 3D response surface plot of the degradation of Ofloxacin as the function of pH and Concentration of Ofx (b). Dose of gamma ray= 3.50 kGy.
Fig.7  The contour plot (a) and the 3D response surface plot of the degradation of Ofloxacin as the function of dose of gamma ray (kGy) and concentration of Ofx; pH= 6.0.
Number pH Dose of gamma ray (kGy) Conc. of Ofx
Log10 (Conc. of Ofx degraded)
Transformed scale
Conc. of Ofx degraded (mM)
Original scale
1 3.0 1.76 1 -0.588 0.258
2 3.0 1.8 1 -0.581 0.262
3 3.0 1.78 1 -0.585 0.26
4 3.0 2.09 1 -0.535 0.292
5 3.0 1.85 1 -0.574 0.27
6 3.0 1.88 1 -0.569 0.269
7 3.0 1.6 1 -0.613 0.244
8 3.0 1.93 1 -0.564 0.272
9 3.0 1.79 1 -0.579 0.264
10 3.0 1.73 1 -0.584 0.26
Tab.4  (a) Solutions for the degradation of Ofx by g- radiolysis – Optimised through RSM CCD
Response Ofloxacin
Log10(Conc. of Ofx degraded)
Transformed scale
Conc. of Ofx degraded
Original scale
Predicted -0.535 0.292
Experimental Confirmation -0.523 0.281
Tab.5  (b) Comparison of predicted response from RSM at original and transformed scale with experimental response
Fig.8  G value interpretation of the degradation of Ofloxacin of various concentrations (0.2-1.0 mM) with absorbed dose at pH 3.0. Dose rate:1.72 kGy/h.
Fig.9  Change  of G-value of Ofx at various concentration of H2O2 with absorbed dose at pH: 3.0; concentration of Ofx: 1 mM; dose rate: 1.72 kGy/h.
Fig.10  Reaction  kinetics for the degradation of Ofx with the addition of H2O2. pH: 3.0; concentration of Ofx: 1 mM; dose rate: 1.72 kGy/h.
Type and Nature of molecule Initial concentration and condition Dose constant,
d, (kGy1)
Rate of the reaction Ref.
Oflaxocin- Antibiotic Conc. of Ofx= 1 mM (361.6mg/L);
Dose rate: 1.72 kGy/h;
28.66 Gy/min
Conc. of
H2O2 = 0 mM
0.1157 0.1157 mM/kGy
(41.83 mg/L/kGy)
Present study
Conc. of
H2O2 = 0.5 mM
0.1594 0.1594 mM/kGy
(57.5 mg/L/kGy)
Present study
Conc. of
H2O2 = 1.0 mM
0.1985 0.1985 mM/kGy
(71.7 mg/L/kGy)
Present study
Conc. of
H2O2 = 1.5 mM
0.232 0.232 mM/kGy
(83.9 mg/L/kGy)
Present study
Conc. of
H2O2 = 2.0 mM
0.1568 0.1568 mM/kGy
(56.69 mg/L/kGy)
Present study
p-nitro-phenol Conc. of
p-NP= 50mg/L;
Dose rate: 185Gy/min
Conc. of
H2O2 = 0.5 mM
0.433 (21.66 mg/L/kGy) Yu et al. (2010)
Conc. of
H2O2 = 1.17 mM
0.572 (28.63 mg/L/kGy) Yu et al. (2010)
Conc. of
H2O2 = 2.35 mM
0.702 (35.1 mg/L/kGy) Yu et al. (2010)
Sulfa-methazine Conc. of Sulfa- methazine= 20mg/L;
Dose rate: 339Gy/min
Conc. of
H2O2 = 0.29 mM
0.0036 (0.072 mg/L/kGy) Liu and Wang (2013)
Conc. of
H2O2 = 0.88 mM
0.0045 (0.09 mg/L/kGy) Liu and Wang (2013)
Tab.6  Comparison of kinetic parameters for the removal of different recalcitrant at various concentrations of H2O2 with the current study
Dose (kGy) pH 3.0 pH 5.0 pH 7.0 pH 9.0 pH 11.0
0.2 mM 1 mM 0.2 mM 1 mM 0.2 mM 1 mM 0.2 mM 1 mM 0.2 mM 1 mM
1 3.6 3.2 5.0 4.2 7.0 6.7 8.3 8.4 10.6 10.2
2 3.3 2.8 5.0 4.1 7.0 6.6 8.4 7.9 10.4 10.1
3 3.2 2.7 5.0 4.0 6.8 6.4 8.3 7.8 10.3 9.8
4 2.9 2.5 4.8 3.6 6.6 6.3 8.1 7.8 10.2 9.6
5 2.8 2.4 4.6 3.4 6.5 6.2 8.2 7.7 10.2 9.6
6 2.6 2.0 4.5 3.4 6.5 6.0 8.3 7.5 10.2 9.5
Tab.7  Decrease  in pH from the initial pH as a response of irradiation on Ofx (0.2 and 1 mM) at the dose rate of 1.72 kGy/h
Fig.11  Radiolytic  degradation of Ofx: Comparison between percentage of degradation and percentage of reduction of TOC; pH:3.0; concentration of Ofx: 0.8 mM.
Fig.12  GC-MS Spectrum of Ofloxacin. (a) Before degradation; (b) after degradation.
Retention Time
Name of the molecule Structure of molecule Area %
Before degradation After degradation
9.54 Tetradecane CH3(CH2)12CH3 1.64 0.339
11.19 Butylated hydroxytoluene 13.186 3.671
18.179 Bis (2-ethylhexyl) phthalate ? 74.178
19.93 Hexadecanoic acid, methyl ester CH3(CH2)14CO2CH3 1.967 0.556
20.07 5,8,11,14,17-Eicosa pentaenoic Acid 0.488 0.126
20.415 1,2-benzene di carboxylic acid 1.236 0.235
20.855 6,9,12,15- Docosatetraenoic acid, methyl ester 0.769 0.145
21.051 5,8,11,14-Eicosatetraenoic acid,methyl ester 0.957 0.186
Tab.8  Degraded  metabolites from GS-MS Spectrum: Before and after degradation
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