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Fenton Treatment of Chlorpyrifos, Cypermethrin and Chlorothalonil Pesticides in Aqueous Solution



Augustine Chioma Affam, Malay Chaudhuri and Shamsul Rahman M. Kutty
 
ABSTRACT

The study examined the effect of operating conditions of the Fenton process on degradation, biodegradability improvement and mineralization of chlorpyrifos, cypermethrin and chlorothalonil pesticides in aqueous solution. Also, the degradation of the pesticides under optimum operating conditions was evaluated. The optimum operating conditions for Fenton treatment of an aqueous solution containing 100, 50 and 250 mg L-1 of chlorpyrifos, cypermethrin and chlorothalonil, respectively were observed to be H2O2/COD molar ratio 3, H2O2/Fe2+ molar ratio 10 and pH 3. Pesticide degradation increased with temperature. Under the optimum operating conditions, complete degradation of the pesticides occurred in 1 min. Biodegradability (BOD5/COD ratio) increased from zero to 0.35 and COD and TOC removal were 69.03 and 55.61%, respectively in 60 min. Due to mineralization of organic carbon, decrease in ammonia-nitrogen from 22-6.1 mg L-1 and increase in nitrate from 0.7-15.2 mg L-1 in 60 min were observed. The study indicated that Fenton process can be used for pretreatment of combined chlorpyrifos, cypermethrin and chlorothalonil aqueous solution or wastewater for biological treatment.

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Augustine Chioma Affam, Malay Chaudhuri and Shamsul Rahman M. Kutty, 2012. Fenton Treatment of Chlorpyrifos, Cypermethrin and Chlorothalonil Pesticides in Aqueous Solution. Journal of Environmental Science and Technology, 5: 407-418.

DOI: 10.3923/jest.2012.407.418

URL: https://scialert.net/abstract/?doi=jest.2012.407.418
 
Received: November 16, 2011; Accepted: July 16, 2012; Published: August 23, 2012

INTRODUCTION

Pest control is a worldwide problem in agriculture, forest ecosystem and environmental management (Bhattacharyya and Bhattacharya, 2006). In an effort to combat the menace of pests, industrial use of pesticides has become prevalent which has led to widespread contamination of the environment including surface water and groundwater (Foo and Hameed, 2010). Groundwater pollution is of increasing concern, especially because about 70% of drinking water comes from groundwater (Tariq et al., 2006). Infiltration of pesticide effluent into groundwater, promoted by spray drift, soil leaching, tile drainage outflow, base-flow seepage, surface run-off, volatilization (diffuse-source inputs), sewer overflows, improper handling of tank mix leftovers, leaking of faulty equipments, incorrect storage of canisters, drippings from agricultural practices, accidental spillage and farmyard deposition (point source pathways) from agriculture, horticulture, forestry, chemical industry and domestic activities (Reichenberger et al., 2007), constitutes persistent and accumulative deterioration of the aquatic environment (Gentz, 2009). Reports have indicated that a minimum of 50 μg L-1 concentration of pesticide is toxic to guppy fish (Sharbidre et al., 2011) and pesticide residues in soil surface layer are higher in concentrations than in soil subsurface layer (Al-Wabel et al., 2011). With agricultural modernization in developing countries in the mid 1960s, the global pesticide industry witnessed a tremendous growth (Binswanger et al., 1998). The increasing concern over pesticides in surface and groundwater has required evaluation of their mobility as a basis of risk assessment (Abdel-Nasser et al., 2011). Detection of pesticide compounds in inland waterways (Leong et al., 2007) and natural waters (Somchit et al., 2009) have been reported. Classification of pesticides is broadly based on their structure with the dominant ones including organochlorines, organophosphates, pyrethroids and carbamates (Al-Masri et al., 2009). Chlorpyrifos (CPF) is a broad-spectrum organophosphate insecticide for use in plant protection and belongs to class II of World Health Organization classification of pesticides (Cox, 1997). It is moderately toxic and prolonged exposure to CPF has been reported to cause anemia although the mechanism has not been elucidated (Ambali et al., 2010). Cypermethrin (CPF) is of the family of pyrethroid and belongs to class II. Pyrethroid pesticides were developed as a synthetic version of the naturally occurring pesticide pyrethrin. They have been modified to increase their stability in the environment (Eneh, 2011). Chlorothalonil (CTN) (a fungicide) belongs to class IV. Degradation/removal of CPF, CPT and CTN in natural water and wastewater has been reported. CPF was degraded by soil microbial action (Hua et al., 2009), CPF and CTN were removed from simulated storm water runoff in constructed wetland (Sherrarda et al., 2004) and CTN was degraded by Bacillus cereus (Zhang et al., 2007). Anodic oxidation at lead dioxide or boron-doped diamond electrode was used to degrade CPF (Samet et al., 2010a, b). Another report compared the effectiveness between UV/O3 Advanced Oxidation Process (AOP) and Poly Aluminium Chloride (PACl) as a coagulant for the removal of chlorpyrifos, diazinon and carbaryl from drinking water (Samadi et al., 2011). CTN was degraded by bimetallic iron based systems and pulsed electric field (Ghauch and Tuqan, 2008; Chen et al., 2009) and CPT alone was degraded by microwave irradiated photo-Fenton reaction (Gromboni et al., 2007). However, from an economic and technical point of view, the use of electrodes is not ideal, especially when oxidizing organic waste where fouling of the electrode can occur (Brillas et al., 2009). The use of oxidative processes for pesticide degradation in natural, wastewater and residual waters has been reported by De Laat et al. (1999). Research has demonstrated that effects of combined pesticides should be taken into account to assess the actual impact of their application and degradation feasibility (Xiaoqiang et al., 2008). This is because some pesticides naturally have little or no toxicity but chemicals they degenerate into during fermentation are highly toxic and dangerous (Gareth et al., 2006). Typical pesticide wastewater characteristics collected from a pesticide company in China were COD 22,000±1000 mg L-1, pH 13-14, BOD5 650 mg L-1 and BOD5/COD ratio 0.03 (Zhenglong et al., 2011). Another pesticide wastewater taken from the production process in China had a COD value of 3242 mg L-1 and pH 6 (Rongxi et al., 2009).

Advanced Oxidation Processes (AOPs) are highly effective for degradation/removal of majority of water pollutants (Pera-Titus, 2004). Oxidation with Fenton’s reagent is based on ferrous ions, hydrogen peroxide and hydroxyl radicals produced by the catalytic decomposition of hydrogen peroxide in acidic solution (Chamarro et al., 2001). Fenton’s reagent has been reported to be effective in the treatment of recalcitrant wastewater (Lodha and Chaudhari, 2007; Gulkaya et al., 2006; Lin and Jiang, 2003) and degradation/removal of single pesticide in aqueous solution (Rongxi et al., 2009; Tamimi et al., 2008; Badawy et al., 2006). The purpose of this study was to examine the effect of operating conditions (H2O2/COD molar ratio, H2O2/Fe2+ molar ratio, pH, temperature and reaction time) of the Fenton process on degradation, biodegradability improvement (BOD5/COD ratio) and mineralization of a combined chlorpyrifos (CPF), cypermethrin (CPT) and chlorothalonil (CTN) pesticides in aqueous solution. High Performance Liquid Chromatography (HPLC) and Fourier Transform Infrared (FTIR) spectroscopy were also used to estimate pesticide concentration and degradation of organic bonds after treatment.

MATERIALS AND METHODS

Reagents: Hydrogen peroxide (30%, w/w) and ferrous sulphate heptahydrate (FeSO4.7H2O) were purchased from R and M Marketing, Essex, U.K. Analytical grade of and chlorpyrifos (CPF) was obtained from Dr. Ehrenstorfer, Germany and cypermethrin (CPT) and chlorothalonil (CTN) were obtained from Sigma-Aldrich, Germany. They were used for analytical identification and determination of pesticide concentration by HPLC. The pesticides used to prepare aqueous solution were obtained from a commercial source and were used as received. Figure 1 shows the chemical structure of the pesticides.

Analytical methods: Pesticide concentration in treated samples was determined by HPLC (Agilent 1100 Series) equipped with micro-vacuum degasser (Agilent 1100 Series), quaternary pumps, diode array and multiple wavelength detector (DAD) at wavelength 230 nm. Chemstation software was installed and used for data recording. The HPLC detection column was ZORBAX SB-C18 (3.0x250 mm, 5 μm). The column temperature was set at 30°C. Mobile phase was made up of 25% buffer solution (0.001 M KH2PO4 in double distilled water) and 75% acetonitrile. Chemical Oxygen Demand (COD) was measured according to the standard methods (APHA et al., 2005). Where the sample contained hydrogen peroxide (H2O2), to reduce interference in COD determination pH was increased to above 10 so as to decompose hydrogen peroxide to oxygen and water (Talinli and Anderson, 1992; Kang et al., 1999). TOC analyzer (Model 1010, O and I analytical) was used for determining Total Organic Carbon (TOC). pH measurement was done using a pH meter (HACH sension 4) and a pH probe (HACH platinum series pH electrode model 51910, HACH Company, USA).

Fig. 1(a-c): Chemical structure of (a) Chlorpyrifos, (b) Cypermethrin and (c) Chlorothalonil

Biodegradability was measured by 5-day biochemical oxygen demand (BOD5) test according to the standard methods. DO was measured using YSI 5000 dissolved oxygen meter. The seed for BOD5 test was obtained from a municipal wastewater treatment plant. Fourier Transform Infrared (FTIR) spectrum was obtained using FTIR-8400S, SHIMADZU.

Pesticide aqueous solution: Pesticide aqueous solution was 400 mg L-1 of pesticides (100 mg L-1 of chlorpyrifos (CPF), 50 mg L-1 of cypermethrin (CPT) and 250 mg L-1 of chlorothalonil (CTN) in distilled water. It was prepared weekly and stored at 4°C. The pesticide aqueous solution had a COD 1130 mg L-1.

Experimental procedure: Batch experiments were carried out in a 600 mL Pyrex reactor with 500 mL of the pesticide aqueous solution. The required amount of iron (FeSO4.7H2O) was added to the aqueous solution with pH adjustment to the required value using sulfuric acid (H2SO4) and mixed by a magnetic stirrer to ensure complete homogeneity. Thereafter, the necessary amount of H2O2 was added to the pesticide aqueous solution. Samples were taken at pre-selected time intervals using a syringe. The samples were filtered through a 0.45 μm membrane filter for COD, BOD5 and TOC measurement and filtered through a 0.20 μm membrane filter for HPLC and FTIR spectra.

RESULTS AND DISCUSSION

Effect of H2O2/COD molar ratio: In determining the optimal H2O2/COD molar ratio, initial H2O2 concentration was varied in the range 35.31-141.25 mM at initial COD 1130 mg L-1 (35.31 mM). The corresponding H2O2/COD molar ratios were 1, 1.5, 2, 2.5, 3, 3.5 and 4. The other operating conditions were pH 3 and H2O2/Fe2+ molar ratio 50. Figure 2a-c show the effect of H2O2/COD molar ratio on pesticide degradation in terms of COD and TOC removal and BOD5/COD ratio. The COD removal after 60 min reaction time was 28.91, 30.26, 37.31, 46.88, 50.23, 42.26 and 37.88% at H2O2/COD molar ratio 1, 1.5, 2, 2.5, 3, 3.5 and 4, respectively. The TOC removal after 60 min reaction time was 17.85, 27.54, 29.73, 34.40, 40.26, 32.03 and 30.09% at H2O2/COD molar ratio 1, 1.5, 2.0, 2.5, 3, 3.5 and 4, respectively. The BOD5/COD ratio after 60 min reaction time was 0.17, 0.21, 0.26, 0.31, 0.33, 0.17 and 0.14 at H2O2/COD molar ratio 1, 1.5, 2, 2.5, 3, 3.5 and 4, respectively. The results indicate that the pesticide degradation increased by increasing the concentration of H2O2 but above H2O2/COD molar ratio 3, the degradation did not improve. This may be due to auto-decomposition of H2O2 to oxygen and water and the recombination of hydroxyl radicals (OH) radicals as in reactions 1 and 2 (Badawy et al., 2006). Moreover, excess H2O2 reacts with ferric ions to form hydroperoxyl radical as in reaction 3 (Kavitha and Palanivelu, 2005). Maximum COD and TOC removal and biodegradability (BOD5/COD ratio) improvement was achieved at H2O2/COD molar ratio 3:

(1)

(2)

(3)

The results agree with the reported results-the optimum H2O2/COD molar ratio was 4.4 for (Fenitrothion, diazinon and profenofos) insecticide aqueous solution and wastewater (Badawy et al., 2006) and 6.5 for palm oil mill effluent (Sinnaraprasat and Fongsatitkul, 2011).

Fig. 2(a-c): Effect of H2O2/COD molar ratio on pesticide degradation in terms of (a) COD removal, (b) TOC removal and (c) BOD5/COD ratio
Fig. 3(a-c): Effect of H2O2/COD molar ratio on pesticide degradation in terms of (a) COD removal, (b) TOC removal and (c) BOD5/COD ratio

Effect of H2O2/Fe2+ molar ratio: To study the effect of increasing ferrous ion concentration (decreasing H2O2/Fe2+ molar ratio) and to obtain the optimum H2O2/Fe2+ molar ratio for degradation of the pesticides in aqueous solution, Fe2+ concentration was varied from 0.94 to 70.62 mM under operating conditions of pH 3, H2O2/COD molar ratio 3 and initial COD 1130 mg L-1. The results shown in Fig. 3a-c indicate that COD and TOC removal efficiency and BOD5/COD ratio improvement increased with increasing Fe2+ concentration. The COD removal after 60 min reaction time was 38.12, 45.06, 60.16, 53.32, 47.11, 30.44 and 25.31% at H2O2/Fe2+ molar ratio 2, 5, 10, 25, 50, 100 and 150, respectively. The TOC removal after 60 min reaction time was 34.31, 47.12, 52.59, 43.66, 37.18, 31.35 and 23.02% at H2O2/Fe2+ molar ratio 2, 5, 10, 25, 50, 100 and 150, respectively. The BOD5/COD ratio after 60 min reaction time was 0.17, 0.19, 0.32, 0.36, 0.25, 0.17 and 0.14 at H2O2/Fe2+ molar ratio 2, 5, 10, 25, 50, 100 and 150, respectively. The degradation did not improve with decreasing H2O2/Fe2+ molar ratio below 10. Presumably, this resulted from direct reaction of OH radical with metal ions at high concentration of Fe2+ (Joseph et al., 2000) as in reaction 4. The H2O2/Fe2+ molar ratio 10 was optimum for degradation of the pesticides in aqueous solution:

(4)

The results agree well with the reported results for different pollutants-the optimum H2O2/Fe2+ molar ratio was 10 and 40 for degradation of chlorophenol and chlorinated aliphatics (Pera-Titus et al., 2004; Tang and Huang, 1997), 6.5 for cresols destruction (Kavitha and Palanivelu, 2005), 5-40 for degradation of aromatic amines (Casero et al., 1997), 1.9-3.7 for degradation of trihalomethanes (Tang and Tassos, 1997) and 2.5 for landfill leachate treatment (Tengrui et al., 2007). In the present of study COD and TOC degradation and BOD5/COD ratio improvement for low H2O2/Fe2+ molar ratio is higher than that for high H2O2/Fe2+ molar ratio. This may be explained by taking into consideration the intermediates formed during reaction. Lower H2O2/Fe2+ molar ratio (higher Fe2+ concentration) causes a high removal of the target compound and formation of early intermediates (Pera-Titus et al., 2004; Gonzalez et al., 2007).

Effect of pH: The pH value has a decisive effect on the generation of OH radicals and hence the oxidation (degradation) efficiency. It is known that OH radical generation occurs in acidic condition. To determine the optimum pH, experiments were conducted by varying the pH in the range 2-6. The other operating conditions were H2O2/COD molar ratio 3, H2O2/Fe2+ molar ratio 10 and initial COD 1130 mg L-1. Figure 4a-c show the effect of pH on pesticide degradation in terms of COD and TOC removal and BOD5/COD ratio. The COD removal after 60 min reaction time was 55.17, 58.48, 52.33, 47.67 and 39.15% at pH 2, 3, 4, 5 and 6, respectively.

Fig. 4(a-c): Effect of pH on pesticide degradation in terms of (a) COD removal, (b) TOC removal and (c) BOD5/COD ratio

The TOC removal after 60 min reaction time was 46.86, 50.34, 43.72, 37.55 and 22.41% at pH 2, 3, 4, 5 and 6, respectively. BOD5/COD ratio after 60 min reaction time was 0.24, 0.36, 0.29, 0.25 and 0.20 at pH 2, 3, 4, 5 and 6, respectively. Therefore, pH is an important parameter in Fenton process and studies have shown that acidic pH levels near 3 are usually optimum for Fenton oxidation (Arnold et al., 1995; Pignatello et al., 1992). Based on the results, the optimum pH for degradation of the pesticides in aqueous solution was 3.0.

Effect of temperature: To study the effect of temperature, experiments were performed at 10, 20, 30 and 40°C. Initial COD was maintained at 1130 mg L-1. The other operating conditions were H2O2/COD molar ratio 3, H2O2/Fe2+ molar ratio 10 and pH 3. Figure 5a-c shows the results of pesticide degradation at different temperature in terms of COD and TOC removal and BOD5/COD ratio. After 60 min reaction time COD removal was 28.39, 50.93, 59.02 and 69.03%, TOC removal was 15.95, 48.73, 52.33 and 55.61% and BOD5/COD ratio was 0.08, 0.0.17, 0.32 and 0.35 at temperature 10, 20, 30 and 40°C, respectively. This is because the number of molecular collisions and reactivity increase as a function of temperature according to the kinetic theory (Loftin et al., 2008). At 10°C there was obvious reduction in degradation because of slow reaction rate between OH radical and the organic structure of the substrate (Kavitha and Palanivelu, 2005). The results agree well with the findings of Kandil et al. (2011) in their investigation of chlorfenapyr degradation.

Degradation of pesticides in aqueous solution under the optimum operating conditions: Figure 6 shows the degradation of the pesticides CPF, CPT and CTN in aqueous solution under the optimum operating conditions (H2O2/COD molar ratio 3, H2O2/Fe2+ molar ratio 10, pH 3 and temperature 40°C). Complete degradation of the pesticides occurred in 1 min. Maximum COD and TOC removal were 69.03 and 55.61%, respectively. The corresponding BOD5/COD ratio was 0.35 after 60 min reaction time (Fig. 7) which is considered adequate for biological treatment as a wastewater is considered biodegradable if BOD5/COD ratio is ~0.4 (Al-Momani et al., 2002).

Fig. 5(a-c): Effect of temperature on pesticide degradation in terms of (a) COD removal, (b) TOC removal and (c) BOD5/COD ratio

Fig. 6: Degradation of CPT, CTN and CPF pesticide under optimum operating conditions

Fig. 7: Pesticide degradation under optimum operating conditions in terms of COD and TOC removal and BOD5/COD ratio

Fig. 8: Mineralization of pesticide in terms of NH3-N and NO3¯-N concentration

In terms of mineralization of organic carbon, concentration of ammonia-nitrogen (NH3-N) decreased from 22 to 6.1 mg L-1 and nitrate (NO3¯-N) increased from 0.7 to 15.2 mg L-1 in 60 min (Fig. 8).

FTIR spectra: Untreated and Fenton treated pesticide aqueous solution was analyzed by FTIR spectroscopy to check for presence of organic bonds. Identified tangential C-C stretching in benzene and hexa-substituted benzene derivatives of chlorothalonil is observed in the range of 1548 and 1265 cm-1 (Dhas et al., 2010). The cypermethrin spectrum showed absorption bands from 1742 to 1076 cm-1 due to carbonyl stretching, C = C stretching in chloroalkenes, ring vibration of benzene, CH2 deformation in R-CH2-CN structure and (C = O)-O-stretching, whereas the absorption bands of chlorpyrifos were located between 1549 to 968 cm-1 due to C = N stretching, pyridine stretching, ring vibration, ring breathing, Cl-C stretching, trigonal ring breathing and P = S stretching (Armenta et al., 2005). In the present study, the band at 1650.95 cm-1 in the untreated aqueous solution in Fig. 9a shifted to 1622.02 cm-1 in the treated aqueous solution in Fig. 9b and the band at 1448.44 cm-1 in Fig. 9a was modified as seen in Fig. 9b, indicating degradation of the pesticides.

Fig. 9(a-b): FTIR spectra of (a) Untreated and (b) Treated pesticide aqueous solution

It can be deduced that, a reduction or an increase of H2O2 and Fe2+ above a certain dose led to a decrease in degradation of the selected combined pesticides. Therefore, initial pH 3, H2O2/COD molar ratio 3, H2O2/Fe2+ molar ratio 10 reagent additions yielded highest oxidation and coagulation of the Fenton process.

CONCLUSIONS

Fenton process is effective in the treatment of an aqueous solution of chlorpyrifos, cypermethrin and chlorothalonil. Under the optimum operating conditions, complete degradation of the pesticides occurred in 1 min. Biodegradability increased from zero to 0.35 in 60 min and COD and TOC removal were 69.03 and 55.61%, respectively. Mineralization of organic carbon led to ammonia-nitrogen decrease from 22 to 6.1 mg L-1 and increase in nitrate from 0.7 to 15.2 mg L-1. Fenton process can be used for pretreatment of combined chlorpyrifos, cypermethrin and chlorothalonil aqueous solution or wastewater for further biological treatment. Based on the results, oxidation and coagulation in Fenton treatment of the chosen pesticide under the above mentioned operating conditions is feasible in removal of COD being one of the most important organic compound parameter to monitor in wastewater treatment before discharge.

ACKNOWLEDGMENTS

The authors are thankful to the management and authorities of the Universiti Teknologi PETRONAS for providing facilities for this research.

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