We examined the removal of abamectin by the electro-Fenton (EF) process and the feasibility of biological treatment after degradation. The effect of the operating parameters showed that abamectin (Aba) degradation was enhanced with increasing temperature. Response surface analysis of the central composite design led to the following optimal conditions for the abatement of chemical oxygen demand: 45.5 °C, 5 mg L−1, 150 mA, and 0.15 mmol L−1 for the temperature, initial Aba concentration, current intensity, and catalyst concentration, respectively. Under these conditions, 68.01% of the organic matter was removed and 94% of Aba was degraded after 5 h and 20 min of electrolysis, respectively. A biodegradability test, which was performed on a solution electrolyzed at 47 °C, 9 mg L−1, 150 mA, and 0.15 mmol L−1, confirms that the ratio of biological oxygen demand/chemical oxygen demand increased appreciably from 0.0584 to 0.64 after 5 h of electrolysis. This increased ratio is slightly above the limit of biodegradability (0.4). These results show the relevance of the EF process and its effectiveness for abamectin degradation. We conclude that biological treatment can be combined with the EF process for total mineralization.

INTRODUCTION

Mites, nematodes, fleas, ticks, lice, and flies are important vectors that transmit diseases to humans, animals, and agriculture worldwide. They also cause large economic losses in the quality and quantity of yields in the livestock industry and agricultural crops (Thanh et al. 2013; Khalil 2015). Due to serious and enormous economic damage caused by parasites species, their control is very important. Currently, the methods used for controlling these parasites are mainly based on the use of pesticides. Among these pesticides, the insecticide abamectin is a natural fermentation product of the soil bacterium Streptomyces avermitilis. Furthermore, abamectin is a blend of avermectins B1a and B1b (about 80% avermectin B1a and 20% avermectin B1b). These two components, B1a and B1b, have very similar biological and toxicological properties (Khalil 2015). Abamectin acts by stimulating the release of γ-aminobutyric acid thus causing paralysis by interrupting the nervous system of targeted insects (Kamel et al. 2007; Erramil et al. 2014). Avermectins have been used as a veterinary drug in livestock, to protect against a broad variety of parasites. In addition to veterinary applications, avermectin is also used to treat onchocerciasis in humans, a disease commonly known as river blindness (Raftery & Volz 2015). Abamectin was also registered as an agricultural insecticide, and it is the most active against the two-spotted spider mite, Tetranychus urticae Koch, which is one of the most destructive pests in ornamental, horticultural, and agricultural crops such as fruits and vegetables worldwide (Kwon et al. 2010). The mode of action of avermectins is not, however, specific to parasitic arthropods and nematodes, and consequently may affect other organisms in the environment (Shinawar Waseem et al. 2012). There are many reports on the persistence of abamectin in soil, soil-feces, and feces for an extended period of 14–70 days in concentrations high enough to exert toxic effects (Kolar et al. 2006). Photo-degradation kinetics of abamectin revealed very limited possibilities for photosensitized degradation of this compound induced by environmental light (Escalada et al. 2008). Furthermore, the excessive residue of abamectin can run off from the sites of application leading to the exposure of non-target aquatic organisms, showing adverse effects on the aquatic environment due to its high toxicity, even at very low concentrations (Shinawar Waseem et al. 2012). Nevertheless, all scientific papers show toxic effects of abamectin at very low concentrations. The LC50 96 h values for the different fish species of rainbow trout, bluegill sunfish, channel catfish, and carp are 3.2, 9.6, 24, and 40 mg L−1, respectively. Likewise, in another report about toxicity of abamectin, it was found that values of lethal concentrations (LC50 96 h) of abamectin for different fish species, are near to those mentioned above, i.e. 3.0 mg L−1 for rainbow trout and 4.8 mg L−1 for bluegill sunfish (Vajargah et al. 2014).

In Brazil, the animal health market of avermectin-containing products generates annual sales of around one billion dollars (Raftery & Volz 2015). By 2011, the use of abamectin reached approximately 100,000 lb (c. 45359 kg) per year due to increased penetration of the cotton market and approval as a nematicide seed treatment on corn throughout the United States. The intensive use of pesticides, particularly abamectin in agriculture and in livestock, were a source of contamination of soil, ground water, rivers, lakes, rain water, and air worldwide (Erramil et al. 2014). This contamination has become a serious environmental problem. However, it has been shown that avermectin interferes with the growth of aquatic invertebrates even at concentrations below those expected to occur in this environment. Furthermore, as many organic compounds may resist conventional water treatment, their presence in water bodies used for water harvesting may also affect human health (Raftery & Volz 2015).

Removing abamectin by biological processes, the most cost-effective solution for wastewater treatment, does not always appear to be relevant for the toxicity of abamectin. By contrast, physical and physicochemical techniques have proved their efficiency for this purpose (Fourcade et al. 2012). Among the physical processes such as adsorption, coagulation, flocculation, electro-flocculation, reverse osmosis, ultra-filtration, these most conventional methods are non-destructive and merely transfer pollutants from one phase to another, which always results in secondary pollution. Physicochemical processes are destructive and are widely used to remove recalcitrant compounds (Fourcade et al. 2012). Among them, we can cite advanced oxidation processes (AOPs). Even though AOPs have been shown to be highly efficient, their operation is still quite expensive. An attractive option is a short AOP pretreatment which leads to the formation of biodegradable intermediates of the recalcitrant pollutants, which can be subsequently degraded in a biological process, with the aim of reducing energy costs (Ferrag-Siagh et al. 2014). Therefore, before the examination of the combination of an AOP with a conventional biological treatment for pollutant removal, the relevance of an AOP pretreatment has to be checked by monitoring some specific parameters (compound concentration or chemical oxygen demand (COD) and biodegradability of the pretreated pollutant solution through biological oxygen demand (BOD5) measurements) (Ferrag-Siagh et al. 2014). The evolution of global parameters like COD, also provides useful information on oxidation, while the BOD5 on COD ratio approximates effluent biodegradability, since a value of 0.4 is considered by several authors as the boundary of biodegradability (Pulgarin et al. 1999).

Among these AOPs, electro-Fenton (EF) is an indirect electrochemical AOP derived from the Fenton reaction, but is also a promising technology for the treatment of wastewaters (Oturan et al. 2009). Indeed, it does not involve the use of harmful chemical reagents due to the fact that the reactants are electro-generated in situ; moreover, the method is easy to handle and the reactors involved are simple. H2O2 is continuously generated by the reduction of dissolved molecular O2 in a mildly acidic aqueous medium (Equation (1)) using various cathode materials (Ferrag-Siagh et al. 2014):
formula
1
Hydroxyl radicals (OH) and Fe3+ ions are then generated from the classical Fenton's reaction between Fe2+ ions and H2O2:
formula
2
Fe2+ ions in the catalytic amount are consumed by Fenton's reaction in the homogeneous medium (Equation (2)) and are regenerated at the cathode by the reduction of Fe3+ ions (Equation (3)):
formula
3
EF was developed and has been widely applied for the oxidation of various organic pollutants such as pesticides, pharmaceuticals, and dyes (Oturan et al. 2009; Ferrag-Siagh et al. 2014). However, there are few reports on the removal of abamectin using AOPs. Erramil et al. (2014) studied the anodic destruction of abamectin acaricide solution by Boron-Doped Diamond (BDD)-anodic oxidation. The effect of using different supporting electrolytes during the galvanostatic electrolysis of abamectin was investigated. The experimental results show that the electrochemical process was suitable for almost completely removing COD, due to the production of hydroxyl radicals on the diamond surface. Under optimal experimental conditions of current density (i.e., 80 mA/cm2), 88% of COD was removed in 2.5 h electrolysis (Erramil et al. 2014). The degradation of abamectin using the photo-Fenton process showed that 70% of the initial amount of the compound was removed within 60 minutes of Ultra-Violet (UV) irradiation, and 60% mineralization was observed after 180 minutes of reaction.

The degradation of ivermectin (IVM) in aqueous solution by photocatalysis with TiO2 in suspension was evaluated. Photocatalysis with UVC (at 253.7 nm) and TiO2 in suspension resulted in the degradation of 98% of IVM (500 μg L−1) in water in 600 s.

EF treatment using a carbon-felt as cathode was considered in this study. The effects of some parameters such as the concentration of catalyst, temperature, current intensity, and initial abamectin concentration were considered.

To evaluate the main interactive effects of the studied variables on the oxidation of abamectin and to determine their optimal values in order to increase the yield of abamectin oxidation, a central composite design (CCD) (24), was developed to predict the removal yield of this pollutant.

The aim of this study was, therefore, to examine the relevance of the EF process for the removal of abamectin and its possible combination with a biological treatment.

MATERIALS AND METHODS

Chemicals and reagents

Commercial abamectin (Vertimec 1.8 Emulsifiable Concentrate (EC)) was obtained from Syngenta (Agadir, Morocco). The pH of the solutions was adjusted by the addition of sulfuric acid solution (H2SO4; 98% purity) or sodium hydroxide (NaOH; 99% purity) obtained from Biochem Chemopharma (Georgia, USA). Methanol (MeOH) of high performance liquid chromatography (HPLC) analysis grade (99.9% purity) was obtained from Sigma-Aldrich (Steinheim, Germany). Ultrapure water (18 MΩ cm of resistivity) was used for HPLC analysis in this study. Catalyst (FeSO4, 7H2O) and anhydrous sodium (Na2SO4) were of analytical grade and supplied by Panreac-Quimica-SA (Barcelona, Spain) and Biochem Chemopharma, respectively. Distilled water was used to prepare all solutions.

The chemical structure of abamectin (Figure 1) is C48H72O14 (in avermectin B1a) + C47H70O14 (in avermectin B1b).
Figure 1

Molecular structure of abamectin.

Figure 1

Molecular structure of abamectin.

Experimental set-up

The electrochemical reactor used was composed of a double envelope cell of 500 mL capacity. This system ensures electrolysis at a constant temperature. The homogenization of the medium was ensured by a stirring speed of 1,000 rpm. All tests were carried out using the experimental device as schematized in Figure 2.
Figure 2

Experimental set-up for EF process.

Figure 2

Experimental set-up for EF process.

Electrochemical process

Electrolysis was carried out with a carbon-felt electrode of 25 cm2 (5 × 5 cm) surface area and 1.27 cm thickness used as a cathode. The anode electrode was in a platinized titanium grid Ti/Pt of 12.5 cm2 (5 × 2.5 cm) and 1 mm thick. The oxygen supply in the solutions was ensured by a diffuser of very fine bubbles of air using a sintered glass (4–8 μm of porosity).

All abamectin solutions were adjusted with pH = 2.9 using sulfuric acid (H2SO4) at 1 mol L−1. The electrolyte (Na2SO4) (0.05 mol L−1) was added for the solutions of abamectin to ensure good conductivity in the medium (6.5 mS cm−2) (Oturan 2013).

Samples were taken at intervals of regular time over a period of electrolysis of 5 h; the hydroxide of iron was precipitated using NaOH at 6 mol L−1. The supernatant was recovered by centrifugation and was used for different chemical analyses. To consider the choice of the pH value, the electrolyte concentration and the stirring velocity were based on earlier studies which used the EF process for degradation of other insecticides and pesticides (Djoudi et al. 2007).

Analytical methods

All samples were filtered through a 0.45 μm membrane filter for various chemical analyses (COD, total organic carbon (TOC), BOD5, and HPLC).

Determination of chemical oxygen demand

To measure the COD we followed the ‘closed reflux, colorimetric method’ for the examination of water and wastewater. The oxidizable matter contained in a sample was oxidized by heating with backward flow in a strongly acid medium with a quantity of potassium bichromate in a closed test-tube. The oxygen uptake by the sample causes a change of color whose absorbance is proportional to the quantity of the reduced potassium bichromate and is measured in equivalents of oxygen.

Determination of biological oxygen demand

We measured BOD5 by following the manometric method, which is based on the principle of the Warburg respirometer, during which the breathing of the biomass is directly measured by ‘IS 602’ type apparatus. A sample was placed in an incubation bottle, connected to a pressure gauge with mercury which was closed with a stopper provided with a pressure pick-up (Oxytop). The selected volume is a function of the desired range of measurements. The measuring apparatus was placed in incubator at 20 °C. The oxygen being consumed by the bacteria for 5 days resulted in the decrease of pressure in the bottles. However, the oxidation of organic matter caused formation of carbon dioxide (CO2), which was trapped by a pellet of KOH and created a vacuum in the bottle (Rodier 1996).

Determination of total organic carbon

The derived organic matter after treatment of the solution was also quantified by TOC, using a carbon analyzer (LCK 385 TOC, Lange Hach). The two phases during the process are: total inorganic carbon, initially expelled using the agitator Fake-x5, then TOC, oxidized out of CO2. The carbon dioxide passes through a membrane in the indicating tank, where it causes a change of color, which is evaluated using a photometer (Hach DR2800).

High performance liquid chromatography analysis

During electrolysis, high performance liquid chromatography (HPLC YL9100) followed the abamectin concentrations. The HPLC was equipped with a standard degasser (YL 9101), a manual injector (20 μL), two pumps (Model Analytical SS-1) and a detector with visible ultraviolet ray (UV/Vis detector YL9120). Analytical separation was performed using a column Teknokroma ODSA120-C18 (250 mm × 4.6 mm, particle size 5 μm) operated at 50 °C. The mobile phase consisted of MeOH–water (90:10, V/V) with a flow of 0.5 mL min−1. For a linear baseline, the system was left to stabilize for 2–3 h. Abamectin was detected at 245 nm wavelength. To perform data processing and acquisition, we used YL Clarity-software.

Adsorption tests

An experiment was realized on the carbon-felt electrode (cathode) by a solution of abamectin (20 mg L−1) under magnetic agitation with 1,000 rpm for 3 h. The samples were taken at two intervals of regular time in a period of 3 h for COD and Aba concentration analysis, to determine the carbon felt adsorption capacity on the Aba molecule.

Comparison between the EF process and electrochemical oxidation

In order to compare the EF process with simple electrochemical oxidation, a few experiments were realized to confirm the efficiency of the EF process on Aba degradation, and the oxidizing power of the OH on the organic matter present in the aqueous solutions. A first experiment was realized under the following conditions: [Aba]0 = 9 mg L−1, [Fe2+] = 0.15 mmol L−1, I = 150 mA, and T = 50 °C, using a carbon-felt cathode and a platinized titanium grid anode. A second experiment was realized with an inert cathode of stainless steel and under the same conditions as the first experiment. A third experiment was also realized but without Fe2+ and under the same conditions as the first one. There was a final experiment without bubbling air but under the same conditions as the first experiment. Samples were taken every hour for 5 h of electrolysis and COD was measured in order to follow the evolution of the organic matter.

Optimization of experimental parameters

The use of a design experiment approach, and in particular the response surface methodology and the CCD, allowed us to calculate the optimal values of the operating parameters affecting the treatment of solutions of Aba by electrochemical process with a minimum number of experiment trials. This type of design comprises a two level factorial design (−1, +1), superimposed by center points (coded 0) (Abdel-Ghani et al. 2009; Benredouane et al. 2016).

The interactions are the driving force of many optimizations of the processes. Without the use of factorial experiments, some significant interactions can pass unperceived, and total optimization cannot be reached (Abdel-Ghani et al. 2009).

The response is expressed as a percentage and represents the abatement of the COD:
formula
4

[COD]0 and [COD]t were, respectively, the initial COD of Aba and its concentration at a given time t (mg L−1). The studied parameters were the initial abamectin concentration [Aba]0, the catalyst concentration [FeSO4, 7H2O], the current intensity (I), and temperature (°C).

The original values of each factor and their corresponding levels are shown in Table 1; the selection of the levels of various factors was carried out because of a preliminary test and the results of previous research (Abdel-Ghani et al. 2009). The pH and time of electrolysis were fixed at 2.9 and 300 min, respectively.

Table 1

Values and levels of the operating parameters

FactorsUnitsLevels
− 10+ 1
X1 mg L−1 12.5 20 
X2 mmol L−1 0.05 0.125 0.2 
X3 mA 100 250 400 
X4 °C 20 35 50 
FactorsUnitsLevels
− 10+ 1
X1 mg L−1 12.5 20 
X2 mmol L−1 0.05 0.125 0.2 
X3 mA 100 250 400 
X4 °C 20 35 50 

The CCD was given by JMP 8.0.2 software and is composed of 24 experiments (runs 1–16) of factorial design, two experiments realized at the center work domain (runs 17–18), and eight-star points (runs 19–26) (Table 2). The correlation of independent variables and response were estimated by a second-order polynomial (Equation (5)) given by the software, using the least-square method as shown below:
formula
5
when the response data were obtained from the test work, a regression analysis was carried out to determine the coefficients of the response model (b1, b2 … bn), as well as their standard errors and their significance. In addition to the constant b0, the response model incorporates (Wang et al. 2012): predicted yield (ŷ); linear terms, corresponding to the variables (x1,x2… xn); squared terms, corresponding to the variables (x12, x22… xn2); and terms of first order interactions for each paired combination (x 1x 2, x 1x 3……xn1xn).
Table 2

Experimental design and results of abamectin oxidation

Natural values of parameters
Coded values of parameters
    
Run no.[Aba]0 (mg L−1)[Fe2+] (m mol L−1)I (mA)T (°C)X0X1X2X3X4y (%) (%)ei (%)Error (%)
0.05 100 20 −1 −1 −1 −1 47.95 48.05 −0.10 0.20 
0.05 100 50 −1 −1 −1 81.13 81.78 −0.65 0.79 
0.05 400 20 −1 −1 +1 −1 24.75 25.08 −0.33 1.31 
0.05 400 50 −1 −1 +1 +1 48.33 49.21 −0.88 1.78 
0.2 100 20 −1 +1 −1 −1 37.90 37.61 0.29 0.77 
0.2 100 50 −1 +1 −1 +1 62.17 62.43 −0.26 0.41 
0.2 400 20 −1 +1 +1 −1 19.09 19.03 0.06 0.31 
0.2 400 50 −1 +1 +1 +1 39.69 40.18 −0.49 1.21 
20 0.05 100 20 +1 −1 −1 −1 23.12 22.70 0.42 1.85 
10 20 0.05 100 50 +1 −1 −1 +1 47.70 47.83 −0.13 0.27 
11 20 0.05 400 20 +1 −1 +1 −1 15.47 15.28 0.19 1.24 
12 20 0.05 400 50 +1 −1 +1 +1 28.35 28.71 −0.36 1.25 
13 20 0.2 100 20 +1 +1 −1 −1 24.78 23.97 0.81 3.37 
14 20 0.2 100 50 +1 +1 −1 +1 34.77 34.51 0.26 0.75 
15 20 0.2 400 20 +1 +1 +1 −1 15.29 14.71 0.58 3.94 
16 20 0.2 400 50 +1 +1 +1 +1 23.84 23.81 0.03 0.12 
17 12.5 0.125 250 35 37.50 38.69 −1.19 3.07 
18 12.5 0.125 250 35 38.00 38.69 −0.69 1.78 
19 0.125 250 35 −1 58.92 56.54 2.38 4.20 
20 20 0.125 250 35 +1 35.82 37.56 −1.74 4.63 
21 12.5 0.05 250 35 −1 38.81 36.93 1.88 5.09 
22 12.5 0.2 250 35 +1 27.88 29.13 −1.25 4.29 
23 12.5 0.125 100 35 −1 39.43 40.04 −0.61 1.52 
24 12.5 0.125 400 35 +1 23.42 22.18 1.24 5.59 
25 12.5 0.125 250 20 −1 28.79 30.67 −1.88 6.12 
26 12.5 0.125 250 50 +1 53.45 50.93 2.52 4.94 
Natural values of parameters
Coded values of parameters
    
Run no.[Aba]0 (mg L−1)[Fe2+] (m mol L−1)I (mA)T (°C)X0X1X2X3X4y (%) (%)ei (%)Error (%)
0.05 100 20 −1 −1 −1 −1 47.95 48.05 −0.10 0.20 
0.05 100 50 −1 −1 −1 81.13 81.78 −0.65 0.79 
0.05 400 20 −1 −1 +1 −1 24.75 25.08 −0.33 1.31 
0.05 400 50 −1 −1 +1 +1 48.33 49.21 −0.88 1.78 
0.2 100 20 −1 +1 −1 −1 37.90 37.61 0.29 0.77 
0.2 100 50 −1 +1 −1 +1 62.17 62.43 −0.26 0.41 
0.2 400 20 −1 +1 +1 −1 19.09 19.03 0.06 0.31 
0.2 400 50 −1 +1 +1 +1 39.69 40.18 −0.49 1.21 
20 0.05 100 20 +1 −1 −1 −1 23.12 22.70 0.42 1.85 
10 20 0.05 100 50 +1 −1 −1 +1 47.70 47.83 −0.13 0.27 
11 20 0.05 400 20 +1 −1 +1 −1 15.47 15.28 0.19 1.24 
12 20 0.05 400 50 +1 −1 +1 +1 28.35 28.71 −0.36 1.25 
13 20 0.2 100 20 +1 +1 −1 −1 24.78 23.97 0.81 3.37 
14 20 0.2 100 50 +1 +1 −1 +1 34.77 34.51 0.26 0.75 
15 20 0.2 400 20 +1 +1 +1 −1 15.29 14.71 0.58 3.94 
16 20 0.2 400 50 +1 +1 +1 +1 23.84 23.81 0.03 0.12 
17 12.5 0.125 250 35 37.50 38.69 −1.19 3.07 
18 12.5 0.125 250 35 38.00 38.69 −0.69 1.78 
19 0.125 250 35 −1 58.92 56.54 2.38 4.20 
20 20 0.125 250 35 +1 35.82 37.56 −1.74 4.63 
21 12.5 0.05 250 35 −1 38.81 36.93 1.88 5.09 
22 12.5 0.2 250 35 +1 27.88 29.13 −1.25 4.29 
23 12.5 0.125 100 35 −1 39.43 40.04 −0.61 1.52 
24 12.5 0.125 400 35 +1 23.42 22.18 1.24 5.59 
25 12.5 0.125 250 20 −1 28.79 30.67 −1.88 6.12 
26 12.5 0.125 250 50 +1 53.45 50.93 2.52 4.94 

RESULTS AND DISCUSSION

Adsorption tests

Figures 3 and 4 represent the measurement of the COD and Aba concentrations, respectively. This measurement showed that the concentration and COD remain unchanged. Therefore, the carbon felt does not have any capacity for absorbing the abamectin molecule. This result is in agreement with other work on other types of pesticides and refractory organic pollutants (Abdel-Ghani et al. 2009).
Figure 3

Time-courses of [COD]t/[COD]0 values during adsorption tests at [Aba]0 = 20 mg L−1.

Figure 3

Time-courses of [COD]t/[COD]0 values during adsorption tests at [Aba]0 = 20 mg L−1.

Figure 4

Evolution of abamectin concentration during adsorption tests at [Aba]0 = 20 mg L−1.

Figure 4

Evolution of abamectin concentration during adsorption tests at [Aba]0 = 20 mg L−1.

EF process and electrochemical oxidation

Figure 5 shows the evolution of the COD removal during the electrolysis time for the four experiments. We note the removal of COD from 1,360 to 531 mg L−1 for the EF process (Experiment 1), which explains the degradation of the organic matter present in the solution by chemical oxidation of OH. In Experiment 2 (Figure 5), we removed COD at 1,156 mg L−1, which results in a weak oxidation of the organic matter due to the virtually zero reduction power of oxygen (Equation (1)) at the stainless steel cathode; the H2O2 absent under these conditions leads to the non-formation of OH radicals sufficient for oxidizing the organic matter present in the solution. The curve of the third experiment shows that in the absence of a catalyst [Fe2+], oxidation does not take place; the removal of COD passes from 1,360 to 1,205 in 5 h of electrochemical treatment, because according to the Fenton reaction (Equation (2)), OH production is ensured by the catalytic reaction of Fenton Fe2+/H2O2. The curve corresponding to the fourth experiment indicates that, in the absence of air bubbling, the oxidation power and the rate of degradation decrease, because of the lack of O2 for the catalytic generation of H2O2 (Equation (1)). This decrease in COD from 1,360 to 790 mg L−1 (Experiment 4) is due to the production of O2 by the oxidation of water at the anode according to Equation (6). Thus, this reaction provides 75% of O2 and provides pH regulation:
formula
6
We conclude that the EF process, compared to unconditioned simple electrochemical oxidation, remains the best process ensuring good oxidation of the organic matter. However, this process without the presence of O2, Fe2+ and specific electrodes remains ineffective against refractory molecules that are very persistent and toxic. The EF process requires an optimization of the operating parameters as a function of the solution to be treated.
Figure 5

Evolution of COD removal during electrochemical experiments: (•) Experiment 1, (♦) Experiment 2, (▴) Experiment 3, (▪) Experiment 4.

Figure 5

Evolution of COD removal during electrochemical experiments: (•) Experiment 1, (♦) Experiment 2, (▴) Experiment 3, (▪) Experiment 4.

Elaboration of the model

The results of the second-order model obtained according to CCD are collected in Table 2. The model coefficients were estimated by standard least-square regression method using JMP 8.0.2 software (Chaudhary & Balomajumder 2014). This software was used to analyze the results and evaluate the adequacy of the model using Student's t-test, R2 test, and Fisher's test.

The significant coefficients of the mathematical model and the validation of the model were estimated by the JMP software (Figure 6).
Figure 6

Estimates of coefficients sorted (captured from JMP software).

Figure 6

Estimates of coefficients sorted (captured from JMP software).

The second-order model was obtained by following the CCD. After discarding the insignificant effects by software, we obtained:
formula
7
The parity plot (Figure 7) obtained by JMP 8.0.2 software showed a satisfactory correlation between the experimental and predicted values (R2 = 0.9949 and adjusted R2 = 0.9789) of the percentage of COD abatement, where the point cluster around the diagonal line indicated an optimal fit of the model, since the deviation between the experimental and predicted values was minimal. Table 2 shows that the difference between the measured and the predicted values did not exceed 3% and the error is less than 6.2%.
formula
formula
According to the regression equation (Equation (7)), temperature appears to be one of the most important parameters (b4 = +10.12) controlling the electrochemical degradation of Aba. The positive sign of the b4 coefficient suggests that increase of temperature increases the yield of electrochemical degradation of abamectin.
Figure 7

Parity plot showing the distribution of observed values versus predicted values of abatement COD during EF treatment (captured from JMP software).

Figure 7

Parity plot showing the distribution of observed values versus predicted values of abatement COD during EF treatment (captured from JMP software).

To study the effect of temperature on the Aba degradation by an EF process, a kinetic study was performed under the following operating conditions during 1 h of electrolysis: 20 to 50 °C temperature, 9 and 20 mg L−1 of initial Aba concentration, 150 mA of current intensity, 0.15 mmol L −1 catalyst concentration [Fe2+], 1,000 rpm stirring speed, and pH = 2.9.

The degradation of aqueous Aba solutions is shown in Figure 8. Irrespective of the initial concentration, Aba degradation was exponential and always led to removal. In addition, degradation rates increased for increasing temperature. This trend was also noted by other studies (Panizza et al. 2007; Basha et al. 2009).
Figure 8

Influence of the temperature on abamectin degradation: (♦) 50 °C, (▪) 20 °C, (▴) 35 °C. (a) [Aba]0 = 9 mg L−1 and (b) [Aba]0=20 mg L−1. I = 150 mA, [Fe2+] = 0.15 mmol L−1, and pH = 2.9.

Figure 8

Influence of the temperature on abamectin degradation: (♦) 50 °C, (▪) 20 °C, (▴) 35 °C. (a) [Aba]0 = 9 mg L−1 and (b) [Aba]0=20 mg L−1. I = 150 mA, [Fe2+] = 0.15 mmol L−1, and pH = 2.9.

At 50 °C temperature, Aba degradation of 94 and 79% is observed for an initial concentration of 9 and 20 mg L−1, after 20 and 60 min of treatment by EF process (Figure 8(a) and 8(b)). This result proves that the reaction of Aba oxidation by the hydroxyl radicals is favored by the increase of temperature. Indeed, the temperature of solution influences the electron transfer rate and the mass transfer rate; Qiang et al. (2003) have shown that the regeneration of Fe2+ is promoted at high temperature. Yahiaoui et al. (2013) also explained in their paper ‘Combination of an electrochemical pre-treatment with a biological oxidation for the mineralization of non-biodegradable organic dyes: Basic yellow dye’ that an increase in temperature reduces the viscosity of the solution, which implies an increase of the apparent rate constant (Kapp) and the apparent mass-transfer coefficient (Km).

Experimental results of degradation for various temperatures showed that abamectin removal followed first-order kinetics, according to Equation (8):
formula
8
with Kapp the first-order rate constant, [Aba]0 the initial abamectin concentration, and [Aba]t the abamectin concentration at any time t.

The high value of R2 (Table 3) of the straight lines obtained by plotting Ln([Aba]0/[Aba]t) versus time at different temperatures, confirms the first-order kinetics of Aba degradation.

Table 3

Apparent rate constant (Kapp), apparent mass-transfer (Km) coefficients and R2 values

[Aba]0 (mg L−1)T (°C)Kapp (min−1)Km (Cm min−1)R2
20 0.062 1.24 0.992 
 35 0.102 2.04 0.993 
 50 0.146 2.92 0.995 
20 20 0.014 0.28 0.998 
 35 0.019 0.38 0.997 
 50 0.026 0.52 0.998 
40 50 0.014 0.28 0.995 
[Aba]0 (mg L−1)T (°C)Kapp (min−1)Km (Cm min−1)R2
20 0.062 1.24 0.992 
 35 0.102 2.04 0.993 
 50 0.146 2.92 0.995 
20 20 0.014 0.28 0.998 
 35 0.019 0.38 0.997 
 50 0.026 0.52 0.998 
40 50 0.014 0.28 0.995 

The values of the apparent rate constant (Kapp) determined from the slope of the straight lines and the apparent mass-transfer coefficient (Km) obtained from Equation (9) (Table 3) increased with temperatures (Panizza et al. 2007):
formula
9
where V is the volume of the solution (mL) and S is the anode surface (cm2).
The apparent activation energy (Eapp) of the Aba degradation can be deduced from the Arrhenius law. According to Figure 9, the apparent activation energy increases from 4.04 to 8.14 kJ mol−1 when the initial concentration of Aba increased from 9 to 20 mg L−1; the value of the apparent activation energy indicated a diffusion process control of the reaction (Oppenländer 2007; Basha et al. 2009). This result indicates that Aba degradation does not require high activation energy and hence the EF degradation of Aba on Ti/Pt electrode can be easily achieved.
Figure 9

Plot of Ln Kapp versus 1/T for abamectin degradation by EF process at an initial abamectin concentration: [Aba]0 = 9 mg L−1 (a) and [Aba]0 = 20 mg L−1 (b) I = 150 mA, [Fe2+] = 0.15 mmol L−1, and pH = 2.9.

Figure 9

Plot of Ln Kapp versus 1/T for abamectin degradation by EF process at an initial abamectin concentration: [Aba]0 = 9 mg L−1 (a) and [Aba]0 = 20 mg L−1 (b) I = 150 mA, [Fe2+] = 0.15 mmol L−1, and pH = 2.9.

The second significant factor with a negative effect (b1 = −9.48) was the initial concentration of Aba (X1). Figure 10 represents linear plots of Ln([Aba]0/[Aba]t) with time at different initial Aba concentrations. The plot reveals that EF degradation of Aba on the Ti/Pt electrode followed first-order kinetics, and the apparent rate constant decreases for increasing concentrations of abamectin (Table 3). This tendency was also noticed by Dirany et al. (2012) in their study: the apparent rate constant Kapp depends on the initial concentration, and decreases when the initial concentration increases. Moreover, whatever the initial concentration, the exponential degradation of Aba always leads to its elimination but to a longer electrolysis time. The time of electrolysis increased from 4 to 60 min when concentration of Aba is increased from 9 to 40 mg L−1.
Figure 10

Time-courses of Ln([Aba]0/[Aba]t) at various initial abamectin concentrations: (♦) 9 mg L−1, (▪) 20 mg L−1, (▴) 40 mg L−1. T = 50 °C, I = 150 mA, [Fe2+] = 0.15 mmol L−1, and pH = 2.9.

Figure 10

Time-courses of Ln([Aba]0/[Aba]t) at various initial abamectin concentrations: (♦) 9 mg L−1, (▪) 20 mg L−1, (▴) 40 mg L−1. T = 50 °C, I = 150 mA, [Fe2+] = 0.15 mmol L−1, and pH = 2.9.

According to Figure 11, the degradation curves show a reduction of 94 to 47% when the concentration increases from 9 to 40 mg L−1. This effect is probably ascribable to the presence of high quantities of organic compounds (Aba not degradable and its by-products), thus for high Aba concentrations (Abdelassem et al. 2010), the reduction in the degradation efficiency can be allotted to the progressive acceleration of a competition reaction between OH and the intermediaries of abamectin oxidation which formed during the degradation process. Indeed, the quantity of formed radicals was the same for all experiments due to the current applied intensity and added ferrous salt.
Figure 11

Influence of the initial abamectin concentration on the electrochemical oxidation process (EF): (♦) 9 mg L−1, (▪) 20 mg L−1, (▴) 40 mg L−1. T = 50 °C, I = 150 mA, [Fe2+] = 0.15 mmol L−1, and pH = 2.9.

Figure 11

Influence of the initial abamectin concentration on the electrochemical oxidation process (EF): (♦) 9 mg L−1, (▪) 20 mg L−1, (▴) 40 mg L−1. T = 50 °C, I = 150 mA, [Fe2+] = 0.15 mmol L−1, and pH = 2.9.

The third impacting factor was the current intensity with a negative effect (b3 = −8.92) on the yield of the electrochemical degradation of Aba. This result confirmed the importance of current intensity in the context of an EF degradation process. Figure 12 shows the relationship between the degradation of Aba and the duration of the electrochemical degradation for various current intensities. The removal efficiency of abamectin increased with current intensities up to 150 mA, while no significant further increase was observed above this value.
Figure 12

Influence of current intensities on abamectin degradation during EF treatment: (♦) 100 mA, (▪) 150 mA (▴), 400 mA. T = 50 °C, [Fe2+] = 0.15 mmol L−1, and pH = 2.9. (a) [Aba]0=9 mg L−1 and (b) [Aba]0 = 20 mg L−1.

Figure 12

Influence of current intensities on abamectin degradation during EF treatment: (♦) 100 mA, (▪) 150 mA (▴), 400 mA. T = 50 °C, [Fe2+] = 0.15 mmol L−1, and pH = 2.9. (a) [Aba]0=9 mg L−1 and (b) [Aba]0 = 20 mg L−1.

The removal efficiency increased from 20 to 45% in the first 20 minutes of treatment time when the current intensities decreased from 400 to 150 mA for 20 mg L−1 of initial Aba concentration (Figure 12(b)).

This speed of faster oxidation under an average current intensity (150 mA) can be explained by the excess production of hydrogen peroxide (H2O2) according to (reaction 1) Equation (1), and also to the faster regeneration of Fe2+ at the cathode (reaction 3) (Equation (3)), leading to the generation of an important quantity of hydroxyl radicals according to (reaction 2) Equation (2), and consequently increasing the efficiency of the treatment by the EF process. However, the EF process is based on the electrochemical reduction of oxygen (O2) on the cathode surface (reaction 10) (Equation (10)), thus it should be noted that for excessive current intensities such as in our experiment (400 mA), the O2 reduction reaction leading to the formation of H2O (Equation (10)) enters into competition with the H2O2 formation reaction (reaction 1) (Equation (1)), which causes a decrease in the rate of degradation of the target compound which Masomboon et al. (2010) explain in their paper ‘Chemical oxidation of 2,6-dimethylaniline by electrochemically generated Fenton's reagent’, that a high current intensity causes production of H2 into the cathode (Equation (11)), thereby reducing the efficiency of a high current intensity. In addition, Dirany et al. (2012) also noticed this tendency in their study on the degradation of sulfachloropyridazine by EF process, when they noted that a decrease in the removal efficiency can be allotted to the gradual formation of more difficult products to oxidize:
formula
10
formula
11
In this study, the last and least significant factor was the Fe2+ catalyst concentration, also with a negative effect (b2 = −3.9). Figure 13 displays the effect of Fe2+ catalyst concentration on the yield of the electrochemical Aba degradation. There was a significant decrease in the Aba concentration with time until reaching 63, 89, and 82% for 0.05, 0.15, and 0.2 mmol L−1 of [FeSO4.7H2O] after 20 min of electrolysis, respectively. The degradation efficiency depended on the initial ferrous ions concentration. It can be seen that increasing the initial Fe2+ concentration from 0.05 to 0.15 mmol L−1 enhanced degradation of Aba by about 26%; while the degradation efficiency was quite constant from 0.15 to 0.2 mmol L−1, in agreement with a possible consumption of the excess ferrous ions by hydroxyl radicals according to Equation (12) (Ferrag-Siagh et al. 2013).
formula
12
Consequently, 0.15 mmol L−1 of ferrous ions was selected and considered hereafter. This value was in agreement with some other reports, such as for instance ‘Tetracycline degradation and mineralization by the coupling of an EF pretreatment and a biological process’ using a carbon felt cathode and a platinum anode (Ferrag-Siagh et al. 2013). Moreover, in the study carried out by Oturan et al. (2010), the removal efficiency decreases when the concentration of Fe3+ increases, because there is an increase in the parasitic reactions consuming the formed OH radicals. Finally, Abdelassem et al. (2010) showed in their study that the optimal concentration in ferrous ions varies between 0.05 and 0.2 mmol L−1.
Figure 13

Influence of the catalyst concentration Fe2+ on abamectin degradation during the EF treatment of [Aba]0 = 9 mg L−1. (♦) 0.05 mmol L−1, (▪) 0.15 mmol L−1, (▴) 0.2 mmol L−1. T = 50 °C, I = 150 mA, and pH = 2.9.

Figure 13

Influence of the catalyst concentration Fe2+ on abamectin degradation during the EF treatment of [Aba]0 = 9 mg L−1. (♦) 0.05 mmol L−1, (▪) 0.15 mmol L−1, (▴) 0.2 mmol L−1. T = 50 °C, I = 150 mA, and pH = 2.9.

Study of the effect of operating parameters

The model equation obtained by CCD was used to determine the optimal values of the operating parameters so that we could obtain the highest COD abatement and reach the biodegradability threshold in a short processing time.

Response surface and contour plots (Figure 14(a) and 14(b)) were drawn using STATISTICA software. The two figures were drawn in a ‘temperature-initial Aba concentration’ plan (the most influential factors affecting the EF process) for values of 150 mA in current intensity and 0.15 mmol L−1 of catalyst concentration (optimal values according to the kinetic of Aba degradation). Analysis of the figures, clearly, indicated that the optimal conditions found for the abatement of the COD were: [Aba]0 = 5 mg L−1, [Fe2+] = 0.15 mmol L−1, I = 150 mA, and T = 45.5 °C, for the initial Aba concentration (X1), catalyst concentration (X2), current intensity (X3), and the temperature (X4), respectively. In these conditions, the COD removal was 68.01% (Figure 14(a)).
Figure 14

Response surface (a) and contour plots (b) showing the effect of temperature (X4) and initial abamectin concentration (X1) on the yield of COD abatement, X3: I = 150 mA and X2: [Fe2+] = 0.15 mmol L−1.

Figure 14

Response surface (a) and contour plots (b) showing the effect of temperature (X4) and initial abamectin concentration (X1) on the yield of COD abatement, X3: I = 150 mA and X2: [Fe2+] = 0.15 mmol L−1.

According to Figure 14(b), and for an initial Aba concentration (X1 = 9 mg L−1), the optimal conditions were: [Fe2+] = 0.15 mmol L−1 (X2), I = 150 mA (X3), and T = 47 °C (X4). In these conditions, removal of COD was 55.67% (Figure 14(a)). To validate the model, an experiment was performed with these conditions, leading to 58.4% removal of COD (Figure 15), namely, in good agreement with the model (55.67% degradation).
Figure 15

Time-courses of biodegradability tests at various time of EF treatment: (♦) COD, (▪) BOD5, (▴) BOD5/COD. [Aba]0 = 9 mg L−1, T = 47 °C, I = 150 mA, and [Fe2+] = 0.15 mmol L−1.

Figure 15

Time-courses of biodegradability tests at various time of EF treatment: (♦) COD, (▪) BOD5, (▴) BOD5/COD. [Aba]0 = 9 mg L−1, T = 47 °C, I = 150 mA, and [Fe2+] = 0.15 mmol L−1.

Biodegradability tests

Figure 15 shows the variation of the COD, BOD5, and ratio BOD5/COD during 5 h of EF treatment performed with optimal conditions. The ratio BOD5/COD increased appreciably from 0.0584 to 0.64 after 5 h of EF treatment, while for a content of significant residual organic matter, 4 h of electrolysis can be more relevant, leading to a ratio BOD5/COD of 0.433 which is above the limit of biodegradability (0.4). Thus, this is the processing time necessary so that our solution is perfectly biodegradable, and this duration of electrolysis was taken into account for a possible biological treatment (Raftery & Volz 2015). Figure 16 shows the rate of reduction of TOC during the EF treatment and confirms the elimination of the organic matter in the optimal conditions, leading to the elimination of 58.14% of TOC for a concentration of 9 mg L−1.
Figure 16

Time-courses of [TOC]t/[TOC]0 values during EF treatment at various initial abamectin concentrations. (♦) 9 mg L−1, (▪) 20 mg L−1, (▴) 40 mg L−1. T = 47 °C, I = 150 mA, [Fe2+] = 0.15 mmol L−1, and pH = 2.9.

Figure 16

Time-courses of [TOC]t/[TOC]0 values during EF treatment at various initial abamectin concentrations. (♦) 9 mg L−1, (▪) 20 mg L−1, (▴) 40 mg L−1. T = 47 °C, I = 150 mA, [Fe2+] = 0.15 mmol L−1, and pH = 2.9.

Biodegradability tests using environmental water

The biodegradability tests and the degradation of abamectin were realized on a real surface water solution (Table 4), after electrochemical treatment according to the EF process. In order to carry out these tests, we used the previously optimized operating conditions. For this purpose, a kinetic study of electrochemical degradation was realized on abamectin solution at 9 mg L−1 (this is the concentration used by farmers) during 5 h of electrolysis. Other operating parameters were as follows: [Fe2 +] = 0.15 mmol L−1, I = 150 mA, and T = 47 °C.

Table 4

Characteristics of runoff from an urban area of the city of Algiers

ParametersValuesStandards
pH 6.58 6.5–8.5 
Conductivity (μS.cm−1 at 20 °C) 179.03 – 
Turbidity (NTU) 90.03 0.5 
Suspended matter (mg L−1100.17 35 
NH4+ (mg L−12.33 0.1 
NO3 (mg L−14.08 50 
NO2 (mg L−15.34 0.05 
PO43− (mg L−10.019 0.4 
SO42− (mg L−130.66 
BOD5 (mg L−118.56 35 
COD (mg L−128.78 120 
ParametersValuesStandards
pH 6.58 6.5–8.5 
Conductivity (μS.cm−1 at 20 °C) 179.03 – 
Turbidity (NTU) 90.03 0.5 
Suspended matter (mg L−1100.17 35 
NH4+ (mg L−12.33 0.1 
NO3 (mg L−14.08 50 
NO2 (mg L−15.34 0.05 
PO43− (mg L−10.019 0.4 
SO42− (mg L−130.66 
BOD5 (mg L−118.56 35 
COD (mg L−128.78 120 

Figure 17 shows the variation of the COD, BOD5, and ratio COD/BOD5. We note a reduction in COD from 1,350 to 440 mg L−1 and an increase in BOD5 to 268 mg L−1, giving a biodegradability ratio of 1.64 after 5 h of electrolysis. This confirms the biodegradability of the effluent. Thus, according to Figure 17, after 3.5 h of treatment, the threshold of biodegradability is achieved (2.5), therefore for better organic matter content, this electrolysis time would be sufficient for any biological treatment.
Figure 17

Time-courses of biodegradability tests on real effluent at various time of EF treatment: (•) COD, (▴) BOD5, (▪) COD/BOD5. [Aba]0 = 9 mg L−1, T = 47 °C, I = 150 mA, [Fe2+] = 0.15 mmol L−1, and pH = 2.9.

Figure 17

Time-courses of biodegradability tests on real effluent at various time of EF treatment: (•) COD, (▴) BOD5, (▪) COD/BOD5. [Aba]0 = 9 mg L−1, T = 47 °C, I = 150 mA, [Fe2+] = 0.15 mmol L−1, and pH = 2.9.

Identification of principal degradation by-products

Aqueous solutions with a concentration of 5.77 × 10−3 mM of abamectin, i.e., 10 mg L−1, were treated in order to characterize as much as possible the reaction intermediates during degradation by the EF process under the optimal conditions.

The liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was used in positive mode in order to identify the organic by-products resulting from degradation. Table 5 gives the main degradation by-products identified.

Table 5

Data of by-products identified by the LC-MS/MS method during degradation of Aba by the electro-Fenton process

By-productsChemical formulaRetention time (min)[M + H]+
Compound 1 Monosaccharide C41H60O11 17.6 729.9 
Compound 2 Disaccharide C14H26O6 10.1 291.35 
Compound 3 α-glycone C34H48O8 16.5 585.74 
Compound 4 C40H54O9 8.6 679.85 
Compound 5 C40H62O11 9.9 719.91 
Compound 6 C30H35O5 13.8 476.59 
Compound 7 C21H25O4 8.2 342.42 
Compound 8 C12H18O2 10.9 195.27 
Compound 9 C15H20O4 7.3 265.31 
By-productsChemical formulaRetention time (min)[M + H]+
Compound 1 Monosaccharide C41H60O11 17.6 729.9 
Compound 2 Disaccharide C14H26O6 10.1 291.35 
Compound 3 α-glycone C34H48O8 16.5 585.74 
Compound 4 C40H54O9 8.6 679.85 
Compound 5 C40H62O11 9.9 719.91 
Compound 6 C30H35O5 13.8 476.59 
Compound 7 C21H25O4 8.2 342.42 
Compound 8 C12H18O2 10.9 195.27 
Compound 9 C15H20O4 7.3 265.31 

CONCLUSION

An examination of the results, presented in this study, reveals the following conclusions:

  • The EF process compared to simple electrochemical oxidation is effective for degrading refractory molecules, but only after optimization.

  • The use of an experimental design methodology allows the determination of the optimum conditions for degradation, while reducing the maximum number of experiments to be realized. The optimization of degradation conditions gives the following optimal conditions: T = 47 °C, I = 150 mA, catalyst = 0.15 mmol L−1, which leads to the elimination of 58.14, 47.85, and 37.4% of total organic carbon for concentrations of 9, 20, and 40 mg L−1, respectively.

  • An increase in temperature leads to an increase in the speed of degradation of abamectin.

  • A biodegradability test was realized on a solution electrolyzed with T = 47 °C, I = 150 mA, catalyst = 0.15 mmol L−1, [Aba]0 = 9 mg L−1; the ratio of BOD5/COD increased appreciably from 0.0584 to 0.64 after 5 h of degradation. Thus, in order to maintain a significant content of residual organic matter for the bacteria, 4 h of electrolysis proves more relevant, leading to a ratio BOD5/COD of 0.433. This improvement of biodegradability was confirmed by the elimination of 78 and 80% of total organic carbon (COT) after 4 and 5 h of electrolysis, respectively.

  • A biodegradability test on a real solution leads to similar results as the aqueous solution.

  • A biological treatment can be combined with the EF process to ensure total mineralization.

REFERENCES

REFERENCES
Abdelassem
K. A.
Bellakhal
N.
Oturan
N.
Dachraoui
M.
Oturan
M. A.
2010
Treatment of a mixture of three pesticides by photo- and electro-Fenton
.
Desalination
250
,
450
455
.
Abdel-Ghani
N. T.
Hegazi
A. K.
El-Chaghaby
G. A.
Lima
E. C.
2009
Factorial experimental design for biosorption of iron and zinc using Typha domingensis phytomass
.
Desalination
249
,
343
347
.
Basha
C. A.
Chithra
E.
Sripriyalakshmi
N. K.
2009
Electro-degradation and biological oxidation of non-biodegradable organic contaminants
.
Chem. Eng. J.
149
,
25
34
.
Chaudhary
N.
Balomajumder
C.
2014
Optimization study of adsorption parameters for removal of phenol on aluminum impregnated fly ash using response surface methodology
.
J. Taiwan Inst. Chem. Eng
45
,
852
859
.
doi:10.1016/j.jtice.2013.08.016
.
Djoudi
W.
Aissani-Benissad
F.
Bourouina-Bacha
S.
2007
Optimization of copper cementation process by iron using central composite design experiments
.
Chem. Eng. J.
133
,
1
6
.
doi:10.1016/j.cej.2007.01.033
.
Erramil
M.
Salghil
R.
Ebenso
E. E.
Messali
M.
Al-Deyab
S. S.
Hammouti
B.
2014
Anodic destruction of abamectin acaricide solution by BDD-anodic oxidation
.
Int. J. Electrochem. Sci.
9
,
5467
5478
.
Escalada
J. P.
Gianotti
J.
Pajares
A.
Massad
W. A.
Amat Guerri
F.
Garcia
N. A.
2008
Photo-degradation of the acaricide abamectin: a kinetic study
.
J. Agric. Food. Chem.
56
,
7355
7359
.
Ferrag-Siagh
F.
Fourcade
F.
Soutrel
I.
Aït-Amar
H.
Djelal
H.
Amrane
A.
2013
Tetracycline degradation and mineralization by the coupling of an electro-Fenton pretreatment and a biological process
.
J. Chem. Technol. Biotechnol.
88
,
1380
1386
.
doi:10.1002/jctb.3990
.
Ferrag-Siagh
F.
Fourcade
F.
Soutrel
I.
Aït-amar
H.
Djelal
H.
Amrane
A.
2014
Electro-Fenton pretreatment for the improvement of tylosin biodegradability
.
J. Environ. Sci. Pollut. Res.
21
,
8534
8542
.
Fourcade
F.
Yahiat
S.
Elandaloussi
K.
Brosillon
S.
Amrane
A.
2012
Relevance of photocatalysis prior to biological treatment of organic pollutants – selection criteria
.
J. Chem. Eng. Technol.
35
,
238
246
.
Kamel
A.
Al-Dosary
S.
Ibrahim
S.
Asif Ahmed
M.
2007
Degradation of the acaricides abamectin, flufenoxuron and amitraz on Saudi Arabian dates
.
Food Chem.
100
,
1590
1593
.
doi:10.1016/j.foodchem.2006.01.002
.
Khalil
M.
2015
Abamectin and azadirachtin as eco-friendly promising biorational tools in integrated nematodes management programs
.
Plant Pathol. Microbiol. J. Biol. Phar. Res.
6
,
26
29
.
Kolar
L.
Flajs
V. C.
Kužner
J.
Marc
I.
Pogačnik
M.
Bidovec
A.
van Gestel
C. A. M.
Eržen
N. K.
2006
Time profile of abamectin and doramectin excretion and degradation in sheep faeces
.
Environ. Pollut.
144
,
197
202
.
doi:10.1016/j.envpol.2005.12.019
.
Kwon
D. H.
Seong
G. M.
Kang
T. J.
Lee
S. H.
2010
Multiple resistance mechanisms to abamectin in the two-spotted spider mite
.
J. Asia. Pac. Entomol.
13
,
229
232
.
doi:10.1016/j.aspen.2010.02.002
.
Masomboon
N.
Ratanatamskul
C.
Lu
M. C.
2010
Chemical oxidation of 2,6-dimethylaniline by electrochemically generated Fenton's reagent
.
J. Hazard. Mater.
176
,
92
98
.
doi:10.1016/j.jhazmat.2009.11.003
.
Oppenländer
T.
2007
Photochemical Purification of Water and Air: Advanced Oxidation Processes (AOPs): Principles, Reaction Mechanisms, Reactor Concepts
.
Wiley-VCH Verlag GmbH & Co. KGaA
,
Weinheim, Germany
, p.
383
.
doi:10.1002/9783527610884
.
Oturan
M. A.
2013
Procédés d'oxydation avancée pour le traitement des eaux polluées par des pollutants organiques persistants. In: Traitement et Épuration Des Eaux Industrielles Polluées [Advanced oxidation processes for the treatment of polluted water by persistent organic pollutants. In: Treatment and Purification of Polluted Industrial Waters]
.
Presses Universitaire de Franche-Comte
,
Paris
,
France
, pp.
309
320
.
Oturan
N.
Sirés
I.
Oturan
M. A.
Brillas
E.
2009
Degradation of pesticides in aqueous medium by electro-Fenton and related methods
.
J. Environ. Eng. Mana.
19
,
235
255
.
Oturan
M. A.
Edelahi
M. C.
Oturan
N.
El kacemi
K.
Aaron
J.-J.
2010
Kinetics of oxidative degradation/mineralization pathways of the phenylurea herbicides diuron, monuron and fenuron in water during application of the electro-Fenton process
.
Appl. Catal. B Environ.
97
,
82
89
.
doi:10.1016/j.apcatb.2010.03.026
.
Panizza
M.
Barbucci
A.
Ricotti
R.
Cerisola
G.
2007
Electrochemical degradation of methylene blue
.
Sep. Purification. Technol.
54
,
382
387
.
Pulgarin
C.
Invernizzi
M.
Parra
S.
Sarria
V.
Polania
R.
Péringer
P.
1999
Strategy for the coupling of photochemical and biological flow reactors useful in mineralization of biorecalcitrant industrial pollutants
.
Catal. Today
54
,
341
352
.
doi:10.1016/S0920-5861(99)00195-9
.
Qiang
Z.
Chang
J. H.
Huang
C. P.
2003
Electrochemical regeneration of Fe2+ in Fenton oxidation processes
.
Water. Res.
37
,
1308
1319
.
doi: 10.1016/S0043-1354(02)00461-X
.
Raftery
T. D.
Volz
D. C.
2015
Abamectin induces rapid and reversible hypoactivity within early zebrafish embryos
.
Neurotoxicol. Teratol.
49
,
10
18
.
doi:10.1016/j.ntt.2015.02.006
.
Rodier
J.
1996
Eaux naturelles, eaux résiduaires, eaux de mer, chimie, physicochimie, microbiologie, biologie, interprétation des résultats. In: L'Analyse de L'Eau [Natural waters, waste water, seawater, chemistry, physicochemistry, microbiology, biology, interpretation of results. In: Water Analysis]
.
Dunod
,
Paris
,
France
, p.
1384
.
Shinawar Waseem
A.
Fang-bo
Y.
Lian Tai
L.
Xiao Hui
L.
Li Feng
G.
Jian Dong
J.
Shun-Peng
L.
2012
Studies revealing bioremediation potential of the strain Burkholderia sp. GB-01 for Abamectin contaminated soils
.
World. J. Microbiol. Biotechnol
.
28
,
39
45
.
Vajargah
M. F.
Hedayati
A.
Yalsuyi
A. M.
Abarghoei
S.
Hajiahmadyan
M.
2014
Acute toxicity test of pesticide abamectin on common carp (Cyprinus carpio)
.
J. Coastal. Life. Med.
2
,
841
844
.
Yahiaoui
I.
Aissani-Benissad
F.
Fourcade
F.
Amrane
A.
2013
Combination of an electrochemical pretreatment with a biological oxidation for the mineralization of nonbiodegradable organic dyes: Basic Yellow 28 dye
.
Environ. Progress Sustain. Energy
33
(
1
),
160
169
.
doi: 10.1002/ep.11774
.