The voltammeter degradation of the phenol was carried out at a microbial electrode. This electrode is based on carbon graphite and clay and modified by bacteria. This electrode, later designated by bacteria-clay-CPE, showed stable response and was characterized by voltammeter methods, such as cyclic voltammetry (CV) and electrochemical Impedance spectroscopy (EIS).

This electrode is tested to treat phenol-containing wastewater. Experimental results revealed that the prepared electrode could be a feasible solution. For the degradation of dangerous phenol pollutants.

Reagents and apparatus

Electrochemical measurements were performed on a voltalab potentiostat (model PGSTAT 100, Eco Chemie B.V., Utrecht, The Netherlands) directed by software (voltalab master 4 software) run under windows 2007. The three electrode system consisted of a chemically modified carbon paste electrode as the working electrode platinum counter and SCE reference electrodes was used.

Bacterial cultivation

The bacterial strain of Staphylococcus aureus ATCC 25923 was used in this study as a bio- material. The strain was grown in Luria Burtani broth and incubated at 37 ° C for 24 h. The suspension of resuspended bacteria was diluted with distilled water to stabilize to obtain the necessary suspension of different concentrations before use.

Electrodes preparation

The clay modified carbon paste electrode (clay -CPE) was prepared by mixing a graphite carbon powder and the desired clay weight. The modified electrodes were immersed in a cell containing bacteria for 15 minutes, thus the bacterial electrode is ready for use. The geometric surface of this electrode was 0.1256 cm2. The electrical contact was made at the back by means of a bare carbon.

The prepared electrode is characterized in electrolytic medium. In a second stage is tested for the electro oxidation of phenol, added in the measurement cell. The cyclic voltammetry was recorded in the range from -2 V to 2 V. Optimum conditions were established by measuring the peak currents in dependence on all parameters. All experiments were carried out under ambient temperature [18]. Provisions were taken for deoxygenation by splashing the solution with nitrogen gas during approximately 5 min. In order to obtain reliable and reproducible results, a new electrolyte was prepared for each handling.

Results and Discussion

The morphology of the electrode surface of Clay was observed by scanning electron microscopy (Figure 1).

Degradation of phenol

The electrochemical degradation of phenol on the surface of the CPE-Clay-bacteria electrode was studied respectively by cyclic and square-wave voltammetry. The VC recorded in the presence of phenol (0.45 mmol / L) in tap water, has 2 peaks in the anodic sweep direction (Figure 5), respectively at 0.6 V, and 1.2 V and a cathode peak near 0 The anodic peaks correspond to the oxidation of phenol to intermediate products. Square wave voltammograms show the 3 peaks observed in the (CV).

CPE-NP-bactérie

CPE-NP-bactérie+phénol

Effect of scanning speed

In Figure 7, we present the cyclic voltammograms, recorded for the graphite carbon electrode modified by clay and bacteria, at different scanning speeds, in tap water containing phenol. The current densities of the different peaks increase linearly with the scanning speed (Fig. 8).

The anodic peaks move towards the positive potentials, as the scanning speed increases, while the cathodic peaks move towards the negative potentials at high scanning speeds [19].

Figure 7: Voltammograms recorded by ECP-Clay-bacteria with 8 mM phenol in 0.1 M NaCl at different scan rates of 40 to 140 mV.s-1.

Figures 160 and 161 show that the oxidation peaks corresponding to the oxidation of phenol are more intense in the presence of bacteria. Bacteria catalyze the oxidation of phenol.

The activity of the bacterium adhered to the Clay -CPE electrode surface calculated for the oxidation of phenol in a solution of tap water is:

α = (1- (0.23 / 0.135)) x 100

The electrode developed, CPE-Clay, modified by bacteria (Staphylococcus aureus) showed a high sensitivity to the detection of phenol in tap water.

The CPE-Clay biosensor showed the best efficiency for the detection of phenol in tap water, of the order of 70.37%. Optimization of the experimental conditions yielded the following values of the following detection limits (DL) and quantification limits (LQ):

          - LD = 6.23.10-9mol l-1, and LQ = and 2.37.10-8 mol l-1.

We have noted that the presence of other species in the solution to be analyzed is a factor that can influence the analytical results. This method is very simple and easy to implement. It is inexpensive compared to other methods and applicable in the field.