**1. Introduction**

24 Electrochemical Cells

44 Electrochemical Cells – New Advances in Fundamental Researches and Applications

Rocchini, G. (1992). The determination of the electrochemical parameters by the best-fitting

Rusling, J. (1984). Fitting tabulated current functions to linear-sweep voltammograms,

Schoukens, J., Pintelon, R. & Rolain, Y. (1997). *Recent Advances in Total Least Squares Techniques*

*and Errors-In-Variables Modeling*, SIAM, chapter Maximum Likelihood Estimation of Errors-In-Variables Models Using a Sample Covariance Matrix Obtained from Small

reaction mechanism from linear sweep voltammograms obtained on a rotating disk

from linear sweep voltammograms obtained on a rotating disk electrode. Part I:

(2010). Bubble nucleation algorithm for the simulation of gas evolving electrodes,

Quasi-one-dimensional steady-state analysis of multi-ion electrochemical systems at a rotating disc electrode controlled by diffusion, migration, convection and

(2002). Steady-state and pulsed current multi-ion simulations for a thallium

Deconinck, J. & Hubin, A. (2010). On the modeling of electrochemical systems with simultaneous gas evolution. Case study: The zinc deposition mechanism,

Modeling of mass and charge transfer in an inverted rotating disk electrode (IRDE)

in acid solutions: Intrinsic kinetic parameters and anion adsorption effects, *Journal of*

Tourwé, E., Pintelon, R. & Hubin, A. (2006). Extraction of a quantitative reaction mechanism

Van den Bossche, B., Bortels, L., Deconinck, J., Vandeputte, S. & Hubin, A. (1995).

homogeneous reactions, *Journal of Electroanalytical Chemistry* 397(1-2): 35–44. Van den Bossche, B., Floridor, G., Deconinck, J., Van Den Winkel, P. & Hubin, A.

electrodeposition process, *Journal of Electroanalytical Chemistry* 531(1): 61–70. Van Parys, H., Telias, G., Nedashkivskyi, V., Mollay, B., Vandendael, I., Van Damme, S.,

Van Parys, H., Tourwé, E., Breugelmans, T., Depauw, M., Deconinck, J. & Hubin, A. (2008).

Vetter, K. (1967). *Electrochemical Kinetics: Theoretical and Experimental Aspects*, Academic Press. Wang, J., Markovic, N. & Adzic, R. (2004). Kinetic analysis of oxygen reduction on Pt(111)

Yeum, K. & Devereux, O. (1989). An iterative method for fitting complex electrode

reactor, *Journal of Electroanalytical Chemistry* 622(1): 44–50.

Theory and validation, *Journal of Electroanalytical Chemistry* 594(1): 50–58. Van Damme, S., Maciel, P., Van Parys, H., Deconinck, J., Hubin, A. & Deconinck, H.

−3 <sup>6</sup> /Fe(CN)

−4

<sup>6</sup> , *Journal of*

with exponential polynomials, *Corrosion Science* 33(11): 1773–1788.

Sorenson, H. (1980). *Parameter Estimation - Principles and Problems*, Marcel Dekker. Thirsk, H. & Harrison, J. (1972). *A Guide to the Study of Electrode Kinetics*, Academic Press. Tourwé, E., Breugelmans, T., Pintelon, R. & Hubin, A. (2007). Extraction of a quantitative

electrode. Part II: Application to the redoxcouple Fe(CN)

*Analytica Chimica Acta* 162: 393–398.

Slichting, H. (1979). *Boundary Layer Theory*, McGraw-Hill.

*Electroanalytical Chemistry* 609(1): 1–7.

*Electrochimica Acta* 55(20): 5709–5718.

*Physical Chemistry B* 108(13): 4127–4133.

polarization curves, *Corrosion* 45(6): 478–487.

*Electrochemistry Communications* 12(5): 664–667.

Data Sets, pp. 59–68.

Electrochemistry constitutes an important discipline that involves many phenomena as mass transfer, migration because of the presence of electric field, and hydrodynamic especially in reactor with large scale.

In fact, electrochemical methods and electrochemical reactors have to be developed in order to resolve many problems in different area (mining, waste water treatment etc).

For measurement by electrochemical methods, probes have to be developed. For example, knowledge of the magnitude of the frictional forces between the solids and the gas-liquid mixture is very important for design of bioreactors. The growth of biomass on solid surfaces may be sensitive to shear stress. In fluidized bed bioreactors the suspended carriers are used for microbial immobilization or enzyme encapsulation. The knowledge of shear stress is important because some micro-organisms and cells attached to microcarriers are sensitive to excessive friction. The aim is to develop and verify a fast and inexpensive method for measuring the frictional forces in multiphase reactors beds.

On the other hand the performance of a multiphase reactor – for example, a bubble columndepends on the knowledge the bubble swarm properties as bubble shape, velocity allowing to determine the gas liquid mass transfer and liquid solid mass transfer.

To establish direct local information and precise bubble dimensions, various probes were used. The electrical resistivity probe was developed to measure the velocity and diameter of a bubble in a conducting liquid medium. In a non-conducting medium, the optical probe is more appropriate.

To ensure easy measurement of bubble sizes in a non transparent conducting medium and to establish direct local information in a reactor, the present work shows the possible use of electrochemical probe.

Electrochemical Probe for Frictional Force and Bubble Measurements

Flow direction

Fig. 1. Concentration and velocity profiles over the electrode surface.

surface averaged over the electrode:

C : concentration, mol.m-3 D : coefficient diffusion, m2.s-1,

Fig. 2. The electrochemical electrode.

(figure 2).

and Innovative Electrochemical Reactors for Electrocoagulation/Electroflotation 47

The instantaneous rate of mass transfer is proportional to the concentration gradient at the

Wall Le Microelectrode

> *y*

1/3 <sup>2</sup> *<sup>w</sup> <sup>a</sup> e*

 

The method can be extended to spherical walls (sphere particle). A sphere is equipped with an inside channel, bent through 90°, in which a gold thread of 1 mm diameter was introduced, cut flush with the surface. A rigid tube serves as support. The microelectrode can be directed relative to the average direction of the liquid by rotating the support

Gold wire Microelectrode

Flow direction

*L*

(2)

v

y

(3)

*<sup>C</sup> N D*

c

The mass transfer coefficient defined as : Ka = N/(C-Cw), Cw is the wall concentration. The analytical solution of (1) allows to determine the local mass transfer coefficient::

*<sup>D</sup> <sup>S</sup> <sup>K</sup>*

Paragraph two develops this aspect, the electrochemical probe developed serves in the same time as a probe able to measure the velocity gradient at the wall of a spherical sphere and to measure the volume bubble in a bubble column.

For the process aspect as the water and waste water treatment, the need of purifying water for human consumption is more and more required. Cleaning wastewater from industrial effluents before discharging is also a challenging work. In fact, innovative, cheap and effective techniques have to be developed.

Electrocoagulation (EC) is an electrochemical method for treating polluted water which has been successfully applied for treatment of soluble or colloidal pollutants, such as wastewater containing heavy metals, emulsions, suspensions, etc., but also drinking water for lead or fluoride removal. A typical EC unit includes therefore an EC cell/reactor, a separator for settling or flotation, and often a filtration step. Indeed, the benefits of EC include simplicity, efficiency, environmental compatibility, safety, selectivity, flexibility and cost effectiveness. In particular, the main points involve the reduction of sludge generation, the minimization of the addition of chemicals and little space requirements due to shorter residence time. The main deficiency is the lack of dominant reactor design and modeling procedures. The literature reveals any systematic approach for design and scale-up purpose. The most papers use laboratory-scale EC cells in which magnetic stirring is adjusted experimentally and the separation step by floatation/sedimentation is not studied.

That's why an innovative reactor is developed in order to optimize the cost of this process. This is the object of paragraph three.
