**3. Innovative electrochemical reactors**

This part describes the electrocoagulation and electroflotation as electrochemical methods to treat waste water. The conventional reactors used and the different disposition of electrodes are pointed out. It is also explained how innovative reactors can improve the process of waste water treatment. Thus, specific energy and electrode consumptions are even smaller without the need for mechanical agitation, pumping requirements and air injection, which could not be achieved in other kinds of conventional gas-liquid contacting devices.

An application is then presented to show the efficiency of electrocoagulation/ electroflotation in removing colour from synthetic and real textile wastewater by using aluminum and iron electrodes in an external-loop airlift reactor. The defluoridation is also showed. The time, pH, conductivity and current density are the most parameters for the removal efficiency and energy consumption.

According to many authors, electrochemical technique such as electrocoagulation, electroflotation, electrodecantation have a lot of advantages comparatively to other techniques. Biological treatments are cheaper than other methods, but for example for the decolorization of dye wastewater, dye toxicity usually inhibits bacterial growth and limits therefore the efficiency of the decolorization. Physico-chemical methods include adsorption (e.g. on active carbon), coagulation–flocculation (using inorganic salts or polymers), chemical oxidation (chlorination, ozonisation, etc.) and photodegradation (UV/H2O2, UV/TiO2, etc.). However, these technologies usually need additional chemicals which sometimes produce a secondary pollution and a huge volume of sludge. Water treatments based on the electrocoagulation technique have been recently proved to circumvent most of these problems, while being also economically attractive.
