Electrochemical technologies are a promising alternative for the treatment of wastewaters containing organic pollutants. The main advantages of these processes include environmental compatibility, versatility, energy efficiency, safety, selectivity, amenability to automation and cost effectiveness. However, the effectiveness of the electrochemical approaches depends strongly on electrode materials and cell parameters (mass transport, current density, water composition, etc.). Then, the use of high performance anodic materials can achieve high efficiency and lower the operating cost. Therefore, several research groups are recently studying the applicability of the electrochemical technologies for treating real domestic and industrial effluents, with the aim of that a diversification of techniques must be sought, adapting the treatment to each situation, as much as possible. In this context, this paper presents an overview of the application of electrochemical technologies to treat industrial effluents in the northeastern region of Brazil, emphasizing the use of direct and indirect electrochemical oxidation processes as an alternative to pollution abatement of effluents generated by textile and petrochemical industries.

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In this work, a synthetic effluent containing methylene blue has been treated by electrochemical oxidation (EO) process at pre-pilot plant scale using a filter-press electrochemical cell reactor. Electrochemical experiments were carried out using Ti/Pt and Ti/IrO 2 -Ta 2 O 5 anodic materials in the presence or absence of chloride ions to study the influence on the decolorization and mineralization of the different oxidant species electrogenerated in situ. The electrochemical experiences have been carried out at different applied current densities (j = 20, 40 and 60 mA cm -2 ) to evaluate the effect of this controlling parameter on the degradation efficiency and the operational energy consumption. Under optimal treatment conditions of 40 mA cm -2 in 0.05 M of Na 2 SO 4 at pH 6.0, solutions of 100 mg L -1 of methylene blue were completely decolorized obtaining 86.0 % of COD abatement after 360 min of electrolysis. The determination of energy consumption allowed to estimate operational costs about 13.36 US$ m -3 . The results obtained provide valuable information regarding the EO process scaling-up, aiming the application of electrochemical technologies to treat actual effluent at real scale.

A BDD-batch reactor with recirculation is presented, for the first time, to the electrochemical treatment of an actual cashew-nut effluent, which is a real environmental problem in the Northeast region of Brazil. This system was characterized in terms of mass transfer coefficient (k m = 2.22 × 10 −5 m s −1 ), which led to a limiting current intensity of 1.91 A. Different parameters, such as, current density, kind of electrolyte and initial pH were evaluated considering the chemical oxygen demand removal, current efficiency, energy consumption, by-products generation and toxicity. The results clearly indicated that the addition of external electrolyte and the change of initial pH are two factors that do not lead to a significant improvement in the degradation of organic matter when compared to the treatment of the effluent as received. Conversely, an increase in current density promoted a COD removal up to 89%, after 150 min of oxidation, due to the enhancement of the generation rate of strong oxidants. Low production of carboxylic acids was also detected over time. Additionally, it seems that the treated effluent can be used to irrigate specific crops, like those applied to the production of renewable fuels, based on the toxicity tests performed.