Cashew-Nut Effluent: An Anodic Oxidation Treatment Using a Batch Recirculation Reactor with BDD Anode

Abstract

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.

Mass transfer and residence time distribution in an electrochemical cell with an air-diffusion electrode: Effect of air pressure and mesh promoters

“…The global mass transfer coefficients (km) were calculated from Eq. ( 15) [30]: (15) where Ilim is the limiting current (A), z is the number of electrons involved in the ferricyanide reduction (i.e., 1 eq mol -1 ) from Eq. ( 4), F is the Faraday constant (96,485.3 C eq -1 ), Ae is the exposed platinum electrode area (90.25 cm²), and C∞ is the bulk ferricyanide concentration of 15 mmol L -1 .…”