Electrochemical oxidation for treating effluents from cashew nut processing using batch reactors

Abstract

• Electro-oxidation using DSA efficiently decreases organic matter from cashew-nut wastewater. • pH conditions about 4.0 are essential to degrade the oil phase of the effluent. • Presence of Cl – ions in the wastewater increases the efficiency of the process. • Higher flow rate reduces energy consumption when compared with stirring reactor. Electrochemical treatment of phenolic effluents produced in the cashew nut processing industry (CNPI) in Northeast Brazil was investigated using a double-faced Ti/TiO 2 RuO 2 anode and two Ti plates as cathodes, in two electrochemical systems (batch reactor with magnetic stirring and recirculation reactor). Parameters evaluated were current density, pH conditions, chloride concentration and inter-electrode distance. Operating conditions that showed best performance for organic matter removal, in terms of chemical oxygen demand (COD), were 35 mA cm −2 , pH 4.0, 1985 mg L −1 of Cl − and 220 L h −1 of flow rate by using recirculation reactor, achieving 97.5% in 360 min of electrolysis. pH conditions about 4.0 were essential to degrade the oil phase of the effluent; while the presence of chloride promoted the electrogeneration of strong oxidants, increasing the efficiency of the process. Also, higher flow rate of the recirculation system reduced the electrical cell potential required for the electrochemical treatment, thus reducing energy consumption (99.58 kWh m −3 ) when compared to that obtained by using batch magnetic stirring reactor (201.6 kWh m −3 ), under same experimental conditions. Results encourage the application of electrochemical technology with mixed oxide electrodes as actual CNPI effluent treatment process, when environmental sustainability, cost and commercial availability of electrodes.