Electrochemical Abatement of Organic Pollutants in Continuous-Reaction Systems through the Assembly of Microfluidic Cells in Series

The electrochemical treatment of wastewater contaminated by organic pollutants was performed under a continuous mode by using, for the first time, various micro-electrochemical cells in series. A synthetic solution of acid orange 7 (AO7), a largely used azoic dye, was chosen as model wastewater. Both the electro-Fenton (EF) method with a cheap compact graphite cathode and electrochemical oxidation (EO) at a boron-doped diamond (BDD) anode were used. EO gave higher abatement of total organic carbon (TOC), but drastically higher energetic consumptions than EF. It is worth mentioning that very different operating conditions were set for EF and EO to optimize their performances. The utilization of three cells in series, all working with EO, allowed an increase in the abatement, but gave rise to quite high energetic consumptions. Conversely, in the case of EF, the utilization of three reactors in series gave rise to a slight increase in the abatement of the TOC, because of the formation of products that are resistant to EF. The utilization of two reactors in series, devoted respectively to EF and EO, each working at optimized operating conditions, gave very good figures of merit in terms of the abatement of TOC and energetic consumption. In particular, high abatement of TOC coupled with drastically lower energetic consumptions than that achieved by the sole EO process were obtained. The effects of current density, flow rate, and initial concentration of AO7 on the process were investigated.