New insights into the improvement of electrocoagulation performance on the basis of a time-integrated performance index: The pivotal role of electrical conductivity

In this study, a time-integrated performance index (TIPI) was proposed to assess the compromise between amounts of removed metallic ions (RMI) and the consumed electric energy (CEE) in wastewater treatment systems based on the electrocoagulation (EC) process. An aluminum electrode-based EC reactor along with a Zn2+ ion-based electrolytic medium was used to assess the effect of electrical conductivity (kappa) in low vertical bar values (215-415 mu S cm(-1)) was used to highlight kappa effects on total electric voltage (U-EC) and EC performance. Measurements of metallic ion concentrations, kappa and U-EC were performed in time. A Nernst-Planck equation-based mathematical model for the time description of kappa was proposed. In all EC tests, time-dependent behaviors on kappa, U-EC and electric current were observed. The kappa experimental data were well fitted by the kappa model, showing profiles modulated by the time behavior of the metallic ion concentrations. The maximum TIPI value (1.2/Wh) was achieved about 10 min electrolysis time, dropping quickly due to a substantial reduction (350 to 50 mu S cm(-1) after 60 min) in kappa and, consequently, an increase in CEE (up to 2 Wh after 60 min). Thus, this drop in kappa value became more evident at the end of shorter electrolysis times related to the low kappa conditions driving towards a significant loss in TIPI. In a global context of the EC performance, TIPI has brought another perspective to address in an optimized EC process, looking for the highest values within a steady state.