Residence time distribution and back-mixing in a tubular electrochemical reactor operated with different inlet flow velocities, to remove Cr(VI) from wastewater

In Mexico, the concentration of Cr(VI) in plating industries wastewater is well above Mexican environmental regulations (0.5 mg/L). The electrochemical Cr(VI) reduction, using iron electrodes has been an alternative process, which has been applied with success to remove Cr(VI) from wastewaters. However, few studies have been performed to evaluate the flow field behavior into the electrochemical reactors. In this work, tests at a novel tubular electrochemical reactor were performed. Five different inlet flow velocities with three different inlet positions (central, lateral and tangential inlets) were tested to evaluate their effect on the reactor performance. To study the flow field behavior throughout the reactor, CFD simulations were carried out. The results showed that at low inlet velocities, the reactor dispersion has strong dependence on the inlet position. On the other hand, when the reactor was operated at higher inlet velocities, the dispersion is reduced and presented similar values for the three reactor inlets. As a consequence of the dispersion reduction in the reactor, the residence time required to reduce the Cr(VI) concentration from 1000 mg/L to <0.5 mg/L, can be decreased until 20%.