Development of an innovative approach for low-impact wastewater treatment: A microfluidic flow-through electrochemical reactor

In this work, a novel approach for the development of fast and low-consuming electrochemical reactors for wastewater treatment is studied. It consists in the use of a microfluid flow-through cell with a very narrow inter-electrode gap (to minimize ohmic drops) and flow-through electrodes (to maximize mass transport towards the electrodes). The ohmic drop was studied for different inter-electrode gap and electrolyte conductivities. A low ohmic drop of 6 Ω was measured using an inter-electrode gap of 400 µm in a liquid electrolyte with 0.7 mS cm−1 of conductivity. The mass transfer coefficient (km) was evaluated at different inlet flow velocities, obtaining 1.45 · 10−5 m s−1 at a velocity of 1.0 · 10−2 m s−1, considerably superior to the data reported for flow-by cells. Finally, the efficiency for wastewater treatment via anodic electro-oxidation with diamond anodes was evaluated. In this work, 100 ppm of clopyralid contained in a synthetic soil washing effluent were completely removed in this system using 2.71–8.54 Ah dm−3 and 12.5–115.0 kWh m−3 at 10 and 100 mA cm−2, respectively. Comparison with a commercial flow-by (Diacell® 101) shows that the novel approach requires between 4 and 10 times less electric charge and from 6 to 15 times less energy consumption. The microfluidic flow-through configuration stand as a promising approach to reduce the environmental impact of electrochemical wastewater technologies.