Integrated electrochemical-adsorption process for the removal of trace heavy metals from wastewater

In the light of the spread of treated wastewater use for irrigation, trace heavy metals pose a great risk to humans and aquatic life. An integrated electrochemical-adsorption (i.e. EC-AD) hybrid system was investigated for the removal of iron (Fe), zinc (Zn), and copper (Cu) traces from synthetic wastewater mimicking industrial wastewater. Slag, a by-product produced in steel industries, was utilized as the adsorbent. The performance of the EC-AD hybrid system was evaluated at mass to wastewater volume ratio (i.e. M/V) ranging from 0.01 to 0.07 g/mL, current density (CD) ranging between 5 and 15 A/m2 and treatment time ranging between 60 and 120 minutes. Furthermore, process kinetics (pseudo-first-order, pseudo-second-order, Elovich, adsorption kinetic models, and Weber-Morris intraparticle diffusion), and adsorption isotherms (Langmuir and Freundlich) were investigated to provide adsorption mechanisms that reflect the interaction between EC and AD processes in the hybrid system. The results indicated that Freundlich isotherm was able to fit the linearized data points compared to Langmuir with Fe and Zn. In addition, kinetic models suggested chemisorption as the predominant removal mechanism of Fe, Zn, and Cu using slag for the EC-AD system. Results showed that the use of EC-AD significantly enhanced the removal efficiency of heavy metal traces from wastewater, reaching 99%.