Techno-economic estimation of electroplating wastewater treatment using zero-valent iron nanoparticles: batch optimization, continuous feed, and scaling up studies

Electroplating manufacturing processes release industrial effluents that comprise severe levels of heavy metals into the environment. This study investigated the utilization of nanoparticles of zero-valent iron (nZVI) for the treatment of electroplating wastewater industry containing multiple heavy metal ions. In batch experiments using Cu 2+ as a single solute, the optimum operating condition was pH 7.3, nZVI dosage 1.6 g/L, time 36 min, temperature 30 °C, and agitation speed 180 rpm, achieving almost 100% Cu 2+ removal efficiency. The adsorption mechanisms were illustrated using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and Fourier transform infrared (FTIR) spectrometer. Moreover, continuous-feed experiments were performed to treat real electroplating wastewater industry via adsorption and sedimentation processes. The system attained removal efficiencies of 91.3% total suspended solids (TSS), 68.3% chemical oxygen demand (COD), 94.2% nitrogen (N), 98.5% phosphorus (P), 66.7% Cr 6+ , 91.5% Pb 2+ , 83.3% Ag + , 80.8% Cu 2+ , 17.4% Ni 2+ , 47.1% Mn 2+ , 54.6% Zn 2+ , 94.7% Fe 3+ , 100.0% Al 3+ , and 42.1% Co 2+ . The removal mechanisms included reduction of Me n + to Me ( n - x )+ /Me 0 by the Fe 0 core, adsorption to the oxide shell as Me(OH) x and Me-Fe-OOH, oxidation of Me n + to Me ( n + z )+ , specific surface bonding, and sequential steps of electron transfer and precipitation. The total cost, including amortized and operating expenses for scaling up the adsorption system, was 4.45$ per m 3 of electroplating wastewater. Graphical abstract