Treatment and operating cost analysis of metalworking wastewaters by a continuous electrocoagulation reactor

Abstract

Environmental pollution is a persistent global challenge of industrialisation. In this study, metalworking wastewater (MWW) containing COD of 17,312 mg/L, TOC of 3155 mg/L and turbidity of 15,350 NTU was treated by continuous electrocoagulation process (CEP). At current densities between 30-90 A/m(2), and reactor retention time (tau) of 35 min (Q = 0.10 L/min), removal efficiencies for COD, TOC and turbidity were 68.0-87.0%, 55.2-77.7% and 85.0-99.6%, respectively for Al electrode. Whereas removals for COD, TOC and turbidity with Fe electrode were 75.1-94.8%, 72.2-89.5% and 88.1-99.9%, respectively. Futheremore, varying flow rate from 0.010-0.20 L/min (tau of 350-17.5 min) at 90 A/m(2), resulted into COD, TOC and turbidity removals of 92.6-71.3%, 83.3-64.9% and 99.9-88.9% for Al electrode and 97.8-78.6%, 94.9-69.9% and 99.9-94.7%, respectively for Fe electrode. Analysis of operating costs (OC) encompassing consumptions of energy, electrodes, chemicals and landfill disposal of generated sludge for 30-90 A/m(2) current density showed a variation from 1.37 to 4.74 $/m(3) and 1.03-3.80 $/m(3) for Al and Fe electrodes, respectively. Similarly, the OC for 0.010-0.20 L/min flow rates were 4.34-4.88 $/m(3) (3.34-1.11 $/kg COD) and 3.58-3.85 $/m(3) (7.73-1.41 $/kg COD) for Al and Fe electrodes, respectively. At optimum conditions (EC time = 40 min, tau = 70 min, and 90 A/m(2)), COD, TOC and turbidity removals from MWW by CEP were 94.3%, 90.1% and 99.3%, respectively with Fe electrodes. At these optimums, the OC was 3.09 US $/m(3) (2.63 US $/kg removed COD). The results showed that CEP was an effective alternative process for treatment of the MWW.