Treatment of printing ink wastewater using a continuous flow electrocoagulation reactor

Printing ink wastewater from printing facilities is difficult to treat because of its heavy pollutant load (chemical oxygen demand - COD, color and total suspended solids - TSS). In this study undiluted printing ink wastewater with high COD (i.e., 20,000 mgL-1) was treated using a highly efficient, continuous flow electrocoagulation reactor with aluminum electrodes. The parameters investigated were: initial COD concentration (4000, 10,000 and 20,000 mgL-1), current density (21, 42 and 83 mAcm-2), and inlet flow rate (6, 8 and 10 mLmin-1). All parameters showed great efficiency in terms of pollutant removal for diluted printing ink wastewater. For undiluted printing ink wastewater treatment, COD, color, and TSS removal were maximized at 6 mLmin-1 flow rate reaching 82%, 98%, and 85% COD, color, and TSS removal, respectively, by applying the lower tested current density 21 mAcm-2. COD, color and TSS removal increased with increasing current density. For undiluted printing ink wastewater and a flow rate of 8 mLmin-1, COD removal was between 42 and 88%, color reduction between 85 and 99%, and TSS reduction between 83 and 98% when the applied current was increased (from 21 to 83 mAcm-2). Lower pollutant removal was observed at the highest flow rate of 10 mLmin-1 for all current densities tested. Process cost calculations in terms of electrical energy, electrode material consumption and sludge disposal, showed that the use of continuous flow electrocoagulation reactor (with flow rate 6 mLmin-1, and at 21 mAcm-2) is an affordable and effective treatment method for printing ink wastewater streams with very high COD. Sludge characterization showed Al-silicate-rich sludge. Particle sizes increased after treatment and Cu and Ti were detected in the sludge. A post-treatment stage is necessary before discharging effluent into water bodies.