Highly efficient and energy-conserved flocculation of copper in wastewater by pulse-alternating current

Copper wastewater from industry is detrimental to plants and environment. There are some problems in the aspects of high efficiency and energy saving during treatment of wastewater. In present work, the novel double iron electrodes technique of pulse-alternating current was applied to flocculate copper in wastewater. The process parameters of the copper removal in wastewater were studied in the developed electrochemical reactors. Scanning electron microscopy, X-ray diffraction, and energy-dispersive spectroscopy were used to characterize the electrocoagulations. The copper residue in the effluent was measured by UV spectrophotometry. The adsorption mechanism was described through the isothermal adsorption curves of copper during flocculation processes. The simulated wastewater containing 100 mg dm^-3 Cu²⁺ and 100 mg dm^-3 NaCl as conductive salt was adjusted to pH 7.8-8 with ammonia or sulfuric acid. At room temperature of 20-25 °C, controlling the flow rate of 3 dm³ min^-1, and applying pulse-alternating current of 40 μA g_Fe^-1, the copper residue in the effluent passing through four-series reactors was reduced to 0.118 mg dm^-3, which was far lower than 0.3 mg dm^-3 (from GB20900-2008). The removal rate of copper could reach 99.882%. The removal of copper in the wastewater treated via our electrocoagulation technique was far more efficient than the conventional DC current coagulation and chemical flocculation. The double iron electrodes were used to reduce the concentration polarization and improved the current efficiency. The significant economic and good social benefit will be promisingly produced if our developed technique is applied in the treatment of industrial wastewater.