Electrocoagulation pre-treatment to simultaneously remove dissolved and colloidal substances and Ca²⁺ in old...

An effective electrocoagulation pre-treatment (ECP) method was proposed to simultaneously solve the problems of the micro stickies deposition and high Ca²⁺ content in old corrugated container (OCC) papermaking wastewater during the recycling process. The optimal ECP condition was investigated. The results indicated that the effect of an Al electrode on wastewater treatment was superior to that of a Fe or Mg electrode. The optimal treatment conditions of the current density, electrode distance and reaction time were 115 A m^-2, 5 cm and 60 min, respectively. After the ECP, the chemical oxygen demand (COD) and Ca²⁺ removal rates were 75.33% and 64.53%, respectively, and the turbidity and dissolved and colloidal substance (DCS) content decreased by 97.1% and 43.68%, respectively. The particle size of flocs in the liquid increased from 1.675 μm to 31.97 μm, and the floc content was 0.78 g L^-1 after ECP. The anode material and energy consumption were 0.1846 kg m^-3 and 4.56 kWh m^-3, respectively, and the cost of treatment was estimated to be 1.11 $ m^-3. The results demonstrate that ECP can effectively remove the micro stickies, COD, and Ca²⁺ in the OCC wastewater, which is conducive to reducing the cost of wastewater treatment and conform to the requirements of sustainable development.