Scaling-up Studies on Electrolysis Using Cation Exchange Membrane for Alum Recovery

Water treatment sludge from coagulation process in Indonesia is generally directly discharged into rivers. This condition may negatively affect the environment and human health. The high concentration of aluminum in the sludge can be potentially recovered as alum coagulant. Laboratory-scale electrolysis using cation exchange membrane (CEM) has proven to increase purity of recovered alum. The use of CEM for alum recovery in a pilot-scale can be used to estimate investment, operation, and maintenance costs in its application. This study aims to examine effectiveness of the pilot-scale electrolysis using CEM for alum recovery from water treatment sludge. The electrolysis cell used plate acrylic material with a batch recirculation reactor system. Feed tank capacity was 5 L with electrolysis cell volume of 400 mL. The cross-sectional area of the electrode was 48 cm². The electrolysis was operated for 10 h. The electric currents used in this study were 400, 600, and 800 mA. Conductivity, pH, total dissolved solids, aluminum, iron, and manganese were measured every hour, as well as concentrations of zinc, lead, chromium, and copper at the initial and end of electrolysis. Results showed that optimum current density was 12.5 mA/cm² with alum recovery efficiency of 68.06% at specific energy consumption of 53.47 kWh/kg. The recovered alum was free from organic impurities, and the main metal component was aluminum with high percentage (91.23%). The electrolysis effectiveness in alum recovery was influenced by the ratio of electrode area and electrolysis cell volume, operation time, and current density. Graphic Abstract: [Figure not available: see fulltext.].