Development of a novel UASB/CO2-stripper system for the removal of calcium ion in paper wastewater

Abstract

Although the Upflow Anaerobic Sludge Blanket (UASB) has been widely used in wastewater treatment, it reveals clogging problems and the removal efficiency of COD was as low as 70% in the treatment of liner paper wastewater containing high concentrations of calcium ions. Calcium ions accumulated in the form of calcium carbonate and the ash content of granules reached 80%, which lowered the specific methanogenic activity of granules to 25% of the initial value. The pH was higher as the pH micro-electrode approached the core of the granule and this was why calcium carbonate was formed inside the granules. A novel process composed of UASB and CO2-stripper was suggested in this study to treat the liner paper wastewater. When the synthetic wastewater containing 5000 mg/l calcium hardness and 3000 mg/l COD was fed to the system, most of the calcium hardness was removed in the CO2-stripper and the removal efficiency of COD maintained a stable value of over 90%.