A fixed-bed column study of solid waste-based calcium silicate hydrate for the phosphate removal

Abstract

The calcium silicate hydrate (CSH) was synthesized from the solid waste residue (SWR) of the Alum Factory, and was used for phosphate abatement from an aqueous solution. Fixed-bed column adsorption experiments were conducted at different flow rates (5, 7.5, and 10 mL/min) and bed depths (6, 9, and 12 cm) at an initial pH and phosphate concentrations of 5 and 5.5 mg/L, respectively. The breakthrough curve analysis was developed and tabulated for the effects of the flow rate and bed depth. Fixed-bed adsorption models, namely the Thomas model, the Yoon–Nelson model, and Bed Depth Service Time (BDST) model were fitted to the experimental data. The R2 values observed for the Thomas model and the Yoon–Nelson model were 0.96 and 0.98, respectively, at the flow rate of 7.5 mL/min and bed depth of 9 cm with the breakthrough adsorption capacity of 5.67 mg/g. The synthesized CSH was also tested for its phosphate removal efficiency using local wastewater treatment plant effluent. About 1,658 mL of real wastewater was treated for 249 min before the standard threshold limit (1 mg/L) was reached. This study prevails that the synthesized CSH could be applied to remove phosphate from real wastewater under a continuous flow adsorption system.