Phosphorous removal from aqueous solution can be enhanced through the calcination of lime sludge

- Calcined lime sludge at 700 °C significantly enhanced the P removal efficiency.
- pH values of the solution significantly increased with increasing P removal efficiency.
- Increased P concentration inhibited the P removal efficiency of the calcined sludge.
- P removal trend followed pseudo-second-order and diffusion-chemisorption kinetics.
- P removal is potentially due to a multi-mechanistic reaction.

Water treatment plants generate an enormous amount of the sludge which is normally treated as waste. In the recent past, many investigations have been focused on developing an economical adsorbent using water treatment sludge to remove phosphorous (P) from aqueous solutions. However, the great extents of the studies have been limited in the use of alum- and iron-based sludges. This study, therefore, investigated the P removal performance of the calcined lime sludge. Calcined lime sludge at 700 °C significantly enhanced the P removal efficiency whereas marginal improvement was noted when the sludge calcined at 400 °C was tested. With increase P removal efficiency, final pH values of the solution also significantly increased. P removal efficiency of the calcined sludge decreased with increasing the initial P concentrations. However, the removal efficiency could be improved by increasing the weight of the sludge. Further analysis demonstrated that P removal trend followed both pseudo-second order and diffusion-chemisorption kinetics signifying the P removal is potentially due to a multi-mechanistic reaction in which, the process is controlled by intra-particle diffusion followed by chemisorptions.