Phosphorus immobilization in Al-drinking water treatment sludge (Al-DWTS) and soil under laboratory conditions

This study assessed the potential reuse of an aluminium coagulated drinking–water treatment sludge (Al–DWTS) as a main substrate in constructed wetland to replace soil for the treatment of P-enriched wastewater. The adsorption isotherm and kinetics of phosphorus (P) removal from high-P solution by Al–DWTS and a local soil from Bailieborough, Ireland, were studied and compared under laboratory conditions. Data of P adsorption were well fitted to the Langmuir and the Freundlich isotherms but the Freundlich isotherm had a higher correlation coefficient. The maximum P adsorption capacity of the Al–DWTS and the soil was 39.4 mg P mg–1 and 9.5 mg P mg–1, respectively, at conditions of pH of 4.0 and temperature of 23 °C. Kinetics studies show that adsorption in both cases followed pseudo-second-order kinetics. The fact that the Al–DWTS exhibited a significantly higher P adsorption capacity at high–P solution compared with the soil suggests that Al–DWTS can be a “novel–waste” bioadsorbent with promising application in wastewater treatment engineering, such as constructed wetland systems.