The potential of phosphate removal from dairy wastewater and municipal wastewater effluents using a lanthanum-modified bentonite

• Adsorption studies for phosphate removal using Phoslock® clay were conducted.
• The modified clay efficiently removed phosphate from dairy and wastewater effluents.
• Residual organics in effluents may reduce the phosphate adsorption capacity.
• The maximum adsorption capacity ratio is 1/69 mg phosphate/mg Phoslock®.

Adsorption is gaining interest as an effective advanced method for treatment of wastewater effluents with a high phosphorus concentration. The present work investigated the use of a bentonite–lanthanum clay (Phoslock®) which effectively reduced the amount of dissolved phosphate. Batch experiments were carried out in order to obtain adsorption equilibrium isotherms and kinetics with phosphate-spiked synthetic solutions. Different doses of Phoslock® clay were examined for their efficiency in removing phosphate from dairy wastewater and from two types of domestic wastewater treatment plant effluents (a sequenced batch reactor (SBR) and an activated sludge plant). The average maximum adsorption capacity ratio was 69 mg Phoslock® per 1 mg of phosphate removed from the phosphate-spiked synthetic solution. Nevertheless, a ratio of 100, 300 and 400 mg Phoslock® per 1 mg of phosphate was found for complete phosphate removal from the effluents of the dairy, the SBR and the activated sludge plant, respectively. The higher ratios are probably due to the presence of dissolved organic matter in the wastewater. Phosphate removal from the effluents was more efficient and faster with the increase in Phoslock® doses (up to 100% removal in the first 15 min for the dairy wastewater). This study shows that bentonite–lanthanum clay can be used to design an adsorption treatment process for phosphate removal from water and wastewater with a low hydraulic retention time and minimal infrastructure.