Concurrent removal of phosphate and ammonium from wastewater for utilization using Mg-doped biochar/bentonite composite beads.

[Display omitted] • Novel porous Mg-doped biochar/bentonite beads were synthesized for concurrent removal of phosphate and ammonium. • SA-Mg@BC/BT showed a high adsorption capacity and stability to phosphate and ammonium. • Fixed-bed column experiments also validated the high performance of SA-Mg@BC/BT treating actual wastewater. • High porosity, MgO active sites and functional groups contributed to the enhanced adsorption capacity. • Nutrient leaching and pot experiments verified the slow-release performance of NP loaded SA-Mg@BC/BT. This study reports a strategy for concurrent removal of phosphate and ammonium by a new adsorbent of Mg-doped biochar/bentonite composite bead (SA-Mg@BC/BT), with a high specific surface area and abundant functional groups to facilitate the adsorption process. The maximum phosphate and ammonium adsorption capacities of SA-Mg@BC/BT reached 132.2 mg/g and 39.5 mg/g respectively, apparently surpassing those of SA-BC/BT in this study and other relevant adsorbents in literatures. The removal ability for phosphate kept stable with coexisting monovalent anions (NaCl, MgCl 2 , KNO 3 and KF), while decreased slightly in the presence of divalent anions (MgSO 4 , CaSO 4 and K 2 SO 4). Interestingly, the adsorption capacity for the ammonium removal was even found enhanced by divalent salts (12.0%, 23.9% and 15.0 for MgCl 2 , MgSO 4 and CaSO 4 respectively) and K 2 SO 4 (17.9%). For the actual wastewater, the excellent concurrent removal ability of 98.3% for phosphate and 35.6% for ammonium was validated, and adsorption capacity in actual wastewater was almost the same as that in simulated wastewater. Such an excellent concurrent removal ability for phosphate and ammonium by SA-Mg@BC/BT can be ascribed to the struvite crystallization, ion exchange and Mg-P complexation formation. Finally, the leaching and pot experiments indicated the slow-release ability of the adsorption saturated SA-Mg@BC/BT as a fertilizer, providing a new possibility of nutrient recovery. [ABSTRACT FROM AUTHOR]