Potentiality of phosphorus-accumulating organisms biomasses in biosorption of Cd(II), Pb(II), Cu(II) and Zn(II) from aqueous solutions: Behaviors and mechanisms.

Heavy metal pollution is consistently a critical global issue, and bioremediation is regarded as one of the most promising approaches. In this work, the biosorption characteristics of Cd(II), Pb(II), Cu(II) and Zn(II) from aqueous solutions using three phosphorus-accumulating organisms (PAOs) biomasses, Ochrobactrum cicero (PAB-006), Stenotrophomonas maltophilia (PAB-009), and Pseudomonas putida (PAB-0031), as biosorbents were investigated. Results indicated that the equilibrium biosorption capacities of biosorbents to heavy metal ions were sensitive to the solution pH, and increased with increasing pH values. The experimental data of Cd(II), Pb(II), Cu(II) and Zn(II) biosorption were in good agreement with the Pseudo-second-order, Redlich-Peterson and Temkin models, implying that the biosorption was a hybrid chemical reaction-biosorption process. In addition, the theoretical maximum biosorption capacities of Cd(II), Pb(II), Cu(II) and Zn(II) were calculated to be 67.84, 80.23, 50.56 and 63.07 mg/g for PAB-006, 59.99, 87.71, 39.26 and 64.00 mg/g for PAB-009 and 68.31, 85.43, 38.97 and 62.85 mg/g for PAB-031, respectively (pH = 5.0 ± 0.1, T = 25 °C), according to the parameters of the Langmuir model. Moreover, ionic strength had negligible influences or slight promoting effects, while humic acid exhibited positive effects on the removal of heavy metals. Further, PABs were stable and displayed excellent reusability. Characterization techniques of FTIR and XPS revealed that surface complexation, ion exchange, hydrogen bonding and electrostatic interaction were the main mechanisms involved in the biosorption process. In summary, the biosorbent PABs possessed high biosorption performance with excellent reusability, and which hold the great application prospect in the treatment of heavy metal contaminated water.