Hydrochloric acid-modified algal biochar for the removal of Microcystis aeruginosa: Coagulation performance and mechanism

The unceasing algae blooms have led to the deterioration of water quality and ecological imbalance in the entire globe, it's urgent to investigate its treatment and resource utilization technology. In this study, treated algae was prepared to produce the biochar and then it was utilized as a coagulant for the removal of Microcystis aeruginosa. To improve the pore structure of algae-derived biochar for improving the removal capacity of M. aeruginosa, hydrochloric acid (HCl) modification was applied and optimized by Box-Behnken model-based response surface methodology. After modification by HCl, the specific surface area, pore volume, and average pore diameter of modified algae-derived biochar (MAB) increased to 38.34 m2/g, 0.073 cm3 /g, and 7.42 nm, respectively. The removal efficiency of Microcystis aeruginosa (The initial cell density: 4 x106 cells/mL) by the MAB reached 99.02%+/- 0.18 under the optimum condition obtained with response surface experiment (dosage of 287.46 mg/L, pH of 8.2, stirring rate of 175 rpm, and stirring time of 6.4 min). At the same time, the removal efficiencies of Chl a, turbidity and total phosphorus of polluted waters reached more than 84%, 91% and 60%, respectively. The dissolved organic matters were removed synchronously, thereby reducing the disinfection by-products formation potential. Electrostatic adsorption has been determined as the predominant force during the coagulation process. In conclusion, the HCl has been proved to be an effective strategy to improve the pore structure and algal removal capacity of MAB, and the MAB could be applied as the suitable materials for the algal coagulation with the advantage of resource utilization.