STUDY ON THE ALUMINIUM SALTS RECOVERY AND RECYCLING DURING MICROCYSTIS FLOS-AQUAE REMOVAL USING COAGULATION SEDIMENTATION

Coagulation-sedimentation process has been increasingly used in the treatment of algae-laden water, however, the cost share of coagulant is still the largest, which makes the cost of algae-laden-water treatment remain high. In this study, the harvested Microcystis flos-aquae biomass which contain polyaluminum chloride (PAC) and cationic polyacrylamide (CPAM) were washed to recover aluminum salts for the purpose of coagulant recycling. The purposes of this study were to reveal whether the presence of CPAM in the coagulation harvested biomass affect aluminum recover, to explore how does HCl concentration and liquid-solid ratio of HCl-biomass affect the aluminum recover efficiency, and to disclose the relationship between the HCl dosage and the amount of Al³⁺ recovered. The results showed that the recoveries of total aluminum salt increased with washing time, and then reached plateau after a certain number of washings. The highest recovery achieved at a higher concentration of HCl or a higher liquid-solid ratio. The recovered aluminum salt could be reused for 5 times, and its removal efficiency was always higher than that of the newly prepared PAC at the same concentration. Further analysis revealed that the extracellular polymeric substances (EPS) were eluted at the same time which enhanced the coagulation. Technical and economic analysis found that PAC recovery and recycling could significantly reduce the chemical cost during algae laden water treatment, from 0.60 to 0.30 RMB/m³. The results of study would be helpful to guide the practice of coagulation based microalgal harvesting for the purpose of coagulant recycling and biomass purification.