Study on the performance and mechanism of high gradient magnetic separation in treating ship ballast water

The discharge of ship ballast water serves as a primary pathway for marine biological invasion, which has caused severe ecological and economic harm worldwide. Consequently, this study assessed the efficacy and underlying mechanism of high gradient magnetic separation (HGMS) as a pretreatment technology for ship ballast water treatment. Initially, operational parameters were optimized through orthogonal experiments, yielding optimal process conditions: a magnetic seed concentration of 0.5 g/L, a PAC concentration of 0.007 g/L, a flow rate of 200 mL/min, a rotational speed of 700 r/min, and a current intensity of 4 A. Under these optimal operational conditions, HGMS consistently achieved a turbidity removal rate exceeding 98%, the removal rate of marine Chlorella > 99%, and the removal rate of Escherichia coli is 63%. Mechanistic analysis revealed that HGMS removes microorganisms through throttling and physical disruption. In summary, HGMS represents an effective pretreatment technology that significantly reduces turbidity and microbial load, thereby creating favorable conditions for subsequent advanced disinfection and offering an alternative solution for shipborne ballast water treatment systems compliant with international regulations.