Removal of Escherichia Coli from Ballast Water Via High-Gradient Magnetic Separation

Abstract Ship ballast water is a prominent medium for the growth of several foreign species. This study aimed to develop a high-gradient magnetic separation (HGMS)-based method to eliminate Escherichia coli and the mechanism underlying E. coli death, per regulation D-2 of the Ballast Water Convention. A novel wheat straw magnetic seed characterized by good flocculation performance, cost-effectiveness, and environmental friendliness was prepared via chemical implantation. The HGMS system using this wheat straw magnetic seed had a significantly higher total suspended solid (TSS) removal rate and E. coli removal rate than a system comprising Fe3O4 (MP) + polyaluminium chloride (PAC) + polyacrylamide (PAM). A hydraulic retention time of 60 s, these rates were increased by 18.5% and 0.15log, respectively. Furthermore, with an increase in magnetic field strength, the E. coli removal rate continued to increase, and Escherichia coli cells were markedly damaged. Lipid peroxide MDA levels increased rapidly over a short period, and a large volume of K+ leaked out, eventually leading to cell death. The present HGMS system using wheat straw magnetic seeds is a novel ballast water pretreatment system with good potential applications.