Modification of sand filtration system with biochar/zero valent iron-biochar for the simultaneous removal of algal cells and microcystin-LR

High-density algal cells and the released algal toxins during harmful algal blooms cannot be effectively removed by traditional sand filtration systems. In this study, bare sand filtration columns were modified by different mass ratios of biochar (synthesized at different pyrolysis temperatures) and used to simultaneously capture algal cells and microcystins from water. We found that the addition of 2 wt% biochar synthesized at 700℃ could effectively remove Microcystis aeruginosa and Chlorella vulgaris cells under both slow and fast filtration flow conditions, and remove the released microcystin-LR in suspension. Effective removal performance with the coexistence of natural organic matters, in real water samples, during 3 transport-elution cycles and continuous operation for 50 pore volumes was also achieved by biochar-modified filtration system. The high algal adsorption capacity due to the wrinkled structure and the less negative charge of biochar contributed to the enhanced removal performance. Moreover, using zero valent iron (ZVI) loaded biochar to modify sand columns would effectively inactivate and inhibit the regrowth of retained algal cells. The results showed that as one type of inexpensive and readily available bio-materials, biochar/ZVI-biochar could be used to modify the sand filtration system for the effective removal of algal cells and toxins from water.