Mitigation of harmful algal blooms using iron-modified clays inside the semi-permeable membrane tubes

Abstract

This study explored innovative methods for mitigating harmful algal blooms (HABs) using iron and chitosan-modified clay to deposit cyanobacteria cells, immobilize phosphate, and adsorb algal toxin microcystin LR (MC-LR). Compared with modified kaolinite, modified sepiolite showed superior capacity in phosphate removal at the same initial PO₄³⁻ concentrations. The maximum capacities of modified kaolinite and sepiolite for PO₄³⁻ adsorption were 20.7 and 30.7 mg PO₄³⁻/g clay. The MC-LR removal by modified sepiolite was 95.5 % - 99.9 % when initial MC-LR concentrations ranged from 20 to 200 μg/L. Modified kaolinite could remove MC-LR by 70 % only when the MC-LR concentration was high (100–400 μg/L). Precipitated phosphate in clay could eventually be released back into the water body. Thus, modified clays packed in semi-permeable membrane tubes were used to recover phosphate from water bodies to minimize the internal cycling of phosphate. The PO₄³⁻ and MC-LR removal by the clays packed in the semi-permeable membrane tubes was much slower, but over 90 % removal of phosphate and microcystin could be achieved in 10 days. Considering its low cost, excellent performance, and eco-friendly properties, the proposed solution has the potential to be used for HAB control and prevention on a large scale.