Removal of Microcystis aeruginosa and microcystin-LR using chitosan (CTS)-modified cellulose fibers and ferric chloride

The occurrences of harmful algae blooms (HABs) and cyanotoxins such as microcystin-LR (MC-LR) are increasing in water reservoirs and compromise drinking water security. In this study, chitosan (CTS) modified cellulose fibers (CF) were developed as a green adsorbent for the simultaneous removal of a model algae cell, Microcystis aeruginosa, and MC-LR. The results showed that the CTS modification could render amine groups (−NH₂) on CF and increased the adsorption affinity toward algae. In the absence of algogenic organic matter (AOM), the algae removal reached 100% at a dosage of 26.7 g-NH₂-CF/g-algae (dry weight); however, at the same CF dosage, the presence of AOM (8.13 mg‑carbon·L⁻¹) strongly reduced the adsorption by NH₂-CF and removal rate of algae cells reached only 3.2 ± 3.0%. When adding FeCl₃ or Fe³⁺ at a concentration of 11.2 mg-Fe·L⁻¹, the inhibitory effect of AOM was dramatically reduced as indicated by the improved algae removal up to 95% at an NH₂-CF dosage of 20.45 g·g⁻¹, because of the reduced energy barrier between NH₂-CF and cells. Moreover, when the Fe³⁺ concentration was increased to 16.8 mg·L⁻¹, 79% of MC-LR was simultaneously removed. Thus, combining Fe³⁺ with NH₂-CF is proven effective to enhance the adsorption and removal of Microcystis aeruginosa and MC-LR and achieve a sustainable mitigation of HABs.