Flocculation of harmful algal blooms by modified attapulgite and its safety evaluation

Natural attapulgite (N-AT) and modified attapulgite (M-AT) were used in this study to evaluate their flocculation efficiencies and mechanisms in freshwater containing harmful algal blooms through conventional jar test procedure. The experimental results showed that the efficiency of flocculation can be significantly improved by M-AT under appropriate conditions. It was found that the attapulgite modified by hydrochloric acid was similar to polyaluminum ferric silicate chloride (PAFSiC). The high efficiency for M-AT to flocculate Microcystis aeruginosa in freshwater was due to the mechanism of bridging and netting effect. Caenorhabditis elegans was used to detect the toxicity of N-AT and M-AT. The results showed that there was no significant toxicity on this organism. Attapulgite is a natural material, which can be readily available, abundant, and relatively inexpensive. Using modified attapulgite to remove the harmful algal blooms could have the advantages of high effectiveness, low cost, and low impact on the environment.

► Modified attapulgite can flocculate Microcystis aeruginosa cells efficiently.
► Netting/bridging is the dominant mechanism that regulated clay-cell flocculation.
► The toxicity studies show that there is no significant toxicity on C. elegans.
► It was found that the modified attapulgite was similar to PAFSiC.
► Advantages of this method are high efficiency, low cost and environmental safety.