Effect and Mechanism of Microbubbles Modified by Amphiphilic Chitosan on Microcystis Aeruginosa Removal During Air Flotation

Algal blooms in lake and reservoir water lead to water quality problems, including water odor, algal toxin, and disinfection byproducts, which threaten the safety of the water supply. A novel dissolved air flotation process that incorporates positively charged bubbles (PosiDAF) can effectively remove algae in lakes and reservoirs. Chitosan (CTS), as a modified bubble agent in the PosiDAF process, has attracted extensive attention due to its natural nontoxicity and good flocculation properties. In this paper, three types of amphiphilic CTS with different lengths of carbon chains were prepared via amphiphilic modification of CTS and were used as bubble modifiers for PosiDAF algae removal experiments. The effects of algae removal under different conditions were compared, and the role of algae-derived organic matter (AOM) was investigated. Results showed that the water solubility of CTS was markedly enhanced after amphiphilic modification, while the crystallinity and thermal stability were decreased. When butyl-N-2 hydroxypropyl trimethyl chitosan ammonium chloride (C4-HTCC) was used as the modifier, the effect of modified air flotation was best, and the removal ratio of algae was 93.47% when the C4-HTCC dosage was 1.0 mg/L. The presence of AOM enhanced the overall effect of algae removal, and electrostatic attraction was the primary adhesion mechanism of the microbubble-amphiphilic CTS-AOM-algal cell system. In addition, adsorption bridging and net trapping also have positive effects on algae removal.