3.2.1 Adhesion mode of microbubble-algae aggregates
The adhesion of microbubbles to algae aggregates is shown in Fig. S5. The adhesion modes of microbubbles to algae include 1-1 (single bubble-single algae), 2-1 (double bubble-single algae), n-1 (multi-bubble-single algae) and n-n (multi-bubble-multi-algae). The first two adhesion modes have one thing in common, that is, algae aggregates are adhered to the lower half of the microbubbles. According to the theory of the interaction between microbubbles and particles, this is because during the floating process of microbubbles, tangential flow is formed around the microbubbles, so that the particles (algae aggregates) adhered to them are gathered in the lower half of the microbubbles.
Due to the high density of algae in the experimental water sample (109/ mL), the algae cells in the water sample exist in the form of algae aggregates, and it is difficult to count when the microbubbles adhere to the algae aggregates in the n-n way. Therefore, only the proportion of three adhesion modes of 1-1, 2-1 and n-1 was counted (sample number 1000). When microbubbles adhered toMicrocystis , the 1-1 mode accounted for 94.6%, the 2-1 mode accounted for 4.7%, and the n-1 mode accounted for less than 1%. When microbubbles adhere to Microcystis , the main adhesion mode is 1-1, that is, one microbubble adheres to one algae cell most easily.