3.3 Effects of the microbubble flotation parameters on microalgae harvest performance
The performance of microbubble air flotation on Microcystisharvesting under different working conditions is shown in Fig.7(A). The concentration of Chla was 844 mg/m3 before air flotation, and the concentration of Chla decreased significantly after microbubble air flotation. Among them, the lowest Chla concentration after flotation in condition 5 was 308 mg/ m3, and the highest Chla concentration after flotation in condition 1 was 532 mg/m3. The recovery rate of Microcystis by microbubble air flotation under different working conditions was sorted from high to low as follows: working condition 5 (63.5%) > working condition 4 (52%) > working condition 2 (50%) > working condition 3 (41%) > working condition 1 (37%). According to the content of 3.2.1, the distribution peak of Microcystis is 90~100 μm, and the adhesion rate is the largest when the particle size of microbubbles is equal to the size of Microcystis . The proportion of bubbles with a particle size greater than 80 μm produced by condition 5 is the largest, and its algae harvesting efficiency is the highest. The proportion of bubbles with a particle size of more than 80 μm produced by condition 1 is the smallest, and its algae collection rate is the lowest. The proportion of bubbles with a particle size of more than 80 μm produced by condition 3 is greater than that of condition 2, but its algae collection efficiency is 9% lower than that of condition 2, which may be caused by the floating of multiple large bubbles observed during the experiment. Because the fast-floating speed of large bubbles disturbed the adhesion of microbubbles to the algae, or caused the desorption of the microbubble-microcystin aggregates that have adhered, thereby reducing the algae collection rate. In the process of harvesting algae by microbubble air flotation, the rate of algae harvesting depends not only on the adhesion of microbubbles to algae, but also on the influence of water flow environment.