2.4 Study on the dynamic rule of “Adhesion–Depolymerization” between microbubbles and microalgae
The following tests were carried out under the optimal conditions based on the above tests. Firstly, a syringe was used to inject 5 mL wastewater containing Microcystis into the air floating column in the upward direction. When the liquid level reached H=400 mm, the high-speed photography system was used to shoot the rising process of microbubbles and microalgae near H=400 mm. The subsequent procedure is the same as 2.3. In the video, the size and number of microbubbles and microalgae was observed, and the adhesion rule between microbubble and microalgae was summarized.
2.5 Optimization ofharvesting performance of microalgae under the regulation of microbubble flotation
(1) Performance of microbubble flotation for harvesting microalgae under different conditions
According to the results of 2.3 and 2.4, the length of the release pipe was the main influencing factors, the following tests were carried out under different working conditions with the length of the release pipe of 10 cm (condition 1), 25cm (condition 2), 50 cm (condition 3), 75 cm (condition 4), and 100 cm (condition 5), respectively (Table S1). The concentration of Chla of the wastewater which containedMicrocystis was firstly analyzed. Then the flotation device was installed. 400 mL microcystis -containing wastewater was prepared and transferred to the floating column. Start the device and stop the water inlet when the liquid level raised to H =450 mm. The air floating time is 60s. After that, the algal residue was scraped from the top of the air floating column, and the remaining water sample was removed from the bottom of the air floating column. 100 mL of the remaining water sample was used to determine the concentration of Chla after air flotation. After the completion of the first air flotation, open the drainage valve at the bottom of the air flotation column to drain the water, and start the device again to clean the air flotation column, so as not to affect the test results. The above steps were repeated 3 times under the same condition. When the experiment under different conditions was complete, the recovery rate of air flotation was defined based on the change of chlorophyll a concentration before and after flotation. The harvesting performance of the microbubble flotation system under different working conditions was compared and analyzed.
(2) Effects of microalgae densities on the harvesting performance of microbubble flotation
According to the results of experiment (1), the optimal condition was selected, and the experimental device was adjusted accordingly. The mixture with different microalgae density were prepared as following: 400, 800, 1200, 1600 and 2000 mL of microalgae containing wastewater were put into five large beakers, respectively. Then 1600, 1200, 800, 400 and 0 mL of fresh wastewater was added into different beakers to form a concentration gradient of 1:2:3:4:5, numbered 1~5 respectively. Then the concentration of Chla in different beakers was determined. The remaining liquids of each beaker were divided into 3 parts with 400 mL volume each. The flotation experiments of different microalgae density were conducted as described above. According to the change of Chla concentration, the effect of algae density on the harvesting performance was investigated.