Fig. 7 Effect of
micro-bubbles flotation on Microcystis sp. harvesting under
different conditions(A) and density(B)
The results of microbubble air flotation treatment of Microcystiswith different density under the condition of condition 5 are shown in
Fig. 7(B). It can be seen from the diagram that with the increase of
Chla concentration from 85 mg/m3 to 844
mg/m3, the recovery rate of microbubble air flotation
to Microcystis also showed an increasing trend. After flotation,
the Chla concentration of density 1 decreased to 54
mg/m3, and the Chla concentration of density 5
decreased to 126 mg/m3. The lowest algae collection
rate of microbubble air flotation for density 1 was 35.6%, while the
algae collection rate for density 5 was as high as 63.5%. The analysis
shows that under low concentration conditions, the number ofMicrocystis colonies is small, and the probability of adhesion by
microbubbles is small; when the algae concentration increased to 844
mg/m3, the number of Microcystis colonies in
the water increased, the probability of microbubbles colliding with them
increased, and the adhesion probability also
increased. Microbubble air
flotation has a better harvesting effect on higher Microcystisdensity.
4.Conclusion
Microbubble air flotation is an effective way for microalgae harvesting.
During the process of microbubble generation, the proportion of
microbubbles with particle size less than 50 μm is optimal with the
pressure of 0.55 MPa, the gas-liquid ratio of 5 % and the length of the
release pipe of 10 cm, and the length of the release pipe is the main
influencing factor, followed by the gas-liquid ratio. No matter a single
microbubble or a combination of two microbubbles, they all undergo
variable acceleration motion during the floating process.
In the process of adhesion, when
the size of Microcystis was 0.6~1.5 times of the
size of microbubbles, microbubbles could adhere to 63% ofMicrocystis . When the size of Microcystis was equivalent
to the size of microbubbles (ratio of 1.03 to 0.9), the adhesion
probability of the two was the largest (both more than 50%).
That can also explain that the
best the harvesting rate of Microcystis (63.5%) was obtained
under the working condition 5 (pressure 0.45 MPa, gas-liquid ratio 5%
and length of the release pipe 100 cm) due to the similar size
distribution of the microbubbles and the Microcystis in this
study. The harvesting performance was also affected by theMicrocystis density and the water flow environment. More
investigations would need to be undertaken for application in large
scale with varied concentrations and other dissolved organic matters.
Acknowledgement
This work was financially
supported by the Key Technologies Research and Development Program
(2017YFE0135500); the National
Natural Science Foundation of China (51908355); the Natural Science
Foundation of Shanghai (19ZR1443700); and the Scientific and Innovative
Action Plan of Shanghai (19DZ1204500).
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