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Harvesting of Microalgae Cells by Dissolved Air Flotation

Author: GaoLiLi
Tutor: LiuTianZhong
School: Ocean University of China
Course: Of Food Science
Keywords: Chlorella Flocculation Flotation separation method PAC Sodium hydroxide
CLC: Q943.1
Type: Master's thesis
Year: 2010
Downloads: 225
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Abstract

Microalgae because of their high photosynthetic efficiency, the use of carbon dioxide, fast growth, abundant photosynthetic products have important applications in the field of food, feed, health care, chemical, environmental, energy, microalgae cultivation and related product development has become an emerging technology industries. Microalgae culture a liquid cell concentration is low, generally only 1-4g / L, and the small size of cells, how cost-effective the cells collected from the culture medium, has become one of the technical bottleneck restricting microalgae technology industry tradition sedimentation, centrifugation, filtration, etc. can not meet the needs of future large-scale industrial production. Chlorella as the research object, study its dissolved air flotation harvesting process, in order to provide a basis for the establishment of economic and efficient harvesting of microalgae dissolved air flotation technology. Paper first analyzed theoretically the saturation dissolved gas dissolved gas water under pressure dissolved air conditions, bubble size, outgassing behavior and its influencing factors; followed by another key process for the realization of the dissolved air flotation, that Chlorella cells floc formation and morphological characteristics of polyaluminum chloride (PAC) as a flocculant polyacrylamide (PAM) as a coagulant chlorella flocculation effect, to determine the best flocculation conditions; once again examines the amount of flocculant add, add the amount of the coagulant aid flocculation reaction time, dissolved air water water flow rate, the volume ratio of water to feed and so the impact of the the chlorella cell flotation recovery factor of concentration optimized by orthogonal experimental of its flotation harvest conditions; explore the feasibility of adding sodium hydroxide to the chlorella flocculation, and preliminary optimization of the flotation operation conditions. The results show that: (1) the establishment of the flotation experimental system is simple in structure, easy to operate. Dissolved air pressure is 0.6MPa, the theoretical dissolved gas up to 108mL / L, the bubble diameter 58.28μm, be able to provide high-quality water containing dissolved gas flotation separation. (2) with the PAC or auxiliary polyacrylamide of Chlorella cells to achieve good flocculation. Determine the optimum flocculating conditions for the the PAC addition amount of 160mg / L, the PAM added amount 6mg / L, reaction time of flocculation 8min, Under this condition, the flocculation rate reached 92.43%, the concentration factor can reach 8.60. Study using the concept of fractal dimension the Chlorella cells floc morphological characteristics, the results show that good correlation between floc fractal dimension and flocculation rate, the smaller the fractal dimension, the higher the flocculation rate, but fractal dimension is too small will reduce the concentration ratio and the the floc grain structure is too loose and friable, strength and low density, not conducive to flocculation and sedimentation and subsequent flotation harvest. Suitable floc tablets fractal dimension in the 1.37-1.54 between the floc particles corresponding average particle diameter is between 400-600μm. (3) the use of the PAC flocculation flotation harvest chlorella, along with the PAC add the amount of increase, flotation recovery ratio gradually increased from 49.94% to 97.95%, but the flotation concentrate the multiples from 16.95 less Little to 9.79; for flocculation with PAC, add the appropriate amount of a polyacrylamide helps reduce difficult flotation tiny amount floc grains, thereby enhancing oil recovery, the excess of the PAM will lead to floc particle structure is too close floc grain density is too big to fail flotation; the flocculation reaction time prolonged help improve floc formation and improve the flotation recovery, but has little effect on the harvest of concentration; dissolved gas water influent flow rate increase help to improve the flotation yield and cell concentration factor; the harvesting liquid feed rate and the dissolved gas water exists an optimal proportion between high and low water dissolved air will lead to the recovery ratio decreased. By orthogonal experiment to determine the the best flotation harvest conditions: PAC dosage 160mg / L, PAM dosage 6mg / L, and the flocculation reaction time is 8min dissolved gas water inlet flow rate of 75L / h, water The volume ratio was 20%. (4) the use of sodium hydroxide, the pH value adjustment the chlorella harvesting liquid can achieve a good flocculation cells, a good correlation exists between the flocculation rate and the added amount of sodium hydroxide. To achieve the same harvest effect, add a small amount of sodium hydroxide dissolved air flotation method for flocculation and sedimentation method, to determine the conditions for: the best solution of dissolved air flotation method in the exponential growth phase and stationary phase chlorella The added amount of sodium hydroxide were 350mg / L and 600mg / L, the the best dissolved gas and water flow rate of 60L / h, the best water volume ratio is 25%; (5) in the logarithmic growth phase and stationary phase of the smaller ball algae harvesting liquid, the flocculating effect of the use of sodium hydroxide to adjust the pH value of the difference is not obvious. But for the flotation process, in the same amount of sodium hydroxide add in the Chlorella cells RECOVERY logarithmic phase was significantly higher than the stabilization period of concentration slightly above the stable phase.

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