The Property Study On Light Conduct Chamber For Evaluating Photosynthesis Rates Of Microalgae

In outdoor cultivation of microalgae photoautotrophy, the stratification phenomenon of light area and dark area in microalgae suspension due to light attenuation is the main limiting factor in microalgae growth. To enhance microalgae’s photosynthesis rates, the light conduct chamber structure which diluting the high intensity sunlight and effectively redistributing it into the microalgae suspension is proposed.The optical parameters and light intensity distribution features of eight different structures of light conduct chambers (LC) are compared and analyzed by the methods of theory designs, experiment and optic simulation. And then study on how the LC affect the mixing of microalgae suspension by the method of computational fluid dynamics is conducted. Finally, the maxima spirulina cultivation experiment has been done.The result shows that the light intensity distribution in microalgae suspension is effected by LC’s light dilution rates, the surface area to volume ratio (SVR) and the LC’s assembly spacing. The share of light area in micoalgae suspension increases with LC’s light dilution and SVR, and decreases with the distance of the assembly spacing. For the plane surface type LC, light intensity is evenly distributed in the output surface, for the curved surface type LC, owing to its some certain light collecting ability, the closer to the LC’s center the higher light intensity it is. Triangle and inner convex arc LC have a good coupling with airlift mixing for their sharp bottom structure which could spilt the bubble rising flow into two symmetry flow along the LC’s transparent wall. As a result, they enlarge the mixing area and elevate the mixing along the light intensity gradient area, and their self-cleaning effect by bubble rising flow prevent microalgae cells from adhering to LC’s transparent wall, which reduce much trouble for cleaning. In outdoor high intensity condition, microalgae’s growth rates could be evaluated by adding LC, after five days cultivation, the final microalgae concentration is18%higher than that in the control group. Only when the light intensity was higher than the microalgae’s saturation light intensity and LC could obvious evaluate photobioreactor’s light area surface, can the microalgae’s growth rate be evaluated by adding LC.Consequently, light conduct chamber not only increases the light area in microalgae suspension and elevates the average light intensity, but also promotes mixing intensity along the light intensity gradient direction when it is combined with airlift mixing technology, which releases the decline of microalgae cell’s growth rate due to light stratification. Therefore it’s promising to be used in microalgae’s large scale cultivation.