Scaling-up And Optimization Of Photobioreactor For Astaxanthin Production Using Heterotrophic Haematococcus Pluvialis

Haematococcus pluvialis is the only biological source of L-astaxanthin(best natural astaxanthin),the strongest antioxidant ever found so far.Therefore,large-scale cultivation of H.pluvialis is the only way to produce natural astaxanthin.So far,the large-scale cultivation technology of H.pluvialis has been mainly the two-stage photoautotrophic method,but this method is low in cultivation efficiency of H.pluvialis and high in land consumption of photobioreactor(PBR),which severely restricts the development of the natural astaxanthin industry.To this end,a novel cultivation mode named "sequential heterotroph-dilution-photoinduction"(SDHP)was developed by our research group.The mode improved the culture efficiency of H.pluvialis and reduced the occupied area of PBRs.Our research group has conducted a preliminary pilot study on the photoinduction process of the heterotrophic cells for astaxanthin production with SHDP technology.To realize the industrialization of this technology,the PBR used in the process urgently needs to be scaled up and optimized.The shear stress is an important parameter for scaling up and optimizing the PBR.However,there is no literature to quantify the shear tolerance of H.pluvialis.Hence,there is no basis for PBR scaling-up.Besides,establishing a model simulating the effects of outdoor light intensity and temperature on astaxanthin is an important basis for photobioreactor optimization.At present,the H.pluvialis photoinduction models reported in the literature are difficult to guide the optimization of an outdoor PBR.Given the above situations,this article first determined the critical shear stress of heterotrophic H.pluvialis,then the optimization and scaling up of the pump in the HTPBR was conducted based on the critical shear stress and a 20 m3 HTBPR was established and a photoinduction base with total HTPBR volume of about 420 m3 for H.pluvialis photoinduction was established.Then,a astaxanthin accumulation model(including astaxanthin productivity model FFBC-ap and FFHT-ap,astaxanthin concentration increasing rate model FFBC-ac and FFHT-ac)of H.pluvialis heterotrophic cells based on the average light intensity inside the PBR and the average temperature of the algae broth was established in the bubble column PBR and the pump-driven HTPBR,respectively.It was verified outdoors,and then the model was used to optimize the VMAPBR and the HTPBR from three perspectives:the geometry,the orientation,and the operating conditions.Finally,the established FFHT-ap model and FFHT-ac model was used to screen and compare the location suitable for photoinduction of heterotrophic H.pluvialis cells around the globe,which also laid the foundation for the globalization of SHDP technology.The main conclusions of this paper are as follows:(1)The critical shear stress of H.pluvialis aplanospores was 19.18～27.32 Pa.There was no significant difference in the impact on the survival rate of H.pluvialis aplanospores with different astaxanthin concentrations.Based on the critical shear stress,the 400 L HTPBR was successfully scaled up to 20 m3.The centrifugal pump equipped with a six-blade semi-open backward curved impeller was the best pump in the HTPBR for photoinduction of heterotrophic H.pluvialis.(2)In the range of algae cell density 0.218～2.5 g L-1 and astaxanthin concentration 0.47%～3.04%,the prediction performance of Cornet light attenuation model was better than Lambert-Beer light attenuation model.When the cell density was low(0.4 g L-1),the light attenuation was sensitive to astaxanthin concentration in the cell.When the density of cell density is high(2.0 g L-1),the light attenuation was not sensitive to astaxanthin concentration in the cell.The relative deviation between the predicted value and the measured value of FFBC-ap model and FFBC-ac model built in the outdoor 3 L bubble column PBR was less than 20%,which showed a good prediction performance.(3)The relative deviation between the predicted value of the FFHT-ap model and FFHT-ac model built in the 15.6 m3PBR and the measured value did not exceed 21.5%,which showed good prediction performance.Based on this,an orthogonalization method was adopted to optimize the five-row parallel HTPBR.The optimal annual area productivity of astaxanthin in the five-row HTPBR reached 22.90g m-2 year-1,which was better than that reported in the literature.(4)Based on the FFBC-ap model and FFBC-ac model established in Chapter 3,the 100 L VMAPBR was optimized.The optimized annual area productivity of astaxanthin in the VMAPBR was 204.39 g m-2 year-1.At the same time,the single-row HTPBR was optimized by the FFHT-ap model and FFBHT-ac model model established in Chapter 4.The optimal annual area productivity of astaxanthin in the single-row HTPBR reached 297.15 g m-2 year-1,which was 45.38%higher than that of the optimized single-row HTPBR and about 12 times higher than the level reported in the literature.(5)The annual astaxanthin yield of the large-scale production sites of H.pluvialis were predicted according to the FFHT-ap model and FFHT-ac model established in Chapter 4,and the results showed that the annual astaxanthin yield of Shidian County,Baoshan City,Yunnan Province,optimized by the model established in Chapter 4,was 22.90 g m-2,while the annual astaxanthin yield in Kaneohe Bay,Hawaii,USA,was 29.98 g m-2,which was most suitable for photoinduction of heterotrophic H.pluvialis.The annual astaxanthin productivity in Gustafsburg in Stockholm,Sweden was only 4.50 g m-2 year-1,which was not suitable for photoinduction of heterotrophic H.pluvialis.The work in this article not only provides a high-performance PBR for the industrialization of H.pluvialis for astaxanthin accumulation based on the high-yield astaxanthin SHDP mode but also lays a foundation for the optimization of outdoor large-scale PBRs.Besides,it also lays an important foundation for the global generalization of SHDP technology.