| Astaxanthin, a good carotenoid additive, has great application foreground in the area offood, feedstuff, cosmetic and pharmaceutic. Culture Haematococcus pluvialis (well known for itsgreat ability to accumulate astaxanthin under certain conditions) for nature astaxanthin is apromising way and has drawn attention from many researchers.On the foundation of abundant laboratory results, people focus on pilot scale culture ofHaematococcus pluvialis in outdoor condition. However, the culture process in pilot scale washeavily blocked by some scientific and technic problems (like bio-contamination and volumeenhancement) due to the influence of its biological characteristics and the inherent weakness inphotobioreactor design. Construction of new enlarged photobioreactors, technological assemblyrequired in application and related biological characteristics were re-conducted during2003-2006 with an aim to provide foundational supports for exploitation of this bioresource.First of all, three new enlarged photobioreactors including column photobioreactor, tubularphotobioreactor and biofilm photobioreactor were established for microalgal application. Thenew built column photobioreactor was simple in structure, cheap in cost and efficient in mixingof the algal culture. The new tubular photobioreactor would break the volume limitation andgreatly enlarged the culture scale compared to the traditional connected tubular photobioreactorthanks to the parallel design. The creative biofilm photobioreactor would effectively prevent thealga from bio-contamination and improve astaxanthin content in cell because of theimmobilization of Haematococcus pluvialis on a water-free matrix. Based on the three closedphotbioreactors, an egineering from algal stock, enlarge culture, astaxanthin accmulation, andbio-contamination prevention to algal collection was established. The crucial parametersincluding culture temperature, light intensity, dissolved oxygen ands pH were well controlled inthe suitable ranges and high quality algal powder was produced too.The relationships of light intensity, light path and cell density of Haematococcus pluvialiswas further studied by analyzing the basic properties of light attenuation in culture. The equationof light attenuation was established: I=I0exp[-(0.113+0.94OD750)L]. On the basis of this equationand the structure of two enlarged photobioreactors , the average light intensity in columnphotobioreactor and tubular photobioreactor woud be obtained by the following equations: Iavg=I0[2αr0+3exp(-αr0)-(1+αr0)exp(-2αr0)-2]/(α2r02) and Iavg=2I0[αr0+exp(-αr0)-1]/(α2r02),α= 0.113+0.94OD750, R2=0.9893. Therefore, the light intensity inside photobioreactors wouldbe calculated according to above equations, and feasible light condition could be maintained bywell adjusting the light intensity in compliance with the incidence solar intensity.Mixotrophic growth results of Haematococcus pluvialis exposed to different temperatureand light intensity showed that high algal biomass and fast cell growth rate would be obtained at24 ℃ and 24μEM-2S-1 light radiation. Outdoor pilot scale mixotrophic cultivation ofHaematococcus pluvialis also indicatd that algal growth rate and biomass would be obviouslyimproved in cold winter and spring. Therefore, mixotrophic culture seems to be a promisingculture mode of Haematococcus pluvialis in application.Finally, the scale-up culture of Haematococcus pluvialis with our new technique and thetraditional open-pond culture mode was compared in different seasons. The main profiles weregreatly improved as below: 3 folds prolong of the cultivation period in a year, 20% shortage ofeach batch culture time, 40% decrease of the astaxanthin accumulation period, 40% increase inalgal biomass for each batch culture and 4 folds increase in astaxanthin content in the biomass.Therefore, the astaxanthin production efficiency in Haematococcus pluvialis was about 35 foldshigher than that of traditional technique yearly, at least in theory. Furthermore, a new culturemode good for H. pluvialis cultivation and astaxanthin accumulation was suggested.
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