Developing cultivation process of Spirulina platensis for the production of C-phycocyanin

  • 廖 經富

Student thesis: Master's Thesis


Global climate change has become a serious problem due to the increasing greenhouse gas emissions The effective ways towards efficient energy conversion reduction of carbon dioxide emissions and carbon dioxide fixation are one of the most critical global issues at present Recently using microalgae especially Spirulina platensis for biofixation of CO2 has been considered as a promising way not only to reduce the greenhouse gases but also to produce useful bioproducts With its characteristics such as high growth rate efficient carbon dioxide fixation ability and capability to survive under alkaline condition S platensis is the most suitable microorganism used for CO2 biofixation Spirulina platensis is also rich in C-phycocyanin (C-PC) which can be applied as colorants nutritious supplements diagnosis reagent and pharmaceuticals Therefore there is undeniably great potential of using S platensis to fix carbon dioxide and simultaneously for C-PC production The study was aimed to redesign the light condition used in flat-type photobioreactor and focus on the influence of light source (from TL5 to LED) light wavelength and light-dark frequency on S platensis The results show that using LED as light source could slightly improve the phycocyanin content but did not influence the cell growth (0 7 g/L/d) The white light wavelength was found to be the best for the growth of S platensis The efficiency of light capturing increased as the light-dark frequency decrease from 60 min:0 min to 30 min:30 min as the C-PC production per light energy increases from 466 to 566 mg C-PC/kW-hr This study also used wastewater from microalgae culture as a part of nutrition sources and water sources to cultivate S platensis The effect of wastewater from different microalgae culture medium replacement ratio and the addition of nitrogen source on cell growth and C-PC production of S platensis was investigated The results show that there is no difference between fresh medium and 25% wastewater from Mb-1 culture and 25% wastewater from ESP-31 culture giving a biomass productivity of about 0 5 g/L/d and a C-PC content of 13% This study chose Mb-1 culture as the wastewater source for the test of medium replacement ratio on semi-batch culture As the wastewater ratio was increased from 25% to 50% and 75% both the biomass concentration and phycocyanin content decreased from 0 5 to 0 3 g/L/d and 13% to 5% respectively When the medium was amended with 25% of wastewater from Mb-1 culture the addition of nitrogen source (0 9375 g/L) can slightly increase the phycocyanin content Large-scale cultivation using 50L raceway photobioreactor (PBR) was also carried out for the biomass and phycocyanin production The results show that the microalgae concentration in various positions in the raceway PBR has no significant difference indicating sufficient mixing of the raceway PBR without the occurrence of microalgae precipitation at certain position in the PBR The maximum biomass concentration can reach up to 1 8 g/L and the biomass productivity was about 0 1 g/L/d which is higher than the reported performance in the literatures The best culture conditions obtained from small scale cultivation were then adapted into the 50L raceway PBR to determine the efficiency of biomass and phycocyanin production in large scale cultivation The conditions applied were as follows: amendment of 25% wastewater from Mb-1 culture; with 0 045M nitrogen concentration; 30 min:30 min light-dark frequency It was found that the growth of S platensis in the large scale raceway PBR with the wastewater-amended medium decreased from 0 1 g/L to 0 08 g/L while the C-PC content increased from 14 1 to 18 5% A rapid phycocyanin content estimation method was also developed using RGB measurement The RGB measurement was conducted on the microalgae samples and the calibration of RGB data and the phycocyanin content determined with conventional method (e g UV-VIS measurement) was constructed via linear regression The results show that a good calibration between RGB data and C-PC content with a R2 value of 0 98 Hence this rapid C-PC measurement method allows instantaneous monitoring of the cell growth condition and the phycocyanin content of S platensis without any delay In summary the strategies of photobioreactor design and wastewater utilization can help in minimizing power and chemical costs by 98% and 27% respectively In addition to cost reduction our approach also has extra benefits of wastewater treatment and recycling of water resources Therefore with the proposed cultivation system S platensis provides great potential in low-cost phycocyanin production with increased environmental sustainability
Date of Award2015 Aug 24
Original languageEnglish
SupervisorJo-Shu Chang (Supervisor)

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