A Study on Carbon Dioxide Fixation and Biomass Composition of Thermosynechococcus sp CL-1 in the Laboratory and Outdoor Environments

Abstract

There is a great potential to assimilate carbon dioxide and produce bio-energy from cellular component by utilizing carbon fixation of photosynthetic microorganisms A thermophile strain Thermosynechococcus sp CL-1 (TCL-1) isolated previously from a hot spring in Taiwan was feasible for using dissolved inorganic carbon (DIC) from the scrubber with regard to “hot” flue gas and used in the present study Two types of culture system continuous and batch with tube photobioreactors were used and fed with carbonate/bicarbonate as C source (DIC 50°C) and nitrate as N source (dissolved inorganic nitrogen DIN) for simulating the absorbent from scrubber of flue gas Lipid and carbohydrate of cellular component could be used as bio-energy precursors and their contents as function of various molar ratios of DIC/DIN was quantified The maximal lipid productivity of about 150 mg L-1 d-1 was obtained while carbon dioxide uptake rate was 917 mg L-1 d-1 at the dilution rate of 0 06 h-1 when both DIC and DIN were not limited Cell mass and cellular compositions were depended on not only limitation of N concentration but also C/N ratio in a batch culture test The fixation of carbon during photosynthesis seemed to switch from the pathway of protein synthesis to forming carbohydrate not lipid under the N-limitation and high C/N ratio for TCL-1 The maximal carbohydrate content was 61% TCL?1 was also cultivated in flat plate photobioreactors in this reearch with dense culture indoors to examine the effects of light source and illumination intensity on the biomass production carbon dioxide fixation and phycocyanin production It showed that biomass production carbon dioxide fixation and phycocyanin production can be increased in flat plate photobioreactors The greatest biomass productivity and carbon dioxide fixation rate were 0 82 and 1 29 g L?1 respectively with white LED illumination for 12 hours It showed no effort in biomass production and carbon dioxide fixation for red light LED The content of phycocyanin of TCL?1 was about 2% with white or red light LED illumination for 12 hours When light/dark cycle was applied the biomass of TCL-1was reduced about 0 1 to 0 2 gL?1 and the content of phycocyanin was reduced about 2 6% during the same dark period of 12 hours The maximum content of phycocyanin for TCL?1 was 5 3% with 1 000 μE m?2s?1 white LED illumination The optimum phycocyanin content of TCL-1 can be determined by the appropriate harvest time The best time for TCL-1 to harvest the phycocyanin is the time before darkness The phycocyanin of TCL-1 is very valuable economically Another goal of this research was to create an outdoor production platform of phycocyanin carotenoid and carbohydrates which is the bio-ethanol precursor The results of previous studies and present cultivation experiments indicated that the maxium carbon dioxide fixation rate for indoor case (5 316g CO2/L/d) is better than outdoor case (maxium 3 41g CO2/L/d) However the carbohydrate content of TCL-1 cultivated outdoors was as high as 70% which was much better than indoor cultivation In addition the cellular contents of phycocyanin and carotenoid both are high light sensitive pigments were much stable when cultivated indoors than outdoors The high carbon dioxide fixation rate and the content of carbohydrate phycocyanin and carotenoid of TCL-1 were addressed to reach the experimental expectation of 60% 5% and 1% under some specific outdoor conditions Consequently the production of phycocyanin carotenoid and carbohydrate under outdoor cultivation is economically fessible

Date of Award	2017 Nov 30
Original language	English
Supervisor	Yun-Hwei Shen (Supervisor)