Characterisation of cyanobacteria cultivation in a tubular baffled photo bioreactor (TBPBR)
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Cyanobacteria or blue-green algae are important resources. In some parts of the world, cyanobacteria are used as a staple food and their ability to fix nitrogen has been explored toincrease the productivity of many crops and transform a barren soil into a fertile one. An interesting property of cyanobacteria is their ability to absorb nitrogen and inorganic phosphorous, so they have been seen in water purification systems. Most interestingly cyanobacteria produce O2 and H2 by the combination of photosynthesis and nitrogen fixing ability; they could potentially become a producer of hydrogen fuel. This project investigates the characterizations of cyanobacteria cultivation in a tubular baffled photo bioreactor(TBPBR). Many benchmarking experiments were conducted in light boxes in order to understand the reaction kinetics and to examine the effects of the ratio of aeration surface over culture volume, light intensity, light quality, light cycle, mixing, initial cell density and temperature on the growth of Gloeothece membranacea and Oscillatoria amoena. Based on the benchmarking results, a tubular baffled photo bioreactor (TBPBR) was designed, constructed and commissioned. Further experiments were conducted using Gloeothece membranacea in order to characterize the continuous cultivation of in this novel photobioreactor; examine the effects of the light saturation and the period of light availability V on cell growth and determine the critical cell density for optimal growth. The kinetics information was extracted and compared with that of the benchmarking trials. The light saturation level for Gloeothece membranacea in the TBPBR was 80 μmole m-2 sec-1, and the minimum light exposure without affecting the growth was 6 hours, same as that in the light boxes. Also, much higher critical cell density (CCD)g of Gloeothece membranacea could be accommodated in the TBPBR than that in the light boxes. Furthermore, the optimum specific growth rate of Gloeothece membranacea was obtained at aeration flow rate of 0.08 vvm and Vol CO2/ Vol air = 6%.