Kinetics of CO 2 Sequestration by Anabaena Variabilis in a Stirred tank Batch Type Photobioreactor

Abstract

Green house gases are strongly responsible for increase in the global warming since they absorb infrared radiations. Therefore, it is the need of the hour to reduce the production of green house gases up to a considerable extent. High emissions of CO2 gas can be found at locations like thermal power plants, steel, cement, oil, automobile industries. Most of the CO2 capture techniques are not environment friendly as they cause leakage of CO2 back to the environment. Recent researches show that carbon dioxide sequestration by microalgae has become one of the alternatives to combat climate change due to the various limitations of the higher plants however, not much work has been done to meet the increasing demand for energy along with replacing the fossil fuels. Biological methods involve the utilization of photosynthesis for sequestering the CO2 and thereby producing various valuable by-products under controlled conditions. This study involves the use of Anabaena variabilis- a cyanobacteria which is cultivated in BG (-N) 11 media under optimum conditions like 28ºC temperature, 7.2 pH, 120 rpm agitation rate, and around 5000 lx light intensity in a stirred tank photobioreactor for 7 days. The effect of varying the gas flow rate as 0.5 lpm, 1.0 lpm and 1.5 lpm on CO2 sequesteration efficiency was studied along with the growth kinetics of Anabaena and protein content estimation. The kinetic parameters calculated like the productivity, CO2 fixation rate, average specific growth rate were higher at 1.0 lpm as 0.052 g/l/day, 0.095 g/l/day, 0.558 l/day, respectively. However, maximum biomass was observed at 1.5 lpm as 0.416 g/l. The protein content was found to be similar in all the batches i.e. 0.14 g/l. Hence, the experimental data shows that 1.0 lpm is the most suitable gas flow rate for mass cultivation of microalgae as well as CO2 sequestration in photobioreactor.