(186i) Carbon Dioxide Sequestration From Air Using Microalgae

Carbon dioxide (CO2) level in atmosphere is considered as the main cause of climate change, and it is becoming a worldwide concern. Using microalgal photosynthesis for CO2 sequestration has recently gained renewed interest because of its high fixation efficiency and the potential of biofuel production as by-product. In our research group, we have designed three different types of membrane-photobioreactor (MPBR) for microalgae cultivation. One is a 10L airlift photobioreactor integrated with a hollow fiber membrane module outside. The effects of the inlet CO2 concentration and the introduction of the membrane module on microalgae CO2 fixation were investigated. Compared with an ordinary photobioreactor, the retention time of the smaller and more uniform gas bubbles in the new membrane-photobioreactor increased from 2 s to more than 20 s, resulting in the enhancement of the CO2 fixation rate from 80 to 260 mg?l-1?h-1. Another is a 5.6 L airlift photobioreactor integrated with hollow fiber membrane and optical fibers inside the reactor. The effects of gas flow rate, light intensity, quality of inner light source, and characteristics of membrane module were studied. The results showed that the rate of CO2 fixation in MPBR was 0.95-5.40 times higher than other conventional reactors. In order to establish if the limitation of CO2 fixation using microalgae was improved in MPBR, we also constructed a membrane-sparged helical tubular photobioreactor, and it indicated that the overall mass transfer coefficient could be obviously increased by introducing a membrane sparger.