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Elevated CO2 level in the closed space or room has much been concerned. Control of CO2 within certain range is one of the most important contents in the life support system. In this paper, a 10 liter membrane-photobioreactor operated with dead end mode was prepared to remove CO2 from air by using the photosynthetic alga, Chlorella vulgaris. The results showed that gas exchange efficiency was improved greatly when the membrane module was adopted. Compared to that in the ordinary photobioreactor, not only the retention time of the smaller and more uniform gas bubble is increased from 2 s to more than 20 s, but also the dissolved oxygen (DO) dropped by a factor of 30, resulting in that the CO2 fixation rate was enhanced 2 from 80 to 260 mg l-1 h-1.

In this paper, a 3 L membrane-photobioreactor was first prepared to study the CO2 removal capability using Chlorella pyrenoidosa. The CO2 was efficiently removed from the airstream when the following operating conditions were set: the inlet airflow of 0.6 L/min, the aeration gas containing 1% CO2, light intensity of 3500 Lx, at 25~30°C and pH at 8.5~9.5. It showed that CO2 concentration in the discharged gas decreased 50% compared to that in the aeration gas, and the removal capacity of the experimental photobioreactor was 0.118 g CO2/(L-medium·h). The medium composition of C. pyrenoidosa for CO2 removal from air was also studied in a 10 L enclosed photobioreactor, in which the proper values of temperature, pH and dissolved oxygen (DO) were controlled on-line. In order to alleviate the influence of DO on the growth of microalgae, N2 was also used to form mixed aeration gas instead of condensed air.