Biogas purification using algae

• Main Author: Au, Kian Lee.
• Other Authors: Wang Jing-Yuan
• Format: Final Year Project
• Language: English
• Published: 2009
• Subjects: DRNTU::Engineering::Environmental engineering
• Online Access: http://hdl.handle.net/10356/15970
• Institution: Nanyang Technological University

Biogas is known as an alternative source of energy, due to the high methane content present in the gas. However, in order to utilize biogas as an energy source, further purification was needed to remove the impurities that were present. Biogas purification/scrubbing using algae involved the use of algae’s photosynthetic ability in the removal of the impurities (mainly CO2 and H2S) present in biogas, leaving a purified biogas containing almost pure methane, which could be used for energy generation. The main objective of this research was to understand how light intensities and different algae concentrations used affect the algae in biogas scrubbing, mainly focusing on the CO2 removal/fixation process. Experiments were conducted on small, enclosed batch reactors with samples inoculated with 2.5ml, 5ml and 7.5ml liquid algae volumes in the samples exposed to different light intensities. The enclosed batch reactors were flushed with synthetic biogas, containing 60% CH4 and 40% CO2 gas, to stimulate the biogas purification process. Five tests were conducted on increasing light intensities and one test conducted on alternating dark and light conditions. Buffered BG11 liquid media was used in the batch reactors for algae growth. The tests conducted yielded an optimum light intensity of 14000 Lux for the maximum CO2 removal rate from the headspace of the batch reactors. In this research, excessive light conditions were known to cause photo-inhibition in algae cells. Mutual shading could also occur in samples with high algal cell densities, affecting the photosynthetic abilities of the algae cultures. There was a high possibility that the CO2 concentrations removed from the headspace of the batch reactors were not the total CO2 consumed by the algae, as shown in the low specific growth rates at the optimum light intensity for CO2 removal. The concentrations of total CO2 consumed, when further investigated through theoretical calculations, were found to differ by about 2 to 5 times from the CO2 concentrations removed from the headspace of the batch reactors. This led to further discussions on the possible pathways of CO2 utilization by the algae and the relation between the pH in the samples. As a recommendation for future research, to understand the application of this algal technology for future practical use, scaling up of the experiment was highly recommended.