A basic model for bi-directional transfer of carbon dioxide and oxygen between digester biogas and a microalgae culture

With increasing anthropogenic influence on earth, fossil fuel usage, the principal emission source of carbon dioxide (CO2), has increased significantly at the risk of depletion in the future. Meanwhile, fossil fuel usage has also been identified as a cause for the increase in the deterioration of climate around the world. Biogas is a valuable renewable energy source that can be an alternative solution for future energy demands and mitigatory strategy for climate change. Biogas is a byproduct from the anaerobic digestion of organic wastes and this results in a gas composed mainly of methane (CH4), CO2 (30–40%) and trace amounts of other gases such as hydrogen sulfide (H2S), siloxanes, and water vapor. Purification and upgrading of biogas is necessary to increase the quality and the productivity of biogas as an energy source. Various technologies are available for biogas impurity removal; physical, chemical and biological methods. Since, physiochemical methods are expensive and environmentally hazardous, biological methods that are more environmentally friendly, cost competitive, and feasible are being developed. One promising biological method is the use of microalgae for the purification of biogas. This method involves the photosynthetic ability associated with CO2 fixation by microalgae using light energy. This research project focused on developing a basic mass transfer model for a biological gas-liquid scrubbing system that uses algae in a liquid medium to purify the CO2 present in the biogas. The model’s ability to simulate the mass transfer of gasses between the algae and the biogas in this scrubbing system was evaluated using a laboratory-based algal-scrubber. The comparison and evaluation of the model to the data collected from the laboratory work provided valuable insight into the main parameters influencing the model and its need for calibration against experimental results. Based on the results of this work, the model provided a reasonable simulation of the scrubber system indicating its potential use as a tool for design and operation of an algal based purification system. Additionally, further recommendations necessary for the research to modify and extend the development and improvement of this model are made