Photosynthetic process for removing H2S and CO2 from biogas using the microalgae Chlorella sorokiniana

Abstract

Biogas is an alternative source of energy that contributes on reducing the emissions of polluting gas in comparison to fossil fuels as well as promoting the treatment of organic waste. However depending on the substrate used in its production, it may have a high concentration of carbon dioxide (CO2) and hydrogen sulfide (H2S); in these cases a treatment is necessary to make its use viable, for comply with current legislation and avoid damage to materials and health. Currently, the most widely used methods are physical-chemical, such as absorption, adsorption, membrane separation, and Pressure Swing Adsorption (PSA), among others. However, these methods are expensive and generate waste that needs to be treated. In this sense, biological methods have proved to be promising alternatives, especially photosynthetic processes using microalgae. This study aimed to evaluate the efficiency in removing CO2 and H2S from biogas through a bench-scale purifier prototype consisting of a photobioreactor and an absorption column, in a continuous biogas flow system. The experiment lasted 240 hours, during which 9 m³ of biogas were treated. In the first 24 hours, the flow rate was 1 L/min, resulting in an average removal of 60.8% of H2S and 20.2% of CO2. Between 24 hours and 240 hours of the study, the average biogas flow rate was 0.54 L/min, and an improvement in removal was observed, reaching 83.4% of H2S and 29.7% of CO2. The system showed efficiency in biogas treatment. However, possibilities for improvement were identified in terms of biogas flow and process, which could further enhance the results presented here.