(155d) Toxicity of Flue Gas In Microalgae CO2 Mitigation Systems

Microalgal-based CO2 capture from flue gas is an attractive mitigation strategy for industry. However, other gases are also present that may be harmful to microalgae growth, such as NOx and SOx. In this study, we simulated flue gas by adding to the culture medium salts of nitrite, sulfite, or bisulfite. Two high CO2 tolerant species were evaluated: an environmental isolate (Rio) and Scenedesmus sp. (UTEX 1589). Toxicity tests were performed in 96-well microplates under an atmosphere of 2% (v/v) CO2 to determine the concentration range of trace gases for microalgae growth. Both algae were able to tolerate concentrations of nitrite (>1600 ppm) and sulfite (400 ppm) higher than those reported in effluent gas. However, bisulfite inhibited growth at 50 ppm. This effect was associated with a drastic decrease in medium pH. As a result, we explored the use of cement dust and CaCO3 to lessen the decline in pH. We used concentrations of 300 ppm and 240 ppm of cement dust and CaCO3, respectively, to increased pH from 2.6 to 5.0. This increment in pH resulted beneficial to the growth of both species, tolerating concentrations of 400 ppm bisulfite (2X upper limit concentration found in flue gas). In all tests, environmental isolate (Rio) generated more biomass than the collection strain. Therefore, our microalgae isolate shows a better tolerance to the flue gas constituents, where cement dust might be a beneficial component of the mitigation system.