Increasing Carbon Dioxide Availability in Microalgae Cultivation Systems by using Triethanolamine

Abstract: In this study we investigated the use of triethanolamine (TEA), a well-known carbon dioxide (CO2) capturing chemical, to increase CO2 availability in microalgae growth media. Microalgae culture used in the study was a mixed culture, in which the dominant species were determined by microscopic analysis as Chlorococcales order of the Chlorophyceae class (i.e. Scenedesmus sp., Chloroccum sp.). The non-toxic triethanolamine concentration was determined by measuring the specific growth rates of microalgae cultures grown in BG11 medium spiked with 1, 2, 5, 10, 20 and 40 mM TEA. It was observed that the growth rate started to drop at TEA concentrations bigger than 20 mM. It was also observed that the biomass growth rate as well as nitrate and phosphate consumption rates of microalgae at 20 mM TEA concentration were similar to those grown without any TEA addition. Based on GC-FID analysis, a decrease in TEA concentration was detected after 6th day of the growth period, but a separate study indicated that this decrease could not be associated with abiotic oxidation, biosorption or sorption by microalgae. Using pre-CO2 loaded BG11 mediums with 20 mM TEA concentration resulted in higher biomass production rates compared to those without TEA addition, when the cultures were not aerated during cultivation. When the cultures were subjected to aeration, the biomass production rates of the cultures with and without TEA addition became close to each other. It was found that most of CO2 loaded in the medium released within a few days of the growth period. Further studies are being conducted to reveal CO2 release mechanisms from CO2 loaded TEA solution to microalgae medium.