Peridotite Dissolution in the Presence of Green Microalgae: Implications for a Geoengineering Strategy of CO2 Sequestration

Enhanced silicate dissolution has been recognized as a potentially promising geoengineering strategy to help remove CO2 from the atmosphere by applying crushed minerals to aquatic systems. However, it has not yet been fully quantified in the presence of eukaryotic green microalgae. Here, we studied the interaction of peridotite with Chlamydomonas reinhardtii (C.R.) and Chlorella pyrenoedosa (C.P.). We found that the peridotite dissolution rate was significantly enhanced by green microalgae. Meanwhile, the interaction between peridotite and green microalgae showed two stages with first-order reaction in the early stage (0-4 or 5 days). The amount of Mg2+ released per algal chlorophyll-a biomass and unit time in the early stage is about an order of magnitude higher than that in the late stage (4 or 5-9 days). The quantified effect of C.P. on the dissolution rate of peridotite is about two times higher than that for C.R. in the early stage. Based on the stoichiometric relation of peridotite dissolution, it is estimated that one milligram chlorophyll-a biomass of C.R. and C.P. can remove 0.44 and 0.24 mg CO2 from the atmosphere in one day via accelerating dissolution, respectively. Besides, the Mg2+ ion released from peridotite can promote the growth of green microalgae in turn. Thus, green microalgae play a positive role in CO2 sequestration via the artificial adding peridotite to aquatic systems, but the issue related to the great deceleration of peridotite dissolution rate after a period of time has to be solved to improve the efficiency of CO2 sequestration in the future.