Potential impacts of effluent from accelerated weathering of limestone on seawater carbon chemistry: A case study for the Hoping power plant in northeastern Taiwan

Abstract

The Hoping power plant (HPP), located on the northeastern coast of Taiwan, is considered an ideal site to test the accelerated weathering of limestone (AWL) technique for fossil fuel CO2 mitigation because the required reactants, seawater and limestone, are readily available and inexpensive to obtain. In this study, we investigated the current status of chemical hydrography at two off-shore stations near the HPP, the results of which can provide a baseline for future evaluations of marine environmental changes arising from the potential implementation of AWL. Additionally, seawater samples collected around the HPP were used to evaluate the effectiveness of CO2 absorption for the One-step and the Two-step AWL reactors, which were designed by the Industrial Technology Research Institute of Taiwan. The results demonstrate that the Two-step reactor is more effective than the One-step reactor in terms of CaCO3(s) dissolution, thus implying conversion of more dissolved CO2 into HCO3− balanced by Ca2 +, which is environmentally benign and can be stored for the long-term in the ocean. The capacity of CO2(g) absorption for the current Two-step reactor was estimated to be 121 μmol kg− 1. However, more efficient conversion of CO2 to ocean alkalinity using this method is possible with optimizing reactor designs and operating procedures. The impacts of the AWL effluent solution on pH and carbonate saturation state (Ω) in the receiving seawater were further examined by conducting a simple mixing simulation. The simulated result indicates that a 10-fold dilution would be sufficient to maintain the pH and Ω changes within a range of 0.2 and 0.8, respectively, which are regarded as constraints for safely discharging wastewater into the ocean.