Environmental Impact Assessment of New Cement Production Blending Calcareous Green Algae and Fly Ash

To improve traditional cement manufacturing, which generates a large amount of greenhouse gases, blending calcareous green algae and fly ash as cement replacement materials is expected to achieve nearly zero carbon emissions. As a calcareous green alga, Halimeda macroloba is a significant producer of biogenic calcium carbonate (CaCO3), sequestering approximately 440 kg of carbon dioxide (CO2) per 1000 kg of CaCO3, with CaCO3 production reported in relation to algal biomass. To assess the new low-carbon/low-waste cement production process, the proposed scenarios (2 and 3) are validated via Python-based modeling (Python 3.12) and Aspen Plus® simulation (Aspen V14). The core technology is the pre-calcination of algae-derived CaCO3 and fly ash from coal combustion, which are added to a rotary kiln to enhance the proportions of tricalcium silicate (C3S) and dicalcium silicate (C2S) for forming the desired silicate phases in clinker. Through the lifecycle assessment (LCA) of all scenarios using SimaPro® (SimaPro 10.2.0.3), the proposed Scenario 2 achieves the GWP at approximately 0.906 kg CO2-eq/kg clinker, lower than the conventional cement production process (Scenario 1) by 47%. If coal combustion is replaced by natural gas combustion, the fly ash additive is reduced by 74.5% in the cement replacement materials, but the proposed Scenario 3 achieves the GWP at approximately 0.753 kg CO2-eq/kg clinker, lower than Scenario 2 by 16.9%. Moreover, the LCA indicators show that Scenario 3 has lower environmental impacts on human health, ecosystem, and resources than Scenario 1 by 24.5%, 60.0% and 68.6%, respectively.