Assessment and Selection of Cyanobacterial Strains for CO₂ Mineral Sequestration: Implications for Carbonation Mechanism

CO₂ mineral carbonation induced by microalgae is an emerging approach to carbon capture, utilization, and storage (CCUS). Freshwater cyanobacteria are common microalgae in nature that can raise the pH of eutrophic waters and drive the precipitation of carbonate. Still, limited studies have been conducted to evaluate and select appropriate cyanobacteria strains for CCUS. Here we present experimental investigations to compare the capacity of different freshwater cyanobacterial strains in converting CO₂ to carbonates. We compare five cyanobacterial strains by monitoring their growth curves. We examine three metrics, the maximum pH of the solution, hydroxide production capacity, and extracellular polymeric substances (EPS) secretion capacity, to assess the capacity for carbon sequestration. Our results indicate that among the five strains, <i>Microcystis aeruginosa</i> shows the highest pH and EPS content per unit cell number, marking the most significant capacity for CO₂ carbonation. We observe carbonate precipitates as hydromagnesite and dypingite. We suggest the negatively charged, hydrophilic EPS can effectively promote the precipitation of magnesium carbonate and inhibit the precipitation of calcium carbonate. Overall, our approach provides a framework for assessing and selecting cyanobacterial strains for CO₂ carbonation, advancing the understanding of the mechanism of microalgae-induced CO₂ Mg-carbonation from the perspective of EPS surface properties.微藻诱导的二氧化碳矿物碳酸化是一种新兴的碳捕获、利用与封存（carbon capture, utilization, and storage, CCUS）技术。淡水蓝藻是自然界中常见的微藻类群，可提升富营养化水体的pH值并驱动碳酸盐矿物沉淀。然而，目前针对适配CCUS需求的蓝藻菌株筛选与评估相关研究仍较为有限。本研究通过实验探究，对比了不同淡水蓝藻菌株将二氧化碳转化为碳酸盐的能力。我们通过监测生长曲线对5株蓝藻菌株进行比较，并选取三项指标——溶液最大pH值、氢氧化物生成能力以及胞外聚合物（extracellular polymeric substances, EPS）分泌能力——来评估其固碳能力。实验结果表明，在5株菌株中，铜绿微囊藻（Microcystis aeruginosa）在单位细胞数下的pH提升能力与EPS含量均为最高，具备最优的二氧化碳碳酸化能力。本研究观测到的碳酸盐沉淀产物为水菱镁矿（hydromagnesite）与水纤菱镁矿（dypingite）。我们提出，带负电荷的亲水性EPS可有效促进碳酸镁矿物的沉淀，并抑制碳酸钙矿物的析出。综上，本研究构建了一套用于评估与筛选适配二氧化碳碳酸化的蓝藻菌株的研究框架，并从EPS表面特性的视角，深化了对微藻诱导CO₂镁质碳酸化机制的认知。