Harnessing green tide Ulva biomass for carbon dioxide sequestration

Green tides, characterised by massive blooms of the seaweed Ulva, pose a significant threat to coastal economies and marine ecosystems. This review explores the potential repurposing of harmful Ulva blooms for carbon sequestration, addressing the critical global issue of CO₂ emission. We conducted a comprehensive literature review and examined the conversion of shoreline Ulva biomass into biochar through pyrolysis, a process that can be implemented directly at biorefineries. This approach not only facilitates carbon sequestration but also mitigates greenhouse gas emissions and enhances soil quality through soil amendments. Our review covers data from 2008 to 2022, focusing on the carbon sequestration potential of Ulva during green tide episodes in China and Korea. Our assessment indicates that Ulva biomass has the potential to sequester approximately 3.85 million tons of CO₂ equivalent (CO₂e), with about 1.93 million tons of CO₂e potentially stabilised through biochar conversion. Furthermore, we conducted a hypothetical techno-economic analysis assessing the sustainability and economic viability of Ulva cultivation and biochar production for CO₂ sequestration. These findings suggest that the combined biomass and biochar production could be financially viable and profitable. Despite the challenges posed by green tides, our review highlights their potential role in mitigating global climate change.