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Doctoral candidate:
Lingxue Guan
Title of thesis:
Integration Pressure-Retarded Osmosis with Direct Air Capture Process for Electricity Production and Decarbonization: Fouling Behavior and Life Cycle Assessment
Opponents:
Dr. Mads Koustrup Jørgensen, Associate Professor at the Faculty of Engineering and Science, Aalborg University, Denmark
Dr. Qianhong She, Associate Professor at the School of Civil and Environmental Engineering, Nanyang Technological University, Singapore
Advisor:
Dr. Bing Wu, Professor at the Faculty of Civil and Environmental Engineering, University of Iceland
Other members of the doctoral committee:
Dr. Christiaan Petrus Richter, Professor at the Faculty of Industrial Engineering, Mechanical Engineering and Computer Science, University of Iceland Dr. Xia Huang, Professor at the School of Environment, Tsinghua University, China
Chair of Ceremony:
Dr. Hrund Ólöf Andradóttir, Professor and Head of the Faculty of Civil and Environmental Engineering, University of Iceland
Abstract:
Direct air capture (DAC) is a promising approach for
carbon dioxide removal, but its substantial energy demand remains a challenge for sustainable implementation. This research investigated the feasibility of integrating pressure retarded osmosis (PRO) with aqueous hydroxide-based DAC to recover energy from high-salinity DAC process streams, focusing on membrane fouling, fouling mitigation, and environmental performance. PRO performance was evaluated under CaCO3 scaling and combined CaCO3-alginate fouling using simulated CO2-captured solutions as draw solutions. The results highlighted that (1) CaCO3 polymorph composition influenced scaling behavior, with amorphous calcium carbonate (ACC) forming denser cake layers that restricted water transport, while calcite formed more porous cake layer with limited influence on water transport; (2) in both NaHCO3-based (pH ~7.59) and NaHCO3/Na2CO3-based (pH ~10.5) draw solutions, hydraulic pressure increased alginate deposition, while higher fouling resistance was associated with greater ACC deposition; (3) the CaCO3/alginate ratio influenced foulant deposition patterns: in the NaHCO3-based solution, more alginate in the draw solution facilitated greater deposition of both alginate and CaCO3, while in the NaHCO3/Na2CO3-based solution, alginate deposition was inversely related to CaCO3 deposition. Nevertheless, ACC deposition remained positively associated with fouling resistance at both pH levels; and (4) periodic water flushing removed ~88-99% of deposited CaCO3 and substantially recovered membrane performance, although most organic foulants remained. Comparative life cycle assessment showed ~0.82 ton CO2-eq net removal per ton of CO2 captured in the hybrid DAC-PRO process, comparable to renewable energy-driven DAC under Icelandic scenario. Overall, the findings demonstrate the technical and environmental feasibility of the proposed DAC-PRO process.
About the doctoral candidate:
Lingxue Guan received her bachelor’s degree in Civil and Environmental Engineering from the University of Iceland in June 2021. Later that year, she started her MS study in Environmental Engineering at the University of Iceland, specializing in renewable energy and hydroelectric engineering, and graduated in June 2023. She began her PhD study in Aug 2023. Her research focuses on membrane-based renewable energy extraction and its integration with carbon removal technologies.
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