Hydrophobic porous polysulfone membrane contactors with gravity-driven Ca(OH)₂ absorption for low-energy CO₂ removal from biogas.

) demonstrated sustained CO₂ removal performance with only gradual efficiency decline, attributed primarily to progressive CaCO₃ precipitation rather than membrane wetting or structural degradation. The novelty of this work lies not in the introduction of new membrane materials or absorbents, but in the system-level demonstration of a pump-free, gravity-driven membrane contactor that integrates low energy consumption, operational simplicity, and stable performance. The results provide practical insights into the design of modular, low-maintenance membrane contactor systems for decentralized and energy-efficient biogas upgrading applications.