A comparative TEA–LCA study of biomethane production through anaerobic digestion and five upgrading technologies: Amine scrubbing, water scrubbing, membrane separation, PSA, and cryogenic separation

Producing grid-quality biomethane from sewage-sludge biogas is promising, yet selecting an upgrading route remains uncertain because mature technologies differ in energy use, cost, methane losses in off-gas or vent streams, and the fate of biogenic CO 2 . This study evaluates anaerobic digestion integrated with five commercial upgrading technologies: amine scrubbing, water scrubbing (WS), membrane separation (MEM), pressure swing adsorption (PSA), and cryogenic separation (CRYO), modelled for a municipal wastewater treatment plant. All configurations deliver grid-quality biomethane, while separated CO 2 is compressed and liquefied where feasible; venting is assumed for the dilute CO 2 stream from WS. Aspen Plus simulations were coupled with techno-economic analysis (TEA) and consequential life cycle assessment (LCA). The results show clear trade-offs. Amine scrubbing has the highest thermal demand (1207 kW), whereas CRYO and MEM have the highest upgrading-unit electricity demands (257 and 201 kW, respectively). Economically, without an additional emission charge, WS is the most attractive option, with the lowest levelized cost of biomethane (LCOM) of 436 €/t, while amine scrubbing is the most expensive (652 €/t). Hypothetical charges on vented biogenic CO 2 and CH 4 progressively increase the LCOM of WS above those of MEM, CRYO, PSA, and amine scrubbing at approximately 36.5, 37.7, 43.2, and 120.4 €/t CO 2 -eq, respectively. From an environmental perspective, consequential LCA shows that PSA, MEM, and CRYO outperform solvent-based routes in human health, ecosystem, and climate performance due to efficient CO 2 liquefaction and avoidance of upgrading-stage venting. In the deterministic base case, PSA delivers the highest net human-health savings and the largest net GHG reduction, whereas WS shows the weakest climate performance. The economic preference for WS depends on emission-pricing assumptions, while PSA, MEM, and CRYO are more suitable for carbon-circular biorefineries.