What technologies are used for biogas upgrading to biomethane?

Biogas upgrading removes CO2, H2S, water, and trace contaminants to produce pipeline-quality biomethane (>95% CH4). Technologies: Water scrubbing - CO2 dissolves in water at elevated pressure (6-10 bar); simple, proven, but high water use; CO2 stripped for reuse. Pressure swing adsorption (PSA) - CO2 adsorbs on activated carbon/zeolite at high pressure, desorbs at low pressure; dry process; 4 vessels cycle between adsorption/desorption. Membrane separation - selective permeation of CO2 through polymeric membranes; modular, compact; CH4 purity depends on membrane stages. Chemical absorption (amine scrubbing) - amines (MEA, MDEA) chemically bind CO2; high purity, regenerates with heat; higher energy use. Cryogenic separation - liquefies CO2 by cooling; very high purity, also captures CO2 as product; energy intensive. Performance comparison varies by: methane recovery (96-99.5%), energy consumption (0.2-0.5 kWh/m3), purity achieved, and scale suitability. Pre-treatment for H2S removal typically required using iron-based adsorbents or biological desulfurization.