Volatile organic compounds in biogas from full-scale anaerobic digestion plants: Implications for CO₂ upgrading and cryogenic liquefaction

• Analyzed 47 volatile organic compounds in biogas from different feedstocks • Ketones and terpenes dominated food waste biogas; aromatics in sewage sludge • Dominant VOCs in biogas produced from different substrates were identified and reported • Desulfurization removed sulfur but had limited effect on non-sulfur VOCs • Low-weight VOCs passed membranes; high-weight VOCs were retained • VOCs in liquefied CO₂ indicate potential purity degradation This study evaluated the presence and impact of 47 volatile organic compounds (VOCs) in biogas generated from a anaerobic digestion plant, focusing on their role as impurities in high-purity CO₂ recovery and liquefaction processes. Biogas samples were collected from food waste (Streams 1 and 2), sewage sludge (Streams 3 and 4), and a mixture of livestock manure and food waste (Streams 5 and 7). Ketones and terpenes were dominant in food waste biogas; aromatic compounds and siloxanes in sewage sludge; and sulfur compounds in the livestock mixture. While desulfurization effectively removed sulfur compounds, it had limited impact on non-sulfur VOCs. Membrane-based gas separation revealed a binary distribution: low-molecular-weight VOCs in the permeate and high-molecular-weight compounds in the retentate. During CO₂ liquefaction at −20 °C and 2 MPa, ketones, esters, terpenes, and sulfur compounds were found in the liquid phase, indicating potential degradation of CO₂ purity. These findings highlight the importance of VOC control in biogas upgrading and CO₂ purification. Overall, the study provides foundational data for developing advanced purification technologies and enhancing resource utilization in renewable energy systems.