Producing pipeline-quality biomethane via anaerobic digestion of sludge amended with corn stover biochar with in-situ CO2 removal

• Published in: Applied energy Vol. 158; no. C; pp. 300 - 309
• Main Authors: Shen, Yanwen, Linville, Jessica L., Urgun-Demirtas, Meltem, Schoene, Robin P., Snyder, Seth W.
• Format: Journal Article
• Language: English
• Published: United Kingdom Elsevier Ltd 15.11.2015; Elsevier
• Subjects: Anaerobic digestion; Biochar; Biomethane; CO2 removal; Sewage sludge; Biomethane; Biochar; Sewage sludge; Anaerobic digestion; CO2 removal
• ISSN: 0306-2619; 1872-9118
• DOI: 10.1016/j.apenergy.2015.08.016

•A novel anaerobic digestion (AD) process with in-situ biogas cleanup and upgrading is developed.•Biochar-amended digester produced pipeline-quality (>90% CH4, <5ppb H2S) biomethane.•Corn stover biochar addition sequesters CO2 and enhances CH4 yield for sludge AD.•Biochar addition increases alkalinity and mitigates NH3 inhibition in the digester.•Digestate from biochar-amended digester is nutrient-enriched and can be used for soil application. This study presents a novel process for producing pipeline-quality biomethane by anaerobic digestion (AD) of sludge with in-situ biogas cleanup and upgrading using corn stover biochar. The biochar has high surface area (105m2/g), high ash content (45.2% dry weight) and high concentrations of potassium, calcium and magnesium (14.2% K2O, 3.9% CaO and 4.2% MgO of the ash content, respectively). The biochar-amended digesters produced near pipeline-quality biomethane (>90% CH4 and <5ppb H2S), facilitated CO2 removal by up to 86.3%, boosted average CH4 content in biogas by up to 42.4% compared to the control digester, close to fungibility of natural gas. The biochar addition enhanced the methane yield, biomethanation rate constant and maximum methane production rate by up to 7.0%, 8.1% and 27.6%, respectively. The biochar addition also increased alkalinity and mitigated ammonia inhibition, providing sustainable process stability for thermophilic sludge AD. The biochar-amended digestate is enriched with nutrients such as potassium, nitrogen and phosphorus, and therefore has great potential for soil applications.