Enhanced in-situ biomethanation of food waste by sequential inoculum acclimation: Energy efficiency and carbon savings analysis. (1st July 2021)

• Record Type: Journal Article
• Authors: Okoro-Shekwaga, Cynthia Kusin; Ross, Andrew Barry; Camargo-Valero, Miller Alonso
• Is Part Of: Waste management. Volume 130(2021)
• Page Start: 12
• Page End: 22
• Publication Date: 2021-07-01
• Subjects: Biomethanation -- Hydrogen -- Food waste -- Biomethane -- Energy balance -- Carbon saving; Hazardous wastes -- Periodicals; Refuse and refuse disposal -- Periodicals; 363.728
• DOI: 10.1016/j.wasman.2021.04.053
• Languages: English
• ISSNs: 0956-053X

Abstract

Highlights: Acclimation to increasing levels of H2 helped to improve H2 utilisation rate. The accumulation of C2–C4 VFA was reversed. Up to 81% CH4 was obtained by in-situ biomethanation against 65% without H2 . Up to 65% potential increase in energy return on investment is obtainable. Increased carbon savings potential of 52–59% is obtainable. Abstract: The increasing rate of food waste (FW) generation globally, makes it an attractive resource for renewable energy through anaerobic digestion (AD). The biogas recovered from AD can be upgraded by the methanation of internally produced carbon dioxide, CO2 with externally sourced hydrogen gas, H2 (biomethanation). In this work, H2 was added to AD reactors processing FW in three successive phases, with digestate from preceding phases recycled in succession with the addition of fresh inoculum to enhance acclimation. The concentration of H2 was increased for succeeding phases: 5%, 10% and 15% of the reactor headspace in Phase 1 (EH1), Phase 2 (EH2) and Phase 3 (EH3), respectively. The H2 utilisation rate and biomethane yields increased as acclimation progressed from EH1 through EH3. Biomethane yield from the controls: EH1_Control, EH2_Control and EH3_Control were 417.6, 435.4 and 453.3 NmL-CH4 /gVSadded accounting for 64.8, 73.9 and 77.8% of the biogas respectively. And the biomethane yield from the test reactors EH1_Test, EH2_Test and EH3_Test were 468.3, 483.6, and 499.0 NmL-CH4 /gVSadded, accounting for 77.2, 78.1 and 81.0% of the biogas respectively. A progressive in-situ biomethanation could lead to biomethane production that meets higher fuel standards for gas-to-grid (GtG) injections and vehicle fuel – i.e. >95% CH4 . This would increase the energy yield and carbon savings compared to conventional biogas upgrade methods. For example, biogas upgrade for GtG by in- situ biomethanation could yield 7.3 MWh/tFW energy and 1343 kg-CO2 e carbon savings, which is better than physicochemical upgrade options (i.e., 4.6–4.8 MWh/tFW energy yield and 846–883 kg-CO2 e carbon savings).