Abstract
Carbon dioxide (CO2) enrichment of anaerobic digesters (AD) was previously identified as a potential on-site carbon revalorisation strategy. This study addresses the lack of studies investigating this concept in up-scaled units and the need to understand the mechanisms of exogenous CO2 utilisation. Two pilot-scale ADs treating food waste were monitored for 225 days, with the test unit being periodically injected with CO2 using a bubble column. The test AD maintained a CH4 production rate of 0.56 ± 0.13 m3 CH4·(kg VSfed d)−1 and a CH4 concentration in biogas of 68% even when dissolved CO2 levels were increased by a 3 fold over the control unit. An additional uptake of 0.55 kg of exogenous CO2 was achieved in the test AD during the trial period. A 2.5 fold increase in hydrogen (H2) concentration was observed and attributed to CO2 dissolution and to an alteration of the acidogenesis and acetogenesis pathways. A hypothesis for conversion of exogenous CO2 has been proposed, which requires validation by microbial community analysis.
Highlights
Anaerobic digestion (AD) stabilises organic wastes while producing biogas with a 50e75% methane (CH4) and 50e25% carbon dioxide (CO2) concentration
The volume of biogas produced by the ADs was measured continuously with a TG05/5 gas meter equipped with a totaliser (Ritter, Bochum, Germany) connected to each of the units (Fig. 1)
This study provides an insight into the effectiveness of using an external bubble column to inject CO2 in ADs through examining biogas quality, amount of CH4 lost and mass transfer efficiency
Summary
Anaerobic digestion (AD) stabilises organic wastes while producing biogas with a 50e75% methane (CH4) and 50e25% carbon dioxide (CO2) concentration. The remaining CO2 present in the biogas, is emitted to the atmosphere with exhaust gas streams. Biogenic emissions of CO2 from ADs just in the UK have been estimated at 0.27 MtCO2 per annum for the water sector (Byrns et al, 2013) and at 0.31 MtCO2 per annum for ADs treating agricultural and community waste (industrial sites not accounted) (Bajon Fernandez et al, Submitted for publication a). Implementation of revalorisation strategies for biogas CO2 could be an option to counteract the increasing greenhouse gas (GHG) emissions of the water sector (Byrns et al, 2013) and to further reduce the carbon footprint of AD
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
