Browsing by Author "Koch, Konrad"
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Item Open Access Effects of CO2 enrichment on the anaerobic digestion of sewage sludge in continuously operated fermenters(Elsevier, 2021-04-15) Muntau, Meriam; Lebuhn, Michael; Polag, Daniela; Bajón Fernández, Yadira; Koch, KonradThe effect of CO2 enrichment in sewage sludge anaerobic digestion (AD) as a potential strategy to improve the biogas yield was assessed at increasing organic loading rates (OLR). Effects on process performance and resilience were evaluated in long-term continuous AD experiments at lab-scale. The specific methane production (SMP) was sustainably enhanced in the test digester compared to a control at elevated OLRs, reaching an increase of 6 ± 12% on average at the highest OLR tested (4.0 kgVS/(m3·d)). The reduction of CO2 via homoacetogenesis, facilitating acetoclastic CH4 formation is proposed as the dominant conversion pathway. Results suggest that sufficient load of easily degradable substances is a prerequisite for intrinsic formation of the reduction equivalent H2 via acidogenesis. The enhanced resilience of the process under CO2-enriched conditions in response to acid accumulation further qualifies this approach as a viable option for improving AD performance by converting a waste stream into a valuable product.Item Open Access Enhancing the anaerobic digestion process through carbon dioxide enrichment: Initial insights into mechanisms of utilisation(Taylor and Francis, 2019-03-19) Bajón Fernández, Yadira; Soares, Ana; Vale, Peter; Koch, Konrad; Masse, Anne Laure; Cartmell, EliseCarbon dioxide (CO2) enrichment of anaerobic digesters (ADs) without hydrogen addition has been demonstrated to provide a potential solution to manage CO2 streams generated in the water and organic waste sectors, with concomitant increases in methane (CH4) production. This study investigates the CO2 utilisation mechanisms, by considering chemical and biological pathways in food waste and sewage sludge ADs. Methanosaetaceae was observed to be the dominant methanogen in sewage sludge ADs (Abundance of 83.8 – 98.8%) but scarce in food waste units (3.5 – 5.8%). Methanosarcinaceae was dominant in food waste (14.3 – 32.4%), likely due to a higher tolerance to the free ammonia nitrogen concentration recorded (885 mg·L-1). Ratios of RMethanosaetaceae (ratio of Methanosaetaceae fluorescence signal between test and control) of 1.45 and 1.79 were observed for sludge ADs enriched once and periodically with CO2, respectively (p-value <0.05), suggesting a higher Methanosaetaceae activity associated with CO2 enrichment. Reduction of CO2 by homoacetogenesis followed by acetoclastic methanogenesis was proposed as a CO2 utilisation mechanism, which requires validation by radiolabelling or carbon isotope analysis.