Kinetic fractionation of stable isotopes in speleothems : laboratory and in situ experiments

In recent years, stalagmites have become an important archive for paleoclimate. Several studies about stable isotope records in stalagmites show a simultaneous enrichment of d18O and d13C along individual growth layers, which is associated with kinetic isotope fractionation. However, to deduce paleoclimatic information from calcite which is precipitated under these non-equilibrium-conditions,it is important to improve the understanding of kinetic isotope fractionation in dependence of local conditions like temperature and drip rate. Within this research work, laboratory experiments with synthetic carbonates were carried out under controlled conditions. The d18O and d13C evolution of the precipitated calcite were studied for different experiment parameters such as the initial composition of the solution, temperature and drip rate. In addition, in situ experiments were carried out in two cave systems in Sauerland (Bunkerhöhle and B7-Höhle). The modern calcite collected at three drip sites was compared with the calcite obtained from the laboratory experiments. All experiments show a distinct isotopic enrichment along the precipitated calcite. Lower drip rates, higher temperatures and higher initial supersaturation with respect to calcite result in a greater total isotopic enrichment and in a lower slope of the linear correlation d18O(d13C). The latter indicates a larger oxygen isotope buffering from the water reservoir. From a comparison with theoretical models it can be concluded that the conversion reactions between the bicarbonate and the carbon dioxid and the exchange reactions between the oxygen isotopes in the bicarbonate and the water reservoir occur faster than predicted from present publications, particularly in case of higher temperatures (23°C). Thus, for higher temperatures other effects might play a role not yet considered in theoretical models

ROS-driven cellular methane formation: Potential implications for health sciences

Abstract Recently it has been proposed that methane might be produced by all living organisms via a mechanism driven by reactive oxygen species that arise through the metabolic activity of cells. Here, we summarise details of this novel reaction pathway and discuss its potential significance for clinical and health sciences. In particular, we highlight the role of oxidative stress in cellular methane formation. As several recent studies also demonstrated the anti-inflammatory potential for exogenous methane-based approaches in mammalians, this article addresses the intriguing question if ROS-driven methane formation has a general physiological role and associated diagnostic potential

Effects of CO2 enrichment on the anaerobic digestion of sewage sludge in continuously operated fermenters

The 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