The role of methanotrophy in the microbial carbon metabolism of temperate lakes

Previous stable isotope and biomarker evidence has indicated that methanotrophy is an important pathway in the microbial loop of freshwater ecosystems, despite the low cell abundance of methane-oxidizing bacteria (MOB) and the low methane concentrations relative to the more abundant dissolved organic carbon (DOC). However, quantitative estimations of the relative contribution of methanotrophy to the microbial carbon metabolism of lakes are scarce, and the mechanism allowing methanotrophy to be of comparable importance to DOC-consuming heterotrophy remained elusive. Using incubation experiments, microscopy, and multiple water column profiles in six temperate lakes, we show that MOB play a much larger role than their abundances alone suggest because of their larger cell size and higher specific activity. MOB activity is tightly constrained by the local methane:oxygen ratio, with DOC-rich lakes with large hypolimnetic volume fraction showing a higher carbon consumption through methanotrophy than heterotrophy at the whole water column level. Our findings suggest that methanotrophy could be a critical microbial carbon consumption pathway in many temperate lakes, challenging the prevailing view of a DOC-centric microbial metabolism in these ecosystems.

Carbon Consumption and Adsorption-Regeneration of H2S on Activated Carbon for Coke Oven Flue Gas Purification

Carbon consumption of activated carbon varies with the sulfur-containing products. In this work, differential thermogravimetric (DTG), electron paramagnetic resonance (ESR), X-ray photoelectron spectroscopy (XPS), and temperature programmed desorption (TPD) were used to reveal the adsorption-regeneration process of H 2 S and the effect of adsorption products on carbon consumption. H 2 S reacts with the C=C bond to form C-S bond as an intermediate state, followed by the formation of elemental sulfur. It directly sublimates at approximately 380 °C , about 30 °C higher than the decomposition temperature of H 2 SO 4 . In the thermal regeneration process, the elemental sulfur in the form of monoclinic sulfur (S 8 ) first breaks into infinitely long chain molecules (S ∞ ) and then into small molecules, finally into sulfur vapor. The desorption of elemental sulfur consumes less oxygen and carbon functional groups, reducing the chemical carbon consumption by 59.8% than H 2 SO 4 . The compressive strength reduces less due to its slight effect on the disordered graphitic structure. H 2 S also reacts with the C=O bond to form H 2 SO 3 or H 2 SO 4 . The desorption of H 2 SO 3 does not require carbon consumption. The decomposition of H 2 SO 4 needs to react with C=C bond to release SO 2 , CO 2 , and CO, and the compressive strength of activated carbon significantly decreases. The carbon consumption originates from two aspects, the one from the regeneration of sulfur-containing products is more than twice of the other one from the decomposition of oxygen-containing functional groups.