Dear PF Forum, I'm interested in composting. I want to understand the benefit of composting. Besides Reducing organic waste Producing fertilizer This composting process also produce energy (methane) if properly managed. I wonder how, without oxygen addition/introduction, in a sealed composter bin, can methane be synthesized? Wiki (https://en.wikipedia.org/wiki/Fermentation) says that CH3COO− + H+ → CH4 + CO2 Okay... So perhaps without introducing energy from outside of the system. Methane can be synthesized. But now I'm wondering about a new thing. https://en.wikipedia.org/wiki/Heat_of_combustion It is said here that CH4 + 2O2 -> CO2 + 2H2O + energy. What I can surmise from that is: A: "Creating CO2" release energy, is this right? B: "Creating H2O" release energy, is this right? C: "Creating CH4" needs energy, is this right? And then, there is https://en.wikipedia.org/wiki/Standard_enthalpy_of_formation CO2 -> -393 H2O -> -242 D: Why these numbers are minus? Is it because "Creating CO2 (or H2O) DOES NOT need energy, but releasing instead" Okay, if this is so, than I can (at least) take it E: So, if producing CO2 releases energy, then PRODUCING CH4 should consume energy, is this right? But also from the same link above: https://en.wikipedia.org/wiki/Standard_enthalpy_of_formation F: Methane -> -74.9. What does this mean? Does this mean: Creating methane also RELEASES energy? So the statements E, F and [A+B+C] seem contradictory to me. Can anyone help? I'd like to understand this first, before I read fermentation. So that I can understand the benefit of composting. Thank you very much.