trashables
That it breaks down materials in one form so that they can be used in another accounts for one reason why a compost bin is considered self-sustaining. A compost bin contains materials, such as kitchen scraps and yard debris, that no longer can or will be used in their existing forms and that may be carted off to landfills or recycled on location into soil amendments, fertilizers and mulches. It discourages additional efforts and expenses off location and, by transforming trashable materials into soil food web enhancers, encourages a continuous cycle of plant growth, product harvest, recycling as compost, plant growth, etc.
Two of the sources of methane are Cattle Farms and Wastes tips. Cows and rubbish tips do release methane as the result of bacteria decomposing waste, but other sources include paddy fields (yes, even rice is harming the environment) and underground natural gas deposits.