Compost, let it rot in place (like national parks that aren't touched), or grazed by cattle all put off about the same greenhouse gas. A bio digester captures the methane and converts it to CO2 and heat. So it might be better for the greenhouse gases, maybe. Key is IMO to do what gets the most benefit along the way. Berkeley or Johnson Su composting offgas less carbon (keep more material in the compost).
I am going to do multiple methods, as what works best for the type of feedstock. A boo digester is a wonderful way to get cooking fuel as a byproduct, but you need a tropical climate to do it year round at a small scale.
"You must be the change you want to see in the world." "First they ignore you, then they laugh at you, then they fight you, then you win." --Mahatma Gandhi
"Preach the Gospel always, and if necessary, use words." --Francis of Assisi.
"Family farms work when the whole family works the farm." -- Adam Klaus
What this means is that composting is climate neutral, not particularly good for the climate (despite the claims on the net). I suppose landfill is worse if it is uncapped - they produce a lot of methane, which is a very potent greenhouse gas.
Simply being has an effect on carbon emissions.
Even dying and decaying will have an effect.
Like grass feed ruminates, composting is something that would happen without human intervention.
I worry more about the stuff that we add to the world, primarily by digging up carbon and burning it.
The other thing we do is destroy the forests, grasslands etc, that actively sequester carbon.
Composting can reduce both of these activities.
Compost, applied to perennials, will promote carbon sequesterion.
Making biochar from the perennials, even more so.
The same biological materials in a landfill will produce nothing positive and contribute nothing going forward.
The process of getting the materials from your house and into the landfill will almost certainly burn carbon would otherwise remain sequestered deep underground.
Composting takes human burned calories that you would otherwise use or store.
Every useful thing you grow from the compost is another thing that doesn't need to be transported to your location using fossil fuel.
It's also not fertilized with petrochemicals, which would likely have been extracted , transported and processed by more fossil fuel.
Further, no carbon sequestering bioms are being destroyed to grow it.
Composting in a biodigester could capture greenhouse gases, and even displace the use of fossil fuels, but it's hard to implement on a small scale.
I think excess biological materials should be used as construction materials,fed to livestock, burned cleanly to displace the use of fossil fuel, or composted, in roughly that order.
Susan, capped landfills have vent pipes that let the methane out, otherwise there would be a significant buildup and we probably wouldn't want to see what happens next. The gases are either vented directly to the air, or collected and treated, depending upon a lot of factors.
I worked on a site near a capped landfill and was warned to not go near the vent tubes because the hydrogen sulfide venting out with the methane was at/near the lethal level. I'm not sure if that was true but I didn't test it either. The vent pipes were taller than head height to prevent just such an accident.
Regarding offgas from composting, this isn't something I worry about. The material is being broken down according to nature and the process is carbon neutral. It might even be negative since I'm continually building up more biomass with the compost in the form of gardens and food forest. And with 10 acres of evergreen forest around me, emissions from my kitchen scraps and garden is nothing in comparison to what mother nature is doing all the time.
I do find biodigestion processes to be interesting and development of home-scale systems would be beneficial, especially if you can capture heat in the process. Or liquid fuels.
it's said that a tree that decomposes creates almost the same amount of greenhouse gasses than it did produce in oxygen it's entire life.
My husband brought me this as we were discussing about renewable energy.
He works with wind turbines and there is it the same.
To produce a wind turbine it will create as much dirt that it safes in it's 20 years runtime.
So actually Windpower is as clean as a tree.
For our farm we did put focus on vermicomposting as the worms seem to shorten the time of emission significantly,
but the absolute record breakers are black soldier flies (hermetia illuciens)
These little critters are going through 15 Kg green waste per square meter in a matter of a day if the "food" is proper served.
So the stuff is gone before the gas comes up.
In modern times is going the right way forward the only way to coming back to nature.
Certainly, a full combustion or decomposition will only release what the plant took out of the atmosphere in the first place. But it is a big difference if that is in the form of CO2 or methane, as the latter has a stronger greenhouse effect. Thus our responsibility to make sure we compost well.