How Much Methane Comes out of Compostable Containers in a Landfill?
When making lifecycle assessments of Buoy products against alternatives, there is one data point that has been hard to nail down: How much methane comes out of compostable containers in a landfill. Having not found a good reference, I decided to just brute-force my way into an estimate. This entry is my journey to that estimate starting with an explanation of why compostable containers are not getting composted in the first place.
The promise of compostables is that they get to a composting facility and are decomposed with aerobic digestion. Aerobic means that it metabolizes in the presence of atmospheric Oxygen. In this case almost all the cellulose in the compostable container would convert to CO2. I hear you saying, wait a second, CO2 is the bad stuff. And yes, we do want to minimize CO2, but if organic stuff is degrading, CO2 is the least problematic greenhouse gas we get. The other one we get is Methane, CH4, which has a global warming effect about 32x more potent than CO2. Bottom line, we'd much rather have things decompose aerobically through composting than without atmospheric oxygen, or anaerobically.
Unfortunately, this plan is not going well. Industrial composters are starting to refuse compostable containers. Composters are in the business of making healthy, usable soil and compostable containers don't make good soil, so ultimately, these business people will not degrade their product by accepting them. If composters won't take compostable containers, most of them will continue going to landfills, as they do today.
A landfill is sealed up without access to atmospheric Oxygen, so compostable containers degrade anaerobically, meaning without Oxygen. In this case, about half by volume converts to Methane (CH4) and half by volume converts to CO2. This seems confusing because in the absence of Oxygen, how could any of the Carbons in Cellulose convert to CO2. The chemical formula for Cellulose is C12, H20, O10, so those 10 Oxygens can be used to make Carbons into CO2 and there are other non-atmospheric sources of Oxygen as well, just not anywhere near enough to efficiently convert all the Carbons to CO2.
To calculate how much Methane would come off a container in a landfill, I got the standard weight of a bagasse (compostable) container, calculated the number of molecules of cellulose in that container, which was some astronomical number around 10 to the power of 23. Carbon Dioxide and Methane take up slightly different volumes, which was corrected for. On converting all the molecules of Carbon in the cellulose of 1000 containers per day for a year, it worked out that 0.9 metric tons of Methane and 2.64 metric tons of CO2 were produced. As Methane is 32 times more potent as a global warming gas than CO2, the combined total in CO2 equivalents is 31.3 metric tons. Since the bagasse that was used to make the containers would have degraded anyway, we should subtract the CO2 from a presumed 100% aerobic degradation of all that mass, so the total impact of anaerobically degrading the compostables in a landfill is 26.02 Metric Tons of CO2.
For the sake of comparison, a year's worth of plastic containers of the same size would have a carbon footprint of 55.1 Metric Tons of CO2, using the conversion of 3 kgs of CO2 per kg of plastic. But before getting excited about how compostables are better, we haven't yet accounted for the water usage and total manufacturing impact of a year of compostables, which comes to around 31 Metric Tons of CO2, making the total impact of compostables around 57 Metric Tons, so pretty much a wash with plastic. I'm not advocating a return to plastic, of course. Plastic has more pollutant effects like creating microplastics which wreak all kinds of havoc. But I do want to refute the notion that compostables are a massive improvement, because they are not.
To make things just a little more complex, it takes around 20 years for a clamshell made from bagasse (sugar cane fiber) to degrade in a landfill. So you don't count all these global warming gasses the moment the compostable container is discarded. It might seem like a benefit that it doesn't gas off right away, but that delay gives our use of compostables a 20-year-long carbon footprint that we really can't do much about once it starts. Every compostable container that goes in the trash produces a slow drip of Methane for two decades, giving a negative momentum to the global warming gasses produced, meaning the sooner we stop using compostables in favor of reusables the sooner we stop that clock.
Any so-called solution that involves throwing something away within 30 minutes of the time you start using it is an inferior solution when compared to reuse. Unfortunately, disposables are also a very good business. Selling anything that is made to be discarded is very profitable, because you get to sell and resell it constantly at high volumes. The green space is choked with people making so-called green disposables. These can be part of the solution in certain use cases, but we urgently need to start down-regulating the amount of stuff we dispose of, period, clothes, containers, phones, everything. Whatever the source, manufacturing is not carbon neutral. Whatever the end-of-life cycle, that's not carbon neutral either.
Because Buoy actively recovers plastic that otherwise would have entered the ocean or some carbon-generating end-of-life cycle, Buoy containers are natively carbon negative. And once in service, they are employed to prevent the use of disposables, making a very virtuous cycle.
© 2023, Buoy, LLC
This was originally posted in 2023 and reposted on this blog in January, 2026.
