3 ms·

I have long wondered why we don't make tonnes of dense bioplastics (like PLA) and burrying them as a means of offsetting CO2 emissions.

bobim 3y ago
Because the company making the PLA wants to make profit out of it? It’s wild how we can imagine anything that would help us to continue derping around at full tilt, but totally lack imagination when it comes about simply slowing down.
Retric 3y ago
We do, it’s called a dump. One downside is they tend to produce a fair bit of methane, but they potentially sequester CO2 across geologic timescales. The other is most of the plastic was sourced from fossil fuels and releases CO2 as part of the manufacture process so it’s not a net gain. Still better than burning it though.
- ZeroGravitas 3y ago
  It's not better than burning it in a facility that captures the energy, even more so if that energy is displacing fossil fuels from electric or home heating grids.
  - soco 3y ago
    But isn't burning it releasing again the CO2, and sequestrating this was the point of the exercise in the first place?
    - ZeroGravitas 3y ago
      We care about CO2 equivalent, so anything that leaks methane is a candidate for being burned instead to reduce impact. And plastic leaks methane from dumps.
      - Retric 3y ago
        Orders of magnitude make a huge difference. Sequestering 99.9% of carbon and releasing 0.1% of it as methane is a major win.
  - Retric 3y ago
    Plastic in trash is a fossil fuel. The carbon comes from oil the same way gasoline does.
- jszymborski 3y ago
  This is interesting. I still have a couple of questions though: - PLA degrades very, very poorly in landfills [0], which leads me to think that if you were to dig boreholes and dump PLA inside it, wouldn't it effectively sequester the CO2 w/o releasing much/any CH4? - PLA (as far as I know) is produced from glucose derived from e.g. corn. In theory this is a process which sequester CO2 from the air and puts it into solid blocks. No fossil fuels or fossil fuel extraction required. So I guess my question is, what's the catch? I suppose agriculture has its own CO2 footprint, but I feel we've gotten pretty efficient at making glucose. [0] https://all3dp.com/2/is-pla-biodegradable-what-you-really-need-to-know/ https://all3dp.com/2/is-pla-biodegradable-what-you-really-ne...
  - Retric 3y ago
    The catch is only ~1% of plastics are bioplastics. The rate of PLA > CH4 in from landfills is basically irrelevant due to everything else we are dumping down there which more easily turns into CH4. As to dumping PLA down bore holes. You can just burry the plant matter without turning it into PLA. So there’s little reason to turn plant matter into PLA to burry unless you have some other use for the PLA at which point it’s a small portion of your waste stream.
    - jszymborski 3y ago
      In my hypothetical situation, we're producing PLA for the sole and expressed purpose of sequestering CO2. My reasoning was that PLA degrades less readily than plant matter, so less likely to release CH4. But I hadn't thought of the fact that if you bury plant matter deep enough, CH4 emissions likely aren't as high a concern.

bobim 3y ago

Because the company making the PLA wants to make profit out of it? It’s wild how we can imagine anything that would help us to continue derping around at full tilt, but totally lack imagination when it comes about simply slowing down.

Retric 3y ago

We do, it’s called a dump. One downside is they tend to produce a fair bit of methane, but they potentially sequester CO2 across geologic timescales. The other is most of the plastic was sourced from fossil fuels and releases CO2 as part of the manufacture process so it’s not a net gain. Still better than burning it though.

ZeroGravitas 3y ago
It's not better than burning it in a facility that captures the energy, even more so if that energy is displacing fossil fuels from electric or home heating grids.
- soco 3y ago
  But isn't burning it releasing again the CO2, and sequestrating this was the point of the exercise in the first place?
  - ZeroGravitas 3y ago
    We care about CO2 equivalent, so anything that leaks methane is a candidate for being burned instead to reduce impact. And plastic leaks methane from dumps.
    - Retric 3y ago
      Orders of magnitude make a huge difference. Sequestering 99.9% of carbon and releasing 0.1% of it as methane is a major win.
- Retric 3y ago
  Plastic in trash is a fossil fuel. The carbon comes from oil the same way gasoline does.
jszymborski 3y ago
This is interesting. I still have a couple of questions though: - PLA degrades very, very poorly in landfills [0], which leads me to think that if you were to dig boreholes and dump PLA inside it, wouldn't it effectively sequester the CO2 w/o releasing much/any CH4? - PLA (as far as I know) is produced from glucose derived from e.g. corn. In theory this is a process which sequester CO2 from the air and puts it into solid blocks. No fossil fuels or fossil fuel extraction required. So I guess my question is, what's the catch? I suppose agriculture has its own CO2 footprint, but I feel we've gotten pretty efficient at making glucose. [0] https://all3dp.com/2/is-pla-biodegradable-what-you-really-need-to-know/ https://all3dp.com/2/is-pla-biodegradable-what-you-really-ne...
- Retric 3y ago
  The catch is only ~1% of plastics are bioplastics. The rate of PLA > CH4 in from landfills is basically irrelevant due to everything else we are dumping down there which more easily turns into CH4. As to dumping PLA down bore holes. You can just burry the plant matter without turning it into PLA. So there’s little reason to turn plant matter into PLA to burry unless you have some other use for the PLA at which point it’s a small portion of your waste stream.
  - jszymborski 3y ago
    In my hypothetical situation, we're producing PLA for the sole and expressed purpose of sequestering CO2. My reasoning was that PLA degrades less readily than plant matter, so less likely to release CH4. But I hadn't thought of the fact that if you bury plant matter deep enough, CH4 emissions likely aren't as high a concern.