Grass Clippings Biochar experiment

Today I tried an experiment with grass clippings where I heated the grass in a covered pot to convert the clippings into charcoal. This conversion is called biochar. The idea is that by turning the carbon in the organic material into charcoal the charcoal can be buried and prevented from gradually turning into carbon dioxide or methane. 

Figure 1: 1.8 (+/- 0.2) pounds of Dried out grass in a 5 gallon steel pot

My initial test run involved leaving the grass clippings in a pile in the yard for a week. This dried them out which removes water from the grass. I assume this will lead to more efficient and effective conversion into charcoal. I think that this also allows me to produce more charcoal as I get more organic material into the pot. It did not rain for about a week, so the grass was very dry. I forgot to take an initial photo, so Figure 1 is actually a refill after I ran my initial sample.

Figure 2: Grass clippings being converted into charcoal by heating with limited oxygen

You can use charcoal to heat the grass, but that probably eliminates the whole point of carbon capture. I picked up sticks in the yard and after a week I had enough to make a reasonable fire. The sticks will eventually turn into carbon dioxide anyways. It would be best if I could cover the fire a bit more to limit thermal energy that does not move into the pot. 

Figure 3: Grass clippings after an hour of burning

After about an hour I peeked inside. There was charcoal, but it was mostly at the bottom. I stirred the mixture a bit to try and move the grass to the bottom. At this point there was an odor coming from the pot that started to get worse. 

Figure 4: Grass clippings after about 4 hours

I did not have to continue heating much because the hot coals were effective for a while. I think that the grass converting to charcoal also produced some thermal energy increases that continued the process. 

Figure 5: Bury the charcoal in the ground

Once the grass has been converted to charcoal you can bury it. If you bury grass clippings they will decompose and turn into methane and carbon dioxide. But charcoal should remain as charcoal for quite some time. 

I ended up with 1.2 (+/- 0.2) pounds of coal. My son was mildly excited that we managed to do a real life Minecraft experiment as well. The beauty of biochar is that you’re using the grass to absorb carbon dioxide from the air and then sequestering the carbon as coal. If you mow and let the clippings sit on the lawn, the grass will decompose into carbon dioxide. If you use clippings in a compost pile the clippings will also degrade. The conversion to charcoal is the key to a more permanent removal. 

Some potential flaws are that burning fuel to capture the carbon is counterproductive. I went with sticks to avoid this. But I also bought the pot and the production of the pot and shipping probably contributed more carbon emissions than I saved. The biggest problem is that this needs to be scaled up a bit to really be effective.

Inspiration for trying this came from the book "Whole Earth Discipline" and this blog post https://www.instructables.com/id/Capture-CO2-with-Lawn-Trimmings/