The big news for global health is carbon. More accurately, reducing carbon emissions. Everywhere you look, something says we need to decrease the amount of carbon, generally in the form of carbon dioxide (CO2) or methane (CH4). Everything alive is made of carbon, uses carbon as a nutrient source, or expells carbon in one form or another.
Waste-to-energy is developed to prevent off-gassing carbon, hydrogen sulfide (H2S), and nitrous oxides (N2O), aka laughing gas, which is nearly 300 times stronger than CO2. According to the EPA, “Nitrous oxide is emitted during agricultural, land use, and industrial activities; combustion of fossil fuels and solid waste; as well as during treatment of wastewater.” (EPA.gov, 2023) Note that much nitrous gas comes from synthetic fertilizers and burning crop residues. Although it only accounts for about 7% of total GHG emissions, it is much more potent than CO2, which takes up the majority of GHGs.
Back to waste-to-energy. Waste-to-energy is done through anaerobic digestors (AD), where the starting material is generally fats, oils, grease (FOGs), food wastes, and livestock manures. ADs are anaerobic, meaning they don’t use air. They are also heated to incubate the materials inside to nurture anaerobic archaea, known as methanogens (microbes that produce methane as a metabolite). It is methane that is the goal as it is an explosive (combustible) gas that can be used to run massive generators to produce electricity.
ADs are not super efficient. Of the 100% of materials that go in, roughly 5% to 10% of the total mass is reduced to methane gas. Therefore, the waste flow does not end at the AD. There are two remaining waste materials, called digestate. Digestate includes liquid and solid waste. These byproducts are marketed as nutrient sources for agriculture. (Hey, we have a great fertilizer for you!) Remember the process uses archaea, specifically methanogens? Methanogens are also considered pathogens, meaning their metabolites are considered toxins. (hmm…) So, how are these materials delivered to the farm? Well, they centrifuge them to concentrate the solid to pull out more liquids. This concentrates the nutrients and the salts in the material. Lastly, the carbon in the waste material is used up through the anaerobic process, leaving what is known as recalcitrant carbon.
Have you ever heard of recalcitrant carbon? I didn’t either until I was working on a farm that was using an AD to produce energy from its dairy manure. It is also known as “dead carbon” or “non-microbially-active carbon.” The following is a definition from Soil Quality.org.au:
Recalcitrant organic carbon – is organic material resistant to decomposition and, in Australian soils, is dominated by charcoal. Recalcitrant organic carbon can take centuries to thousands of years to decompose, and is largely unavailable to microorganisms. Highly weathered soils and soils with a history of burning have a high proportion of recalcitrant organic carbon.
Recalcitrant carbon includes biochar, digestate from an AD, fulvic acid, humic acid, humin, humus, lignin, and weathered soil. The carbon in thermophilic compost is also considered recalcitrant carbon; however, compost is also loaded with beneficial organisms and actually builds healthy soil.
The opposite of recalcitrant carbon is labile carbon. Labile carbon can be consumed by microbes and is considered an “active” type of carbon. It is the portion of the soil that includes living things (microbes, insects, worms, etc.). Thus, it tends to break down quickly. Labile carbon is involved in the carbon cycle and helps with crop success.
Some examples of labile carbon include dead and dying organisms, fresh plant biomass, and roots. Bokashi and other ferments would be considered labile forms of carbon as they are not mineralized forms of carbon.
So, back to the farm! The farm I was working with was a large dairy operation. The lagoon was connected to an AD. The wastewater from the lagoon was pumped into the AD. The methane gas was used to power the lights and a few other things on the farm. The digestate was centrifuged at the end of the cycle. The liquid was pumped through irrigation water out into the fields. Over a period of ten years, the soil, which was mostly sand, became so hydrophobic that irrigation water only penetrated a little over an inch into the sand. Imagine watering sand and the water running off! Weeds could not even grow on the field, and the percentage of organic matter was over 5% (which is fairly high). The point was the digestate essentially killed the soil.
Without plants growing on the soil, it was prone to erosion. The nutrients in the digestate were running off as well. Without plants growing, there is no carbon dioxide being fixed through photosynthesis, no carbon being pumped into the soil to feed and stimulate microbes, no labile carbon component, and likely no life in the soil. This was happening on hundreds of acres. And it was all done in the name of some energy to run their lights and pumps in the dairy. Was it worth it? For a 5% to 10% reduction in total solids?
The farm would have been much better off using the land for grazing and farming, increasing soil organic matter with living plants, preventing erosion, preventing runoff, and producing healthier animals. And they would have done this without spending over a million dollars to install an AD.
To sum up, the AD, which is built to divert GHGs, can create more problems and prevent more sequestration than without it. Personally, I have seen several of these types of units creating more problems than they solved. These have ranged from the example above to odors traveling miles (as in the AD Colorado being shut down from odor complaints up to 40 miles away), fires, deaths, and noise issues (look at the one in Brooklyn, New York). I would argue there are much better ways to deal with organics than to turn them into fuel, odor, and salts. As an old friend used to say, “Waste is a man-age-mental problem.”
What are your thoughts?
Sources:
Bačėninaitė, D., Džermeikaitė, K., & Antanaitis, R. (2022). Global Warming and Dairy Cattle: How to Control and Reduce Methane Emission. Animals: An Open Access Journal From MDPI, 12(19). https://doi.org/10.3390/ani12192687
EPA.gov. Overview of Greenhouse Gases. 10/10/23. https://www.epa.gov/ghgemissions/overview-greenhouse-gases#:~:text=Nitrous%20oxide%20(N2O,as%20during%20treatment%20of%20wastewater.
Soil Quality.org.au. Fact Sheets Organic Carbon Pools - Qld. 2023. https://www.soilquality.org.au/factsheets/organic-carbon-pools
Zhang, H., & Zhou, Z. Recalcitrant carbon controls the magnitude of soil organic matter mineralization in temperate forests of northern China. Forest Ecosystems, 5(1), 1-10. 2018. https://doi.org/10.1186/s40663-018-0137-z