Technical Information on Biochar Made From Agricultural Waste
As Amata Green, LLC begins to emerge from its planning phase and moves into its action phase of “Project Carbon-Reduction in Andalucia” we find that we have amassed a large amount of research and literature on the topic of biochar in relation to agricultural waste. Below is a review and synthesis of some of that literature as it pertains to our project(s). Some of the information below is somewhat technical in nature, so grab your coffee and slippers and get comfortable. To learn more about Amata Green’s biochar projects, you can visit the website at: www.amatagreen.com/investors .
This literature review was put together by one of Amata Green’s talented young interns, Layla Horeff.
Technical Information on Biochar Made From Agricultural Waste
by Layla Horeff
Biochar can be made from agricultural waste by heating it to a high temperature with low or no oxygen through a process called pyrolysis. Before this biowaste can be pyrolyzed,most moisture must be removed. During pyrolysis, thermal decomposition takes place where heating the biomass, without oxygen, expels volatile gasses but leaves the carbon behind. The byproducts of creating biochar include syngas and heat. Production process syngas must be combusted in the system to ensure all nitrogen oxide that is formed does not enter back into the atmosphere. The combustion of the syngas creates heat and can make the whole system self-sustaining if this heat is used to pyrolyze or dry the biomass. This would increase efficiency, as production process heat should be returned into the system to dry the biomas before it starts the pyrolysis process to minimize energy usage. It is important to note that there are two different types of pyrolysis systems.
Fast pyrolysis heats the biomass at a faster rate and produces more oils and liquids, while slow pyrolysis reaches its maximum temperature slower but produces more syngas. There are also many effects of having a high maximum pyrolysis temperature. Increased pyrolysis temperature can decrease yield while increasing ash content, decrease the cation exchange capacity (CEC) while increasing the pH of the biochar, increase the electrical conductivity (EC), increase the carbon content, and increase the concentration of phosphorus (P) and potassium (K), while decreasing nitrogen (N). The reduction in yield can be attributed to the “rapid reduction of oxygen (O), hydrogen (H) and volatile content at high temperature 500°C”. One study found that the pyrolysis of biowaste changed the nutrient contents due to the thermal degradation as there was a loss of volatile compounds (C, H and O) in the original material. This same study shows that agronomic properties of biochar were affected by feedstock and temperature as “the biochar ash content ranged between 25-52% and ash content significantly (P<0.05) increased with increasing temperature”. According to The International Biochar Initiative (IBI), biochar is one the few technologies that is widely applicable, relatively inexpensive, and scalable.
While there are a plethora of biomass options to use as the feedstock in biochar production, it can and should be made from biowaste. Some biowaste feedstock options include crop residues, nut shells, fruit pits, bagasse, yard, food and forestry wastes, and animal manures. There are many benefits to using biowaste as the feedstock, one being that it effectively takes carbon and other greenhouse gasses out of the pollution cycle. It is also worth acknowledging that different feedstocks will produce biochar with different compositions. For example, research has found that crop-derived biochar has some of the best agricultural benefits and the carbon is very stable. Biochar that is derived from woody biomass will have higher carbon content (up to 80% C) because of the rigid ligninolytic nature which retains carbon in the biochar. This differs from biochar made from olive husks as they have high lignin content which “have shown to produce some of the highest biochar yields, given the stability of lignin to thermal degradation”. Manure and food waste as feedstock may have higher amounts of nitrogen and phosphorus. As stated above, the composition of biochar (the amount of carbon, nitrogen, potassium, calcium, etc) is also affected by the duration and temperature of pyrolysis. Testing biochar is essential to knowing the nutrient content of each particular batch. Converting agricultural waste into biochar avoids CO2 and CH4 emissions that would have been generated by the burning or natural decomposition of the waste.
Biochar when it is added to soil has many benefits including increasing the carbon content, mitigating greenhouse gas (GHG) emissions, and increasing agricultural productivity. There is an increase in agricultural productivity because there is more nutrients and better nutrient storage, better soil structure, and higher water holding capacity. Other benefits to soil infused biochar is an increase in food security, a decrease in nitrogen leaching into groundwater, reduced emissions of nitrous oxide, increased water retention, increase in the number of beneficial soil microbes, and more fertile soil. Soil that has enhanced microbial life results in higher soil carbon storage. When soil is fertile, plant growth increases which allows the plant to sequester more CO2 creating a positive feedback loop.
It is extremely possible for biochar projects to be GHG neutral and it is preferable for them to be GHG negative. The burning of fossil fuels is carbon positive as they are taking previously sequestered carbon out of the ground and putting it back into the atmosphere, worsening global warming. Biochar production can be carbon negative by “transforming the carbon in biomass into stable carbon structures in biochar which can remain sequestered in soils for hundreds and even thousands of years”. This allows for a net reduction of carbon dioxide in our atmosphere, even accounting for the energy that is used in transportation, pyrolysis, and drying. According to one study, sustainable biochar production could offset up to 12% of all of the anthropogenic GHG emissions every year. This is based on using only available biomass from agriculture and forestry with no conversion of land to create feedstock. The reason why biochar is such an important tool in the fight against climate change is its long-term persistence in soil according to the IBI.
Currently, there is not much information concerning mixing biochar with other non-pyrolyzed organic biomass to try and increase productivity of a plant. However, it was found that when compost was added to biochar in soil, it “consistently promotes plant growth, with better performances than those observed when composts and biochars are used individually”. Unfortunately, specific amounts of compost and type are unspecified as conclusive research has not yet been done.
This concludes the literature review of biochar related to agricultural waste which was done for, and in conjunction with, Amata Green’s “Project Carbon-Reduction in Andalucia.” If you would like to learn more about Amata Green’s biochar projects, visit: www.AmataGreen.com/investors
Works Cited
Asif Naeem, M., Khalid, M., Arshad, M., & Ahmad, R. (2014). Yield and Nutrient
Composition of Biochar Produced from Different Feedstocks at Varying Pyrolytic Temperatures. Retrieved February 25, 2021, from http://www.pakjas.com.pk/papers/2245.pdf
Biochar - Department of Agriculture. (2019, November 4). Retrieved February 25, 2021, from
https://www.agriculture.gov.au/ag-farm-food/climatechange/australias-farming-future/biochar
Biochar feedstocks - biochar-international. (2018, April 12). Retrieved February 25, 2021, from
https://biochar-international.org/biochar-feedstocks/
Biochar technology - biochar-international. (2018, April 12). Retrieved February 12, 2021, from
https://biochar-international.org/biochar-technology/
Biochar technology - biochar-international. (2018, April 12). Retrieved February 25, 2021, from
Bonanomi, G., Ippolito, F., Cesarano, G., Nanni, B., Lombardi, N., Rita, A., . . . Scala, F. (2017,
August 28). Biochar as plant growth promoter: Better off alone or mixed with organic amendments? Retrieved February 25, 2021, from https://www.frontiersin.org/articles/10.3389/fpls.2017.01570/full
Factory, T. (2013, October 07). Feedstock. Retrieved February 25, 2021, from
https://doctor-biochar.blogspot.com/2013/10/feedstock.html
Soil health - biochar-international. (2018, April 13). Retrieved February 25, 2021, from
https://biochar-international.org/soil-health/
Sustainability & climate change - biochar-international. (2018, April 25). Retrieved
February 25, 2021, from https://biochar-international.org/sustainability-climate-change/.
