How to Make Biochar

Biochar Feedstocks

Sustainable biochar is made from biomass residue materials like rice husks, corn stover, or non-commercial forestry residues.

Feedstock Considerations

Making biochar from biomass waste materials should create no competition for land with any other land use option such as food production or leaving the land in its natural state.

Biomass waste materials appropriate for biochar production include crop residues, as well as yard, food and forestry wastes, and animal manures. Large amounts of agricultural, municipal, and forestry biomass are currently burned or left to decompose, releasing carbon and methane back into the atmosphere. These residue materials can also pollute local ground and surface waters — a large issue for livestock wastes. Biochar production removes these materials from the pollution cycle, while also creating energy as a byproduct of this biomass technology.   

Feedstocks must not contain unacceptable levels of toxins, such as heavy metals, which can be found in sewage sludge and industrial or landfill waste. It is important to study all the aspects of feedstock supply in a local community/business before setting up a biochar operation. Feedstock availability can vary from year to year or month to month. In developing country areas where feedstocks are often used as heating and/or cooking fuel, biochar production can be an important side benefit if done sustainably.

Feedstock Effects on Nutrient Properties of Biochar

The composition of biochar — the amount of carbon, nitrogen, potassium, calcium, etc. — depends on two factors: the feedstock used and the duration and temperature of pyrolysis, or the process with which biochar is made. As an example, biochar produced from feedstocks which have greater contents of potassium, like animal litters, often have higher potassium contents than biochar made entirely from wood, which often have higher carbon contents. However, because pyrolysis conditions greatly affect nutrient properties contents, biochar should be tested on a batch-by-batch basis to determine specific properties.

CORN STOVER

COW MANURE

POULTRY MANURE

Wood Chips

Bagasse

Economic Considerations

Biomass resources that are available in the area of biochar production will dictate the choice of feedstock. Due to collection, alongside transport and storage costs, it often makes the most economic sense to use local feedstocks if they are also an environmentally sustainable option. 

Explore the most basic costs and benefits to consider with feedstock choices. 

  • Feedstock production and collection: If the feedstock is a residue, such as municipal biomass waste, logging or cropping residues, or a by-product such as bagasse, then production is less an economic issue than if the feedstock is purposely grown for the production of biochar—such as switchgrass. In this scenario, the costs and inputs needed for the growing and harvesting of the crop would be included. Revenue in the form of tipping fees may be obtained from certain waste feedstocks.
  • Use tradeoff: This would include the potential nutrient value lost from using feedstock for biochar production rather than as a direct fertilizer on the field. How this trade off works will vary on the area and on the feedstock. For example, chicken litter may be valuable in some areas as a direct fertilizer while in other areas it may be treated as a waste and represent a disposal cost.
  • Feedstock transport: When waste biomass is found far from the place where it will be used, transportation costs can be very high. In some situations it may make sense to densify the biomass by chipping or pelletizing before transport.
  • Feedstock storage and pre-processing: Many feedstocks will need to be dried before pyrolysis. Depending on the feedstock choice, the drying process could occur passively through careful storage or may need more intervention—such as using a drier (thus requiring energy and labor). Energy for drying could in some cases be obtained from the pyrolysis of previous batches of feedstock.