Sustainable agricultural practices help reduce the environmental impact of food production, paving the way for a healthier future.
And while there are various strategies that support sustainability efforts, biochar production is a valuable approach that improves soil quality and assists with organic waste management. In fact, biochar carbon removal technology accounted for 94% of delivered carbon removal credits in 2023, highlighting its growing impact.
However, not all biochar is made the same. Since different feedstock sources have varying properties, some are better suited for specific applications than others.
This article explores the importance of biochar feedstock, including the biochar production process, the impact of feedstock choice on biochar properties, and more.
Key Takeaways
- The key properties of biochar include carbon content and stability, density and porosity, water holding capacity, cation exchange capacity and nutrient retention, surface area and adsorption capacity, and pH and alkalinity.
- Woody biomass is beneficial for carbon sequestration, water filtration, and improving soil aeration and structure.
- Agricultural residues support soil improvement, moderate carbon sequestration, and crop nutrient cycling.
- Animal waste is useful for fertilizer replacement, soil amendment, and composting enhancement.
- Sewage sludge and biosolids contribute to land remediation, heavy metal adsorption, and phosphorus recovery.
What Is Biochar?
Biochar is a carbon-rich material produced by heating organic waste (biomass) through a process called pyrolysis. Producing biochar offers various benefits, including improved soil health, enhanced nutrient retention, carbon sequestration, and climate change mitigation.
In addition to knowing what is biochar, understanding how it’s produced provides insight into its environmental benefits and practical applications.
Understanding the Biochar Production Process
Pyrolysis is the most common method of biochar production. This process thermally decomposes organic material at high temperatures in a low-oxygen environment, resulting in biochar along with byproducts like bio-oil and syngas, which can be used for energy.
For some specific feedstock types, gasification and carbonization are alternative processing methods, each differing in process conditions, oxygen levels, and end products.
While there are various processes that organic waste can undergo, there are 4 important steps required for the successful production of biochar:
- Selection of Feedstock: Biochar can be made from a wide range of source feedstocks. However, there are various factors that must be considered when selecting feedstock, including its density, porosity, and composition. As we’ll see below, different biomass materials are preferred depending on their specific use cases.
- Preparation: Feedstock must then be properly stored to ensure moisture and quality control. During pre-processing, feedstock may undergo drying, decontamination, and other pre-treatment techniques.
- Pyrolysis (or other methods): The next step is the thermochemical decomposition of feedstock. As mentioned, there are various methods that can be used, with pyrolysis being the most common.
- Post-Processing: To enhance biochar effectiveness in agriculture, forestry, and environmental restoration, there are multiple post-production treatments that “raw” biochar can undergo, including leaching, aeration, grinding or sieving to reduce particle size, and chemical or steam activation.
Biochar Properties
So, what are the important properties of biochar?
Before discussing how feedstock material affects biochar, let’s look at the key properties that influence its performance:
- Carbon Content & Stability: Carbon content refers to how much of the biochar is made up of solid carbon, while stability refers to how long that carbon remains unchanged in the environment. In general, feedstocks that have higher carbon content can sequester carbon from the atmosphere and store it in the soil for longer periods.
- Density & Porosity: Density and porosity are fundamental physical properties that control how biochar moves through the landscape and interacts with water, altering soil hydrologic processes such as plant-available water holding capacity. In other words, a high porosity can improve water retention for plant growth and overall soil health.
- Water Holding Capacity: Biochar rich in nitrogen and oxygen may be an effective water retention agent, helping maintain soil moisture. This, in turn, supports plant growth and increases yield.
- Cation Exchange Capacity (CEC) & Nutrient Retention: Cation exchange capacity is the total capacity of a soil to hold exchangeable cations. This is a key property of biochar, as it influences the soil’s ability to hold onto essential nutrients.
- Surface Area & Adsorption Capacity: As stated by Scientific Reports, the surface area and porosity of biochar are among its most important characteristics. These factors determine the quantity and quality of active sites in biochar, enhancing properties such as cation exchange capacity, water holding capacity, and adsorption capacity.
- pH & Alkalinity: Alkalinity is considered a very important property of biochar, as changes in pH have cascading impacts on many soil processes, including nitrogen mineralization, mineral precipitation, ion exchange, and greenhouse gas emissions.
How Feedstock Choice Affects Biochar Properties
Now that we know the properties of biochar, the next step is to evaluate how different biochar feedstock material affects its final characteristics.
Common biochar feedstocks include:
1. Woody Biomass
Woody biomass includes hardwood, softwood, sawdust, and forestry waste.
Biochar produced from pinewood waste via slow pyrolysis helps trap carbon and remove metal contaminants from water. It also has a high calcium content and a low BET surface area, rich in micropores.
- Pros: High carbon content, produces stable, long-lasting biochar, high porosity, good for carbon sequestration.
- Cons: Low in nutrients, may require additional fertilizers when applied to soil.
2. Agricultural Waste
Agricultural waste includes crop straws, husks, nut shells, corn stover, and bamboo.
Agricultural biomass is recognized as an ideal alternative for the development of porous carbon materials due to its accessibility, low price, recyclable qualities, greater carbon content, and environmentally friendly nature. This serves as a valuable approach to crop residue management.
There are also dedicated energy crops, like switchgrass, that show potential as a sustainable source of renewable transportation fuel and biomass-generated electricity.
- Pros: Readily available, some provide moderate nutrients.
- Cons: Ash content varies, certain residues—such as rice husk—have high silica, surface area and porosity of some agricultural waste-derived biochar are poor.
3. Animal Waste
Animal waste includes poultry litter, cattle manure, and by-products from livestock.
When compared to non-amended soil, soil enriched with manure biochar showed increased nutrient availability, higher SOC content, improved soil physical properties, moisture retention, water use efficiency, and enhanced soil enzymatic activities.
- Pros: High in nutrients (especially phosphorus and potassium), increases soil fertility, high cation exchange capacity.
- Cons: Lower carbon content, high ash content.
4. Sewage Sludge & Biosolids
This includes byproducts of municipal wastewater and wastewater sludge.
Sludge biochar is highly efficient, widely applicable, and environmentally beneficial for water pollution control, soil remediation, and carbon emission reduction. However, adsorption capacity and application limitations remain technical bottlenecks for large-scale implementation.
- Pros: Rich in nitrogen and phosphorus, suitable for environmental applications such as soil remediation and water quality improvement.
- Cons: Risk of contamination, regulatory concerns.
Isn’t All Biochar the Same? Which Is Better?
So, which is the best biochar feedstock?
There is no “best” option—during biochar production, the choice of feedstock depends on the intended application.
The following table identifies which feedstock is most beneficial for each use case:
| Woody Biomass | Agricultural Residues | Animal Waste (Manure & Litter) | Sewage Sludge & Biosolids |
|---|---|---|---|
| Carbon sequestration | Soil improvement | Fertilizer replacement | Land remediation |
| Water Filtration | Moderate carbon sequestration | Soil amendment | Heavy metal adsoprtion |
| Improves soil aeration & structure | Crop nutrient cycling | Composting enhancement | Phosphorus recovery |
*Learn more about animal waste management and biosolids management here.
The Bottom Line
As we’ve discussed in this article, the choice of feedstock plays a critical role in biochar manufacturing. At Shapiro, we understand the importance of carefully choosing feedstock depending on its unique application.
There are two projects that we’re proud to say we’re supporting with high-quality feedstock. The Linden Renewable Energy Project—set to become the nation’s largest food waste-to-biogas facility—is supported by our team as part of a network of industry leaders contributing feedstock to the anaerobic digester. We’re also the exclusive provider of feedstock at the Kingsbury Bioenergy Complex.
Our organic waste management company will work closely with you to identify sustainable sources of biochar feedstock to ensure high-quality biochar production. With our biochar services, your company can divert food waste from landfills, reduce its environmental footprint, and achieve its sustainability goals.
Contact us today to learn more about our services.
Baily Ramsey, an accomplished marketing specialist, brings a unique blend of anthropological insight and marketing finesse to the digital landscape. Specializing in educational content creation, she creates content for various industries, with a particular interest in environmental initiatives.
