Biochar is charcoal used as a soil amendment for both carbon sequestration and soil health benefits. Biochar is a stable solid, rich in carbon, and can endure in soil for thousands of years. Like most charcoal, biochar is made from biomass via pyrolysis. Biochar is under investigation as a viable approach for carbon sequestration, as it has the potential to help mitigate global warming and climate change.
Biochar is made by pyrolysis; heating any "feedstock" (anything carbon-based, commonly: plants, wood, food waste) in the absence of oxygen. The heat makes the feedstock break down into gases, and solids, without burning. Usually pyrolysis equipment burns the gases to produce heat and drive the chemical reaction, while retaining the solids. The solid that remains is called char, and is made up of primarily of the element carbon. Because the feedstock varies widely, and the pyrolysis process varies as well,
The burning and natural decomposition of biomass releases large amounts of carbon dioxide and methane to the Earth's atmosphere. The biochar production process also releases CO2 (up to 50% of the biomass); however the remaining carbon content is stable indefinitely. Biochar presents a stable way of carbon storage in the ground for centuries, potentially reducing or stalling the growth in atmospheric greenhouse gas levels. Simultaneously, its presence in the earth can improve water quality, increase soil fertility, raise agricultural productivity, and reduce pressure on old-growth forests. Biochar can sequester carbon in the soil for hundreds to thousands of years, like coal. Such a carbon-negative technology would lead to a net withdrawal of CO2 from the atmosphere, while producing consumable energy.
Biochar is recognized as offering a number of soil health benefits. The extremely porous nature of biochar is found to be effective at retaining both water and water-soluble nutrients. Soil biologists describe biochar as a habitat for many beneficial soil micro organisms. When pre-charged with these beneficial organisms biochar becomes an extremely effective soil amendment promoting good soil and, in turn, plant health. Biochar has also been shown to reduce leaching of E-coli through sandy soils depending on application rate, feedstock, pyrolysis temperature, soil moisture content, soil texture, and surface properties of the bacteria.
Biochar can improve water quality, reduce soil emissions of greenhouse gases, reduce nutrient leaching, reduce soil acidity, and reduce irrigation and fertilizer requirements. Biochar was also found under certain circumstances to induce plant systemic responses to foliar fungal diseases and to improve plant responses to diseases caused by soilborne pathogens.
After you harvest a crop of corn, much of the plant remains in the field and is called corn stover. It includes the stalk, leaves, and cobs that aren't harvested, and makes up about half of the yield.
Wood from deciduous trees (trees that lose their leaves in the fall.) Much heavier, denser, and (usually) slower growing than softwood. Common hardwoods in the northeast include maple, oak, beech, ash, birch, and walnut.
Manure is animal poop. Is there a more elegant way to say that? Surely, but we're just trying to get up to speed. Historically used as fuel, it can be processed by modern equipment into high nutrient biochar.
A tall, woody, perennial grass native to Asia. Imported in the North America and Eurasia, it is beautiful, and grows quickly, especially the sterile hybid: miscanthus x giganteus.
Nut shells, specifically from hard shelled nuts like walnuts, almond and hickory, are often used as feedstock for biochar.
A fast growing tree commonly used in Europe for firewood and biomass production. Like willow and hazel, it is frequently coppiced, but cannot be grown in the Eastern US because of a disease.
The least appealing potential feedstock. The good news, we sure do have a lot of it. It's usually treated at sewage treatment plants and has the potential to be made into biochar.
The wood of conifers -- and yes, it's usually softer than hardwood. Wooden residential construction is done primarily with softwood like southern white pine and Douglas fir. 2x4's are softwood, as is pressure treated lumber, and the vast majority of plywood.
A fast-growing perennial grass often used to generate biomass for ethanol production. Switchgrass can be harvested yearly and is easy to grow.
Willow, especially shrub willow, is a short-rotation woody crop that rapidly produces large amounts of biomass. In the pre-modern era, willow (along with hazel, and poplar) was used to produce firewood all over Europe.
Feedstock (things like wood, corn stover, rice husks, etc.) are quickly heated up to high temperatures (600-1000°F) for a very short period time - from just a few seconds to tenths of a second (flash pyrolysis). This process requires complex and relatively expensive machinery, and shouldn't be tried at home - but has significant advantages: it can work with more types of feedstock and emissions can be better controlled than less sophisticated methods like open-pit or slow pyrolysis.
This process is focused on producing energy and heat from biomass. The feedstock is burned, as is the syngas which separates during the process producing electricity or heat for other processes (like warming a greenhouse). Gasifiers also produce char as a byproduct - less than 5% of the feedstock by weight. Many biochar compost companies source their biochar from biomass power plants that operate larger scale gasifiers.
This kind of pyrolysis focuses on turning wet feedstocks into carbon in what is essentially a large high-pressure cooker. A more complex process than standard pyrolysis, it's not the kind of thing you can do at home, but opens the door to effectively convert otherwise challenging feedstock (like sewage, or algae, for example) into useful products like hydrogen and carbon.
A convenient at-home process for making biochar from wood waste. This process is a controlled open burn using a large metal cone and allows for the small scale production of high-quality and relatively low emission biochar.
Our oldest biochar creation process: dig a big hole, fill it with wood and let it rip. Actual methodologies range in sophistication, size, and efficiency, but this is the original, and likely still most common, process worldwide. It can be a very effective way to product biochar, especially in remote locations, but it is hard to standardize and control.
Heating wood, or a limited set of other feedstocks, slowly - over a period of hours, and with a relatively low maximum temperature (under 600°F) is a way to maximize biochar yield by weight. The biochar produced has a lower internal volume, and a lower fixed carbon content by volume.
Waste biomass abounds, and there isn't always space for it: arbor waste from municipal tree maintenance, corn stover after harvest, walnut shells from shelling facilities, squashed apples after they're turned into cider, barley mash after it's turned into rye. By pyrolyzing this biomass, you can dramatically reduce the area it takes up.
Approximately 10,000MW of electricity are produced every year by more than 200 large biomass power plants in the US. In addition, smaller biomass generators provide off-grid power to people world wide.
Mixed with wood chips, biochar can be used as a livestock bedding. Projects currently underway look to see how biochar reduces odors and potentially reduces the spread of infection and nutrient runoff.
Historically a common feed additive for animals, biochar can be eaten to help digest food and combat toxicity in the body (i.e. activated carbon is the most common treatment for ingested toxins in people). It's currently fed to animals in much of the world, but is currently banned by the USDA as a feed additive. Current research suggests that adding ~1% biochar to cow feed reduces methane emissions by 15% and increases their growth rate.
Manure, especially from confined feed operations and dairies, releases significant amounts of both methane and carbon dioxide. For example, California's Dairy methane emissions contribute up to 5 percent of the state’s carbon footprint. Adding biochar to manure directly, or to the bio-digesters used to process it, decreases methane emissions. Studies are evaluating this application now.
Nutrients, particularly the macro nutrients in fertilizer, nitrogen, phosphorous, potassium help plants grow, but compromise downstream ecosystems, causing algae blooms and dead zones. Biochar acts as a sponge for nutrients, and when placed near cultivated areas, can prevent excess nutrients from disrupting valuable waterways.
Pyrolysis, once underway, is an exothermic process -- meaning it produces more energy, in the form of heat, than it takes in. A lot can be done with that heat: warm greenhouses during winter, dry feedstock, or deliver heat to a process within a factory.
Most of the recent history and research on biochar has focused on biochar effect on soil. High quality biochar is very porous, meaning it has a lot of surface area by volume, and so, a bit like a coral reef does for sea life, biochar provides a home for microbial life. This, in addition to it's ability to soak up nutrients and hold water, make biochar a high quality soil additive, especially for poor soil in dry climates.
Biochar can capture the heavy metals, inorganic compounds, and pathogens in our sewage, and facilitate waste treatment. One of the most common water filters (Brita) uses activated carbon from coconut shells.
Biochar is highly porous, and consequently holds water well. Significant study suggests that biochar can improve water retention by as much as 50% in areas with coarse-textured soil.