Biochar

Reducing greenhouse gases

Reducing greenhouse gases is one of the biggest challenges of our times. The main greenhouse gases are carbon dioxide, methane and nitrous oxide.

Over half of all greenhouse gas emissions is caused by the use of fossil fuel - an obvious way to achieve reductions in emissions therefore is to shift from fossil fuel to renewable energy.

In the U.S., most nitrous oxide emissions are also energy-related, i.e. caused by transport, coal-fired power plants, etc. Therefore, these emissions can also be avoided by shifting to renewable energy.

Globally, most nitrous oxide emissions are caused by agricultural practices. Some 70% of anthropogenic nitrous oxide emissions is caused solely by the practice of adding N-fertilizers (i.e. nitrogen-based fertilizers) to the soil. Furthermore, nitrous oxide constitutes the single most important ozone-depleting emission and is expected to remain the largest throughout the 21st century. It is therefore important to also look at ways to reduce the need for N-fertilizers, in order to both enhance the recovery of the ozone layer and to reduce greenhouse gas emissions.

Pyrolysis of biomass can achieve just that. Pyrolysis produces agrichar, now better known as biochar, which can reduce the need for N-fertilizers and thus avoid nitrous oxide emissions. Biochar  can avoid deforestation and thus avoid associated emissions. Biochar can help with afforestation, thus resulting in more carbon dioxide to be drawn from the atmosphere. Furthermore, pyrolysis of organic waste can avoid emissions of methane and carbon dioxide that would otherwise occur when such waste decomposes.

Organic Waste

Most households now use only one or at most two different rubbish bins, one for general waste and one for recyclables. Those recyclables are typically made up of glass, plastic, cans and paper. It makes a lot of sense to use two bins for recyclables, one for organic and one for inorganic waste.

This way, municipal facilities can collect large amounts of organic waste for pyrolysis. Many people already compost organic waste such as kitchen waste and garden waste in the garden, but all too often such waste ends up along with general waste in landfills.

Analysis in Waikato, New Zealand, shows that some two-third of household waste can consist of paper, kitchen waste, soil and garden waste, as pictured in above image. Such waste now ends up on landfills, where it decomposes over time and emits greenhouse gases, in particular methane.

Physically, methane is natural gas. But as the image below shows, most methane emissions do not originate from use of natural gas or any other fossil fuel. Instead, most methane emissions have an antropogenic and organic origin. More specifically, most methane emissions are caused by household and rural waste.

In other words, it's important to look at ways to avoid such emissions.

The image on the right shows that waste, including wastewater treatment and composting, causes significant amounts of emissions.

Much of this waste is made up of organic household waste. Additionally, crop residues are burned or left to decompose on the land, which also results in greenhouse gas emissions.

Another consideration is the soot that is released when biomass is burned. Apart from being a health hazard, this soot is a significant contributor to climate change, especially in the Arctic, due to its capacity to both trap heat and cause albedo change. 

This could be avoided if such biomass is instead transformed by means of pyrolysis into affordable energy and biochar, a form of charcoal that is totally black. The energy could be used for local transport, heating and cooking, complemented by solar cookers. Furthermore, adding biochar to the soil is not only a good way to store carbon, it also enhances vegetation growth, thus drawing additional carbon from the atmosphere.

Storing carbon by means of biochar burial

Exposure to oxygen in the air makes biowaste emit greenhouse gases. This is the case whether organic material decomposes or is burned in open air. When burned, organic material will normally turn into white ash. Pyrolysis, by contrast, heats up biomass while starved of oxygen, resulting in this black form of charcoal called biochar.

At first, biochar was regarded as a useless byproduct when producing syngas or hydrogen from biowaste, but a closer look revealed biochar's qualities as a soil supplement. Biochar reduces erosion and nutrients runoff. The porous nature of biochar increases retention of water and nutrients, thus enhancing soil fertility and productivity. The honeycomb-like structure of biochar improves the soil's tilth, resulting in more biodiversity, more vegetation and more carbon stored in the soil, in addition to the carbon contained in the biochar itself.

Normally, when biowaste is added to soil, the carbon contained in the crop residue, mulch and compost is likely to stay there for only two or three years. By contrast, the more stable carbon in biochar can stay in the soil for hundreds of years. In terms of soil enrichment, adding biochar just once could be equivalent to composting the same weight every year for decades.

Biochar is now produced for soil enrichment at a growing number of places. The above photo shows biochar in pellet form from Eprida. In Golden, Colorado, Biochar Engineering Corporation is building portable $50,000 pyrolyzers that can produce 1–2 tons of biochar per week. Australian-based BEST Energies has built a demonstration pyrolysis plant with a capacity to process 300 kilograms of biowaste per hour. It accepts biowaste such as dry green waste, wood waste, rice hulls, cow and poultry manure or paper mill waste. The plant cooks the biomass without oxygen, producing syngas, a flammable mix of carbon monoxide and hydrogen. The biochar thus produced retains about half the carbon of the original biowaste (the other half was burned in the process of producing the syngas).

Farming Practices

Burning farm waste in open fields should be avoided. Instead, such waste could become useful input for pyrolysis. Plowing should also be reconsidered. Carbon is important for holding the soil together. Plowing causes oxygen to mix with the carbon in the soil, resulting in oxidation and emission of greenhouse gases into the atmosphere. Plowing cuts the roots of perennials plants and trees that can have deep, extensive root systems that keep carbon stored in the soil, prevent erosion, capture dissolved nitrogen and outcompete weeds (thus reducing the need for herbicides). Plowing makes the soil more prone to erosion and less able to withstand the impact of extreme weather conditions that can be expected to increase with global warming, such as heavy wind and rains, flooding and thunderstorms.

The huge mono-cultures of modern farming have become dependent on plowing and planting of genetically-modified grain seeds, combined with irrigation, fertilizers and pesticides. The separation of farming and urban areas has in part become necessary due to the practice of spraying chemical fertilizers and pesticides. Instead, growing more food on smaller-scale farms should be considered, in gardens and greenhouses within areas currently designated for urban usage. Vegan-organic farming can increase biodiversity; by carefully selecting complementary vegetation to grow close together, diseases and pests can be minimized while the nutritional value, taste and other qualities of the food can be increased.

Furthermore, slash-and-burn practices that transform forests into farmland are often motivated by lack of good quality farmland. By enhancing soil quality and reducing erosion, people have less reason to resort to slash-and-burn practices and the extra carbon dioxide that ends up in the atmosphere as a result.

Feebates to assist biochar

Back in 2007, when this article was originally written, it was accompanied by a call for fees on fossil fuel, meat and N-fertilizers. The proceeds of fees on fossil fuel would then subsidize local rebates on clean alternatives such as solar and wind power, in a manner similar to the better-known car feebates, which impose fees on polluting cars to fund rebates on clean cars. This would facilitate a shift to alternative energy. Similarly, it makes a sense to facilitate a shift to alternative farm practices, by imposing fees on livestock products and N-fertilizers, with the proceeds funding local rebates on biochar burial. Additionally, local councils can make annual rates for rural land dependent on an increase in carbon content.

Vegan-organic food can be produced with minimal emissions. Legumes such as peas, beans, lentils and peanuts don't need N-fertilizers and can in fact add nitrogen to the soil for other types of vegetation. Sweet potatoes and pineapples also require little or no N-fertilizers. Biochar can assist with such a change in agricultural practices. Biochar burial stores carbon in the soil, as a long-term solution to keep carbon dioxide out of the atmosphere. This enriches the soil, reducing the need for N-fertilizer and avoiding associated nitrous oxide emissions, while enhancing vegetation growth, which draws additional carbon dioxide out of the atmosphere. Furthermore, pyrolysis of biowaste gets rid of waste that would otherwise cause greenhouse gas emissions.

Production and transport of livestock and their feed accounts for nearly 80% of agricultural emissions. The carbon content of soil and vegetation decreases with plowing and slash-and-burn practices. Furthermore, raising cattle, growing feed for cattle and the associated crop residue causes large amounts of emissions.

A 2007 study led by Nobel prize-winning chemist Paul Crutzen indicates that the current ways of growing and burning biofuel actually raise rather than lower greenhouse gas emissions. The study concludes that growing some of the most commonly used biofuel crops (rapeseed biodiesel and corn bioethanol) releases twice the amount of nitrous oxide, compared to what the International Panel on Climate Change (IPCC) estimates for farming. The findings followed an OECD report that concluded that growing biofuel crops threatens to cause food shortages and damage biodiversity, with only limited benefits in terms of global warming. Some studies also raise concerns that N-fertilizers inhibit methane oxidation.

Nitrogen Fertizliers (N-Fertilizers)

Nitrogen is added to soils naturally, greatly enhancing growth of vegetation. For every kilogram of nitrogen that is deposited on the forest floor (by rainfall, for example), an extra 400 kg of CO₂ can be absorbed.

Biochar will enhance growth of microbes, and help retain phosphorus and potassium in soil. Depending on the sources, biochar can also supply phosphorus and potassium to the soil. But biochar will supply little nitrogen. Furthermore, the suggested shift to no-till will increase organic matter, and this can immobilize nutrients, including nitrogen. Farmers may therefore want to add N-fertilizers to the soil to enhance crop yield.

Problem is that producing N-fertilizers from fossil fuel and associated transport will cause carbon dioxide emissions. Globally, around 4% of natural gas is turned into hydrogen for the production of fertilizers. N-fertilizers can therefore better be produced locally, jointly with biochar, from hydrogen produced by pyrolysis of biowaste, which can avoid such carbon dioxide emissions. This method is followed by Syngest, who proposes a pyrolysis plant that will produce both biochar and ammonia. Getting biochar and N-fertilizers from the same producer can also result in supply of a mix of soil enhancers that is more suitable for local conditions.

Another problem with the use (and especially overuse) of N-fertilizers is nitrous oxide emissions. A feebate - fees on N-fertilizer, funding rebates on local sales of biochar - therefore makes sense and will discourage overuse. If N-fertilizers are to be used, they are better produced and supplied jointly with biochar.

In conclusion, recycling biowaste by means of pyrolysis is an excellent method to achieve multiple goals, including the disposal of organic waste while avoiding associated methane emissions, producing renewable energy and biochar, which can bury carbon in the soil and enrich the soil. Biochar make the soil less prone to erosion and more fertile, resulting in increased vegetation growth that draws more carbon dioxide from the atmosphere and produces more food. Pyrolysis will also produce syngas and hydrogen, which can be used to power transport or can produce nitrogen-based fertilizers while avoiding carbon dioxide emissions normally associated with production and transport of fertilizers. This overall result comes with positive feedback, i.e. it is self-reinforcing, in that increased vegetation growth will lead to additional input for pyrolysis ovens, which in turn results in further carbon that can be buried in the soil.

To assist the production of biochar, fees are proposed on sales of livestock products and N-fertilizers, to fund rebates on local sales of biochar, as pictured below and as further described in Towards a Sustainable Economy.

[ the diagrams are part of Towards a Sustainable Economy ]