INOM EXAMENSARBETE TEKNIK, GRUNDNIVÅ, 15 HP , STOCKHOLM SVERIGE 2020
Development of biochar in
Sweden
A study on the agricultural effects of biochar
through an international comparison
ILI ATALLA
GABRIEL KURT
KTH
TRITA TRITA-ABE-MBT-20144
Acknowledgements
We want to begin by thanking everybody that helped us with the project that includes Peter Hagström, Cecilia Sundberg, Britt Marie-Alvem and finally our parents that gave us inspiration and food when times were hard.
Sammanfattning
Biokol fungerar som en kolsänka och är en metod att bekämpa klimatförändringar. Det har även visat sig vara effektiv inom jordbruk då den ökar skörden genom att förbättra jordens vatten hållfasthet,näringsupptag samt öka pH. Sverige är ledande i biokol med 12 producerande faciliteter och därmed incitament att utveckla biokol. I rapporten jämförs olika fältstudier i Sverige och internationellt. Fältstudierna var baserade på grödan, jordtyp, klimat, råmaterialet och pyrolys metoden.
Varierande resultat har observerats kring biocools användning och detta beror på de olika faktorerna där biokol applicerats. Därmed rekommenderas det att biokol skräddarsys genom bland annat specifik pyrolys metod och råmaterial. Mer omfattande information kring biokol använding i olika området krävs för att kunna skräddarsy biokol. Biokol verkar dock mest
effektiv inom näringsfattiga områden både inom jordbruk och skog,specifikt boreala och tropiska zoner.
Abstract
Biochar represents a new approach to fight global warming through its ability to reduce carbon dioxide emissions by carbon fixation. It has been proven to be efficient in increasing harvest through the effects of increasing WHC, pH level and the uptake of nutrients. Sweden has 12 biochar production facilities and therefore represents an interesting biochar developer. In this report, Different field studies on the use of biochar were compared both in Sweden and
internationally. The field studies were identified based on crop type, soil type, climate, feedstock and pyrolysis method. Stockholm Stad was even observed as a consumer of biochar that is supplied by Stockholm Exergi in Sweden. Varying results have been observed on effects of biochar, mainly due to the different conditions in which it is applied.
Due to the variable effects of biochar on the observed factors, it is recommended for the capability to customise the biochar by choosing the specific pyrolysis method and the type of feedstock. To have a better understanding and ability to customise biochar more extensive information is needed on biochar use and application in different areas. Biochar seems to respond most effectively to nutrient poor soils in both agriculture and forestry. Tropical and boreal forest seem to benefit the most from biochar application compared to temperate zones.
Table of content
1.Introduction 1
1.1 Background 1
1.2 Aim 2
1.3 Methodology 2
1.4 The Global Goal of sustainable development 2 1.5 The market of biochar in Sweden 3 2 Biomass as a renewable energy resource 3
3.Pyrolysis processes 4
3.1 Pyrolysis methods 5
3.1.1 Fast pyrolysis 5
3.1.2 Slow pyrolysis 5
3.1.3 Other technologies 5
3.2 Impact of pyrolysis methods 6
3.3 Secondary reaction 7
3.4 Feedstock 7
4 Carbon sink and biochar production 8
5 Application of biochar 10
5.1 Application of biochar in Swedish urban cities 10 5.2 Application of biochar in Swedish farming 12 5.3 International studies on the application of biochar 13
5.4 Biochar on forestry 17
6 Results 17
7 Conclusions 19
Nomenclature
Bio-oils/Liquid by-products are by-products that forms after the pyrolysis process Bdw Bone dry weight
Carbon sequestration is the process of long-term storage of different forms of carbon inorder to reduce the effect of global warming.
Pyrolysis is the process in which biomass is heated in an environment with very low or no oxygen. PSM Phosphorus solubilising microbes are microorganisms that can hydrolyse insoluble forms of phosphorus into soluble forms which can then be absorbed by plants.
Secondary reaction is a reaction that takes place during the pyrolysis process creating more char. BDW bone dry weight
WHC Water holding capacity WTP Willingness to pay
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1.Introduction
1.1 Background
Climate change is the change in temperature that occurs in the lower atmosphere and the ocean. It is caused both naturally and anthropogenically by the emissions of greenhouse gases. In short, greenhouse gases are emitted by, among others, the industry and transport sector, in which they rely highly on the use of fossil fuels. Greenhouse gases, not just carbon dioxide but also N2O,
CH4, CF2Cl2 or CFCl3, descend to the atmosphere trapping heat from the earth causing the
increase in global temperature (Marland 1985).
Climate change is considered to be one of the world’s largest problems. It is difficult to forecast accurate effects of global warming, but scientists are certain in increasing sea levels and extreme weather (Horikawa 2013). Global warming has shown higher effects in certain regions than others but in general it is considered to be a global problem. This latest action to find a global solution through the Paris agreement. 197 parties have signed into an agreement to combat climate change. The agreement has a goal to keep the global mean temperature from increasing more than 1.5°C (UNFCCC 2015). It has been predicted that with an increase of 1.5°C further consequences of global warming will be observed. If the world reaches a 2°C increase the effects will enhance, for example it is estimated that 10 more million people will lose their homes (Mcgrath 2018). A method to fight climate change is through carbon sequestration where CO2 is
taken from the atmosphere and stored. The method makes it possible to actually therefore reduce the amount of CO2 in the air rather than just reducing the production of CO2. For the purpose of
reducing the greenhouse effect, Stockholm Stad, Stockholm municipality has set a goal to reduce CO2 with 240,000 tonnes yearly (Jawad 2018).
One option to reduce CO2 emissions is using biochar. Biochar works as a form of carbon
sequestration when it is used with soil fertilisers. The use of biochar is a technique that is 2000 years old. Biochar functions as a soil amendment due to its porous structure allowing it to retain nutrients and water. The biochar in the earth works as a carbon sink at the same time it increases food production with more harvest. Biochar consists of a range of materials that go through a pyrolysis process. Organic materials are heated up in an oxygen free environment that results in a solid material that is enriched with carbon. Biochar can have different structural and physical properties depending on what feedstock is used to create it and how it is produced in the
pyrolysis process. The produced biochar with its positive effects is considered to be a beneficial combat tool against climate change. By-products that are produced through the process can even be used as carbon negative fuels (Lehman 2015).
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1.2 Aim
The aim of this report is to provide a scientific research and background to allow further usage of biochar, more specifically in Sweden. The research motivates the management and handling of biochar for a more environmentally friendly system in both the energy and agriculture sector. The research aims to provide knowledge for a more optimised usage of biochar through the method used to produce the biochar, the crop type, and the soil type. This knowledge is aimed to benefit potential farmers, stakeholders, and environment ministries. Providing knowledge on the development of biochar in Sweden encourages biochar usage for stakeholders. It allows further knowledge to improve the technology and efficiency for agriculture applications.
1.3 Methodology
The question is answered through a deep literary analysis and an interview performed with Britt-Marie Alven a landscape architect with trees speciality at Stockholm Stad, the municipality of Stockholm. The interview is performed through a video call and has taken place the 13th of April. Literature derives to a large extent from scientific reports conducted in the past 15 years. Primary databases used are Google scholar, primo and ScienceDirect. Most frequently used search words were: Biochar, Biomass, Pyrolysis, Fertilisation, Soil amendment and Carbon sequestration,
Information and data provided by Stockholm Stad and studies performed south of Sweden are compared with international data to provide a local understanding of the usage of biochar. Information presented is related to the type of biochar produced in adjustment to the crop, climate and soil types that are found in Sweden.
1.4 The Global Goal of sustainable development
Among the 17 goals that are agreed on for a better world by 2030, this research represents work to tackle several goals such as Zero Hunger, Affordable and Clean Energy, Responsible
Consumption and Production, and Industry, Innovation and Infrastructure.
The paper aids to reach target 2.1 in zero hunger, which is intended to stop hunger for all people through providing nutrition (Sustainable Development Goals n.d.). This research investigates biochar as a fertiliser which can be used by farmers in the food industry. This can be applied in both developing and developed regions. As this research promotes the use of biofuel, it aids in reaching target 7.2 to increase global percentage of renewable energy. Biofuel usages go hand in hand with biochar production and therefor helps increase the renewable energy share, as in target 7.2 (Sustainable Development Goals n.d.). The research benefits mainly target 12.2 in which a more in-depth research is performed to help determine the sustainable progress for the natural resources, biofuels, in both the consumption and production aspects. Lastly, by providing an option for several industries to take use of this sustainable method with the use of biochar and biofuel, this helps upgrade industries for higher sustainability, as in target 9.4. The target promotes to upgrade industries to be more sustainable, with higher resource-use efficiency and
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the use of cleaner techniques. Biochar is a sustainable technique with the fact that it is provided from nature and goes back to nature. It is a sustainable circular flow that has a potential to limit greenhouse gas emissions. (Sustainable Development Goals n.d.).
1.5 The market of biochar in Sweden
Waste Management in Sweden, in cooperation with Stockholm Exergi, has performed a study to reveal the WTP of biochar in Sweden (Stockholm Exergi n.d.). Biochar has shown several benefits but when it comes to the Swedish market, biochar has the highest value in its usage in agriculture. Biochar shows to increase fertility and harvest and has even shown to be beneficial to minimise mineral leakage to the Baltic Sea as it suffers from overfertilization. Biochar has even shown to be beneficial in other areas. Biochar is used in animal feed to reduce antibiotics usage and increase hygiene. It can also be used as a filter to clean water. The usage of biochar as a filler in concrete is seen as a potential material to substitute other limited resources such as gravel. These benefits are predicted by Waste Management in Sweden to be more valuable in a few years in the future and are mostly determined by financial investments in the different sectors.
Today, for agricultural usage, biochar has reached a market price of 2,600 SEK to 3,000 SEK per cubic meter. According to a survey by Waste Management in Sverige, biochar for farmers shows a WTP up to 3,000 SEK per ton, while the WTP for its usage as a filler in concrete today has shown to be 100 to 150 SEK per ton (Andersson 2018).
The benefits of biochar are being more and more familiar with it as a fertiliser but the benefits in feedstock and a filter material is still limited. The interviewees did show interest in biochar despite their limited knowledge when it comes to its benefits.
2 Biomass as a renewable energy resource
Biochar is created by biomass in pyrolysis when it comes to the compositions of the biomasses, woody and agricultural biomass are most suitable for production of biochar as they are high in carbon and oxygen. Other biomasses, such as aquatic biomass, have high hydrogen content and are seen nowadays suitable for hydrogen production (Manoj et al. 2014).
Biomass is considered as a renewable energy source. In concept, biomass represents an energy resource with zero net emission for the greenhouse gas of CO2. The amount of CO2 picked up through the growth process equals to the amount released through combustion. Therefore, bioenergy consumption is not included in a country’s official emission inventory that has been put together by the Organisation for Economic Cooperation and Development (Gregg 2010).
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Despite it being a renewable resource, biomass usually has negative properties as an energy resource. Biomass has a low heating value, high content of moisture and volatile components, and fibrous nature. Biomass that is acquired from living organisms such as plants, woods, forestry residuals. This type of biomass is called lignocellulosic biomass and consists of cellulose, hemicellulose and lignin. The three components are linked through non-covalent bonds.
What the three components consist of is that cellulose is mainly a homopolymer of D-glucose, linked by β-1,4 glycosidic bonds with the molecular formula of (C6H10O5)n. Hemicellulose
consists of glucose, mannose, xylan, xylose, arabinose, galactose and sugar acids. While lignin is composed of a complex organic polymer that consists of phenyl-propane monomers such as coniferyl, trans-p-coumaroyl, and sinapyl alcohols. Lignin is mostly thermally stable compared to the other two components. Different types of biomass have different compositions of these components thus leading to different biochars (Jechan et al. 2019).
When it comes to chemical composition of biomass, it consists mainly of carbon, oxygen, sulphur, nitrogen and ash. Other elements that could be found are alkali metals, alkaline earth metals and heavy metals. The distribution of these elements is different depending on the type of biomass analysed. sewage sludge consists of more sulphur compared to for olive tree wood. Proportion of C, H and O determine the fuel property and combination of these elements help determine the heating value of the biomass. Nitrogen and sulphur have less contribution as they are found in less amounts. However, the existence of these components helps in forming high energy bolds of C-N, H-N and C-S, H-S. They are observed to have more energy than C=O, C–O and O–H bonds. With the low amount of N, S and NOx, biofuel represents an environmentally friendly energy resource to prevent acid rains, when compared to fossil fuels (Manoj et al. 2014).
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.Pyrolysis processes
Pyrolysis is the process in which organic material is converted into a solid carbon rich char through heating with low or complete absence of oxygen. Organic matter comes in form of manure, organic wastes, bioenergy crops, or crop residues. As seen in figure 1, organic matter undergoes partly pyrolysis or is used as a biofuel to provide energy. Part of the energy provided can even be used in the pyrolysis in the form of residual heat. Pyrolysis gives by-products such as volatile matters that can be part liquid and gas. Ash is also produced through the inorganic materials in the process which can be used for its liming effects. Many important factors of biochar are affected by the pyrolysis process. These include the physical and structural
properties. Factors outside also play a part in the biochar formation such as soil type and weather in the area where biomass was collected. Quantity of char and by-products are also affected by the process. The Structure of biochar which correlates to its physical properties are connected to the pyrolysis process and feedstock used. The pyrolysis process can be manipulated to shape the biochar or its by-products to best fit its purpose (Lehmann 2015).
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Figure 1: The cycle of biomass through the pyrolysis process to produce biochar, adapted from International Biochar Initiative.
3.1 Pyrolysis methods
There are 2 main types of pyrolysis methods named fast pyrolysis and slow pyrolysis.
3.1.1 Fast pyrolysis
Fast pyrolysis uses higher heating rates and less vapour time which demands the use of smaller particle fuels for the pyrolysis process. There are many different reactors used for this process among these are vacuum pyrolysis systems and fluidised beds. The process is mainly used to create bio-oils which are the liquid by-products created through pyrolysis that can be used as fuels (Brownsort 2009).
3.1.2 Slow pyrolysis
Slow pyrolysis compromises of traditional and modern production of biochar. The process uses lower temperatures around 400°C and the targeted product is the char due to the lower quantity of by-products produced such as biofuels. Traditional production often uses a kiln, mound or pit where by-products disappear through the smoke contributing to climate change. Modern
production that is used at an industrial scale usually includes biomass moving through a modified kiln in a controlled action (Brownsort 2009).
3.1.3 Other technologies
Other technologies than slow and fast pyrolysis exist but are not often used. There is e.g. flash pyrolysis which is sometimes called very fast pyrolysis. In the process biomass is moved swiftly through a heated tube with the use of gravity or gas. Higher temperatures and shorter residence time for the biomass is seen in this process (Brownsort 2009).
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3.2 Impact of pyrolysis methods
Biomass contains cellulose, hemicellulose and lignin and other materials called extractives which include smaller organic materials and minerals. These materials and their distribution will affect the quantity of biochar and the volatile matter that is produced. When temperature is reached, hemicellulose, lignin, smaller organic particles and cellulose start breaking down creating condensable vapours which basically are both liquid and gas byproducts. Lignin also
decomposes to the solid char while the minerals from the extractives become ash. Vapours that are created can form a secondary char when combined with the hot char. This secondary reaction is beneficial when the aim is to produce maximum char in a reaction (Brownsort 2009).
Pyrolysis performed in various methods leads to the change of charcoal's physical properties and chemical construction. Traditional and modern methods of slow pyrolysis generally range
temperatures around 400-600°C, meanwhile fast pyrolysis can have temperatures in the 800°C’s. These different pyrolysis methods change the properties of charcoal produced. Chemical changes occurred in the 400-600°C range such as the increase in carbon content and decrease of hydrogen and oxygen content. Physical attributes for the charcoal change in the higher temperatures and stays stable in 8c00-1000°C. Pore size increases significantly around the 600°C range and increases further with the increase of temperature (Tintner 2019). Pore size relates to biochar ability to hold water as well as its ability to adsorb gases and other liquids. Pyrolysis temperature is a big factor for the pore size of the biochar. In Japanese Cedar pore size was 120 /g when using 400 °C this increases however to 460 m3/g when using 900 °C as the pyrolysis temperature (Ogawa 2005).
Structural complexity can be lost through phenomena such as sintering, fusion or plastic
deformation during the pyrolysis process. Therefore, it is important to control the process during production. The phenomena increase with higher heating rates, long processing times and high ash content in feedstocks. For example, eucalyptus feedstock had high content of ash leading to the loss of microporous structure demanding pre-treatment of feedstock before pyrolysis. Higher heating was found to local melting of cell structures and phase transformations while at lower heating rates volatiles escaped through pores maintaining structure, showcasing slow pyrolysis as a safer method (Lehmann 2015).
Moisture content affects the pyrolysis process products, but this is dependent on the method used. Traditional methods such as kilns demand more fuel to be added for pyrolysis but if the moisture content is low then the process is self-maintaining. Fast pyrolysis methods can not have a high moisture content to operate around 10% moisture is the max. The evaporation otherwise prevents the increase of temperature while slow pyrolysis is not that sensitive to moisture content. Particle size that is placed in the pyrolysis process also affects the quantity of solid char and liquids produced. Larger particles lead to an increase in the production of char by increasing the reaction between primary vapours and hot char. Smaller particles increase the production of liquids which is often the goal in fast pyrolysis. However constant temperature and other factors such as moisture during the pyrolysis process is hard to maintain even at the more advanced plants. Meaning differentiation between yields is evident. The effect of constant temperature is enhanced on slow pyrolysis processes through the longer process time (Brownsort 2009).
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3.3 Secondary reaction
Secondary char is created when primary vapours and hot char are combined during the pyrolysis process. This reaction leads to the decrease of quantity and quality of liquid by products but increases the amount of char produced. The reaction can therefore be manipulated depending on the goal of the process. Gas flow in the reaction will affect the secondary reaction. Higher gas flow will lead to the exit of the primary vapours which decreases secondary char production. This is preferred in fast pyrolysis and the lower gas flow is preferred in the slow pyrolysis to increase the char yield. A higher pressure will increase the activity of vapours and therefore the production of secondary char while pyrolysis under vacuum will lead to less production of secondary char. Higher temperatures lead to the reduction of char yield due to the increased volatilisation of the char while lower temperature and longer residence time increase char yield. Liquid yields are more complex and have maximum yields in the temperature span of 400-550°C dependent on conditions and equipment used. Higher temperatures will lead to an increase in vapour decomposition and therefore reduction of liquids and increase in gas yields. (Brownsort 2009). When pyrolyzation temperature is changed from 300°C to 800°C biochar yield is
decreased from 66.5% to 25.6%. However fixed carbon increases from 55.79% to 93.51%. Ash content increases from 0.67% to 1.26% this affects the pH level which increases from 7.6 to 9.7 (Ogawa 2005).
In general factors that lead to the increase of the reaction between vapours and hot char will promote the secondary reaction and thus increase char yield. Hence, the secondary process can be manipulated through several factors. The increased production of char is more beneficial if the goal is to increase the carbon sequestration or to be used as soil amendment. The increased production of bio-oils which are by-products of pyrolysis are more beneficial if the purpose is to create fuels (Brownsort 2009).
3.4 Feedstock
The choice of feedstock will give different yields from the process. With different types of feedstock, this will result in different physical and chemical properties of the biochar (Kloss 2012). Biomass components will change depending on where and when it was harvested. For example, weather is different from time to time making it so feedstock can have different moisture levels when collected (Brownsort 2009). Using lignin rich feedstock increases char yield because the char derives from the lignin during the pyrolysis process (Deb 2016). Using biomass with high inorganic material will increase the ash content after pyrolysis which
increases the biochar liming effect. Meaning biomass with higher inorganic materials functions better for liming (Lehman 2015). The ability to also customise biochar to specific deficiencies in the soil is possible and was found to increase corn yields compared to non-specific biochar. However, corn yields were not significantly increased, and actually annual production dropped 30%. This was due to weather fluctuations on critical stages of the corn's growth (Novak 2019).
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4 Carbon sink and biochar production
Carbon sequestration is the act of storing carbon dioxide for a long period of time. It is a tool to combat climate change through taking carbon dioxide from the atmosphere and storing it elsewhere. Biochar can function as a carbon sink. Photosynthesis is performed by plants that store CO2 which is partially stored long term in the biochar after the pyrolysis process. Otherwise
the carbon dioxide is released from plants or other organic material through natural decaying. The amount of carbon dioxide that is fixed through the biomass can vary depending on what kind of organic material that is taken through pyrolysis, different amounts of CO2 will be stored. An
old forest will contain more CO2 than a new forest due to the fact that it has had more time to
store CO2 (Lehnman 2009).
There are several ways to go about using biochar for its carbon storing abilities. It can be
combined with forestry and agriculture for its soil amending properties. For the case of forestry, we look at the case study performed in southern Sumatra Indonesia with a tree plantation
company called Musa Hutan Persada, in short MHP. MHP has been planting a fast-growing tree species called Acacia Mangium. When trees are harvested, the main trunk is taken but wood residues which are classified as leaves, twigs branches and branches are left over, in the pulp process excess bark is left unused. The wood residue and excess bark are taken and used as feedstock for the production of biochar. The biochar is then used for soil amendment in the forest but is also used for water purification and fuel. The biochar used for water purification or as a soil amendment functions as a carbon sink. Using data from MHP we know that the annual production of logs is around 2.1 million m3 which is around 932,400 Mg on bone dry weight (bdw) using a conversion factor of 0.444. Through a collaboration with Kyoto university it was calculated that around 17.8% of the tree is residue. As shown in table 1, This is calculated to be around 162,000 Mg-bdw per year (Ogawa 2005).
The excess bark from the pulp process was calculated to be around 14,500 Mg-bdw per year of dry bark. Adding these numbers give us the approximation of total of unused wood which comes to 176,500 Mg-bdw per year. Biochar production trial was conducted with a traditional hume pipe kiln which was chosen due to its large capacity and accessibility. The biochar yield was found to be around 23.1% and fixed carbon was found to be around 75.6% for the wood residue. For the pulp mill, the biochar yield was 68.2% and 48.2% of the carbon was fixed. It was
estimated that all biomass could be carbonised and using these numbers above means that roughly 28,000 Mg-C per year from wood residue is fixed in the biochar, as seen in table 1. 50% of the biochar from the wood residue would be used as a soil amendment and the other 50% as a carbon neutral fuel. Meaning around 14,000 Mg-C per year would be stored and the other 14,000 Mg-C would be released into the air when combusted. An estimated 4,400 Mg-C per year would come from excess bark and all of it was to be used as soil amendment. External fuels are
however used for this production, distribution, and transport of biochar by the use of machines, equipment, production of biochar and firewood. It is estimated that around 2,600 Mg-C per year is used for the wood residue and around 400 Mg-C per year for the pulp mill. Giving a total of around 3,000 Mg-C per year of external fuels and 18,400 Mg-C per year in sequestered carbon, see table 1. Meaning in total 15,400 Mg-C per year would be sequestered. Soil conditions would
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be improved in the forest leading to an increase in growth and local jobs would also be created (Ogawa 2005).
Table 1 Values concerning the case study in Sumatra Indonesia, Ogawa (2005)
Excess bark Wood residue
Total weight 14,500 Mg bdw total weight 162,000 Mg-Bdw Yield and fixed carbon
percentages
Biochar yield is 68.2% 48.2% fixed carbon
23.1% yield of biomass 75.6% fixed carbon Fixed carbon 4,400 Mg-C/year 28,000 Mg-C/year Fixed carbon in soil 4,400 Mg-C/year
100% soil amendment
14,000 Mg-C/year 50% soil amendment External fuels 400 Mg-C/year external fuel 2,600 Mg-C/year external
fuel
Another case that also involves biochar in forestry was conducted in a semi-arid region in west Australia where eucalyptus trees were incorporated into cereal cropland. Purpose of this is to solve the salinisation and acidification problem through the use of biochar that is produced from the eucalyptus trees. Oil Malle company (OMC) would extract eucalyptus oil from the leaves and use the wood residue to produce biochar or power generation. The problem of acidification arrives from series cultivation and the use of chemicals in the plantation. The furnace used for carbonisation has a temperature between 500-600°C, around 20% of the dry biomass was transformed into biochar with 80% fixed carbon. A 1000-hectare plantation was used for this study where initial harvest would begin after 10 years and each year 1000 hectare would
additionally be planted. Coppicing method would be used on the eucalyptus trees unlike the case in Indonesia where the trunks were entirely removed. The carbon sequestered was in the form of eucalyptus trees, coppices and biochar on the ground even after harvest a large amount of CO2 is
stored in the coppice of the trees. Coppice regrowth maintains carbon sequestered to a mean of 146,000 Mg-C. 20% of the eucalyptus tree that is removed is converted into biochar. Over a 35-year period and 10,000-hectare plantation 342,000 Mg-C is sequestered by eucalyptus trees 547,000 Mg-C during the same period is fixed by the biochar. Total carbon sequestered in the 35-year period 547,000 Mg-C by biochar, 146,000 Mg-C by the coppice of the tree and 342,000 Mg-C on the rest of the tree. Coppicing methods for mallee eucalyptus trees sequester more carbon when the trunk is stored (Ogawa 2005).
The last case took place in Kyushu Japan using biochar in an urban manner where heat surplus was taken from a garbage incinerator to be used in the production of biochar. Traditional garbage incinerators release dioxins which has caused a range of problems for the nation causing many local governments to change incinerators which use gasification or ash melting systems. These types of incinerators produce surplus heat. Biomass is taken from waste wood from several local
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sawmills and from tree thinning. Biochar is used for non-fuel purposes among these are
agricultural production, sewage disposal, water purification and house constructions. Meaning all the biochar produced will function as a carbon sink. As a furnace for the project an internal-rotary kiln is used. It produces approximately 358 Mg-C per year with the temperature of 500-600°C; some of the biochar is mixed with manure which is 30% dry. 59.5 Mg-C per year of external fuels are needed for energy in the production of biochar. Meaning 298 Mg-C per year is sequestered. The amount is small, but it utilises surplus heat and the area researched is a
relatively small city with roughly 300,000 of population. Cities with biomass waste could produce more biochar (Ogawa 2005).
In Sweden Stockholm Exergi is in collaboration with Stockholm Water and Wastewater. Stockholms City are working on introducing a facility, localised in Högdalen, that takes in garden wastes to be converted to either district heating or biochar. According to Stockholm Exergi, 15% of Stockholm’s garden wastes are turned into either heat or biochar. The garden wastes come from natives of Stockholm that dispose of their wastes in the Stockholm Watten recycling centre.
Stockholm Exergi is considered as a main producer of biochar in the Stockholm region. Biochar produced by Stockholm Exergi is performed at the temperature of approximately 600 °C through slow pyrolysis. 50% of the carbon atoms are locked from the organic feedstock into the biochar
structure, which results in the reduction of 50% CO2-e.
Stockholm Exergi plans to produce around 100,000 tonnes of biochar per year from various biomasses. Which is equivalent to 450,000 tonnes of carbon dioxide emission per year. Through the distribution process of biochar, around 10,000 tonnes of CO2-e emission is emitted, This
allows Sweden to reduce around 440,000 tonnes of CO2-e emissions. The CO2-e emissions are
calculated with the correspondence of methane reduction with the usage of biochar in feedstocks (Jawad 2018).
5 Application of biochar
5.1 Application of biochar in Swedish urban cities
Biochar is used in tree reservoirs in Stockholm. The main purpose of the biochar is to pick up nutrients, increase the WHC and even the contamination that is collected from the plant bed. Furthermore, has Stockholm its continuous goal to lower the carbon dioxide and provide a well-established tree environment for its inhabitants. According to Britt-Marie Alven, a tree specialist at Stockholm Municipality, biochar has shown significant effect on the trees in which the stem radiance has increased with the use of biochar. Alven claims that trees can play an important function in cooling down through water bodies in generally warmer urban cities such as Stockholm (Alven 2020).
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Biochar used by Stockholm Municipality is supplied by the biochar facility that is run by
Stockholm Exergi. The feedstock used in the production consists of 15% of the garden wastes in Stockholm. According to Britt-Marie Alven, the supplied amount of biochar from garden wastes is not considered enough and Stockholm Municipality demands to buy more biochar.
Biochar is combined in Stockholm through different models that consist of layers with varying functions. A thin biochar layer that is not enriched with nutrients. It has the theoretical effect that it would absorb previous contaminations in the plant bed. It is even thought to be used as a filter to refine surface water (Stål et al. 2017). A method that is used in garden beds involves the application of structured soil with a fraction of 90-150 mm which is placed in a layer of 250-300 mm that is compressed with a vibrator. Above it, a 20 mm layer of biochar that is enriched with nutrients is flushed with high pressure of water. The enriched biochar ends up being combined in cavities with macadam. The macadam has the function to create an airy soil layer in which biochar can be flushed through the cavities. A mixture consists of 75% stone chips mixed with 25% biochar (Booman 2017). Another mixture has been tried instead of structural soil is a mix of 85% macadam and 15% nutrient enriched biochar with compost in a 32-63 mm layer (Stål et al. 2017).
Uptake of nutrients plays an important role to maintain the growth of the trees. The
microorganism life in the planting bed has a function to break down nutrients to mineral form to be taken up by the trees. Newly created planting beds would lack the microorganism life and therefore would require time for it to be established. Nutrients are provided in balanced form in sacks that contain both water and nutrients in liquid form. Nutrients in balanced rate are
important to avoid leakage and deficiency as they can affect the photosynthesis process.
Nutrients are provided in the following proportions. They are recommended according to table 2.
Table 2. Recommended nutrient proportions for tree plants. The amount used within a 20% uncertainty is acceptable (Stål et al. 2017) Macronutrients Proportions Nitrogen (N) 100 Phosphor (P) 13-19 Potassium 45-80 Sulphur 8-9 Magnesium 5-15 Calcium 5-15
The tree reservoirs in Stockholm are watered within the period 15th of April to the 30th of August. Trees with a stem circumstance of 20-25 cm or more are water with 140 L for each week. The total amount of nutrients of around 2 promille is mixed with the water that is served to
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the trees. The watering season can be extended to after the 30th of september depending on the climate conditions (Stål et al. 2017).
5.2 Application of biochar in Swedish farming
Biochar usage in farming is continuously growing. With around 12 biochar production institutes in Sweden, farmers find it suitable to use available biochar as it is considered economically wise for crop efficiency and possibly lower the amount of required fertilizers. Small and big biochar production institutes can be found in Stockholm, Katrineholm, Uppsala, Ransby and Götene; according to Nordic Biochar Network.
The usage of biochar in farming in Swedish soil has been tested in two different soils. Biochar has been tested south of Sweden in Ejlertslund which is located outside Simrishamn. The test in Ejlertslund investigates the effect of biochar with nitrogen as a fertilizer. The test examines the effect of using different amounts of biochar with nitrogen fertilizer. Another field test has been performed in Sandby gård in Skåne. The experiment in Sandy gård tested the effect of biochar with different supplies of nitrogen, phosphorus, and potassium. The experiment in Simrishamn is tested for 2010, 2012 and 2013, while Sandy gård is tested for both 2014 and 2015 (Laxmar 2017).
Both studies have shown positive effects of biochar with the increase of harvest in biochar addition. The field studies had similar conditions when it comes to climate and source of biochar, but the soil type and crops grown show to differ. The study in Skåne focused on nitrogen
addition with biochar and has shown the results of with the addition of both more of either nitrogen or biochar there is an increase in harvest. The study even shows the necessity of
nutrients for biochar to function properly. It proves that the uptake of nutrients has no or negative effect of biochar when used without any added nitrogen. This demonstrates the positive of the addition of nitrogen with biochar, see table 3. The studies did however show differences on the effect of biochar. In the study in Borrby, it has shown that the harvest starts to be inefficient and even has a small negative effect when a certain amount of biochar is reached. After 5 ton of biochar there was no increase in harvest when 10 or 15 ton were used. While the harvest keeps on increasing with added biochar despite the amount. Furthermore, the study of Borrby shows all the significance of a mix of nutrients when nitrogen, phosphorus, and potassium, shown in table 3. With the addition of phosphorus and potassium there was a higher amount of harvest than with only nitrogen. Nitrogen effects seem to have a higher effect however with the lower amount used (Laxmar 2017).
13 Table 3, Effects of biochar perform in field studies in Sweden
Source of Biochar
Crop Location Climate Type of pyrolys-is Soil type Effect of nitrog-en Effect of Phosph-orus Study Other effects Corn and seed Autumn grain Sweden, Skåne Temper ate climate Not specifie d Sandy Soil, 5% clay and 1.5% organic material Positiv e effect Not measured Laxmar (2017) Increase in pH, more of both biochar and nitrogen resulted to higher harvest Corn and seed Spring grain (KWS Irina) with spring wheat Sweden, Borrby Temper ate climate Not specifie d Clay soil with 28% clay content, 3,2% soil organic matter Positiv e Effect Positive effect with potassiu m Laxmar (2017) Negative effect on the harvest with the addition of biochar without the addition of nutrients
5.3 International studies on the application of biochar
Biochar can be found as a useful soil fertilizer in agriculture with an overuse of nitrogen fertilizers. Nutrients such as nitrogen are important in plants to improve their metabolism and grow. Nitrogen is mainly picked up by ions of NH4+ and NO3− (Naeem et al. 2017).
Phosphorus (P) is also necessary in plants to produce primary and secondary metabolites. It has an important role as a constituent of nucleic acids and phospholipids (bio membranes). It is highly essential for the energy metabolism of cells. The absorption and translocation of P takes place by a hyphal net outside the roots that spreads in the soil (Nell et al. 2009). Nitrogen loss via runoff can volatilize and cause damage to water and soil quality. Biochar has been shown to significantly reduce NH4+–N and NO 3−–N leaching to a NO 3−–N fertilized soil. Biochar helps in mitigating N leaching losses, with even improvement in WHC, absorption of NH4+ and improved N immobilization (Hao 2013).
It is also beneficial for increasing crop productivity by increasing use efficiency and stimulating nutrient uptake through crop roots. However, biochar does not often contain high levels of
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nitrogen and phosphorus. Chemical analysis performed on slow pyrolysis, below 500°C, biochar made from wood, shows that the content of phosphor and nitrogen is very small. Specifically, it does not measure over 0.9g/kg and phosphor 0.7g/kg therefore it provides little nutrients for plants (Deb 2016). In general, most biochar’s have low content of nitrogen but higher levels of phosphorus. Demanding the addition of compost and other fertilisers (Thomas & Gale 2015). It does however increase the absorption and retention of nutrients for plants by mobilising nutrients such as organic and inorganic phosphor. Biochar’s pore size is important for the transportation of nitrogen and phosphorus. Wood biochar pores mostly range between 1um to 15um in size which is good for transport of phosphor. As shown in table 3, in most cases biochar seems to increase the availability of phosphor but not nitrogen (Deb 2016).
A further study on biochar by Schulz & Glaser 2012, experiments on the use of biochar together with organic and inorganic fertilisers such as household garbage. The soil used was fertile rich soils with organic matters and nutrients, known as terra preta (de Indio). The study shows that the addition of biochar does not influence phosphorus retention. In contrast to other studies, phosphate retention did not increase despite the pH value being near neutral which optimum for phosphate immobilisation, see table 3. The study even observes no effect on leaching of N and P. According to the study, the biochar with compost has even shown best results when it comes to plant growth and C sequestration, but N and P retention has shown no effects (Schulz & Glaser 2012).
As seen above varying results for biochar are often seen and are dependent on factors such as crop species, soil fertility status and the biochar properties. The biochar properties depend on factors mentioned above such as feedstock and pyrolysis method, which have been demonstrated in table 3. A case study was performed to look at biochar's effect on productivity on different soils and crops. Biochar was produced in all 3 areas with lignin rich wood and slow pyrolysis though different species of wood. Biochar was added 10 tons per hectare. 3 treatments were used, one combining phosphorus solubilising microbes and biochar, adding biochar alone and finally only adding PSM which works as the control because all tropical and temperate zone area plants contain PSM. PSM are bacteria in plant roots that grow and therefore increase the surface area of the roots and its ability to absorb nutrients. Biochar leads to an increase of PSM mass and thus increases the ability to absorb nutrients. 4 different crops were used; these were tomato crops, leaf crops, grain crops and fruit crops. One of the areas researched was a farm in India which has a topsoil of sandy clay which consist of 44% sand, 52% clay and 4% silt and oxisol substrate. The farm has received no agrochemicals the past 20 years and soil nutrients were low, specifically 234 kg nitrogen per hectare and phosphor was at 2.8 mg per kg. Another was a farm in Thailand which had silt loam where 5% is sand, 6% is clay and 89% is silt and the farm has had no chemical input for the last 10 years. Nitrogen content was high with 660 kg per hectare available phosphor was 10.45 mg per kg. Glass houses in the UK had fine silt loam with 30% sand, 29% clay and 41% silt inceptisol substrate. Soil contained rich organic compost mixed with rock phosphate. Available nitrogen was moderate at 443.3 kg per hectare and phosphor was very high at 106.33 mg per kg (Deb 2016).
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The yield results were different in the countries. Radish, rice, and tomato showed improvement in India with the treatment using biochar and PSM. In general, all grain crops and root crops benefited substantially from the treatment. Effects were varying between fruit crops as Capscium in the UK did not gain much positive effects while tomatoes in India did. Biochar by itself did not have a large positive impact on crop productivity only when it was combined with PSM. In general, it seems that biochar combined with PSM has had the most beneficial effects on the more nutrient poor soil in this case India. In general, Thailand and the UK more nutrient rich soils did not get a substantial effect. More specifically soils with poor phosphorus content like the one in India gained the most benefit from added biochar and PSM. Through a separate study conducted with 3 types of soil with varying phosphorus content showcased that the increase of phosphorus in soil diminished areas increased the effects of biochar added with PSM. It was shown that after the critical phosphorus in soil was reached there was no further increase in crop yield with the addition of PSM and biochar. However, all the tests performed in the study
indicate that biochar alone did not substantially affect crop productivity. When combined with PSM increase in productivity was seen. PSM by itself also did not increase productivity only when it was combined with biochar. However, this may only be the case for certain soil types and crops (Deb 2016).
Another case where biochar has benefited a soil with low nutrients is in Northern Germany, shown in table 4. The experiment was performed on sandy soil where biochar has shown an increase in yield through WHC. Their study shows further how the usage of biochar with different fertilisers help increase in their maize yield. According to the results, low biochar amounts of 1 and 10 Mg ha-1 resulted in minor effects on WHC and soil and plant properties.
However, the low amount of 1 Mg ha-1 has shown a significant increase of mineral fertiliser efficiency. The addition of 1 Mg ha-1 has led to an increased maize yield by 20% when combined
with commercial mineral fertilisers. When combined with compost, the maize yield increased to 26% compared to pure compost. When it comes to the uptake of nutrition by maize plants, biochar seems to increase P, K and Zn uptake; more or less doesn’t effect N, Mg, Ca, Mn, Co, Cr and Pb uptake, and lowers Na, Cu, Ni and Cd uptake Glaser et al. (2014).
However, on the contrary meta-analysis by Simon et al. (2017) showcase only increased crop yields on tropical areas and negative effects on arable temperate zones. Showcasing the various effects of biochar on different soils. On average temperate zones did not increase in yields unlike tropical areas. One explanation is that tropical areas are low on nutrients and pH, so the biochar applied adds a limiting effect and increases nutrient availability in a scarce area. In arable temperate zones pH and nutrient content are higher leaving little room for improvement. Negative impacts were also found on temperate soils which can be connected to biochar, increasing the pH over optimal levels leading to the immobilisations of key micronutrients. Especially considering the biochar used had a pH of 9. On average it was found that biochar decreased crop productivity by 3% on the temperate area while its increased productivity in the tropics by 25% (Simon 2017).
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Table 4. International field studies on the use of biochar and its effects on different crops and climate conditions
Source of biochar
Crop Location Climate Type of pyrolysi s
Soil type Effect on nitrogen
Effect on Phosphor us
Study Other effects
Giant reed (Arundo donax L.) Maize Chenya, Shadong province (China) Humid subtropic al 500°C Slow pyroloy sis Air- dried, 60% soil mosture content Increase in nitrogen retention and reduction in leaching Not measured Hao et al. 2013 Increase in CEC, increase in pH level, Improvement in WHC Green cuttings Kalvin silage maize (ID 12835) Northern Germany Temperat e climate 650°C (Fast pyrolysi s) Sandy soil (Field condition) No effects Increase in uptake Glaser et al. 2014 Increased WHC, no negative effects of biochar Beach-wood- retort Oat (Acenu Satica L.) Weidenbe rg, Germany Temperat e condition s 400°C Weathere d tropical soil (terra preta)
No effect No effect Schulz & Glaser 2012 Increased soil pH but lower during second growth period Rich lignin wood Fruit crops,Gra in crops,Ro ot crops,Lea f crops India Tropical condition s 350-500°C (Slow pyrolysi s) Sandy clay, consists of 44% sand,52% clay No effect Increase effect Deb 2016 Retain soil moisture, reduce pH of acidic soils Rich lignin wood Fruit crops,Gra in crops,Ro ot crops,Lea f crops Thailand Tropical condition s 350-500°C (Slow pyrolysi s) 5% is sand,6% is clay 89% is silt No effect Positive effect Deb 2016 Not mentioned Rich lignin wood Fruit crops,Gra in crops,Ro ot crops,Lea f crops United Kingdom Temperat e zone 350-500°C (Slow pyrolysi s) 30% sand, 29% clay and 41% silt inceptisol substrate No effect Positive effect Deb 2016 Not mentioned
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5.4 Biochar on forestry
Biochar has potential to function greatly combined with forestry due to biochar's ability to enhance the nutrient uptake, reduce the bioavailability of toxic materials and increase retention of nutrients. It has been shown that biochar has the ability to absorb heavy metals and sulphates as well as other toxic materials for plants. Due to the ash in biochar pH in soils increase which helps combat acidity in the soil. In a wetland area affected by toxic materials through mining it was found that biochar contained 40 times the amount of metal contaminants compared to the surrounding soil. As in agriculture biochar can increase the nutrient uptake for trees but is necessary to combine with fertilisers, depending on the soil, due to the lack of nutrients in
biochar alone. Several studies on biochar's effect in forestry showcase a mean of 41% increase in biomass for woody plants, high response in the early stages of the plants which are less than 6 months old. The increase declined over time due to the plant's natural curve. The increase in biomass is more prominent to tropical and boreal areas which in general have soils with less nutrients. More specifically patterns indicate that increased growth was connected to the
limitation of phosphor. However northern temperate zones with low phosphorus content did not grow. Possible explanations are low nitrogen content or low phenolic content. Further on
increase on growth was found more on angiosperms than conifers. A possible explanation to this is that conifers have a lower nutrient uptake and are adapted to areas with low nutrients and temperature. Variability between studies is however high due to several factors such as pyrolysis conditions and char (Thomas & Gale 2016).
6 Results
In the current situation, the use of biochar is limited to the available production in the area. According to the interview with Britt-Marie Alven, garden waste used for the production of biochar is not sufficient for their use. Currently, Stockholm Stad has the use of biochar important to create a functioning cycle to deal with gardens and even has a positive effect in reducing carbon dioxide emissions. In several studies the rich lignin wood used as a main source of biochar. This is probably highly related to the effect that lignin rich feedstock would help in increase in char yield during the pyrolysis process (Deb 2016). However, the use of different sources of biochar could be important to be available. According to Novak (2017), different sources of biochar have different effects depending on the soil deficiencies. Therefore, a varying way of producing biochar can be seen to be important to meet specific conditions.
From case studies observed, some effects were contradictory to each other. The effect of nitrogen retention was not observed in some studies while nitrogen has been effectively related with biochar in others. This indicates furthermore on how differences in soil conditions, type of crop, source of biochar or climate are essential to indicate how biochar would reflect on the crop growth. The complexity of biochar creates difficulties in consistently creating biochar with the same properties due to for example changes in weather. From the field studies, nitrogen retention seems to be more significant in studies in Sweden. Stockholm Stad includes a higher amount of nitrogen content to Stockholm trees in the supplied nutrients, as shown in table 2. Both the field
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studies in Borrby and Skåne reveal a higher effect of nitrogen when combined to the soil than the observed international studies, see table 3 and 4.
As mentioned, biochar performance as a soil amending tool varies highly. However, biochar seems to work most effectively on soils with poor nutrition as is shown in the case studies in India and northern Germany. However, in the meta-analysis by Simon (2017) it was conducted that biochar had a negative impact on yields in temperate zones. Which is contradictory to previous results from other studies such as the one in Northern Germany. The possible explanation for this is that biochar was applied to temperate soils with already high nutrient content and moderate pH. Leaving little room for improvement and increasing pH above optimal levels. This indicates that biochar should only be applied to soils with poor nutrient content and/or acidic soils. Grain crops and root crops were found to have the most effects according to Deb (2016). In Sweden much of agriculture consists of growing grain crops which should give biochar an advantage especially in combination with nutrient poor soil.
In the study performed by Deb et al. (2016), it was found that biochar by itself did not increase crop yields only when it was combined with PSM. However, PSM was not mentioned in other studies researched and yet increases in crop yield was found. Possibly PSM was applied and not mentioned or PSM is not necessary on certain soils. The factors which affect biochar effects are many and therefore studies regarding biochar demand extensive information on the methods used. For example, the biochar properties, pyrolysis conditions, soil type and climate just to mention a few.
Biochar can however play a bigger role in Sweden by applying it in forestry due to Sweden's large volume of forest biochar has a big potential. Even though biochar applied to forests found larger increases in growth on boreal and tropical areas. Temperate zones still showed an increase in growth as well as Swedish trees in an urban setting. As showcased with the case study in Indonesia wood residue from the forest can be taken and applied to the forest to function as a carbon sink, simultaneously increasing the growth of the Swedish forest. A possible
improvement for the Swedish forest as a carbon sink could be the addition of coppicing methods as seen in the case study in Australia. Coppicing method of trees proved efficient as a carbon sink due to the carbon being stored in the coppice. This could be applied into Swedish forestry in combination with biochar to increase the carbon sink. Large quantities of wood residue is
available in Sweden, however complications may arise from removing wood residue from one area and applying its biochar to another thus removing nutrients from one area and applying it to another. Research regarding biochar use in forestry is limited and more research is needed for a more definite answer. Biochar should first be tested on Swedish forest to control its effects due to the nature of biochar varying results. If it does not prove effective on Swedish forestry wood residue can still be taken for the production of biochar if it proves effective on agriculture. Biochar in an urban setting has also positive effects by increasing tree growth; it further increases air quality and cooling effects on cities.
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7 Conclusions
Biochar presents varying results in all sectors studied due to the different conditions where it is applied. This motivates more in depth understanding of how biochar usage is affected by these factors so that biochar can be customized depending on usage. This will allow further usage in the Swedish market and possibly motivates further actors to take advantage of biochar.
Currently, there are 12 institutes in Sweden that are responsible for the production of biochar and the usage is determined by the production in that region. Due to the varying effects in different conditions as in crop type, soil type, and climate can it be an important factor for the producers to provide a customized supply of biochar. The supplier could customize their biochar by changing the feedstock and the pyrolysis method used.
Generally, biochar has shown positive effect in the field study performed in Skåne and Borrby. According to studies, biochar seems to function at best on low quality soils concerning
agriculture. Biochar should therefore be tested on Swedish soils with poor nutrients content and high acidity. Regarding forestry, biochar seems to be most efficient in tropical and boreal zones despite that biochar has proven to be effective on Swedish trees in an urban environment.
Biochar should therefore be tested on Swedish forest because of the high quantity of forest in the country a large opportunity exists for biochar on Swedish forest. Different types of available and affordable biochar should be tested on Swedish forestry and agriculture to test their effects.
8 Future work
More studies regarding biochar's effect on forestry should be studied too due to the lack of research in the area. The information can prove to be more beneficial in countries with high % of landmass covered by forest such as Sweden. Biochar's different effects on different factors such as soil type, crop type and pyrolysis condition need further study to best tailor or have a
functioning biochar. This is encouraged through performing studies that experiments on changing a single factor and keeping other factors. An example is experimenting the same soil and biochar type with different crop types. This will allow a further understanding of the different factors individually.
Due to the importance of the factors regarding the application of biochar scientific papers should contain information regarding the origin, application and preparation of the biochar used in the research. This would help unravel the complexity of biochar by being able to research biochar's effects on different factors. PSM combined with biochar research was also scarce and should be further researched.
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