Use of Biochar in Organic Food Production and Effects on Missouri Soils

Transcription

1 Use of Biochar in Organic Food Production and Effects on Missouri Soils What is biochar? By: M. R. Bayan, Environmental geochemist and soil scientist Biochar is one of the oldest soil amendments. A soil amendment is a product that when properly applied improves soil quality and fertility. Biochar is essentially charcoal that is produced in a special way from heating the air-dried plant material (biomass) in an oxygen depleted environment. The longevity of biochar in the soil environment and its effectiveness as a soil conditioner is directly influenced by the way it is produced. Normally, a biochar that is produced at highest treatment temperature (HTT) values above 750 degrees Fahrenheit (400 degrees Celsius) is superior to a char that is produced at a lower HTT value (Downie, et al., 2009; Bayan et al., 2014). The charcoal that is produced at a higher thermal value has more total pore space and is safer to use than a charcoal that is produced below 570 degrees Fahrenheit (300 degrees Celsius). When used properly, biochar has the ability to improve soil quality and promote plant growth resulting in better yield. Biochar can store moisture and nutrients in the soil environment. A properly produced biochar also provides an optimal environment for growth of necessary microorganisms that play a significant role in nutrient cycling within the soil environment. Biochars are not the same and they can be roughly classified based on their biomass feedstock precursors and the way they are produced (HTT, rate of heating, and exposure time to HTT). An impartial laboratory that is certified and specializes in testing products such as black carbon should test biochars before they are incorporated into topsoil. In the absence of any regulation involving biochar and its safe use, consumers should at least make sure vendors provide a legitimate certificate issued for their biochars from the International Biochar Initiative (IBI). The IBI is a nonprofit organization that disseminates information about biochar and can be accessed at When used properly, biochar has the ability to enhance soil quality by improving soil chemical, physical, and biological properties. As a result, it increases plant growth and yield. When biochar is produced properly, and applied to a soil that is in need of amendment, it may reduce use of agrichemicals in food production. A charcoal that is produced through torrefaction process (explained later) is not considered biochar in this fact sheet; it is referred to as simply a char. A char that has not been produced properly through the pyrolysis process may not be safe to use as a soil amendment. This fact sheet intends to provide information about biochar and its safe use 1. To better understand the potential of biochar use in agriculture and industry we start with a brief review of carbon in the environment. Carbon in our environment Carbon is a chemical element that has been known to man for over five millennia. It is the key element of all living cells. It occurs in all parts of the environment; the rocks, the water and the air. In rocks, it mostly exists in the form of calcium carbonate (limestone), in the fresh water as carbonate ion and in the 1

2 air as carbon dioxide (CO 2 ). Plants use the Sun s energy, carbon dioxide from the air and water and nutrients primarily from the soil to produce food, feed and fiber through a process called photosynthesis. During the history of planet Earth, a great deal of carbon dioxide was removed from the air especially in the Carboniferous period that ended about 300 millions ago and lasted for 60 million years; burial of the plants through geologic processes produced today s coal deposits. It should be made clear that coal is not biochar and its properties are far different from those of biochar. The carbon dioxide level in the atmosphere has varied over time. In recent years, however, it has been increasing. The overwhelming majority of the climate scientists believe that human activities are to be blamed for much of the increase in atmospheric CO 2. Carbon content of biomass versus the carbon content of biochar The carbon content of biomass varies between 45 to 50% (oven-dry basis) (Schlesinger, 1991). Biochar has higher carbon content than biomass. A biochar that is produced at 750 degrees Fahrenheit and higher always consists of higher carbon than a biochar that is produced at lower HTT values (Bayan, 2014a). Although biochars that include more carbon have better quality and are more recalcitrant in the soil environment (better soil amendments), it is the ratio of their hydrogen to carbon that is used to classify their quality (Krull, et al., 2009). Normally biochar from herbaceous feedstock (for example, switchgrass and giant miscanthus) rank higher than the ligneous (woody) biochars (when produced through similar pyrolysis processes) in terms of their hydrogen to carbon ratio. But, the H:C ratio of some biochars produced from woody plants such as willow trees come fairly close to match those of the herbaceous biochars that are produced under the same thermal conditions (Bayan, 2014a). Are all biochars the same? Obviously not! The biochar quality is affected by the following parameters: 1. The biomass precursor that biochar is produced from. 2. The pyrolysis conditions in which biochar is produced. Pyrolysis refers to the process of heating the biomass in an oxygen deprived enclosure to produce biochar. There are different types of pyrolysis based on the: 1. Rate of heating; 2. The highest thermal treatment (HTT) in the chamber; 3. How long the biomass is allowed to stay in the pyrolyzer at the HTT. 3. Handling of the biochar after production; for example, was biochar exposed to water, residues from other processes, etc. When purchasing biochar, you should demand a certificate that is issued by the International Biochar Initiative (IBI) which is a non-profit international organization of scientists and biochar producers and enthusiasts. To ensure the safety of their product and to improve the quality and effectiveness of biochar for agricultural use, the emerging biochar industry normally has no issues applying for a certificate through the IBI. If biochar is not produced properly, it can pollute soils with compounds such as PAHs (polycyclic aromatic hydrocarbons), dioxins and furans, heavy metals, etc. The test should clearly indicate the level of PAHs listed in the footnote 1 of this fact sheet in addition to the metal element contents such as arsenic, cadmium, lead, chromium, manganese, mercury, nickel, vanadium, etc. There might be other sources of pollution depending on the precursor biomass that is used for biochar production. If pure lignocellulosic biomass is used (without plastic or rubber contaminants) the resulting 2

3 biochar should be safe when produced through slow pyrolysis but there are times that biochar is coproduced with other products that might introduce undesirable levels of contaminants to the final product. A safe technique to produce your own biochar will be discussed later in this fact sheet. How does biochar work in the soil environment? During the past few years, biochar has been the focus of many scientific investigations. From what we know: All biochars that are produced through the slow pyrolysis include some nutrients immediately after their production. Normally, herbaceous biochars include more nitrogen than the ligneous biochars. The nutrient content of biochars, however, is not enough to sustain plant s optimal growth during it life cycle (Bayan, 2014ab). Therefore, biochar is not considered to be a fertilizer. All biochars contain some mineral matter (ash). The ph of water-saturated samples of all biochars produced through the slow pyrolysis from biomass that is available in Missouri is in the alkaline range (Bayan, 2014ab). This alkaline ph helps increase nutrient availability in low ph soils. All biochars have a higher specific surface area than their biomass precursors. The pores in biochar retain water and nutrients and provide optimal conditions for beneficial microorganisms to grow especially when biochar comes into contact with growing roots. The pore volume of biochar is affected by the way it is produced (Bayan et al., 2014). All biochars have surface charges at lower ph values that make them capable of retaining certain nutrients such as potassium, calcium, magnesium, etc. (Bayan, et al., 2014). All biochars are capable of retaining water in their cavities. This can help plants cope with adverse effects of drought when grown on a soil that is treated with biochar (Joseph, et al, 2009). Biochars do not denature soil enzymes and do not reduce soil enzyme activity in the long-run; therefore, biochars do not have a negative effect on nutrient cycling in the soil environment (Bayan, 2013b). Biochars are capable of retaining some nutrients preventing them to be lost to moving water or air in the soil environment. This may reduce fertilizer use to achieve maximum yield. Preparation for application Biochar should be crushed to pass a 1-centimerter (about 3/8 of an inch) sieve before its application to soil (Figure 1). The herbaceous biochar strands may have a length averaging about 3/8 of an inch before application to soil. Figure 1. Biochar should be crushed before it is mixed with soil 3

4 How to apply biochar to soil Biochar should be mixed with the top cm (6-8 inches) of soil. To maximize its amending effects, biochar should not be broadcast over the soil; it should be tilled or disked into the soil (Figure 2). Before Biochar Application 60 Days after Biochar Application Figure 2. Biochar should be mixed with the soil. It improves soil structure by promoting aggregate formation. (Photos: M.R.B). Effect of biochar on plant growth When applied properly to the soil, biochar promotes plant growth and increases yield (Bayan, 2014b; 2013a; Vaccari et al., 2011) (Figures 3 & 4). The secret to a successful crop production involving biochar is a good understanding of both soil and biochar, in addition to other factors involved in plant growth. Is it possible for biochar to reduce plant growth and decrease yield? The answer is yes. For example, if biochar is used at higher rates than necessary, it has the potential to negatively affect plant growth. If biochar is applied to a soil with high ph and electrical conductivity it has the potential to reduce yield if water is a limiting factor. Therefore, the beneficial effects of biochar can be reaped when the farmer develops soil and crop management techniques based on a good knowledge of biochars, soils and the needs of agronomic and vegetable crops. Figure 3. Soybean growth and yield increased significantly by 2% application of giant miscanthus biochar in this greenhouse experiment (Bayan, 2013a) Figure 4. Biochar application to soil improved root growth and nodulation in soybean plant. Roots grew toward and surrounded the biochar pieces to absorb water and nutrients (Bayan, 2013a) 4

5 Application rate Biochar is a soil amendment meaning that it works well when the soil is in need of an amendment. When biochar is applied to a high quality soil, its benefits may not be apparent. The optimal rate of biochar for the soils in central Missouri is between 2% to 4% by weight. At the rate of 2% biochar, the application rate to a depth of 15 cm (6 inches), on a soil with the bulk density of 1.3 g/cm 3, is 17.4 short tons per acre. At this rate, 800 lbs of biochar is needed for every 1000 ft 2 of land. There is no need for biochar application to a Mollisol (soil that is high in organic matter content and base cations) even though application rates less than 2% should not lower yield when biochar is applied to a Mollisol. Vertisols are another order of soils that exists in a few counties in Missouri (Mississippi, New Madrid, Pemiscot and parts of Scott and Stoddard). Due to high ph and base saturation in Vertisols, application of biochar may initially increase the osmotic pressure in the rhizosphere causing plasmolysis of meristematic plant cells. The biochar could be rinsed thoroughly before it is applied to Vertisols. Biochar lowers soil bulk density and improves hydraulic conductivity; therefore enhancing the quality of soils with a claypan (a clayey layer within the soil profile that is compact and impervious). The following soils in Missouri will benefit from biochar use: Most Entisols (soils that are young or recently formed), Inceptisols (more weathered soils than Entisols and show some degree of horizon formation), Alfisols (more developed soils than Entisols and Inceptisols and form under deciduous trees although could have been cultivated after formation), Ultisols (more highly weathered, older soils, more acidic than Alfisols). For a description of these soil orders refer to the Cooperative Soil Survey at: Spot application of biochar Biochar can be applied to a 4 ft 2 area of soil before transplantation or seeding. Use a spade or shovel to remove soil from a 4 ft 2 area to a depth of 6- to 8-inch and transfer the soil into a wheelbarrow. Mix biochar (3.5 lbs) with the soil in the wheelbarrow thoroughly before backfilling the pit with the soil mixture from the wheelbarrow (Figure 5). Figure 5. Spot application of biochar before and after tomato transplantation and mulching. (Photos: M.R.B). Effect of biochar on water retention by soil Biochar will retain water in its pores but before it could do so it has to be soaked with water for a length of time. When applied to the soil, the dry biochar is hydrophobic but after a period of about a month, its pores become saturated with water and can serve as a temporary water reservoir that plants will benefit from at the time of drought. In a greenhouse experiment involving soybean as a test plant, the %5 application rate of biochar reduced water consumption significantly as compared to the control pots. The herbaceous biochars stored more water than the ligneous biochars. At 2% application rate, no significant reduction in water consumption was noticed over the control. When biochar is used to cope with the negative effects of drought on plant growth, biochar should be applied at its maximum recommended rate of 4% by weight for soils in Missouri (except for Mollisols and Vertisols) (Bayan, unpublished data). 5

6 Can biochar be activated? Yes, biochar can be modified after its production by additives or further chemical treatments. Furthermore, biochar can be produced to address specific needs; agricultural, industrial, or environmental in nature. It can be mixed with organic amendments (such as compost or manure). This is particularly helpful in organic farming and vegetable production. To accomplish this, biochar can be mixed with compost or manure. We have had good results with the following compost and biochar mixture rates for tomato plants: Three quarts (about 3 liters) of good quality compost is mixed with 3.5 pounds (1.6 kg) of crushed biochar. This compost/biochar mixture is then added to soil that is removed from a 4 ft 2 of ground (to a depth of 6 inches) in a wheelbarrow. Backfill the pit created by removal of soil and plant seedling at the center of the application area. Cover the soil with mulch and water as necessary. This mixture should work with other vegetable crops. Do not use biochar around acid loving plants unless it is thoroughly washed to remove alkalinity. The relationship of biochar to bioenergy production The process that produces biochar (pyrolysis) also produces bioenergy in the form of biogas and biofuel. The non-condensable gases that are produced through pyrolysis consist of carbon monoxide, methane, ethane, hydrogen and others. Fast pyrolysis of biomass generates lower biochar than slow pyrolysis. The pyrolysis process therefore can be fine tuned to produce different proportions of byproducts, solid (biochar), gaseous (biogas) and liquid (tarry substances). The slow pyrolysis produces more biochar but less biogas or liquid substances. How to build a slow pyrolyzer Before we describe how a simple pyrolyzer can be fabricated we will talk a little about types of pyrolysis of biomass. Remember that pyrolysis involves thermal decomposition of biomass in an oxygen deprived environment. Three products of this decomposition are: gas, condensable vapors (source of bio-oil) and biochar. In a similar but different process called torrefaction, charcoal is produced in some regions of the world such as in Caucasus, Central Asia, and in the Middle East. We should distinguish between torrefaction and pyrolysis. What is torrefaction? Torrefaction is slow heating of biomass (less than 120 degrees Fahrenheit per minute that is <50 C min -1 ) in an oxygen deprived environment between 400 to 570 degrees F (not exceeding 570 degrees) ( C). This process produces charcoal that resembles biochar; it has many of the characteristics of biochar but it lacks the potency of biochar and may contain pollutants such as PAHs, furans and dioxins (see footnote 1 ). Charcoal that is produced through torrefaction helps plant growth and has positive effects on soil properties but there is the risk of pollutants that it may include. Furthermore, its half-life in soil environment is not as high and its chemical and physical properties are not as enhanced as the biochar produced through pyrolysis. The product of torrefaction of woody (ligneous) biomass produced in some regions of the world (Caucasus, Central Asia, and Middle East) is called charcoal and is used primarily for heating purposes (and for cooking purposes). Do not confuse this char with biochar. For further information about torrefaction see Shankar Tumuluru et al. (2011). 6

7 What is Slow Pyrolysis? Pyrolysis involves heating of the biomass feedstock in an oxygen deprived environment to thermal values above 750 degrees (400 degrees Celsius). This may sound like an arbitrary thermal value but it is a safe one. The quality of biochar is affected by the biomass feedstock; our experiments indicate that for example, willow biochar acts differently from the oak or pine biochars. There are two major types of pyrolysis: 1. Slow Pyrolysis; 2. Fast Pyrolysis. Torrefaction is excluded from this list altogether although some refer to torrefaction as mild pyrolysis (see Shankar Tumuluru et al., 2011). Facts about Slow Pyrolysis: Has been used for thousands of years and is still in use around the world. Feedstock is air-dried and chopped or shredded into smaller pieces before pyrolysis. Normally cedar or small part of the load is combusted for the initial heat input. The biomass is exposed to heat over a long period of time and is exposed to highest thermal treatment (HTT) for longer time (for example, over 30 minutes to hours). The rate of heating (how fast the temperature increases) is slow and the entire process may take over 6 hours or longer. The biomass is exposed to thermal energy ranging from F ( C). More biochar is produced (in our experiments between 25 to 31% of the original air-dried weight of the biomass). Facts about Fast Pyrolysis: The biomass is exposed to HTT of about 900 degrees F (about 500 C, or higher) for seconds. The rate of heating is fast and the entire process will take minutes to complete. Biomass must be dried (less than 10% moisture) and reduced in size (1/16-1/8 inches, mm) before pyrolysis. As compared to slow pyrolysis, less biochar is produced (about 12% of the original weight of the biomass). 60 to 75% of the biomass weight is converted into oil. Double barrel pyrolyzer The following is an improvement over the double-barrel designs available on the Internet. 1. A 85-gallon outer Steel Drum, Cam Lock Closure Included (about $209 each) (approximately 321 liters, 59 cm in diameter, 23.5-inches) with lid. Cut out a 4-inch (10.2 cm) circular portion of the lid. 2. A 30-gallon inner Steel Drum, Cam Lock Closure Included (about $138 each), (approximately 114 liters, 49 cm in diameter, inches). (Figure 6). 3. Galvanized Gas Vent, 4-inch by18-inch (10.2 x 46 cm), (about $9.98). 4. Galvanized Hood Connector (about $7.68). 5. Trim coil (about $25). 24 x 50 at $96.99 per roll. (One quarter roll used per unit). 6. Homesaver Flexwrap Insulation. 1 x 24 x 50 at $187 per roll. (Half roll used per unit). 7

8 Figure 6. The inner drum fits inside the outer barrel leaving enough space for initial woody fuel (photos: M.R.B.) The 85 gallon drum can be cut down from 38.5 inches in height (98 cm) to 31.5 inches (80 cm) for easier handling. Air intake holes 9/16-inch (1.4 cm) in size should be drilled 4 inches (1.2 cm) from the bottom of the outer barrel on a line every 6 inches. Note that 9/16-inch in size holes (for outgassing of the biomass) should be drilled on the lid of the 30 gallon drum. These holes will let the gases to be released from biomass to enter the larger drum to burn out sustaining the pyrolysis process until its completion. Also note the small drum positioned with its lid facing down in the larger barrel. The 30-gallon barrel is filled with air-dried chopped or shredded biomass and then inverted inside the 85- gallon barrel and centered. The space between the smaller barrel and the larger barrel is filled with dry wood (preferably cedar) and ignited. The lid is positioned on the top of the larger barrel and secured. The stack is then positioned on the top covering the circular hole. This pyrolyzer will produce approximately 18 to 24 lbs (8-11 kg) of biochar from 60 lbs (27 kg) of dry wood. The design will consist of an optional thermocouple equipped with type K probe and an inch thick fiberglass blanket wrapped and secured by sheet metal (aluminum) to insulate the outer perimeter surface area of the larger drum. A cyclone effect pulls the air through the lower and upper holes in the larger barrel resulting in a clean combustion producing heat (>400 C). The heat pyrolyzes the biomass in the inner barrel. The combustible gases that escape from the biomass will also burn cleanly and sustain the temperature between 400 and 600 C. The process would be complete in a few hours. Other uses of biochar In recent years biochar has been used for purposes other than a soil amendment. In addition to its agronomic values, scientists and engineers are finding novel values for biochar. For example, biochar is now being used in poultry industry as a disease and odor control agent and livestock farming as a feed supplement, and in metalworking as a reducing agent. Biochar is being used to clean water and to absorb odor. It is used in batteries and as building material. A Swiss biochar scientist, Dr. Hans-Peter Schmidt (2014) has found 55 uses for biochar and counting. The economic relevancy of biochar system What is a biochar system? A biochar system is based on the use of biochar in agriculture and industry for cost effective production and to promote sustainable use of resources while safeguarding the environment (Lehmann and Joseph, 2009). Can a biochar system contribute to economic growth? The biochar system can lead to economic growth if biochar itself is produced sustainably as a co-product of the bioenergy production from the biomass. Therefore, ideally biochar production should be seen as part of a larger design that includes biochar as one of its products but not the sole product. As biochar finds more uses in agriculture and industry, its value will increase. The biochar industry, however, will succeed when biochar systems are custom tailored for a region based on region s specific needs and biochar is produced sustainably as a carbon negative practice. 8

9 What is a carbon negative practice? When the biomass (e.g. in the swamps) were buried due to cataclysmic events in the past history of planet Earth, the nature practiced a carbon negative act! The carbon from the atmosphere was sequestered through photosynthesis and, as an essential component of biomass, was buried in the earth for good. Although biochar properties are completely different from those of coal, when biochar is mixed with the topsoil (15 to 20 cm), the carbon is effectively removed from the atmosphere and buried in the soil helping plants grow better. The biochar can persevere in the soil for hundreds of years. What is a carbon positive practice? Any practice that involves combustion of carbon that has already been permanently removed from the atmosphere and buried in the earth (such as coal and hydrocarbons) is a carbon positive practice. What is a carbon neutral practice? When a tree or parts of it die, the fallen parts disintegrate, decompose and eventually change into carbon dioxide that is returned into the environment. In other words, the carbon that was temporarily removed from the atmosphere by photosynthesis is returned back to the atmosphere in a short span of time. Hence, in the atmospheric carbon budget there is no net change. This is an example of a carbon neutral process. When people burn the wood in their fireplace, they exercise a carbon neutral practice. When biochar is made in a double barrel pyrolyzer as explained above, minimal amount of biomass is combusted to start the pyrolysis process, the combusted biomass here is carbon neutral but the resulting biochar, if mixed with the soil, constitutes a carbon negative practice. A biochar system normally includes all these process but the net result is carbon negative. Acknowledgement The author is thankful to USDA for supporting his research project: Characteristics of Biochar Produced from Different Feedstocks and Effects on Soil Physicochemical and Biological Properties (MOX- BAYAN). Some of the findings of the project are included in this report. References ATSDR (1995). Public Health Statement for Polycyclic Aromatic Hydrocarbons (PAHs). Bayan, M.R., Sinkarev, A.A, Grigoryan, B.R., Liang, X. (2014). The Specific Surface Area and Pore Volume of Charcoals Prepared from Various Herbaceous and Ligneous Feedstocks through Torrefaction and Pyrolysis. nference%20agenda.pdf Bayan, M.R. (2014). Elemental Analysis of Biochar Generated from Herbaceous and Ligneous Biomass (in review). Bayan, M.R. (2014c). Effect of Biochar from Herbaceous and Ligneous Biomass Feedstocks on Soybean Growth and Nodulation. Journal of Negro Education. (In Review). Bayan, M.R., Valeyeva, A.A., Grigoryan, B.R. (2014). Sorption of Methylene Blue by Charcoal Produced through Torrefaction and Slow Pyrolysis from Switchgrass. (Abstract). Midwest Biochar Conference. Champaign, Illinois. August 8, da.pdf Bayan, M.R. (2013a). Biochar effects on soybean growth and nodulation. June 14, Champaign, Illinois Organized by IBG, ISTC, and USDA. Bayan, M.R. (2013b). Long-term effects of biochar on select soil enzyme activities June 14, Champaign, Illinois Organized by IBG, ISTC, and USDA. 9

10 Downie, A., Crosky A., Munroe, P. (2009). Physical Properties of Biochar. In: (J. Lehmann and S. Joseph, editors), Biochar for Environmental Management Science and Technology. Earthscan, Washington, DC. Pages: EPA (2008). Polycyclic Aromatic Hydrocarbons (PAHs). Office of Solid Waste Washington, DC January Joseph, S., Peacocke, C., Lehmann, J., Munroe, P. (2009). Developing a Biochar Classification and Test Methods. In: (J. Lehmann and S. Joseph, editors), Biochar for Environmental Management Science and Technology. Earthscan, Washington, DC. Pages: Krull, E.S., Baldock, J.A, Skjemstad, J.O., Smernik, R.J. (2009). Characteristics of Biochar: Organo-chemical Properties. In: (J. Lehmann and S. Joseph, editors), Biochar for Environmental Management Science and Technology. Earthscan, Washington, DC. Pages: Lehmann, J. and Joseph, S. (2009). Biochar Systems. In: (J. Lehmann and S. Joseph, editors), Biochar for Environmental Management Science and Technology. Earthscan, Washington, DC. Pages: Shankar Tumuluru, J; Sokhansanj, S.; Wright, C.T.; Boardman, R.D.; Hess, J.R. (2011). Review on Biomass Torrefaction Process and Product Properties and Design of Moving Bed Torrefaction System Model Development ASABE Annual International Meeting, Louisville, Kentucky, August 7 10, INL/CON PREPRINT Schlesinger, W.H. (1991). Biogeochemistry: An Analysis of Global ChangeAcademic Press, San Diego. CA (1991). Schmidt, H-P (2014). The use of biochar as building material cities as carbon sink. Ithaka Institute for carbon intelligence. Journal of ecology, winegrowing and climate farming. Vaccari, F.P; Baronti, S.; Lugato, E.; Genesio, L.; Castaldi, S; Fornasier, F; Miglietta, F. (211). Biochar as a strategy to sequester carbon and increase yield in durum wheat. European Journal of Agronomy. 34: Polycyclic aromatic hydrocarbons (PAHs) are a group of chemicals that form in all type of processing of organic carbon sources such as lignocellulosic biomass. This type of biomass includes trees, shrubs, grasses, manure, et cetera. PAHs are hazardous chemicals (EPA 2008). PAHs are hazardous carcinogenic chemicals. Furthermore, they are recalcitrant meaning that they persevere in the soil environment. Charcoals that are produced through torrefaction may enhance soil fertility and promote plant growth but they may reduce the soil quality by their PAHs content (Bayan, 2014). The federal government has set regulations to protect people from the possible health effects resulting from exposure to PAHs through eating, drinking, or breathing (ATSDR, 1995). In a study this author found that the PAHs content of charcoal was reduced significantly as the production temperature increased. Table 1 shows the results of PAHs analysis. The PAHs content refers to the sum of the following PAHs: naphthalene, acenaphthhylene, acenaphthene, fluorine, phenanthrene, anthracene, fluoranthene, pyrene, benzo (a) anthracene, chrysene, benzo (b) fluoranthene, benzo (k) fluoranthene, benzo (a) pyrene, indeno (1,2,3,c,d) pyrene, dibenz (a,h) anthracene, benzo (g,h,i) perylene. Table 1. PAHs content of charcoal produced from three biomass feedstocks through torrefaction and slow pyrolysis. Biomass Torrefaction Slow Pyrolysis Torrefaction/Slow Pyrolysis C mg/kg C mg/kg Corn stover Switchgrass Willow The charcoal produced through torrefaction of corn stover included 35 times more PAHs (18 mg/kg) than the biochar produced through slow pyrolysis from the same biomass between 400 and 600 degrees Celsius (0.41 mg/kg). According to ATSDR (1995), PAHs are present in tobacco smoke, smoke from wood fires, creosote-treated wood products, cereals, grains, flour, bread, vegetables, fruits, meat, 10

11 processed or pickled food, and contaminated cow s milk or human breast milk. Food grown in contaminated soil or air may also contain PAHs. Cooking meat, or other food, at high temperatures, which happens during grilling or charring, increases the amount of PAHs in the food (ATSDR, 1995). Combustion of fossil fuels also involves production of these chemicals. More Information about Biochar: Biochar. Center for Sustainable Environmental Technologies. Iowa State University. Biochar is an investment in soil. Iowa State Daily. Illinois Biochar Group. Biochar News. Sadaka, S., Boateng, A. A. Pyrolysis and Bio-Oil. University of Arkansas Division of Agriculture. FSA Schahczenski, J. (2010). Biochar and Sustainable Agriculture. National Sustainable Agriculture Information Service. 11