Key words

biochar; pyrolysis; kilns; organomineral complexes; wood vinegar; NPK fertilizer

6.1 Introduction

The International Biochar Initiative defines biochar as:

The properties of biochars are dependent mainly on the chemical and physical properties of the feedstock and on the final heat treatment temperature (Rajkovich et al., 2011). The properties are also dependent to a lesser extent on the rate of heating, the kiln pressure and atmosphere, and the type of pre- or post-treatment (Amonette and Joseph, 2009). Recent papers by Singh et al. (2010), Rajkovich et al. (2011), Kookana et al. (2011) and Uchimiya et al. (2011) have summarized a large amount of the published data on the characteristics of biochars.

Biochars can be divided into three broad categories (Joseph and Lehmann, 2009). The categories are:

For each of these feedstocks the initial moisture content and particle size can alter the final properties of biochars.

Recent research suggests that for a given feedstock and heating rate, there is a significant difference in the physical and chemical properties of biochars depending on whether they are produced between (±50°C) 300–400°C, 400–500°C, or >500°C. There is also a considerable difference between biochars made from woody materials and those made from crop residues, manures and sludges. It should be noted that biochars made from paper sludge and chicken manure that have high contents of calcium compounds can have quite different properties from biochars made from other high mineral ash materials (Enders et al., 2012).

Research undertaken by Singh et al. (2010), Rajkovich et al. (2011) and a review by Kookana et al. (2011) indicate that biochars made at temperatures lower than 400–450°C have a higher concentration of oxygenated functional groups, radicals, water and organic soluble compounds that can improve germination, stimulate microbial growth and induce systemic resistance and hormesis (beneficial response to low dose of toxin) (Graber et al., 2010; Elad et al., 2010). Compared with biochars made at above 450°C, these biochars have a lower pH, higher adsorption of ammonia (especially bamboo), but lower adsorption of most other gases (Mingjie, 2004), relatively low water-holding capacity (Krull, 2010), and little loss of metals and non-metals due to volatilization (Enders et al., 2012). The electrical conductivity can be higher or lower depending on feedstock and temperature (Shinogi, 2004; Singh et al., 2010). The ability to adsorb heavy metals depends on the type of biochar.

Biochars produced from crop residues and grasses between 400 and 500°C have a high CEC and water-holding capacity. This could be partly attributed to the clay attached to the feedstock (Krull, 2010). There appears to be considerable concentration of organic compounds and acid and basic functional groups on the surfaces of wood biochars until reaction temperatures exceed 450°C (Singh et al., 2010). However the type and concentration of functional groups appear to be different between high and low mineral ash biochars and between different time and temperature regimes for producing the biochars. Considerable increase in surface area, pore volume and mesoporous area occurs for most woody biochars although not necessarily for high mineral ash biochar once the final pyrolysis temperature exceeds 450°C. Fellet et al. (2011) found that biochars produced from orchard prunings at 500°C can adsorb significant concentrations of some heavy metals. For woody biochars produced above 500°C but below 600°C, there is high adsorptivity of some organic molecules (McLaughlin et al., 2009), high surface area and volume of sub-100 nm pores (Downie et al., 2009), high volume of pores above 100 nm, high stability and degree of condensation, and high pH.

16.2 Effects of application of biochar to soil

Once biochars are placed in soil, their physical and chemical properties undergo complex changes. A recent review by Joseph et al. (2010a) and Lehmann et al. (2011) detail the possible reactions. Important findings are summarized in the following discussion. When biochars with a high concentration of soluble minerals and oxygenated organic molecules on their surface are added to moist soil (or are followed by a rain event) there is a change in the pH, EC, and Eh (reduction or redox potential) around the particle, probably within the first week, as the minerals dissolve and/or ions are exchanged on the surfaces of the surrounding clay particles.

Rain events can result in soil colloidal particles migrating into the pores of the biochar and reacting with the carbon surface to produce biochar-organomineral complexes (Fig. 16.1). The limited data available indicate that the type of reactions taking place and the stability of the compounds retained on the surface depend on the type of biochar and the conditions under which it was produced (Spokas and Reicosky, 2009; Nguyen et al., 2010). Any significant reaction involving the biochar, the soil minerals and dissolved organic matter could lead to a substantial change in the properties of the biochar (e.g., pH and EC).

When biochars produced at low temperatures are added to moist soils, a considerable quantity of soluble organics can be released to the soil solution. As noted by Graber et al. (2010), Dixon (1998) and Light et al. (2009), some of the labile organic compounds on the surfaces of biochar can stimulate seed germination, growth of fungi, nutrient uptake and reduction in pathogens.

Enhanced CO₂ emissions can be observed during the first months after biochar has been added to soil. These enhanced emissions are partly attributed to biochar surface oxidation that has both a chemical and biological basis. It is possible that the mineral matter in the biochar and the water-soluble organic compounds on the external and internal surfaces provide nutrients for microorganisms to grow faster as well as catalysing the breakdown of organic matter (Amonette et al., 2006). It is also possible that chemical oxidation occurs when there is a large difference in electrochemical potential between the different mineral and carbon regions in an individual particle.

Surface oxidation of biochars increases the potential for hydrophilic interactions with a range of soil organic and inorganic compounds. This is more significant in high mineral ash biochars (Lima and Marshall, 2005). Greater reactivity of biochars with mineral matter could further promote physical protection of biochar and labile organic matter, and thus long-term stability (Brodowski et al., 2006; Keith et al., 2011). Once roots, and in particular their root hairs, interact with the biochars, a wider range of reactions can occur, through the uptake of nutrients by the plants, and the release of root exudates. This enhances both complexation reactions and microbial activity in the rhizosphere. Over a period of time, physical disturbances, interactions with microflaura and microfauna, and complex abiotic and biotic reactions with all soil constituents, will break larger biochar particles into smaller pieces and lead to the formation of biochar organomineral aggregates (Joseph et al., 2010b).

16.3 Agricultural uses of biochar

The Australian Aborigines may have been the first people to produce biochar in order to increase the food available to them (Bird et al., 2008). Fire-stick farming included lighting smoky fires when grass and scrub was moist to produce high concentrations of biochar, which increased the growth of green shoots that in turn attracted the kangaroos. Aborigines likewise used fire to promote the growth of edible tubers (Jones, 1968). Aborigines in the South East of Australia also made oven mounds that comprised charcoal, minerals, organic matter and clay.

Amazonian dark earth (ADE) has been studied over the last 20 years. These soils consist of particles that have a very heterogeneous phase structure consisting of a high carbon material (probably derived from the weathering of charcoal made in open fires) surrounded by mineral phases that include clay, calcium carbonate, calcium phosphate, calcium hydroxide, potassium and sodium chloride, iron oxides and titanium dioxide. These mineral and high carbon phases (Fig. 16.2) are often bound together by organic matter, some of which is high in calcium and/or nitrogen (Chia et al., 2011). Steiner (2006, 2008) reports that Amazonian village women collect all available types of organic matter at the settlement (bones, wood, leaves, chicken manure), as well as rotten tree trunks of particular species. This mixture is burned in an open smoky fire and then it is blended with soil that had previously been burnt in a hot woody biomass fire. The final mixture is used to grow vegetables and herbs. This technique could have been used by Indians in the past, and the ageing of this biochar mineral organic mixture could have led to the formation of ADE.

Biochar has been used in agriculture in Japan and China for hundreds of years (Ogawa and Okimori, 2010). Biochar is made at different temperatures for different applications, although Ogawa and Okimori (2010) note that most biochar is made between 400°C and 600°C. Biochar has been mixed with manure and applied to rice fields and home gardens to maintain soil fertility. The smoke from the production of biochar has also been captured and refined for use as a biopesticide and a growth promotor for at least 40 years (Ogawa and Okimori, 2010).

In Costa Rica, a farmer has established an organic fertilizer business that uses a modified form of a technique (Bocashi) developed in Japan over 30 years ago (Joseph et al., 2010b). Biochar produced at a sugar factory is mixed with manure and minerals (mainly dolomite). Microorganisms collected from the nearby mountains, as well as Japanese produced efficient micro-organisms (EM), are grown in a mixture of molasses and rice bran. The microorganisms are then mixed with the minerals, manure and biochar and composted in a pit in the absence of air before being aerobically composted.

Villagers in Northern Vietnam have developed a technique of soaking wood and bamboo in the clay and mineral-rich sludge at the bottom of ponds at the edge of rice paddies (Fig. 16.3). A significant volume of biochar and ash remains when this artificially aged biomass is burned in an open fire. The biochar and ash is then used in home gardens to grow vegetables. Ash and biochar from the burning of straw on fields is also used in conjunction with NPK fertilizer. This practice is over 40 years old. Women interviewed said that it increases the plant yield and reduces requirements for NPK fertilizer.

Large deposits of dark earths have been found in Africa (Fairhead and Leach, 2009). Rademakers (2009) notes that some tribes collect big piles of elephant grass or any other type of savannah grass, dry it, pile it so as to make long strips, cover the big rows of grass with a layer of mud, and then leave it to dry. After the mud has dried and hardened, they open one part of the strip and set fire to the grass within. The fire travels slowly through this ‘kiln’, which provides a low oxygen environment, and chars all the biomass. After this operation, they crush the mud layer, and the char beneath it. They repeat the effort several times to create layers of char and crushed mud. This then becomes their soil bed, on which they start planting crops when the rains arrive. The rains turn this soil layer into a more fertile soil.

6.4 Production of biochar

Many different pyrolysis kilns, retorts, ovens, and stoves have been designed and are being operated throughout the world. However, there is a lack of independent assessment of their performance especially the emissions profile (CO, NOx, N₂O, VOCs) during start-up, steady state operation, and shut-down.

16.4.1 Household devices

A range of small pyrolytic stoves for use by households or by farmers can be purchased or their designs are available on the web. Many different biochar stoves have been developed and tested (Carter and Shackley, 2011). They generally can be categorized into two distinct design types: microgasifiers operate by direct combustion of the feedstock, while retort-like stoves indirectly heat the feedstock, to convert it to biochar. The first utilizes small pieces of woody biomass, shells and pellets that are placed into a chamber where pyrolysis takes place in limited air. Pyrolysis gases are allowed to rise up from the biomass and combust in excess secondary air. The most common name used for these is a TLUD (top lit updraft) gasifier or stove. There have been many variations on this type of stove and a comprehensive overview is given by Roth (2011). Many of these newer stoves have lower fuel consumption and lower emissions than open fires (Roth, 2011).

The second type of stove has a chamber (retort) where residues such as rice husks, straw, sawdust and manure can be converted into biochar under the influence of heat from a separate combustion chamber burning scrap wood or biomass. Gases escaping from the pyrolysing residues in the retort flow into the combustion chamber and are burnt. More recently, new designs have been developed with an inner combustion chamber where large pieces of wood can be burnt. The wood combustion chamber is surrounded by another chamber where other biomass is added. This type of stove is illustrated in Fig. 16.4.

16.4.2 Ovens, retorts and kilns

Both the Japanese and the Chinese have developed a range of kilns that are cheap to manufacture and produce biochar over a range of temperatures. Some of these kilns have been in operation for over 100 years (Industrial and Engineering Chemistry, 1931). Figure 16.5 illustrates two of the simple batch kilns that are being operated by small enterprises.

Japanese techniques produce high and low temperature biochars. In some of the kilns, wood is stacked vertically which allows rapid heat transfer up the internal pores (xylem and phloem). An external fire is ignited and combustion gases flow into the kiln. Steam is produced at the bottom of the wood and rises through the vertical pore channels efficiently transferring heat to the wood. The rate of heating of the biomass varies depending on the specific application. Figure 16.6 shows one practice where the biomass is slowly heated for a long period of time at temperatures below 150°C (ARECOP, 1994). This long steaming time at low temperatures slowly degrades the lignocellulosic structure of the biomass and results in a biochar that probably has quite different chemical and physical properties from those produced at higher firing rates and temperatures. The thermally treated wood may have higher water absorption, larger pore sizes and broadened pore size distribution (Hietala et al., 2002), and higher diffusion coefficient of water along the tracheid axis. Long heating times lead to deacetylation, and the released acetic acid acts as a depolymerization catalyst, which further increases polysaccharide decomposition (Fengel, 1966a, 1966b).

Another firing procedure used is to bring the kiln temperature to 400°C as quickly as possible and to hold this temperature for two days before either cooling the kiln or raising the temperature to 600°C, or for very dense charcoal to 1,200°C. In these kilns there is a diffusion of moisture and low molecular weight organic compounds from the inner core of the wood to the outer char layer during the holding time at 400°C. Complex reactions take place resulting in the formation of a heterogeneous carbon mineral matrix.

Beehive kilns have been used extensively in China to make bamboo biochar and to collect wood vinegar (Fig. 16.7). Smoke coming from the kiln is captured in a funnel and then condensed in bamboo pipes before dropping into clay pots for refinement (Mingjie, 2004). The liquid is allowed to age for a month by which time three phases form. The bottom phase is tar which is used as an energy source. The top phase comprises water soluble organics. The middle phase is the vinegar which can be further refined by passing it through bamboo biochar.

A batch retort developed originally for production of fuel charcoal by Chris Adam is now being built around the world for production of biochar. Bob Wells and Peter Hirst in the USA have modified this retort (Fig. 16.8) to reduce the level of emissions and to allow the energy to be utilized for heating as well as creating the option of placing it on a mobile platform (Hirst, 2010). The wood or other feedstock is loaded from the top, the chamber is sealed, and a fire is started in the attached firebox to begin the indirect heating of the feedstock chamber. The pyrolysis gases from the heated charge are then pulled off, run through a condenser to remove the oil and other condensables, and then injected into the fire chamber to continue the indirect heating of the charge to the desired temperature. Heat energy can be removed for heating a greenhouse, hydroponics system or other structure, or can be used in a separate process. The result is a very efficient and clean running system. The retort can produce about 300 kg/day of biochar as well as liquid co-products and heat energy. Unloading is fast and easy with a built-in vacuum system. The unloading system that vacuums out the finished char breaks down the particle size, and adds a mist of moisture to control dust. The cost of the kiln is approximately US$75,000 in 2012.

A ring kiln developed by Ian McChesney of Carbon Gold is being operated in Belize and the UK (see Fig. 16.9). The charge of wood or residues for making the biochar is placed on the outer ring of the kiln. The inner chamber has a firebox in which firewood is placed. Air is supplied through the top and the combustion gases pass through the pyrolysing wood. The syngas catches alight and is burnt in the middle chamber. Many different designs of TLUD biochar ovens manufactured from 200 litre drums are now in use throughout the world. A version has been field tested in Vietnam and has been operated by a women’s group to make a mixed biochar from rice straw, rice husks, tea clippings and bamboo (Fig. 16.10). To this was added clay and lime to slow the decomposition of the rice straw. The yield of biochar was approximately 37% with an average temperature of 450°C in the bed of pyrolysing material.

16.5 Larger-scale commercial production of biochar

Large-scale production of fuel charcoal on a continuous basis has been carried out in rotary kilns, vertical retorts and rotary hearth furnaces for over 100 years (Brown, 2009). Over the last 30 years a wide range of different pyrolysis units have been developed to produce biochar and in some cases to produce energy and bio-oils (to be used as a fuel or chemical additives). It is not possible to list all of the different designs. The following is a description of a sample of the different types of units that have been developed. There are only a small number of plants in operation throughout the world and very little data on their performance.

Kansai Corporation of Japan has developed a moving bed pyrolyser to convert rice husks and sawdust to biochar and to produce heat for drying or heating in rice mills and sawmills. Units are in operation throughout Japan, although details are not available on the numbers and the operating performance.

ICM LLC in the USA has built a screw pyrolysis system with an input of two ton/hr. In this unit the steam produced in the first section is taken to the back of the kiln where it is combined with the syngas. Air is injected along the kiln and the syngas is burnt in a thermal oxidizer. This unit has run for over 2,000 hours. The hot gas produced from this unit can be used to power an organic Rankine cycle engine or to provide heat to generate steam for a steam turbine.

Pacific Pyrolysis (previously BEST Pty Ltd) has developed a three-stage process that has as its main components a drier, a torrefier/pyrolyser and a gasifier (Fig. 16.11). The pyrolyser has a series of paddles inside that move the biomass over the hot surface of the kiln. Part of the syngas is used to heat the pyrolysis kiln. A gas clean-up system consisting of a gas cooler, particulate filter, a tar cracking unit and a scrubber can be added to produce a gas that can fuel an internal combustion engine, an organic Rankine cycle engine or a steam turbine. This system can be tailored to produce a range of different types of biochars. A pilot plant has been run extensively over 5 years and manufacture of their first demonstration plant may be operating in 2014.

BiG (www.blackisgreen.net) has built a number of rotary hearth pyrolysis kilns that can process between 250 and 500 kg/hr of biomass. Among those bigger kilns are also transportable ones which have been in operation on an irregular basis for the past two years. They cost $200,000 to $300,000. Figure 16.12(a) shows a small BiG unit used in Australia.

Pro-Natura has developed a swept drum pyrolyser (Fig. 16.12(b)) with a separate vortex burner for use in developing countries. The unit can process 250–500 kg/hr and has been tested on a range of feedstocks in Africa and France. Energy Farmers Australia Pty Ltd (Fig. 16.13) has built a continuous auger feed pyrolyser suitable for a range of feedstocks. This unit uses augers and mixers to move the biomass along a trough. An LPG burner heats the unit up and starts the feed pyrolysing. The syngas from the pyrolysing material mixes with air and ignites. The LPG burner is turned off and the radiation from the syngas keeps the pyrolysis process going.

Russell Burnett developed a screw continuous pyrolysis two-stage system (Genisis) with feed input of 200 kg/hr with moisture content of 25% (Fig. 16.14). These units use the syngas to dry and then pyrolyse the feed in two separate chambers. The unit has a scrubber and a drop-out tank to cool the wood vinegar. The wood vinegar is added to compost to increase microbial growth within the pile. Independent emissions testing has been carried out with olive seed as the input fuel. The composition of the flue gas was: CO 2.5mg/m³, NO_x 100mg/m³, hydrogen sulphide 0.043mg/m³, CO₂ = 4.1%, and O₂ 17.4%. Polyaromatic hydrocarbons were not detected on the biochar produced in this machine at 550°C.

The Sanli New Energy Company has developed an open-core down-draft gasifier (Fig. 16.15) that has a throughput of approximately two tonnes/hr of mixed agricultural residue. A limited amount of air is drawn in through the top of the unit and the gas is taken out halfway down the reactor. Biochar forms in the middle of the reactor. Visual examination indicates that there is a temperature distribution between the outer walls where much of the air flows and the inner core. It is probable that the temperature of the biochar varies from 400°C in the middle to 550°C on the outer walls. The gas is cleaned and then cooled in three condensers and the different fractions of the condensate are separated. The middle fraction is further refined and sold as wood vinegar. The cool cleaned gas is then utilized to run an engine to generate electricity. Their main factory consists of three units that operate throughout the year.

16.6 Testing biochar properties

To fully characterize biochars involves using a range of tests some of which are complicated and expensive. Much of the research work undertaken to determine key properties of biochars uses chemical, physical, microscopic, electrochemical and spectroscopic techniques. Each technique provides an important part of the puzzle and the reader is referred to Joseph and Lehmann (2009) and Joseph et al. (2010a). The Japanese have developed a simple standard for biochars (www.nittokusin.jp) which is presented in Table 16.1. The biochar must only be produced at a temperature above 400°C. It must meet laws related to improvement of crop fertility.

The Chinese National Standardization Technical Committee for Bamboo and Rattan (SAC/TC263/SCX) has developed a standard for bamboo biochar. The bamboo is classified by size and shape according to the finished products, which include tube charcoal, charcoal tablets, broken charcoal, granular carbon and carbon powder. There are six categories of diameter sizes: 0.18–0.5 mm, 0.5–1 mm, 1–3 mm, 3–5 mm, 5–10 mm and 10–20 mm. The biochar is also categorized by use: ‘personal use, fuel charcoal, building decorative bamboo charcoal, bamboo charcoal with environmental protection, agriculture, forestry, and horticultural charcoal’. All biochars must be odour free.

First-grade biochar must have a moisture content between 9.0 and 12.0%, ash content between 4.5 and 6.5% and a fixed carbon content between 75.0 and 85.0%. To determine the quality of the biochar, the samples are placed on white paper in a well-lit environment and then a person will smell the charcoal to ensure there is no odour, and will observe if it has a metallic lustre after it is broken, showing that it is fully pyrolysed.

After extensive consultation with stakeholders, IBI has established a protocol for testing biochars at different levels. Key measurements include pH, EC, H/Corg ratio, total and available N, P and total K, total metal content, liming capacity, and particle size distribution (See Appendix in Section 16.10). Other more complex measurements include total porosity and surface area. It is also recommended that basic toxicity measurements be done (Table 16.2).

16.7 Markets and uses for biochar

The most developed commercial markets for biochars exist in Japan, China, Taiwan and Korea. Biochar is an integral part of vegetable production, animal husbandry and forestry. China is now the largest producer of biochar with over 140,000 tonnes of biochar and biochar blends being produced in the last year. There also appears to be significant production of wood vinegar that is used as a biopesticide and for promoting the germination and growth of certain species of trees and plants. This increase in production has been stimulated by government grants and contracts and by the collaboration between researchers in China and Europe/US/Australia.

The principal uses of the biochar are (Pan et al., 2011):

Essentially two approaches are being taken for developing biochar-based fertilizers. The first approach is to produce either an organic granulated fertilizer that has a high N and smaller P and K contents, utilizing fermented biomass, amino acids, extra minerals and biochar (Fig. 16.16), or a compost-biochar mixture. The fertilizer is sold (wholesale) for approximately $A300–350/tonne. The second approach mixes biochar with chemical fertilizer ingredients in various proportions. There was little detailed information provided on the formulations and the results of field trials with these different formulations. Preliminary results of field trials carried out by Nanjing Agricultural University have indicated that yield improvements of greater than 20% can be achieved when wheatstraw biochar is reacted with clay and NPK fertilizer (Joseph et al., 2013). One company (Biotechnology Co, Anhui) mixes NPK with rice husk biochar and a liquid clay binder in a vapour electro-heat roller dryer to produce a granule. Total nutrient content varies from 40–45% with N : P₂O₅ : K₂O ratios of 15 : 15 : 15 and 18 : 11 : 11 depending on crop and soil.

Sanli New Energy Company, situated near Shangqiu City, has been in operation for 5 years and produces more than 10,000 tonnes of biochar a year. The company has expanded and now has seven smaller plants in Henan Province, and it is selling products all over China. The factory sells biochar to other companies who then mix it with chemical and organic fertilizers, it makes its own NPK/biochar granule, and it sells wood vinegar. The factory also collects excreta from local schools, which pay a nominal amount for the collection. It then filters the waste through the biochar to increase its nutrient content. The company sells to industrial tobacco farms and small fruit and vegetable farmers who buy crop-specific versions of the biochar + fertilizer mixes. Significant purchases are made by government agencies, that purchase pure biochar for land remediation, or biochar + fertilizer for state-owned farms where they aim to reduce their inorganic fertilizer use. The selling price direct from the factory is approximately $300/tonne.

There are many smaller operations producing bamboo charcoal in areas where bamboo proliferates. The amount being produced is not known but appears to be greater than 100,000 tonnes per year (Dr Zhong, Bamboo Research Institute, pers. com.).

Japan, like China and other parts of Asia, has a long history of using biochar not only for agriculture but for health and hygiene, and for animal husbandry. Biochar is used for remediation of land and forest, for horticulture and cereal production, and for improving the quantity and quality of compost. Ogawa and Okimori (2010) have the following comments on the present industry:

Bamboo, rice husk and certain types of hardwood and broadleaf bark are the preferred feedstock for most applications. Biochar is often pretreated with compost made from high-quality input materials (e.g., rice bran, chicken manure) and/or smoke water (wood vinegar) to make specific products that are used to grow high-value products such as mushrooms. Trials have been carried out with mixtures of chemical fertilizer and biochar. Ogawa and Yambe (1986) report the following:

Ogawa also reports that:

Discussions with the Japan Biochar Association has highlighted markets where high prices are being paid (>$500/tonne) for biochar of the correct quality. These markets include the production of mushrooms, flowers, animal husbandry and ornamental trees.

The volumes of biochar being sold in Europe, Australia and North America are relatively small. Possibly the biggest use is in growing orchids. Prices range from $500 to $1500/tonne for wood charcoal and as high as $7000/tonne for high mineral ash products, e.g. Black Earth Products, www.blackearthproducts.com.au.

Carbon Gold in the UK sells horticultural products that have a mixture of biochar and other additives. Their biochar complex soil improver sells for about £7 per 1 kilo tube that contains 900 g of biochar. They also sell a seed compost with biochar and an all purpose biochar compost. The composts contain:

Trials in Switzerland with the use of biochar with compost in vineyards have been underway for over 3 years with reports of significant increases in amino acids and polyphenols of the grapes compared with the controls (Schmidt, 2011).

Palaterra has developed a process for mixing sludges from a biogass digester with waste wood biochar and anaerobically digesting this mixture (http://www.palaterra.eu). It is a four-stage process that takes only four weeks to complete: first the green waste and biochar are soaked in the liquid digestate and mixed. Stage two is a period of hot aerobic decomposition. The third stage is anaerobic lactic acid fermentation. Finally, it is dried and bagged as a finished product.

16.8 Conclusion and future trends

In most countries, except for those in North Asia, the quantities of biochar that are being produced and sold are well below 20,000 tonnes/year. A considerable number of small companies are now marketing biochar mixes mainly for use by the home gardener. Developing a viable large-scale industry in Europe, North and South America and Australia/NZ is proving to be difficult. From both producers of biochar products and technology providers the following constraints have been identified:

To develop a viable industry, considerable technical, commercial and financial support needs to be given to the growing number of smaller companies who are either developing products or production technology. Substantial funds need to be allocated to develop biochars and biochar blends that are suitable for a range of soil types and crops. Ongoing testing and optimization of these products must be funded to ensure that enhanced soil properties and yields are maintained.

Demonstration plants in urban areas need to be funded and approvals given by local authorities and EPAs to gather long-term emissions data for a range of available residues and wastes. Larger-scale pyrolysis plants must be integrated into existing process industries that generate residues and require both heat and power. Development agencies need to allocate long-term funds to undertake biochar projects in developing countries where biochar is made both at a household and a village level from a range of available residues.

Even with the constraints noted above, the future for biochar industries appears to be very positive. Scientists, engineers and farmers are cooperating to develop designs that have significantly lower capital costs than those produced by commercial companies. Small companies are developing niche markets for blended products. Larger waste management companies are starting to collaborate with the smaller start-up ventures.

6.10 Appendix: IBI; Standardized product definition and product testing guidelines for biochar used in soil