Blaise Pascal Bougnom, Brigitte Amalia Knapp, Francois-Xavier Etoa, and Heribert Insam

Abstract Infertility of acid soils is a major limitation to crop production on highly weathered and leached soils throughout the world. The main characteristics of these soils are their low pH, low levels of organic matter, Ca, Mg, P, or Mo deficiency, Al or Mn toxicity, or both, and very low mineralization and nitrification rates. Lime is generally recommended to correct soil acidity, but lime is unaffordable for resource-poor farmers in the tropics. Many alternatives have been proposed, and among them products from organic waste materials, e. g., composts, have proven to be an efficient alternative to the use of lime. Wood ash is a potential source of trace elements, nutrients, and lime. Wood ash could be used as an additive to fertilizer, and wood ash admixture to organic wastes prior to composting is known to improve compost quality and may reduce the amount of compost required to raise the pH to suitable levels. Wood ash compost as a liming agent as a replacement for lime could potentially aid in remediating acidity and base deficiency as well as boosting the soil microbial pool in tropical agricultural soils.

7.1 Introduction

Agricultural primary production is essential for maintaining human life. Sustaining the productivity of soils is important for future generations, but the way to maintain productivity is often disputed. Intensive agriculture is based on the use of large quantities of pesticides and other chemical substances aiming at increasing yields, but the price to pay is the deterioration of soil quality and the environment, water pollution, the emergence of new pathogens that are more and more resistant to pesti­cides, and the threat to human health from the consumption of pesticide residues

B. P. Bougnom (H) and F.-X. Etoa

Laboratory of Microbiology, Department of Biochemistry, University of Yaounde I, P. O. Box 812,

Yaounde;, Cameroon

e-mail: bpbougnom@uy1.uninet. cm

B. A. Knapp and H. Insam

Institute of Microbiology, University of Innsbruck, TechnikerstraBe 25 d, 6020 Innsbruck, Austria

H. Insam and B. A. Knapp (eds.), Recycling of Biomass Ashes,

DOI 10.1007/978-3-642-19354-5_7, © Springer-Verlag Berlin Heidelberg 2011

entering the food chain as well as inhalation of toxic gases. These practices, however, are beyond the reach of resource-poor farmers in the tropics, because of their high cost. On the other hand, agricultural and forestry products are exported from tropical to western countries; together with nutrients like nitrogen, phosphorus and potassium, present in this biomass. Sustainability issues are thus becoming more important, reflecting the need for long-term fertility and environmental protection. A sustained agricultural system is one in which the sum of income extracted every year is sustained over years without altering the natural resource levels (Yunlong and Smit 1994). Organic farming principles and objectives are achieving good crop yields by using techniques which minimize the human impact on the environment (Rigby and Caceres 2001). Organic farming can allow resolution of the problem of disposal of organic wastes that human beings have to get rid of and which are a valuable source of nutrients for plants, and serve the purpose of soil conditioners. That allows the carbon cycle to be closed and thus greenhouse gas emissions to be reduced.

Besides organic wastes, ashes from biomass incineration are also worth consid­ering for agricultural recycling. Wood energy production is classified as a form of green energy production because it is both carbon neutral and renewable (Kumar 2009). In many African regions, fuel wood constitutes 61-86% of primary energy consumption and generates large amounts of wood ash, which are just discarded to the natural environment without any control, causing serious environmental pro­blems (Samir Amous 1999). On the other hand, in Europe and North America, the increased use of wood to produce bioenergy generates huge quantities of wood ash that are currently deposited at high cost. That ash, known to be rich in nutrients and lime, could be returned to depleted soils as a supplement to organic fertilizers by suitable management practices (Bougnom et al. 2009). Addition of wood ash to compost is among the available possibilities, and the compost produced could be used for forest fertilization as well as for agricultural purposes such as replenishing depleted and/or acid soils (Bougnom et al. 2009, 2010; Kuba et al. 2008). In this chapter, we explore the possibility of using both compost and wood ash as an addi­tive to remediate tropical acid soils. The problem of soil acidity is also explained to inform the reader about the origin of this phenomenon and its consequence for soil fertility as well as the mechanisms by which organic wastes could alleviate soil acidity.

The data were obtained in industrial testing with manufacturing batches of about 1,750 t of brick. The daily production capacity of the plant where the tests were performed is, depending on the format and characteristics of the brick manufac­tured, approximately 750 t/day. Such large test runs are necessary to assess with sufficient accuracy, considering the latency of the tunnel kiln, the effects of addi­tions or substitutions on the firing process, emissions into air, and the energy consumption.

The use of ashes as an addition to the brick feed must take into account that in the clay free calcium ions are available for a pozzolanic reaction with some compo­nents of the biomass ash. This reaction is not immediate but rather slow and certainly accelerated by temperature. This reaction can cause problems in extru­sion: stiffening associated with a loss of plasticity and hence denting of the extruded strand. It is hence necessary to hinder or delay this behavior either by adding the ashes, as done for polystyrene, for example, directly prior to extrusion or by hydrophobizing the ashes at least partially with a suitable agent. In brick making
the two most suitable agents are waste glycerine from the production of biodiesel and waste antifreeze from the car industry. So far, no industrial tests with waste antifreeze compounds have been carried out. The trials were carried out with glycerine-treated ash.

The fruit and the wood combustion ashes were mixed in a 30:70 ratio and then subjected to hydrophobization with waste glycerine. The ashes were added to the raw material feed prior to its storage in the silo for souring. The raw material characteristics are indicated in Table 9.2. The mix was made up of 20% by volume of ashes and 80% by volume of clay. The use of ashes resulted in a noticeable reduction of the density and hence substantial improvement of the thermal perfor­mance of the finished product, as summarized in Table 9.3.

The reduction in unit weight is tied to a lower setting density. In the tests carried out, a reduction of about 8% of fuel was observed. A certain percentage can certainly be attributed to the energy content, body fuel, of the biomass ash.

Extrusion data were collected automatically and show that the power require­ment of the extruder was lowered by 8%, whereas the density achieved is lower. The overall savings in production costs, considering that the ash is delivered free of charge to the brick plant, is estimated to be about 7.5%.

Reactive swelling was not observed, at least at the percentages used in the tests. The bricks manufactured with the addition of the biomass ashes are of good quality. The analytical data for the raw ashes used and the brick manufactured are given in Table 9.4. No significant changes to the leaching values were found between a standard brick and a brick formed from the addition of biomass combustion ashes.

9.2 Conclusion

When hydrophobized biomass ashes were not used, the extrusion power require­ments increased rapidly to a point where the tests had to be stopped because of excessive power requirement.

The results of the tests with hydrophobized ashes are as follows:

• Lower power requirement of the extruder at almost the same cutting frequency but at the same time a higher extrusion pressure

• Reduction of the water content of the brick by 2.5-3.0% (wt)

• Reduction of drying cracks

• Reduction of fired sulfate visible on the surface of the brick

• Substantial modifications to the firing curve

These results are positive. A problem, at least with the ashes used in the test, is that they are not delivered in a way that allows the brickyard to accept them, without any major and costly modifications to the plant. Most are delivered in big bags. This requires extra effort and expense on the part of the brickyard. If the ashes were delivered in trucks, an appropriate silo, similar to one used for coal or pet coke, could be installed. Another unresolved problem is the seasonality of the ashes. A storage bunker to overcome this problem usually cannot be accommodated in a brickyard. Once the producer of the ash has resolved these problems, a brickyard can certainly become an ideal recycler for this type of waste.

Liming is defined as the application of ground calcium and/or magnesium carbo­nates, hydroxides, and oxides. Liming the soil is the most common and oldest method for reducing soil acidity. Liming is often performed through high-dose applications of products such as calcitic lime (CaCl2) and dolomitic lime [CaMg (СОз)2]. The aim is to increase the soil pH and therefore to modify the physical, chemical, and biological parameters of the soil. Studies have shown that liming materials affect the activity and composition of microbial populations and can create better environmental conditions for the development of nonacidophilic microorganisms, resulting in increased microbial biomass and soil respiration (Neale et al. 1997; Tate 2000). Nevertheless, liming has some limits; the effec­tiveness of surface application of lime to soils under a particularly no-till system withregard to subsoil acidity is uncertain, agricultural liming materials are rela­tively insoluble, and lime effects may be restricted to the top few centimeters of the soil surface for many years (Shainberg et al. 1989; Costa and Rosolem 2007).

Large quantities are generally required to improve plant growth, and for many resource-poor farmers in the tropics carrying out semisubsistence agriculture, its use is effectively prevented by the unavailability or the high cost of lime, or both (Haynes and Mokolobate 2001).

In 2006, 1.3 million tonnes of combustion residues was produced (estimate for 2008: 1.5 million tonnes) and almost 80% was utilised. A summary of the quantities and types of combustion residues is provided in Table 11.1. The presentation is split into more categories than is usual in surveys, because mixtures of fuels, some of

them particular to a type of industry and to type of furnace, are important for the properties of the residues.

As one may see, the problem for a provider of materials is that the sources are numerous and small. For example, the 600,000 t/year of MSW incineration (MSWI) residues is produced by more than 25 plants. Many district heating plants produce less than 2,000 t of mostly wood-based ash per year. The smallest ones, as well as small sawmills, do not produce more than 1 t/year. The really small capacity furnaces are not included in these figures, e. g. pellet furnaces in individual homes, or farm units firing agricultural residues.

If one sums up all categories of solid biofuels and mixtures, the total quantity of ash from solid biofuels is of the order of 370,000 t/year.

All types of furnaces are used, grate furnaces, pulverised fuel (PF) furnaces and fluidised bed furnaces, the latter being perhaps more common in Sweden than in the rest of Europe. The capacities range from a few hundred kilowatts to a couple of hundred megawatts on a fuel basis. Small furnaces up to 10 MW fuel are usually grate furnaces, and fluidised bed furnaces are preferred from 20 MW fuel and upwards. PF furnaces are not so common in Sweden. All these types of furnaces have their particularities, which affect the properties of the residues; see Sect. 11.2.4.

Beatriz Omil, Federico Sanchez-Rodriguez, and Agustin Merino

Abstract The aim of this study was to evaluate the effectiveness of multiple applications of biomass ash to acid soils. The study was carried out in two stands of Pinus radiata D. Don, aged 13 and 15 years, in the province of Lugo (northwest Spain). The soils in the stands were developed on lutites and migmatites. Experi­mental plots (each 1,225 m2) were established, and the experimental treatments were as follows: control (untreated), ash (addition of 4.5 Mg dry matter ha-1 year-1 in 2003, 2004, and 2005) and ash plus P (addition of ash plus phosphate fertilizer in 2003).

The ash was generated in a moving grate furnace, and had the following characteristics: pH 8.9 -13.5, high concentrations of K, Ca, Mg, and P, and low N content and low concentration of heavy metals.

The responses of the forest stands, evaluated as the effects on forest nutrition and tree growth, were measured in 2005, 3 years after the initial treatment. The results showed that continuous fertilization with ash improved the nutritional status and growth of Pinus radiata D. Don stands, and resulted in increased contents of the main macronutrients in needles and soil.

6.1 Introduction

The Galician timber industry makes an important contribution to the regional economy. Forest land covers more than 60% of the total area, and the annual timber harvest is approximately 7,000,000 m3. The wood is used in sawmills and to prod­uce paper, particle board, and fiberboard. Lignocellulosic by-products generated in the latter industries are used in biomass incineration plants to meet increasing energy

B. Omil (H), F. Sanchez-Rodriguez, and A. Merino

Forestry Faculty, Escuela Politecnica Superior, University of Santiago de Compostela, 27002 Lugo, Spain

e-mail: beatriz. omil@usc. es

H. Insam and B. A. Knapp (eds.), Recycling of Biomass Ashes,

DOI 10.1007/978-3-642-19354-5_6, © Springer-Verlag Berlin Heidelberg 2011 needs and to reduce waste production. The by-products mainly consist of bark (from pine, eucalyptus, and a small amount of birch, depending on the type of manufacturing) and to a lesser extent sand, dust, and panel fragments. The volume of these by-products created annually is approximately 900,000 m3 and that of other by-products is approximately 40,000 m3.

This source of energy is considered neutral from an environmental point of view, as it releases the same amount of CO2 to the atmosphere as trees have removed. Combustion does not affect global warming or the greenhouse effect and has several advantages, such as a reduction in the use of fossil waste and the reuse of waste that has no value other than being a source of energy.

Biomass ash is produced as a result of this process (on average, combustion of wood produces 6-10% ash; Gaskin and Risse 2002). Ash is considered a non­hazardous waste (ERL codes 100101 and 100103, bottom ash and fly ash, respectively) and is therefore stocked at dumping sites. However, to reduce these stocks, alternative uses of the waste are being investigated, e. g., for production of enamel and glass (Xirokostas et al. 2001), as a building material for tracks or rural paths, for amation of coal mine (Gil-Bueno and Monterroso 1998; Seoane and Leiros 2001), as an absorbent for the removal of dichlorodi — phenyldichloroethane (DDD) and dichlorodiphenyldichloroethylene (DDE) ori­ginating from pesticides (Gupta and Ali 2001), and as an additive in cement production (Van Der Sloot and Cnubben 2000). The latter use is not recom­mended because of the high level of C in the ashes. In this case, wood ash is usually used as a pozzolan (a siliceous and aluminous material). Despite not having binding properties, pozzolan reacts with finely divided calcium hydroxide in the presence of water to form compounds with cementing properties at room temperature (ASTM 1994).

Nevertheless, wood ash contains nutrients such as P, K, Ca, and Mg, which are present in relatively soluble forms (the NPK content is typically 0-1-5). Apart from these macronutrients, the waste contains oxides, hydroxides, and carbonates. The waste is therefore highly alkaline and contains low amounts of heavy metals (Erich and Ohno 1992; Korpilahti et al. 1998; Demeyer et al. 2001; Miller et al. 2002; Solla-GullcSn et al. 2006). For all these reasons, application of wood ash to forest soils may be of interest as regards the environmental management of such waste, improvement of the nutritional status of forest plantations, and completing the CO2 cycle (Torre-Minguela and Giraldo 2006). Fertilizer is added in an attempt to replenish the nutrients exported as a consequence of the extraction of biomass after final harvesting.

However, despite the high productivity of Galician forests, most Pinus radiata D. Don plantations are deficient in nutrients such as P, Mg, and Ca (Sanchez — Rodnguez et al. 2001; Zas 2003), which can be attributed to the strongly acidic soils and to the extraction of nutrients as a result of the management of the plantation in medium rotations (less than 40 years). Fertilization with wood ash would also contribute to the sustainability of the stands, intensive exploitation of which results in large losses of nutrients.

Cacao (Theobroma cacao) is a small evergreen tree in the family Sterculiaceae or Malvaceae. Cacao is grown in more than 30 countries around the world in Africa, South America, and Asia, principally in areas that fall within 20°N and 20° S of the equator (FAO 2009). The cacao tree is an understory tree, growing best with some overhead shade. The seeds of the cacao tree are used to make cacao and chocolate. The fruit, called a cacao pod, contains 20-60 seeds, usually called beans. The pods consist of the husks and the beans. Every bean is surrounded by a thin shell. The pods are harvested, the husks are removed, and the beans are dried and fermented. After fermentation, drying, and packing, the beans, including the shells, are trans­ported to the location of the cacao industry.

Results of foliar analyses may differ depending on environmental factors. The date of sampling, the age of the plants, and the type of parent material found below the plantation must be taken into account.

The foliar concentration of N tends to decrease in response to application of biomass ash, as expected from the low N content in the ash and its immobilization in the soil. However, an increase in N concentration has been observed in some peat soils, which can be attributed to a higher mineralization as a consequence of an increase in pH and availability of nutrients (Weber et al. 1985). In a prior study, Solla-Gullon et al. (2006) also detected an increase in foliar N concentration in Pseudotsuga menziesii plantations in Galicia.

In this study, the foliar values of P were prone to increase, as observed by Moilanen et al. (2002), Ludwig et al. (2002), and Solla-GullcSn et al. (2008). This positive response may be the result of the symbiotic association between ectomy — corrhizal fungi that colonize the ash. These fungi increase the solubility of the content of P in the ashes, thereby promoting the uptake of ash by trees (Mahmmood et al. 2003). Use of a diagnostic system based on the N-to-P ratio showed that a balance between N and P was achieved, since it did not exceed the normal ratio ranging from 6 to 16 (Raupach 1967). These values are similar to the average value of 12.0 reported by Solla-Gullon et al. (2008) for Pinus radiata in Galicia.

Foliar K concentration also increased slightly in the WA and WAP plots, confirming the relationship between plant and soil concentration (Zas 2003). Increases in plant K concentration in response to the application of ash have been reported earlier (Moilanen et al. 2002; Solla-Gullon et al. 2008). However, no differences were observed by Hytoonen (2003).

Despite the higher availability of Ca and Mg in the soil, foliar tree analysis did not reveal significant increases in concentration for these elements. This is consis­tent with the findings of some studies in which concentrations did not increase, or increased only slightly (Hytonen 2003; Moilanen et al. 2002; Ludwig et al. 2002). Other studies in which greater amounts of ash were applied revealed increases in the foliar concentration, which lasted for a few years (Solla-GullcSn et al. 2008; Arvidsson and Lundkvist 2002).

In most cases waste disposal laws and regulations require that the waste to be disposed of be accompanied by some kind of analytical data. However, such data are generally insufficient to determine whether the waste can be used in brick. For a typical brick factory the information that is required is listed in Table 9.1 (Moedinger and D’Anna 2002; Moedinger 2003, 2004).

It is essential that the quality and composition of the waste in use at the brick plant be continuously monitored so one is aware of any sporadic fluctuations in composition that could detrimentally affect the manufactured product. Long-term

Table 9.1 Basic information for testing the potential waste material for inclusion in a brick body

production tests are necessary to establish eventual variations in the composition and the impact on the product or production process.

Some of the potentially detrimental results on brick products or the production process caused by various wastes can be offset by the use of appropriate “correc­tive” additives:

• The concentration of chromium and chlorates with respect to their possible volatilization on firing and their subsequent concentration in the flue gases and potential effects on the refractory material of the kiln

• Odor and smells

• Heavy metals

• Organic contamination

• Chemical contamination

• Particle size distribution

• Water absorption

• Content of carbonate minerals

• Soluble salts

Organic waste materials used to tackle soil acidity include undecomposed plant materials, composts, manures, peats, and coal products. Organic amendments are suitable for resource-poor farmers, as these farmers are unable to buy large quantities of lime and fertilizer phosphorous needed for their lands because of economic reasons. Some authors have reported an increase in soil pH after addition of organic materials to soil, followed by a decrease of aluminum saturation and an improvement of plant growth, depending on the type of residue, its rate of application, and the buffering capacity of the soil (Hue 1992; Noble etal. 1996). The rise of soil pH is due to the flow of protons from the soil (lower pH) to the organic matter sites (higher pH), decom­position of less stable materials in the soil resulting in mineralization and nitrification of organic nitrogen, and microbial decarboxylation (Haynes and Mokolobate 2001; Wong and Swift 2003). A long-term increase of soil pH is dependent on the balance between proton production and consumption in the system (Helyar and Porter 1989). The role of humic substances in increasing phosphorous availability is unclear. Some authors have reported the role of humic substances contained in organic matter in competing for adsorption soil sites and subsequent decrease in phosphorous adsorp­tion (Bolan et al. 1994; Perrott 1978), whereas other authors have stated the unim­portance of soil organic matter in increasing phosphorous availability (Borggaard et al. 1990). Humic substances concomitantly with organic acids, organic residues, and release of inorganic phosphorous have been found to be the main factors involved in increase of available phosphorous. A decrease in aluminum phytotoxicity is directly linked to phosphorous availability.

A conceptual model of the major processes that lead to the detoxification of soil aluminum and an increase of phosphorous availability when wood ash compost is applied to acid soils is summarized in Fig. 7.1.

In the EN 14588 standard, biomass is defined as “material of biological origin excluding material embedded in geological formations and transformed to fossil”. When discuss­ing solid biofuels, one generally assumes that the fuel has to have 100% biological origin and that it is a virgin material, not a waste. A few points should be made here.

Peat is normally regarded as something between a renewable and a fossil solid biofuel. From our point of view, peat is a biomass because:

It agrees with the definition in the standard.

The annual formation of peat in Sweden and Finland is much larger than the yearly harvest.

Vast peat land areas have already been drained in Sweden and in Finland, and these areas now leak climate change gases; utilising the energy that the oxidation releases is much better than not using it at all.

Harvesting old peatlands increases the rate of growth of new peat.

This being said, peat is a minor fuel: woody biomass represents 48% of the fuel supplied to district heating systems in Sweden, on an energy basis. Peat represents only 5%, but it is often used for its comparatively high sulphur content as an auxiliary fuel to abate corrosion.

Unless the biomass is harvested solely for energy and used as is, most solid biofuels are actually wastes. For example, logging residues are considered as virgin biomass although technically they are residues from the conventional exploitation of forests. Analogously, residues from sawmills, board production, and pulp and paper mills combusted at the mills for the energy needs of the mills are somewhere between virgin biomass and wastes. Waste biomass is still biomass according to EN14588. For example, often 85% of the energy in MSW is biomass, and industrial biomass waste contains normally somewhat less than that.

Incineration is destruction of waste without utilisation of the energy produced. This does not occur in Sweden, where all waste-burning plants provide heat to district heating systems and most of them are cogeneration plants. The Swedish High Environmental Court wanted to regard all combustion of industrial or municipal waste as incineration. It has, however, been overruled by the Advocate General of the EU: if the main purpose is to generate energy, then this is co-combustion, even if all fuel fractions are wastes.

To keep within the purpose of this review of the Ash Programme, we will not consider residues from the combustion of MSW. The review deals with other non­fossil fuels, i. e. those originating from wood or peat. The properties of these residues are discussed in Sect. 11.2.4.