In this case it is assumed that the beans are transported to the Netherlands. The beans are stored in the harbor before transport to the cacao processing plant. Beans are broken to nib and the shells are separated. The nib is processed to cacao products. The shells are combusted or used as gardening material. All materials are transported by road or water. An example of cacao shells is given in Fig. 8.3.

For the scenarios it is assumed that the cacao shells are combusted in a circulat­ing fluidized bed combustion plant to produce heat and power. This is a type of boiler for production of energy from biomass on a large scale (so-called bioenergy

flue gas

plants) (Fig. 8.4). The general data of the bioenergy plant that were used in this study are given in Table 8.1. Sand is used as bed material. Some limestone is used to capture sufficient SO2 to meet the Dutch emission requirements.

The predicted chemical composition of the filter ash is presented in Table 8.2. The macroelements are also expressed as oxides (this does not mean that these elements

are present as oxides). The main nutrients in filter ash are potassium, calcium, and phosphorus. Thermodynamic calculations were performed to predict the potential compounds in cacao ash under equilibrium conditions. These were performed using FactSage©. The main compounds will be K2SO4, K2CO3, and Ca5HO13P3. It is assumed that the filter ash contains 5% residual pyrolized cacao shells (carbon).

Heavy metal concentrations have to be considered when wood ash is recycled to forests; thus, the quality of the applied ash is of great concern to avoid accumulation of heavy metals in the environment (Stupak et al. 2008). In a microcosm experiment performed by Fritze et al. (2000), Cd derived from wood ash application on forest soils did not show any harmful effects on the microbial activity or fungal and bacterial community structure. In the same experiment, ash treatments were found to induce a shift in archaeal community patterns, whereas Cd alone or with ash did not have an influence (Yrjala et al. 2004). When looking at the heavy metal contents of forest berries (Rubus chamaemorus, Vaccinium vitis-idaea, Vaccinium uligino — sum) or mushrooms (Russula paludosa, Lactarius rufus, Lactarius trivialis, Suillus variegates, Paxillus involutus) on different Finish forest sites after wood ash fertilisation (4-14 t ha-1), Moilanen et al. (2006) observed no accumulation of heavy metals or even a decrease in the long term. Similar results were found in six Pinus radiata plantations repeatedly fertilised with 4.5 t wood ash per hectare in northwestern Spain, leading to a decrease of Zn, Cu and Cd levels in some mushroom species, which was attributed to an increase in soil pH. Only Mn concentrations were elevated in all mushroom species investigated (Amanita mus — caria, Russula sardonia, Tricholomapessundatum, Laccaria laccata, Micenapura, Suillus bovinus, Xerocomus badius). Heavy metals did not accumulate in tree needles or ground vegetation (Omil et al. 2007). Another aspect of recycling ashes back to the soil is the accumulation of 137Cs (Hedvall et al. 1996). However, application of wood ash at a level of 3.0 and 4.2 kg ha-1 contaminated with 30-4,800 Bq 137Cs per kilogram on different coniferous forest sites in Sweden did not significantly increase radioactivity in the biological system (soil, field vegetation, tree parts) when measured 5-8 years after ash amendment, which was partly attributed to the antagonistic effects of wood ash K on 137Cs (Hogbom and Nohrstedt 2001). This finding was confirmed in a 100-year-old Scots pine (Pinus sylvestris L.) stand on Fe podsol in central Finland, on which ash fertilisation (1,2.5 and 5 t ha-1) led to a reduction of 137Cs concentrations in lingonberries (Vaccinium vitis-idaea L.) analysed 2 and 7 years after application of ash (Levula et al. 2000).

Earlier studies revealed that Pinus radiata shows a good response to fertilization (Sanchez-Rodnguez et al. 2002; Omil et al. 2005; Solla-Gullon et al. 2008). However, this response varies depending on the age of the trees, on the density, and on the nutritional needs (Zas 2003). The demand for elements such as N and P increases during the first years of life, a maximum of 6-8 years (Turner and Lamber 1986). Ca and Mg, which do not suffer retranslocation before needle fall (Ericsson 1994), may cause problems in forest crops since the demand for these elements by higher plants tends to increase with age (Turner and Lamber 1986).

Analysis of covariance revealed that improvement in soil nutritional status leads to higher tree growth from the second year of treatment onward, confirmingthe findings of other studies (Bonneau 1995; Vesterinen 2003). This is due to the site quality (ecological conditions, soil physical properties, weather, and water avail­ability of the trees): under adverse conditions fertilization does not improve soil nutritional status. Thus, the response was more significant in plots on lutites (of lower site quality) than in plots on migmatites. This confirms the results reported by other authors, mainly for rich soils (Silfverberg and Huikari 1985; Ferm et al. 1992; Emilsson 2006). Production may be improved by application of a higher dose of ash, although there is a risk of leaching contamination and increased heavy metal concentrations.

The application of other types of waste such as slag and dairy sludge was found to increase tree height growth (Virgel-Mentxaka 2002; Omil et al. 2005). The combination of ashes with certain organic wastes has considerably increased the growth of agricultural crops (see Chap. 4, Nieminen 2011). However, the amount of N applied must be taken into account. Prior studies revealed that the tree structure of this species may be affected by N and P stresses (Will 1985). Although height growth is not usually altered, radial growth in both stem and branches was most sensitive to addition of these elements. These changes have important impli­cations such as the loss of apical dominancy in fertilized trees and possible stem distortions, resulting in a decrease in the economic value (Will 1985; Hopmans and Chappell 1994).

3.4 Conclusions

Fertilization with bark ash improved the nutritional status of Pinus radiata planta­tions, and increased the contents of the main macronutrients in the needles. How­ever, some limiting nutrients such as P did not exceed critically low levels, so there is some room for improvement in the fertilization treatments. The effects on the needles were also inconsistent, and delay and the intensity of the effects depended on the time of application. The third application of ash significantly improved the diameter and height (and so the volume) growth in one of the plots (lutites) relative to the control treatment. It may be concluded that only after careful site evaluation ash application is indicated, otherwise the costs may exceed the benefit.

Body fuels, i. e., combustible substances added to the brick feed that are then combusted upon firing the brick, have been in use since the Egyptians added straw to the brick feed. Owing to the remaining organic content, biomass combus­tion ashes might be considered a low calorific value body fuel.

A tunnel kiln (Fig. 9.2) works as a counterflow heat exchanger. In the tunnel kiln packs of bricks set on a car train on rails move through the kiln one after the other. During their journey, the cars move toward, through, and past the stationary firing section at the center of the structure. During its travel, the brick set on the kiln car is slowly, ideally uniformly, heated up to the required firing temperature and then cooled down again (Fig. 9.3). Heat transfer within a tunnel kiln and within the

usually densely packed bricks on the kiln car takes place primarily by forced convection of the turbulent kiln gas flow, and, limited to the firing zone, by radiance of the burner flame to the brick. Further heat transfer by conduction from brick to brick occurs at the contact surfaces of the tightly stacked bricks. At a temperature range of 150-350°C the volatile proportion of any organic addition made to the brick feed is released as low-temperature-carbonization gases. These gases are usually conveyed to the chimney or to an appropriate postcombustion system.

As heating of the bricks set on the kiln car does not take place uniformly across the section of the brick, release of low-temperature-combustion gases at different points of the travel through the kiln can cause problems. The firing curve pictured in Fig. 9.4 shows the delayed reaction of the energy rich additions to the clay body:

Vertically stacked brick Brick stacked in Brick stacked in direction of flow and

direction of air flow

Fig. 9.3 Methods of stacking bricks on kiln cars

The combustion of the energy content in the core of the pile occurs later than that on the perimeter.

Only at a temperature of about 550-600°C do the temperature differences between the lower and the upper layers of the brick stacked on the kiln car diminish considerably.

The problems of using body fuels featuring a high percentage of volatiles is explained here with the example of paper sludge: At a temperature of about 150°C, all water that is still present in the cellulose is evaporated. This evaporation process is concurrent to driving out water still present in the clay body and extends into the first phases of release of crystalline water. At temperatures between 100 and 200°C, volatile substances are dissociated and evaporate, releasing carbon monoxide, hydrogen, and hydrocarbons.

Recent research by the author has shown the effects of concurrent combustion (a substance with an otherwise higher ignition temperature is ignited by the combustion of a substance with a lower ignition temperature) and the impact on the energy balance of a tunnel kiln. Such an example is pictured in Fig. 9.5 for a brick feed with 20% of paper sludge added to the clay in addition to a 1.5% of a bituminous coal featuring a high volatile content.

The above-mentioned differential thermal analysis (DTA) is of particular inter­est when it is compared with the DTA for the same basic mix but with 1.5% of anthracite and less than 2.5% of volatiles instead of the bituminous coal in the previous example. The DTA in Fig. 9.6 shows release of energy at the same temperatures as in the previous case but a second, smaller peak is observed at higher temperatures as well. This second peak has a positive impact on the thermal balance of the kiln.

An effect similar to that observed for the anthracite/paper sludge mix was observed in the tunnel kiln when a biomass ash/paper sludge mix was fired. This effect has to be confirmed in further and longer-lasting tests to prove that, biomass combustion ashes contribute positively to the energy balance of a brick tunnel kiln.

Bundling different residues into one use in Table 11.2 does not contradict our attention to detail in Table 11.1. The properties of individual combustion residues need to be taken into account even when considering the same use. All quantitative information on the properties of ash that has been determined in the Ash Programme as well as all information from Swedish R&D projects on ash is stored in a database, Allaska. It is available in Swedish and English at http://www. askprogrammet. com.1

11.2.4.1 Pulverised Fuel Furnaces

Pulverised fuel (PF) furnaces are often very large furnaces converted from furnaces for coal or oil to biomass. The fuel must be ground finely for it to be injected into the 1rThe Web site of the Ash Programme will soon be incorporated into that of Varmeforsk (http:// www. varmeforsk. se), but visitors will be redirected to the Varmeforsk Web site.

burners. This is not a very common type, as one usually prefers to retrofit such a furnace with a grate or to convert it to a fluidised bed furnace. However, when there are severe constraints on space in an existing combustion plant, a new PF furnace may be attractive.

The major part of the residues is fly ash. Having passed through high tempera­tures, 1,200°C and more, fly ash consists of small glassy particles that can yield pozzolanic reactions as in Portland cement. Biomass fly ash is not as good a binding material as coal fly ash, but it is very suitable for road building.

In converted coal or oil furnaces, the bottom ash usually has high contents of unburned carbon and it may be used as fuel in fluidised bed furnaces. It is a poor road building material because of its high water uptake. However, it may be used as low-quality filling material.

A pot experiment in a greenhouse was performed. Two soils were used; a sand (Elverum) and a sandy loam (0ksna) (Table 3.1). The soils were selected for this experiment because of the low content of readily available K, Mg and P which was found by Jeng et al. (2006). Although the soils were sampled at the same locations as the soils used in the experiments of Jeng et al. (2006), assuming low concentra­tions of readily available P and K, analyses of the soils selected for this experiment showed higher concentrations of readily available K (Table 3.2) than were found in the previous investigation [Elverum 7.6 mg readily available K (100 cm3)-1, 0ksna 8.6 mg readily available K (100 cm3)-1]. According to 0gaard et al. (2002), no yield response to applied K can be expected if the concentration of readily available K exceeds 10 mg (100 cm3)-1 (8 mg 100 g-1 and bulk density 1.25 mg m-3).

The experiment was designed to supply NPK similar to that supplied by use of the compound mineral NPK fertilizer Yara Fullgj0dsel® 21-4-10. On the basis of the contents of N and P in MBM, and of K in different crushed rock powders and BWA (Table 3.3), the amounts of different components in the experimental design (Table 3.4) were calculated using the following assumptions for calculation of effective amounts of NPK:

1. The N effect of MBM was estimated as 80% of Kjeldahl N as equal to mineral N based on Jeng et al. (2004).

2. The P effect of MBM was estimated as 50% of total P equal to the effect of mineral P (Jeng et al. 2006).

3. The amount of K extracted by 1 M HNO3 from crushed rock powder and by 7 M HNO3 from BWA was estimated as plant available and equal to mineral K.

Although the total amount of NPK applied differed between the treatments, based on the assumptions for effective amounts of N, P and K, it was intended to obtain almost the same effect of NPK as mineral NPK (treatments 3-12).

The pot size was 7.5 l, and the height of the soil in the pots was 20 cm. The fertilizer level was based on normal fertilization recommendations for cereals in Norway (120 kg N ha-1), and the concentration of plant nutrients in the pots should be at the same level as in a 20-cm-deep plough layer. All amounts of added fertilizer were calculated on a hectare to pot basis. There were three replicates. The crops used in the experiment were spring barley (Hordeum vulgare cv Kinnan) and spring wheat (Triticum aestivum), and the amounts of K applied (60 kg K ha-1) were in line with normal fertilization recommendations for cereals in Norway. Seeding was performed in May with 30 seeds in each pot. After germination the weakest plants were removed, leaving 20 plants per pot. Unfortunately, barley seeds from two different batches were used, and uneven germination of barley was recorded owing to poor germination of the seeds from one batch. However, in the pots with fewer than 20 plants, the lack of plants was partly compensated for by an increased number of tillers. A mean of 19 ears per pot was found at harvest for both barley and wheat. Therefore, the effect of uneven germination was found not to have a significant influence on the yield.

The intended temperature in the greenhouse was 15°C at night and 20°C during the day, but on warm days with outdoor temperature above 20°C the temperature inside the greenhouse was somewhat higher than the outdoor temperature, reaching 30°C during some summer days. The pots were initially irrigated 3 days a week, but in

warm periods irrigation was carried out almost daily to prevent drought. The irrigation caused no leaching of plant nutrients from the pots during the experiment.

The nutrient balances were calculated on the basis of effective amounts of P and K applied and uptake of P and K in wheat grain. In the experiment straw was not harvested and nutrient uptake in the straw is therefore not included in the calcu­lations of nutrient balance. After the experiment had finished, soil samples from all treatments from both the wheat and the barley experiments with both soils were taken (0-20 cm), 48 samples in total. The samples consisted of nine subsamples, three from each pot. The results for the soil samples in Table 3.7 represent means for both soils and both crops.

3.2.2 Statistical Analysis

One-way analysis of variance was carried out. For multiple comparisons the Ryan- Einot-Gabriel-Welch (REGWQ) multiple range test was applied with a signifi­cance level of P = 0.05, and the means presented followed by the same letter are not statistically different.

7.3.1 Compost

Compost is a product derived from composting that is high in nutrients and rich in humic acids. Nutrients are usually bound organically and thus released at a moderate speed (Gobat et al. 2003). Mature compost contains a diverse community of microorganisms; addition of compost to soil modifies considerably its biological,

Decomposition of organic residues
and chelation with ash panicles

Release of soluble humic material
and aliphatic organic acids

Reduction in the quantity
of exchangeable Al

Fig. 7.1 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

physical, and chemical properties in the short term as well as in the long term (Ryckeboer et al. 2003; Fuchs 2009). The use of compost in agriculture aids in replenishing and maintaining long-term soil fertility by providing optimal condi­tions for soil biological activity and a slow flow of nutrients adapted to the needs of the crop (Gobat et al. 2003).

The calcium carbonate equivalent (CCE) content was determined by analyzing the evolution of CO2, after reaction with dilute hydrochloric acid, in a Bernard calci — meter (MAPA 1986). The total organic carbon content was determined by dichro­mate oxidation of the samples and subsequent titration with ferrous ammonium sulfate (Yeomans and Bremner 1989). The total Kjeldahl N was determined by semimicro-Kjeldahl digestion (Bremner and Mulvaney 1982). The total concentra­tions of P, K, Ca, Mg, Na, Fe, Mn, Cu, Zn, Cd, Ni, Pb, and B were analyzed by inductively coupled plasma mass spectrometry after digestion of samples in con­centrated aqua regia (McGrath and Cunliffe 1985).

5.2.3 Statistical Analysis

Statistical analyses were carried out using the Statistical Package for Social Science (SPSS® Windows version 13.0) and Excel Statistics 2003 for Windows.

In Cote d’Ivoire the production of dried beans in 2005 was 740 kg/ha (Elzebroek and Wind 2008). According to ADM Cacao (2007 Interview with F. de Kort ADM

Cacao 22 November 2007. Koog aan de Zaan, the Netherlands), 10% of the beans consist of a shell, which means that per hectare 74 kg cacao shells is produced.

For the environmental impact of transportation many data are available. In this study the Eclipse data were used. Eclipse (Environmental and Ecological Life Cycle Inventories for Present and Future Power Systems in Europe) was funded by the EU and was carried out in 2002-2003. One of the objectives of Eclipse was to provide a harmonized set of public, coherent, transparent, and updated data on new and decentralized power systems for life cycle analyses.

The transportation by road in Europe is carried out by means of a heavy lorry trailer (401). The transportation by sea is carried out by means of a bulk carrier. The transportation by road in Cote d’Ivoire is carried out with a medium lorry. In Table 8.3, an overview is given of the emissions per ton kilometer of these vehicles. An overview of the assumed distances used in this study is given in Table 8.10. Transport of cacao beans to the Netherlands and transport of shells to bioenergy plants are not included, as these are present in both scenarios.

Wood ash is not only a valuable fertiliser in forest ecosystems, it can also benefit agricultural soils, especially acid soil types.

Analysing the impact of wood ash (5 and 201 ha-1) on an Italian agricultural soil regarding its physicochemical, microbiological and biochemical properties, Perucci et al. (2008) observed increasing pH values and electrical conductivity as well as decreasing microbial biomass C in the first months after application, but no long­term effects of ash amendments were found. Enhanced crop production for barley (Hordeum vulgare L.) and canola oil seed (Brassica rapa L.) was monitored when Boralf soils in central Alberta were supplemented with wood ash (12.5 or 25 t ha-1) in combination with N fertiliser (Patterson et al. 2004a). Although wood ash was, moreover, found to positively influence canola seed oil content, it may impair oil quality owing to an increase in the concentration of glucosinolate (Patterson et al. 2004b).

Combining wood ash with N sources is an interesting option for designer com­posts or fertilisers. Admixture of 8 and 16% wood ash and organic wastes prior to composting did have positive effects on the composting process (temperature, microbial activity) and the quality of the final product (no increase in heavy metal concentrations, improved nutrient balance) (Kuba et al. 2008). In comparison with mineral and organic fertilisers, wood-ash-amended compost was superior for the recultivation of a Tyrolean ski run, increasing plant cover and soil microbial biomass and respiration (Kuba et al. 2008) (Fig. 1.2). Composts produced with 8% wood ash admixture fostered utilisation of C sources (polymers, carboxylic and amino acids, alcohol, and carbohydrates) in a MicroResp™ assay and led to a change in microbial community structure, whereas compost with 16% ash altered bacterial and fungal community composition, but did not enhance C utilisation (Bougnom and Insam 2009). Bougnom et al. (2009, 2010) demonstrated that compost produced with wood ash supplement (8 and 16%) may be a cheap alternative to liming in tropical areas, where many soils are characterised by a low pH. Wood ash alone also significantly increased pH and electrical conductivity in a tropical soil in Cameroon and was found to supply nutrients to the soil (Voundi Nkana et al. 2002). Besides raising soil pH, wood ash amendments (4 and 6 t ha-1)

on an acid soil in Nigeria improved maize grain yield (Mbah et al. 2010). As lime or artificial fertilisers are unaffordable for resource-poor farmers, wood ash may be an alternative for improving soil fertility in agricultural soils in the tropics (Voundi Nkana et al. 1998; Bougnom et al. 2010; see Chap. 7, Bougnom et al. 2011). Wood ash application of up to 41 ha-1 on tropical soil in Uganda was observed to enhance bean (Phaseolus vulgaris) and soybean (Glycine max. L) biomass, but led to higher Cu, Zn, Cd and Pb concentrations in edible plant parts (Mbaherekire et al. 2003). Analysing the effect of wood ash application as well as combined wood ash and compost amendments on soil microorganisms, Odlare and Pell (2009) revealed toxic effects of wood ash on potential denitrification in an arable soil on a short­term and a long-term basis. Compost was, however, able to mitigate these heavy — metal-related negative effects of the ash.