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.

In accordance with earlier studies, wood ash increased nematode abundance (Hyvonen and Huhta 1989) in the autotrophic experiment (Nieminen 2009) but not in the heterotrophic experiment (Nieminen 2008b). Although nematodes were not identified, it is probable that their diversity was less in the simpler heterotrophic experiment, and this could partly explain their different response. Another major difference between the two experiments was that in the experiment without plants, soil moisture was kept optimal throughout the experiment, whereas in the pot experiment with plants, the organic soil dried considerably after grass harvest.

The increase of nematode numbers after loose wood ash application in field lysimeters with pine seedlings was mostly due to increased abundance of bacterial feeders, in other words, the ratio of bacterial feeders to fungal feeders increased (Liiri et al. 2002b). Liiri et al. (2007) found that loose wood ash reduced the abundance of fungal-feeding nematodes, but no effect on nematodes was evident in another microcosm study by Liiri et al. (2002c). The results are in broad accordance with an increased ratio of bacteria to fungi after ash application reported elsewhere (Baath et al. 1995; Perkiomaki and Fritze 2002), although Liiri et al. (2002b) did not detect ash effects on the ratio of bacteria to fungi. This illustrates that given sufficient response time, microbe-feeding nematodes can reliably indi­cate ash effects on soil microbes. It remains unclear why nematodes are not always responsive to wood ash. One possible reason for this is the initial community composition. For example, in Liiri et al. (2002c), the abundance of fungal-feeding nematodes was low and highly variable at the beginning of the experiment, which obviously made it difficult to observe changes in the ratio of bacterial feeders to fungal feeders.

4.2 Conclusion

In summary, laboratory experiments have shown that wood ash effects on dominant enchytraeids depend on labile carbon availability to the decomposer food web. The fact that increased carbon availability alleviated wood ash effects on enchytraeids without changing the pH supports a view that wood ash effects on soil animals are partly indirect consequences of altered food resources. In other words, food limita­tion magnifies negative wood ash effects. Although the effects of loose wood ash are well known, knowledge of the effects of granulated ash and ashes amended with organic materials on soil organisms in boreal coniferous forests is still incomplete.

Acknowledgements The study was financially supported by the Runar Backstram Foundation and the Maj and Tor Nessling Foundation. I appreciate the cooperation of the Jyvaskyla Soil Ecology Group, help with Table 4.1 from J. Haimi, V. Huhta, M. Liiri and H. Setala, and con­structive comments on the manuscript by two anonymous reviewers.

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.

Wood ash application at rates of 1 and 5 t ha-1 in a Scots pine stand in central Finland decreased numbers of the enchytraeid worm Cognettia sphagnetorum, and slightly changed the soil microarthropod community. Soil chemical parameters were also influenced by these treatments, whereas microbial communities were only affected by the higher ash concentration (Haimi et al. 2000). Enchytraeid size and abundance were found to be reduced in microcosms containing 30 g humus from a Norway spruce forest and amended with 480 mg wood ash, but the negative effect could be offset by sucrose, indicating that the impact of wood ash on soil animals in forest ecosystems is mainly linked to C input rates. Negative effects may thus be avoided by minimising C limitations for decomposers (Nieminen 2008; see Chap. 4, Nieminen 2011).

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

3.2.1 Chemical Analysis

Total metals, P and S in crushed rock, bottom ash and plant material were extracted by 7 M KHNO3 and determined by inductively coupled plasma optical emission spectrometry according to ISO 11885 (ISO 2007). The pH of the soil was deter­mined in a solid-water suspension (1:2.5, v/v). Readily available P, K, Mg, and Ca in soil were determined by extraction with 0.1 M ammonium lactate and 0.4 M acetic acid (pH 3.75) in a solid-to-solution ratio of 1:20 (w/v) (Egner et al. 1960). Nonexchangeable K was extracted by 1 M HNO3 according to Pratt (1965). The particle size distribution of the soils was determined according to Elonen (1971). Total N was determined as Kjeldahl N as described by Bremner (1960).

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.

The large quantities of combustion residues may be swallowed only by a mass market, that of materials for civil works. The largest single use in 2006 was as a

construction material in the closure of landfills (as well as for capping), with approximately 650,000 t; see Table 11.2. The financial incentive for this use is the possibility to waive the tax on waste sent to landfill: the materials are used and replace virgin materials. However, many currently active landfills will be closed within the next 10-15 years. It should be noted that backfilling cavities in Table 11.2 concerns mostly air pollution control (APC) residues from combustion of MSW.

Spreading to forest soils is a small area of use, with approximately 35,000 t/year, but is of vital importance for the sustainability of the production of solid biofuels from biomass harvested from forests. The relevant biomass fraction is the logging residues, and harvesting it on top of the extraction of timber and pulping wood in conventional forestry not only removes the mineral nutrients in the residues that if left in the forest would have been available to the next generation, but also exacerbates the natural acidification of forest soils by conventional forestry.

Rogelio Nogales, Gabriel Delgado, Mar Quirantes, Manuel Romero, Esperanza Romero, and Eduarda Molina-Alcaide

Abstract Wet and dry olive cakes are the most important wastes generated when olive oil is produced. In recent years, both olive wastes have been incinerated to produce electricity, and thereby large amounts of fly and bottom ash are generated. In this study, physical, physicochemical, and chemical characteristics of olive waste ashes produced in Andalusian biomass power plants were analyzed to evaluate their suitability for agriculture. High variability among fly and bottom ashes may be ascribed to the origin of the olive waste and the combustion temperature. Waste olive ashes, which contained all particle sizes, showed high values of pH, salinity, water holding capacity, calcium carbonate equivalent, and P, K, Cu, and B contents. In contrast, moderate values were recorded for Ca, Mg, Zn, and Ni. Nitrogen is scarce in olive waste ashes; they thus can only be part of any fertilization strategy.

5.1 Introduction

The renewable energy consumption in the EU will increase from 11.6% in 2009 to 20% by 2020. Biomass is the main (61%) resource for the renewable energy consumed (10th EurObserv’ER 2010). In Spain, the contribution of renewable energy tp total gross domestic consumption in 2008 was 7.6%, of which biomass up 5.1 Mt (47% of total renewable energy, INE 2010).

Olive oil production is one of the most important industries in Mediterranean countries. In Spain, olive tree cultivation mainly occurs in Andalusia. In 2008, 600 x 103-900 x 103 t olive oil was produced in this region, using the two-phase centrifugation systems as common (90%) extraction technology (Fig. 5.1). This system generates huge amounts (between 2.5 and 3.5 Mt/year in Andalusia) of a

R. Nogales (H), M. Quirantes, M. Romero, E. Romero, and E. Molina-Alcaide Estacion Experimental del Zaidin (CSIC), Profesor Albareda, 1, 18008 Granada, Spain e-mail: rogelio. nogales@eez. csic. es

G. Delgado

Department of Edaphology, University of Granada, Campus Universitario de la Cartuja, 18071 Granada, Spain

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

DOI 10.1007/978-3-642-19354-5_5, © Springer-Verlag Berlin Heidelberg 2011

waste called crude wet olive cake, or alperujo, which is composed of olive pulp, stones, and skins together with residual oil, and water added during the oil extrac­tion process. Alperujo is an acidic, semihumid waste, rich in organic matter and potassium. After drying (less than 1% moisture), its low heating values ranges from 15 to18 MJ kg-1. Part of this waste is dried and treated with solvents to obtain olive-cake oil and a waste called dry olive cake, or orujillo. The orujillo (0.6-0.9 Mt/year in Andalusia) has recalcitrant organic matter, high potassium content, and low heating values between 14.5 and 20 MJ kg-1 (Agencia Andaluza de Energia 1999; Alburquerque et al. 2004; Caputo et al. 2003; Nogales et al. 1998).

In recent years, both olive wastes are being used as fuel for electrical energy production. In Andalusia, ten biomass power plants have been established and produced 0.81 TWh (80% of the total renewable electricity generation in this region) in 2009. In general, the previously mentioned olive wastes, alone or mixed with other wastes, are burned in conventional boilers at 450°C. The heat released is used to heat water to turn a steam turbine, which generates green electric energy. In some biomass power plants, fluidized-bed combustors at 850°C are used as boilers. The combustion of olive wastes for energy production generates great amounts of fly ash and bottom ash (between 4 and 8% of the total burned olive wastes) as end waste. In general, this end waste is landfilled in sites adjacent to the biomass power plants. However, the use of landfills for ash disposal is expensive and is being discouraged by more stringent regulations and public opposition.

Numerous studies focused on chemical characteristics of ash produced by coal combustion or gasification (Ahmaruzzarman 2010; Hytonen 1998; Jala and Goyal 2006). In contrast, ash generated from biomass has received less attention and most of the research has focused on ash from woody biomass combustion (Demeyer et al. 2001; Kuba et al. 2008; Someshwar 1996; Vance 1996; see Chap. 6, Omil et al. 2011). Other ashes have been characterized, such as those from the pulp and paper industry (Naylor and Schmidt 1989; Muse and Mitchell 1995) and those produced
by the incineration of municipal solid waste (Zhang et al. 2002) and biosolids (Benitez et al. 2001; Merino et al. 2005) or other agricultural wastes (Mozaffari et al. 2000). However, information is not available concerning the characteristics of ashes from olive waste combustion.

The aim of this study was to analyze the physical, physicochemical, and chemi­cal characteristics of fly ash and bottom ash produced in Andalusian biomass power plants, which use olive wastes (wet and dry olive cakes) as fuel, to evaluate their suitability for use in agriculture.