Soil pH and Ca, Mg, K, P, and S levels increased slightly after ash application. No leaching loss was observed after several applications of ash. Furthermore, microbial activity increased and ammonium and nitrate concentrations decreased as a conse­quence of N immobilization. No effects due to heavy metals were observed in the soil solution, and the availability of Mn and Zn increased slightly after the third application of ash.

3.3.1 Nutrition

The Pinus radiata plantations were initially deficient in P, K, and Mg (Table 6.4), as often found in this type of acid soil plantation (Mesanza et al. 1993; Romanya and

Vallejo 1996). In contrast, foliar N concentrations were sufficient (15 mg g-1). Repeated application of wood ash to the soil did not have any effect on foliar concentration 3 years after the initial treatment. Although the concentrations of basic cations such as Ca2+ and Mg2+ increased significantly in the soil, foliar analysis did not show any significant changes in the needles after the treatment. This may be the result of tree growth and the consequent dilution effect.

Supplemental fertilization with slow release of phosphorus (WAP treatment) increased the foliar concentration of the element throughout the study (Fig. 6.3). The differences between treatments are more significant for the soils over migma — tites than for those over lutites. However, repeated application of wood ash did not increase the levels of P in needles.

The filter ash is transported by means of a heavy lorry trailer from the bioenergy plant to a mine in Germany. The distance is assumed to be 250 km. The amount of ash transported is 6.7 kg, which corresponds to 1.68 t km. The total PK nutrient demand has to be provided by synthetic fertilizer (243 kg) under the same condi­tions as described in scenario 1. The transport distance corresponds to 194 t km. In Table 8.11, an overview is given of the total emissions in scenario 2.

8.4.3 Comparison of the Two Scenarios

In Table 8.11, the emissions caused by the two scenarios are compared. The emissions caused by scenario 1 and by scenario 2 are about the same, which is not surprising because of the low level of replacement of the PK fertilizer that can be obtained. However, the potential CO2 reduction per kilogram of filter ash is significant, namely, about 0.40 kg CO2/kg filter ash.

In this study some assumptions have been made. In the sensitivity analysis, the influence of these assumptions on the emissions is determined.

• All of the phosphorous and potassium present in the ash is available as nutrient. If the availability of both elements drops below 40-45%, then the CO2 and SO2 emissions in scenario 1 will be higher than those in scenario 2.

• The transport distance within Cote d’Ivoire is 800 km. If the transport distance is 500 km, the CO2 emissions in scenarios 1 and 2 decrease to 160.3 and 161.9 kg, respectively. If the transport distance increases to 1,000 km, the CO2 emissions are 179.3 and 180.9 kg, respectively. This means that the absolute value in both scenarios will be influenced to a small extent, but the difference between the values in both scenarios remains the same.

• The transport distance within Cote d’Ivoire is the same for the filter ash and the PK fertilizer. If the transport distance of the ash is about 1,500 km more than that for the PK fertilizer, then the CO2 emissions in scenario 1 will be higher than those in scenario 2.

Harvested shoots were dried at 60°C, weighed, ground with a plant mill, and stored for further investigations. The P content in plant tissue was measured after dry ashing using the molybdovanadate method (Page et al. 1982). Plant P uptake was calculated by multiplying the P content of the shoots and shoot biomass.

The soil samples were air-dried and sieved (2 mm) before analysis. Soil pH was measured in 0.01 M CaCl2 using a 1:2.5 soil-to-solution ratio. For characterization of soil P pools, different methods were used. The method described by Van der Paauw (1971) was used to determine water-extractable P (Pw) with a soil-to-water ratio of 1:25. The P concentrations in the extracts were measured by the phosphomolybdate blue method via flow-injection analysis. The content of double-lactate-soluble P (Pdl) (photometric method) was quantified according to Blume et al. (2000). By means of the ammonium oxalate method (Schwertmann 1964) the extractable amount of P (Pox) allows the estimation of the amount of inorganic P being adsorbed on amor­phous iron and aluminium oxides in the soil. Pox and the oxalate-soluble aluminium and iron contents (Alox, Feox) in soil were extracted and their concentrations were determined by inductively coupled plasma optical emission spectroscopy (ICP-OES; JY 238, Jobin Yvon, France). With use of these data, the P-sorption capacity [PSC (mmol kg-1) = (Alox + Feox)/2] and the degree of P saturation [DPS (%) = Pox/ PSC x 100] could be calculated according to Lookman et al. (1995) and Schoumans (2000). Total P was analysed after aqua regia dissolution in a microwave oven (Mars Xpress, CEM, Kamp-Lintfort, Germany) followed by ICP-OES.

Furthermore, the sequential P fractionation method developed by Hedley et al. (1982) was used. Different P fractions of decreasing bioavailability (resin-P, NaHCO3-P, NaOH-P, H2SO4-P) were extracted step by step by using stronger extracting agents. The remaining P in the soil sample after the extraction steps is considered as residual P. The residual P content was determined by subtracting the amount of extracted P from the total P content [residual P = total P — (resin-P + NaHCO3-P + NaOH-P + H2SO4-P)] as described by Schlichting et al. (2002). Total P was determined by aqua regia digestion in a microwave oven.

2.2.2 Statistics

Soil and plant data corresponding to four spatial replications were subjected to two- and one-factorial analysis of variance (general linear model). The results are reported as main effects and interactions. The means of soil and plant parameters were compared by the Duncan test. Significances were determined at p < 0.05. Significantly different means were indicated by using different characters. The statistical analysis was carried out using SPSS 15.0.

Aluminum is a light metal that makes up 7% of the earth’s crust and is the third most abundant element, after oxygen and silicon, plant roots are therefore almost always exposed to aluminum in some form (Ma et al. 2001). Aluminum exists in soils in many harmless forms, including hydrous oxides, aluminosilicates, sulfates, and phosphates (Haynes and Mokolobate 2001). Aluminum inhibits plant growth by affecting plant roots and development (Delhaize et al. 1993; Ma et al. 2001), inhibiting both cell divisions in the apical root meristem and cell elongation (Blamey et al. 1983). Roots become stubby and brittle; root tips and lateral roots become thick and occasionally necrotic brown (Mossor-Pietraszewska 2001). These effects restrict the ability of the plant to take up nutrients and water, leading to nutrient and/or water stresses (Rout et al. 2001; Haynes and Mokolobate 2001). Plants in acid soil, owing to aluminum solubility at low pH, exhibit a variety of nutrient-deficiency symptoms, with a conse­quent decrease in yield. Aluminum toxicity is linked with phosphorus, calcium, magnesium, or iron deficiency syndrome (Rout et al. 2001). To overcome the lack of productivity in aluminum toxic soil, the first step is to treat acidity, which will promote better root growth and function and will allow nutrients and water to be taken up more effectively by the plant.

Claes M. Ribbing and Henrik G. Bjurstrom

Abstract The Swedish Ash Programme is an applied R&D programme aimed at demonstrating uses for combustion residues (ash) and providing an improved understanding of these residues for the purpose of resolving regulatory questions. Fuels are biomass, wastes, peat — any solid fuel but coal. The progress in the Ash Programme since its inception in 2002 is reviewed. The hierarchy for biomass ash is recycling to forest soils as compensation for the removal of mineral nutrients first, and use in civil works second. Assessment of the environmental impact in view of permitting procedures for civil works and ecotoxicity are particularly addressed.

11.1 Introduction

The Swedish Ash Programme is an applied R&D programme aimed at demonstrat­ing uses for combustion residues (ash) and providing an improved understanding of these residues for the purpose of resolving regulatory questions. It is a collaborative undertaking implemented since 2002 by Varmeforsk, the Swedish Thermal Engi­neering Research Institute, and co-financed by the ash producers, i. e. the combus­tion plants, and the government, principally through the Swedish Energy Agency. The Swedish Environmental Protection Agency and the Swedish Road Administra­tion also contribute financially.

The vision moving the Ash Programme is:

“Combustion residues are resources in a sustainable society”

Since its inception in 2002, the Ash Programme has supported more than 100 applied R&D projects, most of them co-financed by other organisations. Including

C. M. Ribbing (*)

Svenska Energiaskor AB, Torsgatan 12, 111 23 Stockholm, Sweden e-mail: claes. ribbing@energiaskor. se

H. G. Bjurstrom

AF-Engineering AB, 169 99 Stockholm, Sweden e-mail: henrik. bjurstrom@afconsult. com

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

DOI 10.1007/978-3-642-19354-5_11, © Springer-Verlag Berlin Heidelberg 2011 currently ongoing projects to be concluded by the end of 2011, they represent an investment of approximately €9 million. All of these are short actions aimed directly at a specific question, demonstrating on a large scale the utilisation of combustion residues or monitoring the environmental impact of a large-scale application. The programme does not support traditional university research over a period of several years.

The results achieved in the Ash Programme between 2002 and 2008 were reviewed in a contribution to the 2009 International Waste Management and Landfill Symposium (Bjurstrom et al. 2009). They are also described in a synthesis in English available from Varmeforsk’s Web site (Bjurstrom and Herbert 2009). These results will be summarised briefly in this review, as a background to the themes focused on here, ash from solid biofuels and the regulatory process, which will be developed in more detail.

The areas of use targeted by the Ash Programme are (1) as a geotechnical material, e. g. in roads or other civil works, (2) in landfill construction and closure and (3) as mineral nutrients in wood ash recycled to forest soils. Issues common to all these areas are the chemistry of ash and environmental aspects.

The results obtained and the conclusions presented within the projects are those of the scientists. Environmental authorities do not automatically agree with the conclusions. To be more specific, bones of contention are the official environmental target “A non-toxic environment” and whether considering wastes as a resource is politically correct.

Two recent studies (Nieminen 2008b, 2009) focused on the interaction between wood ash and carbohydrate supply in microcosms. The enchytraeid C. sphagne — torum was chosen as the target organism because of its importance in boreal forest soil, and because studies have consistently shown that it is sensitive to wood ash. The abundance of microbial-feeding nematodes provided information on microbial production.

Nieminen (2008b) studied the interactive effects of sucrose and loose wood ash on enchytraeids and nematodes in organic Norway spruce forest soil from which enchytraeids had been extracted using the Baermann wet funnel technique (O’Con­nor 1957). After extraction, the humus was sieved, weighed into 20 cotton-plugged glass jars and 20 individuals of the enchytraeid C. sphagnetorum were returned and each microcosm was inoculated with microflora and microfauna. Nieminen (2008b) treated the microcosms with loose wood ash (480 mg per microcosm,

1,0 kg ha-1) and sucrose (1.6 g per microcosm, 1.3 Mg C ha-1) in a full factorial design.

After a 3-month incubation at constant temperature, the dry matter content of organic soil was 22 ± 0.5% (mean ± standard error, n = 20) irrespective of treat­ment (Nieminen 2008b). Addition of wood ash increased the soil pH from

5.2 ± 0.1 to 6.9 ± 0.2 in both sucrose-amended and non-amended soil. Sucrose addition increased and wood ash addition reduced enchytraeid length. Sucrose addition increased nematode abundance by more than 100% on average. Wood ash addition alone decreased enchytraeid abundance compared with the control (Fig. 4.1).

Nieminen (2009) studied the interactive effects of three levels of solid sucrose (0, 0.88 or 8.8 g, equalling 0, 100 and 1,000 kg C ha-1; the intermediate treatment was omitted in the original article) and two levels of birch ash (0 or 1.175 g per microcosm, equalling 500 kg ha-1) in pots containing a layer of organic Norway spruce forest soil on mineral soil. In addition to one Norway spruce (Picea abies (L.) H. Karst. ssp. abies) seedling, these pots also contained the grasses Deschamp — sia flexuosa (L.) Trin. and Calamagrostis epigejos (L.) Roth and the experiment was continued in a greenhouse for one growing season (Nieminen 2009).

Wood ash increased the soil pH from 5.4 ± 0.06 to 5.7 ± 0.06 irrespective of carbon addition (Nieminen 2009). Sucrose increased the moisture of organic soil from 40 ± 0.02% to 57 ± 0.11% fresh mass in C1000 (analysis of variance, sucrose x ash F224 = 4.9, p = 0.017; control: simple effect of sucrose F2,24 = 11.4, p < 0.001), but this was partially counteracted by wood ash (mois­ture percentage 46 ± 0.05% in AC1000; F124 = 7.5, p = 0.011). Enchytraeids went close to extinction in control pots, but in C1000 treatments reached 1.8 times the initial density regardless of wood ash (sucrose F2,24 = 10.5, p < 0.001).

Enchytraeid length varied from 3.66 ± 0.28 mm in C1000 to 5.07 ± 1.46 mm in AC1000 ash-treated pots and the wood ash effect was significant. Wood ash increased nematode abundance (ash F124 = 5.6, p = 0.027). The nematode com­munity in control pots consisted mainly of bacterial feeders (50% of individuals; in particular, Rhabditis sp.) and predators (Mononchus sp.), and all others amounted to less than 25% of individuals.

Angelo Saraber, Marian Cuperus, and Jan Pels

Abstract A case study has been formulated concerning the use of ashes from combustion of cacao residues (shells) for electricity production and for nutrient recycling to the original soil. The effect in terms of kilograms of fertilizer per hectare and the environmental impact of closing the nutrient and mineral cycle are quantified. If the ashes are used as fertilizer, this fertilizer will only replace about 2% m/m of phosphorus and potassium that is necessary to fulfill the nutrient demand. This means that the contribution of the ashes is small. Furthermore, nitrogen has to be added as fertilizer. There is also a small advantage of reduction of CO2 emissions by nutrient recycling; this reduction is negligible from the point of view of the plantation, but from the point of view of the filter ash, the potential emission reduction is significant. This study shows that ashes from stand-alone combustion of certain agricultural residues are an potential valuable mineral source for elements such as phosphorus and potassium.

8.1 Introduction

Biomass is one of the sustainable sources of energy that is used for today’s production of electricity and heat. Sustainable use of biomass for energy production encompasses many aspects. They range from social aspects such as security of food supply and workers’ health to environmental aspects such as clean emission and protection of nature. Although interesting and relevant, this study is limited to only one of those aspects: the role of ash management in nutrient recycling and emission reduction. In Finland and Sweden, for instance, ashes from peat and wood combus­tion are utilized for fertilization in forestry (Emillson 2006). In 2004, about 27,0001

A. Saraber (H) and M. Cuperus,

KEMA, P. O. Box 9035, 6800 ET Arnhem, The Netherlands e-mail: asaraber@vliegasunie. nl

J. Pels

ECN, P. O. Box 1, 1755 ZG Petten, The Netherlands

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

DOI 10.1007/978-3-642-19354-5_8, © Springer-Verlag Berlin Heidelberg 2011 was used for forest fertilization in Finland. Certain wood ashes contain high amounts of calcium compounds, which make them suitable as an alternative liming agent. The calcium carbonate equivalent may be 26-59% depending on the source (Ohno and Erich 1990). Other biomass ashes may also be interesting for fertiliza­tion, such as ash from cacao residues as suggested by Simpson et al. (1985), which contain high amounts of potassium.

The Netherlands is one of the biggest producers of cacao products in the world, but all cacao beans are imported from other countries such as Cote d’Ivoire, one of the largest (40%) producers of cacao beans. Some of the process residues (shells) is currently used for direct co-combustion for power generation and some is used in gardening as soil cover. Cacao residues (shells) contain about 8-10% m/m ash-forming matter, which mainly consists of potassium and phosphorous, which are interesting nutrients for agriculture. The caloric value of cacao shells is about 19-22 MJ/kg (higher heating value), whereas the water content is 7-13% m/m (ECN 2010).

An interesting step forward would be to use the ashes from cacao residues as a source for nutrients by recycling the ashes back to the plantations where the cacao was grown or to use them as raw material for fertilizer production. In this case study, the impact on the nutrient balance and reduction of CO2, NOx, and SO2 emissions has been assessed. Disposal of the ashes in a mine is used as a reference.

The key to utilising combustion residues as well as other mineral wastes in civil works and keeping them out of landfills is the assessment of the environmental impact in the permitting procedures. This was one of the main reasons for creating the Ash Programme: a method of computing impact had to be developed and numerical values for the properties have to be fed into the method. This work was performed in conjunction with environmental authorities, but this does not mean that these authorities reach the same conclusion in their assessment.

Initially, concepts similar to the “end of waste” presently discussed in the EU were considered, but as an assessment still has to be done, the method of the Swedish Environmental Protection Agency for assessing the impact of contami­nated soil on health and the environment was chosen as a starting point and adapted to the pilot cases (Bendz et al. 2006):

• A non-surfaced road in a forest, with a comparatively thin layer of ash

• A surfaced road with MSWI bottom ash in the subbase, with a comparatively thick ash layer

The purpose of the assessment is to define the boundary between a low risk level and a not low risk level (in legalese terms, as “no risk” does not exist and “high risk” will not be allowed). Below the boundary, a simplified procedure could be defended, for example only giving notice to the environmental authorities. Above the boundary, a full permitting procedure would of course be necessary, with a detailed analysis of the expected local environmental impact.

All mechanisms for dispersal from the body of the road and for human exposure were described in the model. The model is conservative: a plausible worst-case
scenario is assumed, yielding rather large safety margins. For example, the most exposed person is assumed to live all his or her life within 20 m from the road, 30% of this person’s intake of vegetables is home-grown close to the road (hardly washing them) and when the road is disused after some 60 years, it is used as a recreation area by adults and children, assuming 40 windy days per year and person.

The result of these first computations is that dispersal of dust yields the dom­inating health risk (Bendz et al. 2006). Criteria based only on leaching to ground­water yield significantly larger limit values for, for example, heavy metals in the combustion residues. In the simulations, even with MSWI bottom ash, leaching from several roads yields insignificant increases in heavy metal content in the recipients of two catchment areas (Wik 2009).

To put this result in perspective, the composition and leaching properties of most combustion residues are such that, if correctly used, these residues present a “low risk” to health and the environment. The only ones that cannot satisfy the upper limit values for low risk are APC residues from MSWI and fly ash or APC residues from combustion of impregnated wood.

The low risk limit values for some of the trace elements are shown in Table 11.7. Two references are given in Table 11.7 for the sake of comparison. The first reference is a set of limit values derived by the Swedish Environmental Protection Agency after the Ash Programme had published its proposal (Swedish Environ­mental Protection Agency 2010). The purpose of this set is to define a boundary below which the user of a waste material does not even need to give notice of his or her use of these materials. These values are substantially lower as they represent the 90th percentile of concentrations in soil. The boundary defined by the Swedish Environmental Protection Agency and that proposed by Bendz et al. (2006) and later updated (Bendz et al. 2009) are not the same. The second reference is the recommended limit values for ash spread to forest soils as nutrient compensation (Swedish Forest Agency 2008).

Note the comparatively low concentration found for arsenic, 15 mg/kg dry substances, the immediate reason for which is that arsenic is genotoxic. One should keep in mind though that the results in Table 11.7 are the first results based on conservative models, conservative assumptions and uncertain data. For the time being, it is recommended that ash with an arsenic content in excess of this value should not be left on the surface when the road is abandoned.

Wood ash is applied to forest soils to alleviate nutrient depletion and soil acidifica­tion, either alone or in combination with N fertiliser. Wood ash is also applied as lime replacement, providing base cations to increase soil pH (Steenari et al. 1999; Meiwes 1995; Brunner et al. 2004). This liming effect can be attributed to Ca and Mg carbonates in the ash as well as to its fine structure (Pitman 2006). Arvidsson and Lundkvist (2003) observed an increased soil pH after 3 Mg ha-1 wood ash application in young Norway spruce (Picea abies) stands. Moreover, concentra­tions of exchangeable Ca and Mg as well as the effective cation-exchange capacity were elevated compared with the control. As salts contained in the ash started to dissolve after application, high K, Na and SO4 concentrations were also found in the soil (Augusto et al. 2008). Jacobson et al. (2004) reported an increased soil pH and base-cation content 5 years after amendment with self-hardened and crushed ash (3, 6 or 9 t ha-1) or pelleted ash (3 t ha-1) on two different coniferous sites in Sweden, whereby the ash formulation did not have an effect on soil chemistry despite differences in solubility. Basic substances used to amend soil may, however, foster nitrification and nitrate leaching in soil ecosystems and hence enhance soil acidity, counteracting the positive effects of wood ash application (Meiwes 1995). Since ash components bind to organic substances in the humus layer of forest soils, fertilisation effects of wood ash amendments on soil acidity and extractable Ca and Mg were found to last for many years (Bramryd and Fransman 1995; Saarsalmi et al. 2001, 2004, 2005; Mandre et al. 2006). The impact of wood ash applications (9 and 18 Mg ha-1) on soil properties in different tree stands (European larch, aspen and poplar) was evaluated in a 7-year experiment in Michigan, revealing that wood ash was able to foster long-term productivity and repeated applications may even have the potential to make up for biomass-C losses due to plantation management operations (Sartori et al. 2007).

Repeated application of ash did not produce significant changes in foliar concen­trations of any of the elements. However, the application produced an increase in the concentration of Zn, Cu, and Ni in needles in the plots on lutites (Table 6.5). This was not observed in 2006. The foliar concentration of Cd was closely related to soil acidity and therefore the concentration of Cd decreased from the third applica­tion of ash onwards.