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.

Although roads are not a particularly suitable use for residues for logistical reasons, they are the type of civil works with the best developed set of requirements, against which constructions with combustion residues may be assessed. Fly ash, preferably from solid biofuels or sludges from the pulp and paper industry, has been used in non-surfaced gravel roads and bottom ash is now also beginning to be used.

Non-surfaced roads have been built using fly ash in Sweden for some time. However, through the introduction of the Finnish experience with this technology (Lahtinen 2001) as the starting point within the Ash Programme, a convenient impulse was given to renewed development. In successive projects, fly ash from biomass has been characterised, recipes have been developed and a few test roads have been built (Macsik and Svedberg 2006; Macsik et al. 2009). A short summary of the results is as follows: bearing capacity and freeze-thaw resistance have increased, fly ash replaces natural materials of about twice its volume, which leads to a significant reduction in weight and height. For the good properties of biomass fly ash to be optimally exploited, and for conservation of fly ash resources, ash should be used to stabilise bad or worn-out road materials. Adverse impacts on the environment could not be observed during the monitoring of construction and use of the roads.

Bottom ash from solid biofuels is also used for roadwork. An example is a private road north of Norrtalje, where approximately 5,000 t of mixed bottom and fly ash from a grate furnace have been used since 2006; see Fig. 11.1. It was possible to run 40-t lorries on the road even when it was flooded by melting snow, which is remarkably good. Infiltration in the body of the work is very slow, which indicates that the environmental impact should be minor. The impact of an ash pile stored for 7 years on the place has been investigated: the uptake of heavy metals in ash by plants and berries did not lead to any increased levels in the plants.

The ash of solid biofuels also has binding properties and it has been utilised in concrete applications. One project involved replacing Portland cement in panel stope mine filling, where large blocks or “stopes” of ore are removed, creating a large cavity. These stopes are backfilled using concrete (cement and mine tail­ings) to stabilise the mine. In full-scale trials, biomass fly ash from grate furnaces could replace 50% of the Portland cement. The other use of solid biofuel ashes demonstrated in the Ash Programme is as filler in low-quality concrete. However, the chloride content of the ash may pose corrosion problems for steel reinforce­ment bars.

Fig. 11.1

Plots on lutites and migmatites were selected for this study in order to compare two plantations of the same age, but located over two different geological materials.

The following figures include the estimated marginal means of the dasymetric variables: total height and normal diameter (corrected in the covariance function, data from the plots before the treatment in 2003 are used as a covariate). A statistical analysis comparing between levels of the factor “treatment” corresponding to each level of the factor “time” and the levels of the repeated means is also included.

Different effects were observed in both types of plots. In the first plot (Fig. 6.4), the statistical analysis revealed significant increases in height and diameter growth as a result of the application of ash and phosphorus, mainly from 2005 onwards. The time-treatment interaction revealed some differences between the treatments, with benefits to both plots. In the second plot (Fig. 6.5) increases in the normal diameter for WA and WAP treatments were significant. The different response of the plantations may be due to the differences in the nutritional state, as indicated by the different site index values (18.7 and 23.1 m in the lutites and migmatites, respectively).

Fig. 6.3 Foliar macronutrients in soils over lutites and migmatites. Control untreated, WA applications of 4.5 Mg wood ash ha-1 for three consecutive years (2003, 2004, 2005), WAP single applications of 4.5 Mg wood ash ha-1 and 0.1 Mg P2O5 ha-1

-j

‘O

Fig. 6.4 Estimated marginal means of Pinus radiata D. Don in plots over lutites. Control untreated, WA application of 4.5 Mg wood ash ha-1 for three consecutive years (2003, 2004, 2005), WAP single applications of 4.5 Mg wood ash ha-1 and 0.1 Mg P2O5 ha-1. In the repeated measures analysis, the sphericity assumption was not valid and therefore values of P-Huynh Feldt were used in univariate tests of their interactions. Ht total height, Dn normal diameter

Fritz Moedinger

Abstract The addition of biomass ashes to a brick feed has been investigated in a full-scale industrial production process over several days. The addition of biomass ashes to the brick feed is part of an ongoing research and development project targeted at substituting or combining quarried raw materials with suitable waste materials. In this chapter some of the early results of the first industrial trial runs with biomass ashes are presented. The main scope of this ongoing research and development project is reduction of production cost, generation of additional revenue from gate fees, and improvement of product characteristics.

9.1 Introduction

Besides other methods of recycling biomass ashes as described in other chapters in this book (see Chap. 1, Knapp and Insam 2011; Chap. 6, Omil et al. 2011; Chap. 11, Ribbing and Bjurstrom 2011), another option is to use the ashes for producing construction materials such as concrete (see Chap. 10, Berra et al. 2011) and brick.

For the production of ceramic bricks, the predominant raw material used is mineral clay. Any good brick clay should have low shrinkage and low swelling characteristics, consistent firing color, and a relatively low firing temperature, but at the same time produce an adequately dry and fire-strength brick. The guiding rule of choice on wastes and by-products must rest on their compatibility with the original (host) raw material being used, whereas they must not degrade the final product by focusing simply on making it a repository for wastes. Thus, it is necessary to

F. Moedinger

University of Staffordshire/Recuperi Industriali S. r.l. Fritz Moedinger, Via Don Bosco 10, 39042

Bressanone, Brixen, Italy

e-mail: fritz. moedinger@gmail. com

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

DOI 10.1007/978-3-642-19354-5_9, © Springer-Verlag Berlin Heidelberg 2011 establish a company-and-production — site-specific “tailor-made” quality product standard. In general, the firing of a mineral mass rich in aluminum silicate such as brick clay allows permanent stabilization of almost all heavy metals included except chromium (Anderson and Skerratt 2003).

In most humid tropical and subtropical regions where acid soils prevail, warm and moist conditions result in weathered soil types. These tropical soils are depleted in available phosphorus, and usually the total phosphorous level is low, ranging from

0. 01 to 0.1% (Chen and Ma 2001). Much of the phosphorus is bound to aluminum and iron complexes during pedogenesis (Walker and Syers 1976). Through adsorp­tion and precipitation mechanisms aluminum forms insoluble and stable comple­xes with inorganic and organic phosphates, forming highly insoluble phosphorous compounds; therefore, their solubilization is a prerequisite for phosphorous uptake by plants. Soils suffering from aluminum toxicity are generally associated with phosphorous deficiency. The phosphorous-use efficiency in such soils is around 10-15% in the best situations (Verma et al. 2005). The low phosphorous status of these soils is of great concern because large amounts of phosphorous need to be applied to raise the concentrations of available soil phosphorous to an adequate level (Sanchez and Uehara 1980). Low phosphorous availability is considered to be one of the main limiting factors to plant growth in acid soils, in addition to human wealth in tropical areas (Barber 1995; Sanchez 2002). For temperate soils, ash amendments have been shown to alleviate phosphorous deficiencies (see Chap. 2, Schiemenz et al. 2011).

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.

8.2.1 Methodology and Starting Points

The starting point is that the whole chain has to be analyzed to assess the environ­mental effects involving closure of the nutrient and mineral cycle. Interviews with representatives from the cacao industry and a literature study were used to define the parameters and to describe the scenarios. The most important part of this chain analysis is the definition of the parameters. The so-called base unit is the most important issue, as it expresses the product under study. The functional unit in this study is fertilization of 1 ha of land in Cote d’Ivoire, on which cacao trees are grown together with shade trees. Further, the effect categories have to be determined, which are the parameters of environmental impact, namely, the nutrient balance and the CO2, NOx, and SO2 emissions.

The starting points for this study are:

— The cacao plantation is situated in Cote d’Ivoire, and the beans are transported to the location of the cacao industry in the Netherlands.

— The cacao shells are a 100% natural residue of the beans and are thermally processed in a stand-alone power plant (so-called bioenergy plant) in the Netherlands.

— The efficiency of the nutrients is comparable to that of the commercial fertilizers which are used on the plantation. Also, the effect of trace elements and

contaminants which are present in the ashes is comparable to that of the commercial fertilizers.

The chemical composition of the ashes is predicted with a modified version of the KEMA Trace Model® (KEMA 2005). The model is an empirical and statistical computer model to predict emissions and ash composition of a dry pulverized coal — fired boiler including biomass co-combustion. A modified version of the model has been developed for fluidized bed boilers, taking into account the lower combustion temperature, the use of inert or reactive bed material, and the distribution of ash and bed material.

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.

The bottom ash used in this study was generated in moving grate furnaces and did not contain fly ash. This is a major difference from fluidized bed combustors, which produce an ash mix. The analysis thus revealed lower concentrations of N, P, K, Mg, and S than those reported by other authors (Ohno and Erich 1990; Korpilahti et al. 1998; Demeyer et al. 2001; Miller et al. 2002; Solla-Gullon et al. 2006). In accordance, heavy metal concentrations were relatively low compared with those of other waste products used in agriculture, e. g., slurry from wastewater treatment plants and coal ash (Arvidsson and Lundkvist 2002; Hytonen 2003).

Fig. 6.5 This figure is a result of Pinus radiata D. Don for plots over migmatites. Control untreated, WA application of 4.5 Mg wood ash ha-1 for three consecutive years (2003, 2004, 2005), WAP single applications of 4.5 Mg wood ash ha-1 and 0.1 Mg P2O5 ha-1. In the repeated measures analysis, the sphericity assumption was not valid and therefore values of P-Huynh Feldt were used in univariate tests of their interactions

In compositional terms, good brick clay should feature:

• Grain size distribution (sieve line): A high percentage of larger particles requires higher sintering temperatures, resulting in a greater energy requirement and longer firing times.

• Accessory minerals: Quartz, feldspar, and amphibole have an effect on the sintering behavior and might result in undesired colors.

• Organics: Create voids in the finished product. If the organics have a high sulfur content, this might have effects on color, the fumes, and the kiln atmosphere.

• Sulfur: Pyrite and marcasite release SOx on firing, creating large-diameter pores in the brick that might reduce compressive and flexural strength.

• Carbonate minerals: Calcite, dolomite, and other carbonate minerals, such as ankerite and siderite, do have, if finely dispersed, an effect on the release of low — temperature-carbonization gases owing to the formation of channels and funnels but in larger quantities will reduce the compressive and flexural strength of the final product and might lead to chipping on the surface.

• Alkalis: A low alkaline earth content, magnesium and calcium being the most common, is desirable to avoid firing interactions which could promote discolor­ation of the final product.

• Metal oxides and hydroxides: Goethite and hematite, for example, both contain­ing iron oxide (the chief colorant responsible), which ideally should be in the range 5-12% (for good strong color), are the main origin of the red brick color.

• Natural radioactivity of the raw materials (radon).

Adding foreign substances to influence the physical properties of the finished product or the workability is nothing new. It is important to distinguish between “additions” to the clay body (such as saw dust or paper sludge), and “substitutions” (such as sewage sludge, ash, or treated aluminum salt slag) that replace a part of the original clay body. The distinction between “addition” and “substitution” for extraneous materials is not always straightforward or easy: Any substance that is added to the original clay body without substitution of clay modifying its inherent characteristics might be considered an addition. A substitution, on the other hand, may be viewed as any material that for a required volume of brick reduces the quantity of clay needed to achieve that specific volume target. A substitution can also modify the clay body.