Ashes from Secondary Fuels as a Prime Resource for Soil Conditioning

Flemming Frandsen, Veronika Hansen, Henrik Hauggaard-Nielsen, Dorette Müller-Stöver

Publikation: Bidrag til bog/antologi/rapportKonferencebidrag i proceedingsForskning


The search for alternatives to commercial fertilizers becomes increasingly important, considering their energy-intensive production and the use of non-renewable resources such as rock phosphate. The reutilization of residues from bioenergy processes for plant nutrition is an important factor to save fertilizers and to realize nutrient cycling in agriculture to a greater extent.

Fly ash generated as a by-product of thermal biomass conversion for heat and power production can potentially be used as a fertilizer in cropping or forestry systems. However, the use of ashes as promising future fertilizers has received little attention, possibly because they were not generated in significant amounts. The expected global expansion of the bioenergy sector will result in comprehensive increases in ash quantity, opening up for new business cases also including the residuals produced. Such ashes contain nearly all essential plant nutrients [Bhattacharya and Chattopadhyay, 2002], except nitrogen (N), which is generally oxidized and released to the gas phase at high temperatures, and therefore not found in ashes in significant quantities [Demeyer et al., 2001]. The key determinants of biomass ash chemistry are the actual biomass species converted and the nature of the thermal conversion process. A relatively low furnace temperature between 500 and 700 ˚C is critical to the retention of nutrients, especially potassium (K), and determines the concentrations of potentially toxic metals in the ash. The physical form of the ash in soil application is important, with loose ash releasing Ca, K and Na more rapidly than granulated ash [Pitman, 2006; Obernberger and Supancic, 2009].

Plant nutrient availability in ash can vary a lot with regard to ash chemistry. Regarding phosphorus (P), promising results were found for the fertilizer effect and solubility of P for wood ash [Nkana et al., 1998] and for poultry litter ash [Codling et al., 2002]. The fertilizer effect of ashes also depends on soil type, soil characteristics, and cultivated crops [Nkana et al., 1998; Mozaffari et al., 2002; Eichler-Löbermann et al., 2008]. Besides being a source of nutrients itself, the application of biomass ashes may influence the form and availability of e.g. P by changing chemical parameters of the soil, mainly the pH [Muse and Mitchel, 1995]. Furthermore, ashes containing unburned carbon (C) have the potential to increase soil organic C content, and thereby not only improve the soil quality, but also C-sequestration in the soil, and, thus, mitigate climate change.

Ash from natural solid biomass fuels m a y also contain significant amounts of heavy metals, which has to be considered for the utilization strategy applied. Fly ash may contain significant concentrations of Cd, Cu, Cr, Pb and As, which prevents its use as fertilizer. Therefore, the nutrient and rather heavy metal poor fractions (bottom ash and coarse fly ash) seem to be more suitable for fertilizing and soil improvement purposes than the fine fl y ash, which is probably better industrially utilized or disposed of. Apart from the sustainable recycling of biomass ash to the soil, other promising ash utilization methods like use in road and civil construction, the use in landscaping, or, the use as an additive in industrial processes like cement production exist today [Obernberger and Supancic, 2009].

This paper ties up the relation between formation of ash and its potential utilization as valuable alternative to commercial fertilizers.
TitelProceedings: Impacts of Fuel Quality on Power Production
StatusUdgivet - 2014
Udgivet eksterntJa
BegivenhedImpacts of Fuel Quality on Power Production 2014 - Snowbird, Utah, USA
Varighed: 26 okt. 201431 okt. 2014


KonferenceImpacts of Fuel Quality on Power Production 2014

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