03.08.2015   Recycling of Biomass Ashes

Fertilizer Composition

The chemical composition of biomass ash varies depending on the combustion technique used, the type of material used in the combustion (tree species and

Table 6.3 Elements (kg ha 1; Cd g ha 1) applied in different treatments

N

P

K

Ca

Mg

Mn

Fe

Zn

Cu

B

Cd

Ni

Control

WA

16.2

35.4

251.1

516.9

154.8

37.5

190.5

4.2

2.1

0.9

9.6

2.7

WAP

4.5

61.8

83.7

172.3

51.6

12.5

63.5

1.4

0.7

0.3

3.2

0.9

The nutrients applied in wood ash (WA) treatment are the sum of three applications of 4.5 Mg ha 1 in 2003, 2004, and 2005 (P 3 g kg-1, K 19 g kg-1, Ca 38 g kg-1, Mg 11 g kg-1, Mn 3 g kg-1, Fe 14 g kg~ Zn 0.3 g kg-1, Cu 0.2 g kg-1, B 0.1 g kg-1, Cd 0.7 mg kg-1, Ni 0.2 g kg-1)

Подпись: Fig. 6.2 Appearance of the plots after application of wood ash

original material, bark, stem, braches, etc.), the storage conditions, etc. (Vance 1996; Blander 1997; Obernberger et al. 1997; Larsson and Westling 1998). The material used in this study was bottom ash generated in moving grate furnaces in three biomass plants in Spain (FINSA, Financiera Maderera). Chemically, this type of ash is less reactive than ash generated in fluidized bed combustors (equivalent neutralizing value 18% CaCO3) since it contains a high percentage of unburned materials. The composition and the quantity of elements provided by such ash are shown in Table 6.3. The concentration of heavy metals is very low (bottom ash), especially in comparison with other waste such as sewage sludge and coal ash (below the limits established by the EU-European Community (1986) and the US Environmental Protection Agency).

However, there are some drawbacks associated with bottom ash which may hinder the spreading process, such as the high humidity (55%) and the high

proportion of coarse elements (more than 20% larger than 4 mm) such as slug, unburned wood swath, and metals.