# Insights into PCDD/Fs and PAHs in Biomass Boilers Envisaging Risks of Ash Use as Fertilizers
## 3 Experimental Part
### Results and Discussion
#### 3.2.2 Chemical Composition, PCDD/Fs and PAHs in Ashes
The higher levels of PCDD/Fs in ashes were correlated with poor burnout of ashes, which resembles the case of FAGE. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & \multicolumn{2}{c}{**BFB1**} & \multicolumn{2}{c}{**BFB3**} & \multicolumn{2}{c}{**BFB4**} & \multicolumn{2}{c}{**GF**} \\ \multicolumn{2}{c}{**ng/kg**} & \multicolumn{2}{c}{**Ash Blend**} & \multicolumn{2}{c}{**Ash Blend**} & \multicolumn{2}{c}{**Ash Blend**} & \multicolumn{2}{c}{**Ash Blend**} \\  & \multicolumn{2}{c}{**BA**} & \multicolumn{2}{c}{**FA**} & \multicolumn{2}{c}{**BA**} & \multicolumn{2}{c}{**FA**} & \multicolumn{2}{c}{**BA**} & \multicolumn{2}{c}{**FA**} & \multicolumn{2}{c}{**BA**} & \multicolumn{2}{c}{**FA**} \\ \hline  & ND(2.0) & & ND(2.0) & & ND(2.0) & & ND(2.0) & & 88 & ND(2.0) & 447 \\  & 1 & & ND(12) & & ND(12) & & 43 & ND(12) & & 93 & ND(12) & 386 \\  & 1 & ND(12) & & ND(12) & & 49 & ND(12) & & 191 & ND(12) & 620 \\  & 1 & ND(12) & & ND(12) & & ND(12) & & 23 & ND(12) & 111 & ND(12) & 386 \\  & 1 & ND(12) & & ND(12) & & ND(12) & & 26 & ND(12) & 131 & ND(12) & 468 \\  & 2 & ND(12) & & ND(12) & & ND(12) & & 27 & ND(12) & 202 & ND(12) & 640 \\  & 1 & ND(12) & & ND(12) & & ND(12) & & ND(12) & & 64 & ND(12) & 183 \\  & 1 & ND(12) & & ND(12) & & ND(12) & & ND(12) & & 35 & ND(12) & 333 & ND(12) & 976 \\  & 1 & 1 & ND(12) & & ND(12) & & ND(12) & & 10(12) & & 93 & ND(12) & 244 \\  & OCDF & & & ND(12) & & ND(12) & & ND(12) & & 27 & ND(24) & 333 & ND(24) & 366 \\  & 2 & 3 & ND(12) & & ND(12) & & 26 & ND(2.0) & & 11 & ND(2.0) & 122 \\  & 1 & ND(12) & & ND(12) & & ND(12) & & 18 & ND(12) & 48 & ND(12) & 264 \\  & 1 & ND(12) & & ND(12) & & ND(12) & & ND(12) & & 48 & ND(12) & 366 \\  & 1 & ND(12) & & ND(12) & & ND(12) & & 18 & ND(12) & 48 & ND(12) & 264 \\  & 1 & ND(12) & & ND(12) & & ND(12) & & ND(12) & & 48 & ND(12) & 366 \\  & 1 & 1 & ND(12) & & ND(12) & & 18 & ND(12) & & 83 & ND(12) & 1220 \\  & 1 & 1 & ND(12) & & ND(12) & & 13 & ND(12) & & 45 & ND(12) & 793 \\  & 1 & 2 & ND(12) & & ND(12) & & 121 & ND(12) & & 584 & 20 & 9048 \\  & OCDD & & & & & & & & & & \\ \hline \(\Sigma\) PCDD/F MB [FOOT  
In general, results show that WHO\({}_{1998}\)-TEQs are higher than I-TEQs, and WHO\({}_{2005}\)-TEQs are lower than WHO\({}_{1998}\)-TEQs, and also lower than I-TEQs. Taking in account that dl-PCB are not included in the study and considering only FA blends, the correlations obtained are as follows:  
\[\text{(WHO}_{1998}\text{-TEQ}\text{(PCDD/F))}=1.11\times\text{(I-TEQ)} \tag{5}\]  
\[\text{(WHO}_{2005}\text{-TEQ}\text{(PCDD/F))}=0.99\times\text{(I-TEQ)} \tag{6}\]  
\[\text{(WHO}_{2005}\text{-TEQ}\text{(PCDD/F))}=0.90\times\text{(WHO}_{1998}\text {-TEQ}\text{(PCDD/F))} \tag{7}\]  
The correlation (6) of WHO\({}_{2005}\)-TEQ with I-TEQ is similar to the correlation (4) obtained from [PERSON] et al. [74]. Analogous to the fate of heavy metals that are not destroyed in combustion systems and concentrate/enrich in fly ash [245], pre-existing PCDD/Fs in fuels may also enrich in fly ashes. Only under proper combustion conditions they can be destroyed or removed from flue gases [246]. In addition, they may suffer transformations, like dechlorination of the high chlorinated congeners to the lower substituted and more toxic hexa, penta, and tetra PCDD/Fs. As an example, one can calculate the possible magnification of a pre-existing quantity of PCDD/F in biomass, as follows: considering that 100 ng/kg of OCDD present in biomass are not destroyed, and that 80% of the OCDD is transferred to ESP fly ashes [247] (which may represent about 0.5% of the fuel biomass), the levels of OCDD in ESP fly ashes would reach 16,000 ng/kg, corresponding to about 5 ng WHO\({}_{2005}\)-TEQ/kg. However, if some 10% of this OCDD dechlorinates and forms 1,2,3,7,8-PeCDD or 2,3,7,8-TCDD, the corresponding TEQ could reach 1600 ng WHO\({}_{2005}\)-TEQ/kg in ash. This shows that even relatively low PCDD/Fs contents present in the forest biomass, or any other fuel, may produce fly ashes with high TEQs.