# 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
\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**} \\  & **BA** & **FA** & **BA** & **FA** & **BA** & **FA** & **BA** & **FA** \\  & **(_n_ **= 12)** & **(_n_ **= 12)** & **(_n_ **= 12)** & **(_n_ **= 12)** & **(_n_ **= 4)** & **(_n_ **= 4)** & **(_n_ **= 6)** & **(_n_ **= 6)** \\ \hline C\% & 0.1–0.5 & 1.4–5.6 & \(<\)0.1–0.4 & 0.9–1.7 & 0.1–0.3 & 1.2–3.8 & 0.7–4.2 & 5.1–12 \\ S\% & 0.01–0.07 & 0.3–1.4 & \(<\)0.01–0.01 & 0.2–1.3 & \(<\)0.01 & 0.2–1.2 & \(<\)0.01 & 0.1–0.8 \\ Cl\% & 0.01–0.22 & 1.3–8.1 & 0.004–0.02 & 0.14–2.2 & 0.006–0.03 & 0.31–0.66 & 0.007–0.01 & 0.23–1.4 \\ Cu mg/kg & 13–36 & 35–90 & 19–51 & 49–85 & \(<\)10–57 & 30–167 & 33–43 & 38–92 \\ Ni mg/kg & \(<\)10 & 24–65 & \(<\)10 & 16–83 & \(<\)10 & 13–21 & 11–21 & 14–28 \\ Cr mg/kg & 11–30 & 33–95 & 11–21 & 40–125 & \(<\)10–24 & 38–70 & 47–73 & 41–60 \\ Zn mg/kg & 25–194 & 22–249 & 28–186 & 159–357 & 32–244 & 82–358 & 27–45 & 115–765 \\ Pb mg/kg & \(<\)10–12 & 22–135 & \(<\)10–23 & 39–173 & \(<\)10–58 & 31–133 & \(<\)10 & 14–75 \\ Cd mg/kg & \(<\)4 & \(<\)4 & \(<\)4 & \(<\)4 & \(<\)4 & \(<\)4–5 & \(<\)4 & \(<\)4 \\ Hg mg/kg & \(<\)0.001 & 0.01–0.22 & \(<\)0.002 & 0.10–0.31 & \(<\)0.001 & 0.08–0.16 & \(<\)0.005 & 0.05–0.52 \\ Mn mg/kg & 581–1160 & 2671–6482 & 125–830 & 914–3282 & 229–433 & 1016–1526 & 1452–2094 & 1648–4264 \\ Fe\% & 0.4–1.6 & 0.9–3.5 & 0.4–1.1 & 1.6–3.9 & 0.4–0.7 & 1.3–1.7 & 2.6–4.6 & 2.3–4.1 \\ Al\% & 0.6–3.3 & 1.9–6.6 & 0.7–2.7 & 3.5–8.2 & 1.8–2.3 & 3.8–6.0 & 5.6–8.1 & 5.1–8.5 \\ Ca\% & 1.5–5.7 & 8.2–31 & 0.8–4.8 & 3.0–15 & 0.5–3.2 & 3.9–17 & 3.4–6.7 & 3.0–8.2 \\ Na\% & 0.2–2.7 & 0.8–2.3 & 0.1–0.6 & 0.6–1.6 & 0.1–0.3 & 0.6–1.2 & 0.5–0.8 & 0.6–0.9 \\ K\% & 0.5–2.8 & 3.9–7.5 & 0.5–2.2 & 2.5–4.5 & 1.6–1.9 & 3.4–3.7 & 3.0–3.5 & 3.1–4.8 \\ Mg\% & 0.2–2.5 & 1.3–2.8 & 0.1–0.5 & 0.7–1.6 & 0.1–0.2 & 0.7–1.1 & 0.8–1.2 & 0.9–1.6 \\ P\% & 0.1–0.3 & 0.3–0.7 & 0.02–0.1 & 0.3–1.1 & 0.04–0.1 & 0.4–3.8 & 0.2–0.3 & 0.3–0.5 \\ Si\% & 33–40 & 7.5–23 & 32–37 & 16–27 & 39–40 & 21–29 & 25–30 & 19–25 \\ \hline \hline \end{tabular} Notes: n—number of individual samples analyzed, BA—bottom ash (Table 3), FA—fly ash (Table 3).  
\end{table} 
Table 6: Chemical composition of biomass ash samples (min–max), in dry base. dechlorination of the original OCDD and HpCDD contained in biomass might have occurred [120,209], giving rise to several congeners, including the more toxic tetra and penta PCDDs. PCDD/Fs contents of FABFB4 being higher than those of other BFB boilers appears to be consistent with its constitution (only ESP ashes). In the case of FAGE, although it is a mix of ESP+EC ashes, the levels of PCDD/Fs are even higher, which can be related to the higher C (5.1-12%), possibly enhancing PCDD/Fs formation and/or higher adsorption [128,143]. In the BA blends only OCDD and H\({}_{7}\) CDD were detected, with the exception of BABFB1 that also contains 2,3,7,8-TCDD, OCDF and one H\({}_{7}\) CDF isomer. The corresponding FABFB1 contains more congeners, resulting in a higher TEQ than in BABFB1, despite its slightly lower \(\Sigma\)PCDD/F. The similar FABFB3 contains even more congeners, including TCDD and P\({}_{5}\) CDD, thus, although having similar \(\Sigma\)PCDD/Fs, its TEQ is more than twice that of BABFB1. Similar to what is observed for biomass and other samples (Table 4), different assumptions for ND have significant impacts on \(\Sigma\)PCDD/Fs and TEQs of ashes, as can be seen in Table 7.  
Comparing with published results [143], TEQs in the studied BA match those of bottom ash from combustion of native wood, or waste wood, depending on the ND option. As for FA, TEQs obtained are more similar to those of fly ash from residual wood combustion (18-6300 ng I-TEQ/kg), than from native wood (1.5-4.0 ng I-TEQ/kg). The higher TEQ of FAGE also matches the I-TEQ range of fly ash from waste wood combustion (730-21,000 ng I-TEQ/kg).