# Slow Pyrolysis as a Method of Treating Household Biowaste for Biochar Production
## 3 Results and Discussion
### Properties of the Biowaste
#### 3.1.1 Proximate Analysis Results of Tested Biowaste  
The high moisture content of the biowaste samples tested requires pre-drying before slow pyrolysis. The analyzed kitchen biowaste had a moisture content of 68.10%, which is lower than the reported values in the literature, where food waste can reach up to 80% [1] or even 92.36% [49]. This discrepancy may arise from the varying compositions of biowaste. For instance, food waste comprising peelings, raw vegetables, and fruits tends to have a higher moisture content compared to waste containing drier components like bread, eggshells, pasta, or rice. Garden waste typically contains 50-60% moisture [1; 50].  
However, spring garden waste in this study showed a higher moisture content (81.53%), likely due to grass being collected post rain or the inclusion of moist food waste such as vegetable peelings. Autumn garden waste had a moisture content of 63.51%, slightly above the values cited in the literature [1; 50].  
Kitchen biowaste showed the highest volatile matter content at 76.55%, slightly exceeding the 71.00% reported in the literature [31; 49]. Spring and autumn garden biowaste samples showed similar values--42.43% and 43.75%, respectively--considerably lower than the literature values for garden waste (84.50%) [50] and shredded green waste (77.60%) [51].  
The kitchen biowaste sample had an ash content of 6.81%, lower than the 10% reported in some studies [31; 49]. In contrast, both garden biowaste samples contained significantly more ash than the 1.00% reported for garden waste [50; 51]. Spring garden waste contained 17.75% ash, while autumn garden waste had an extremely high ash content of 43.83%, comparable to that of municipal solid waste's organic fraction (44.30%) [30]. These high values likely indicate contamination from soil or rocks gathered during collection using rakes or spatulas. The autumn sample appears to be more contaminated than the spring one.  
The fixed carbon content in kitchen biowaste (16.64%) and autumn garden biowaste (12.43%) is comparable to the literature values of 18.50% for food waste [31; 49] and 15.00%  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Kitchen Biowaste** & \
\begin{tabular}{c} **Spring Garden** \\ **Biowaste** \\ \end{tabular} &
\begin{tabular}{c} **Autumn Garden** \\ **Biowaste** \\ \end{tabular} \\ \hline \multicolumn{4}{c}{Proximate analysis (\% wt.)} \\ \hline MC (total moisture content) (wet basis) & 68.10 & 81.53 & 63.51 \\ VM (volatile matter content) (dry basis) & 76.55 & 42.43 & 43.75 \\ A (ash content) (dry basis) & 6.81 & 17.75 & 43.83 \\ FC (fixed carbon) * (dry basis) & 16.64 & 39.82 & 12.43 \\ \hline \multicolumn{4}{c}{Ultimate analysis (\% wt.) (dry basis)} \\ \hline C (carbon content) & 43.36 & 31.94 & 29.99 \\ H (hydrogen content) & 7.03 & 4.53 & 4.02 \\ N (nitrogen content) & 3.12 & 2.84 & 1.19 \\ S (sulfur content) & 0.10 & 0.07 & 0.03 \\ O (oxygen content) * & 38.87 & 42.82 & 20.92 \\ CI (chlorine content) & 0.71 & 0.05 & 0.01 \\ \hline \multicolumn{4}{c}{Other measurements (dry basis)} \\ \hline HHV (higher heating value), MJ/kg & 17.24 & 10.60 & 11.16 \\ LHV (lower heating value), MJ/kg & 15.69 & 9.60 & 10.27 \\ CCs (combustible compounds) (\%wt.) & 93.19 & 82.25 & 56.17 \\ OS (total organic matter content) (\%wt.) & 90.06 & 81.77 & 55.32 \\ MS (total mineral substances content) (\%wt.) & 9.94 & 18.23 & 44.68 \\ C\({}_{\rm org}\) (total organic carbon content) (\%wt.) & 37.47 & 35.29 & 23.18 \\ pH (wet basis) & 5.18 & 9.20 & 8.62 \\ \hline \multicolumn{4}{c}{* by difference.} \\ \end{tabular}
\end{table}
Table 1: Properties of the tested biowastes.  
for garden waste [50; 51]. However, the spring garden waste sample showed a significantly higher fixed carbon content at 39.82%.