# Efficiency of Chemical Toilet Sewage (CTS) Co-Fermentation with Typical Energy Crops
## 3 Results
### Portion Digested (Digestion Coefficient) and Digestate Characteristics  
The feedstock composition had a profound effect on the volatile solids in the digestate. Variants V1 to V3 had the lowest statistically comparable (\(p\) = 0.05) levels of organic matter (Table 7). The value fell within the narrow range of 68.2 \(\pm\) 0.9% TS (V1) to 69.7 \(\pm\) 1.4% TS (V2). Significantly lower organic compound removal rates were found for higher CTS doses. The volatile solids in dry matter peaked in V6 at 72.6 \(\pm\) 1.4% TS. The portion digested ranged from 64.4 \(\pm\) 1.8% (V3) to 70.7 \(\pm\) 0.5% (V4). No relationship was found between the variant and the digestion coefficient (Table 7). Studies have revealed no relationship between the level of toxicity in the organic substrate and digestate and digestion coefficient. The coefficients of determination were R\({}^{2}\) = 0.124 and R\({}^{2}\) = 0.1434, respectively (Figure 5a). There was also no correlation between the digestion coefficient and the amount of biogas (R\({}^{2}\) = 0.233) and methane (R\({}^{2}\) = 0.1892) produced (Figure 5b). \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Variant**} & \multicolumn{6}{c}{**PARAMETER**} \\ \cline{2-10}  & **Phosphorus** & **Nitrogen** & **Calcium** & **Magnesium** & **Potassium** & **TS** & **VS** & **\(\mathbf{\eta_{r}}\)** \\  & **(mgP/gTS)** & **(mgN/gTS)** & **(mgC/gTS)** & **(mgMg/gTS)** & **(mgK/gTS)** & **(\%)** & **(\%)** & **(\%)** \\ \hline
1 & 2.46 \(\pm\) 0.90 & 8.42 \(\pm\) 1.71 & 29.43 \(\pm\) 3.12 & 1.66 \(\pm\) 0.34 & 3.8 \(\pm\) 0.9 & 12.4 \(\pm\) 1.1 & 68.2 \(\pm\) 0.9 & 68.5 \(\pm\) 1.0 \\ \hline
2 & 2.62 \(\pm\) 1.12 & 9.76 \(\pm\) 1.32 & 31.47 \(\pm\) 5.53 & 1.39 \(\pm\) 0.42 & 4.1 \(\pm\) 0.6 & 11.7 \(\pm\) 0.9 & 69.7 \(\pm\) 1.4 & 69.7 \(\pm\) 1.1 \\ \hline
3 & 2.37 \(\pm\) 0.73 & 8.63 \(\pm\) 2.63 & 32.61 \(\pm\) 5.92 & 1.47 \(\pm\) 0.77 & 3.6 \(\pm\) 1.3 & 13.9 \(\pm\) 1.8 & 68.9 \(\pm\) 1.7 & 64.4 \(\pm\) 1.8 \\ \hline
4 & 2.50 \(\pm\) 0.46 & 8.11 \(\pm\) 1.47 & 33.65 \(\pm\) 3.27 & 1.19 \(\pm\) 0.31 & 3.5 \(\pm\) 0.9 & 11.2 \(\pm\) 0.6 & 70.3 \(\pm\) 0.8 & 70.7 \(\pm\) 0.5 \\ \hline
5 & 2.19 \(\pm\) 0.38 & 10.73 \(\pm\) 1.81 & 32.79 \(\pm\) 4.32 & 1.82 \(\pm\) 0.72 & 4.4 \(\pm\) 1.1 & 12.7 \(\pm\) 1.1 & 71.1 \(\pm\) 2.3 & 66.4 \(\pm\) 1.7 \\ \hline
6 & 2.13 \(\pm\) 0.61 & 9.91 \(\pm\) 2.27 & 29.62 \(\pm\) 3.85 & 1.50 \(\pm\) 0.53 & 4.0 \(\pm\) 1.0 & 10.9 \(\pm\) 1.2 & 72.6 \(\pm\) 1.4 & 70.6 \(\pm\) 1.3 \\ \hline
7 & 2.43 \(\pm\) 0.21 & 11.62 \(\pm\) 0.69 & 30.25 \(\pm\) 5.23 & 1.71 \(\pm\) 0.21 & 3.8 \(\pm\) 0.5 & 11.4 \(\pm\) 0.8 & 71.4 \(\pm\) 2.5 & 69.7 \(\pm\) 1.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: TS, VS and fertilizing substances in the digestate (by variant). Figure 4: Correlations between (**a**) CTS in the feedstock and VFA/total alkalinity, (**b**) FOS/TAC and specific biogas/CH\({}_{4}\) production. Changes in the feedstock composition did not produce significant changes in other digestate parameters, and differences between the variants were not statistically significant (\(p=0.05\)). TS ranged between \(10.9\pm 1.2\%\) FM (V6) and \(13.9\pm 1.8\%\) FM (V3). The choice of feedstock mix had little effect on the content of fertilizing substances. Variations in the phosphorus, nitrogen, calcium, magnesium, and potassium levels were negligible (Table 7). The digestate profile is given in Table 7. According to [PERSON] et al. (2022) [44], the co-digestion of feedstocks can potentially enhance biogas harvesting and nutrient (NPK) management in a biocircular economy, provided appropriate mixtures are used. Another study, conducted in four provinces of Rwanda on biodigesters connected with toilets, concluded that the resultant digestate is a rich and safe fertilizer with adequate NPK levels [45].