## 3 Results and Discussion
### Compost Characteristics
#### 3.1.1 Physicochemical Parameters
\begin{table}
\begin{tabular}{l c c c c c} \hline \hline
**No** & **Parameters** & \begin{tabular}{c} **Compost 1** \\ \(n\) = 3** \\ \end{tabular} & \begin{tabular}{c} **Compost 2** \\ \(n\) = 3** \\ \end{tabular} & \
\begin{tabular}{c} **MAC * \\ **Bulgarian Norms** \\ \end{tabular} &
\begin{tabular}{c} **MAC ** \\ **EU Norms** \\ \end{tabular} \\ \hline I & \multicolumn{5}{c}{Physicochemical parameters} \\ \hline
1 & Moisture, \% & \(21.8\pm 1.67\) & \(17.9\pm 1.45\) & 10\% & - \\  & Cv, \% & \(7.66\) & \(8.10\) & & \\
2 & pH (H\({}_{2}\)) & \(9.27\pm 0.18\) & \(9.17\pm 0.18\) & - & - \\  & Cv, \% & \(1.94\) & \(1.96\) & - & - \\
3 & EC, mg s cm\({}^{-1}\) & \(1.74\pm 0.05\,^{\circ}\) & \(2.57\pm 0.08\,^{\circ}\) & \(\leq\)3 & - \\  & Cv, \% & \(2.87\) & \(3.11\) & \(13.3\pm 1.83\) & \\
4 & TOC, \% dm & \(8.03\pm 1.41\) & \(13.3\pm 1.83\) & \(15\%\) & - \\  & Cv, \% & \(17.6\) & \(13.8\) & & \\ \hline II & \multicolumn{5}{c}{Macronutrients} \\ \hline
5 & TKN, \% dm & \(1.48\pm 0.28\) & \(1.96\pm 0.35\) & & - \\  & Cv, \% & \(18.9\) & \(17.8\) & - & - \\
6 & P, \% dm & \(0.41\pm 0.04\,^{\circ}\) & \(0.69\pm 0.05\,^{\circ}\) & & \\  & Cv, \% & \(9.75\) & \(7.24\) & - & - \\
7 & K, \% dm & \(0.89\pm 0.05\,^{\circ}\) & \(1.80\pm 0.08\,^{\circ}\) & & - \\  & Cv, \% & \(5.61\) & \(4.44\) & - & - \\
8 & Mg, \% dm & \(0.53\pm 0.02\,^{\circ}\) & \(0.67\pm 0.02\,^{\circ}\) & & \\  & Cv, \% & \(3.77\) & \(2.98\) & - & - \\ \hline III & \multicolumn{5}{c}{Carbon ratios} \\ \hline
9 & C:N ratio & \(5.42\pm 0.44\) & \(6.80\pm 0.71\) & & - \\  & Cv, \% & \(8.11\) & \(10.4\) & - & - \\
10 & C:P ratio & \(16.7\pm 1.82\) & \(19.3\pm 1.58\) & & - \\  & Cv, \% & \(10.8\) & \(8.18\) & - & - \\ \hline IV & \multicolumn{5}{c}{Heavy metals} \\ \hline
13 & Zn, mg kg\({}^{-1}\) dm & \(174.3\pm 5.2\) & \(188.2\pm 6.4\) & \(>\)400 & 200 \\  & Cv, \% & \(2.98\) & \(3.40\) & & \\
14 & Cu, mg kg\({}^{-1}\) dm & \(41.2\pm 0.5\,^{\circ}\) & \(52.1\pm 0.6\,^{\circ}\) & & \\  & Cv, \% & \(1.21\) & - & \(1.15\) & \(>\)100 & 70 \\
15 & Pb, mg kg\({}^{-1}\) dm & \(29.1\pm 0.2\,^{\circ}\) & \(22.4\pm 0.5\,^{\circ}\) & \(130\) & 45 \\  & Cv, \% & \(0.68\) & \(2.23\) & & \\
16 & Cr, mg kg\({}^{-1}\) dm & \(23.3\pm 0.2\,^{\circ}\) & \(26.2\pm 0.3\,^{\circ}\) & \(60\) & 70 \\  & Cv, \% & \(0.85\) & \(1.14\) & & \\
17 & Ni, mg kg\({}^{-1}\) dm & \(9.12\pm 0.05\,^{\circ}\) & \(10.2\pm 0.07\,^{\circ}\) & & \\  & Cv, \% & \(0.54\) & \(0.68\) & & \\
18 & Cd, mg kg\({}^{-1}\) dm & \(<\)0.9 *** & \(<\)0.9 *** & 1.3 & 0.7 \\
19 & Hg, mg kg\({}^{-1}\) dm & \(<\)0.3 *** & \(<\)0.3 *** & 0.45 & 0.4 \\ \hline V & \multicolumn{5}{c}{Microbiological parameters} \\ \hline
20 & _Escherichia coli_, CFU g\({}^{-1}\) & \(<\)1.0 & \(<\)1.0 & \(<\)100 & - \\
21 & _Salmonella_, CFU 25 g\({}^{-1}\) & Not detected & Not detected & Not allowed & - \\ \hline VI & \multicolumn{5}{c}{Indexes} \\ \hline
11 & Fertility index, FI *** & 3.40 & 4.33 & - & - \\
12 & Clean index, CI *** & 4.26 & 4.13 & - & - \\ \hline \hline \end{tabular} Notes: * MAC—maximum allowable concentration according to [55]; ** MAC according to [56]; *** limit of quantification of the method; *** fertility index and clean index are calculated on a scale from 1 to 5, with 5 indicating the most beneficial effect to plant growth (FI) (Table 1) and the lowest heavy metal polluting potential (CI), respectively (Table 2); differences between Compost 1 and Compost2 are significant at \(p<\)0.05—; \(p<\) 0.01—\({}^{\circ}\); \(p<\) 0.001—\({}^{\circ}\).  
\end{table} 
Table 3: Mean \(\pm\) SD values of the monitored parameters of the tested composets. substrates (Table 3). The increased pH up to 9 at the end of the composting process is a result of CO\({}_{2}\) release, mineralization of the intermediates, good aeration of biomass and ammonia production from protein degradation [25, 61].