## 3 Results and Discussion
### Biological Characterisation of Biosolids
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Parameters**} & \multicolumn{4}{c}{**Biosolids Analysed for Each Season of the Year**} \\ \cline{2-5}  & **Spring** & **Summer** & **Autumn** & **Winter** \\ \hline MBC (mg C\({}_{\text{mic}}\) kg\({}^{-1}\)) \({}^{\intercal}\) & 966.6 \(\pm\) 46.4 b & 1251.9 \(\pm\) 134 a & 1149 \(\pm\) 115 a,b & 587.2 \(\pm\) 76.7 c \\ MBN (mg N\({}_{\text{mic}}\) kg\({}^{-1}\)) \({}^{\intercal}\) & 84.25 \(\pm\) 10.6 b & 109.3 \(\pm\) 1.4 b & 304.7 \(\pm\) 32.9 a & 119.0 \(\pm\)20.1 b \\ C\({}_{\text{mic}}\)/N\({}_{\text{mic}}\) & 11.66 \(\pm\) 2.09 a & 11.46 \(\pm\) 1.32 a & 3.82 \(\pm\) 0.77 b & 5.07 \(\pm\) 1.32 b \\ DSH (mg INF \({}^{\star}\) kg\({}^{-1}\) h\({}^{-1}\)) \({}^{\intercal}\) & 2631.8 \(\pm\) 147 a & 2209.5 \(\pm\) 119 a & 2426.1 \(\pm\) 230 a & 2277.6 \(\pm\) 225 a \\ FDA (mg F \({}^{\star}\) kg\({}^{-1}\) h\({}^{-1}\)) \({}^{\intercal}\) & 342.7 \(\pm\) 40.0 b & 279.7 \(\pm\) 30.0 b & 437.96 \(\pm\) 44.2 a & 368.6 \(\pm\) 24 a, b \\ DSH/FDA (mg INF mg\({}^{-1}\) F \({}^{\star}\)) & 7.78 \(\pm\) 1.35 a & 7.99 \(\pm\) 1.26 a & 5.55 \(\pm\) 0.22 a & 6.21 \(\pm\) 0.84 a \\ URS (mg N-NH\({}_{4}^{\star}\) kg\({}^{-1}\) h\({}^{-1}\)) \({}^{\intercal}\) & 186.0 \(\pm\) 17.1 a & 194.5 \(\pm\) 23.0 a & 109.8 \(\pm\) 7.7 b & 186.5 \(\pm\)13.7 a \\ qCO\({}_{2}\) (mg C-CO\({}_{2}\) g\({}^{-1}\) C\({}_{\text{mic}}\) d\({}^{-1}\)) & 157.95 \(\pm\) 7.40 b & 124.31 \(\pm\) 13.5 b & 115.42 \(\pm\) 11.6 b & 270.19 \(\pm\) 32.9 a \\ qFDA (mg F \({}^{\star}\) g\({}^{-1}\) C\({}_{\text{mic}}\) h\({}^{-1}\)) & 356.27 \(\pm\) 56.7 b & 223.27 \(\pm\) 4.84 b & 381.57 \(\pm\) 26.9 b & 636.39 \(\pm\) 106 a \\ \hline \hline \end{tabular}  
* The results are the mean \(\pm\) standard deviation (3 replicates). Rows with different letters are significantly different according to [PERSON]’s analysis with \(p\leq 0.05\). \({}^{\intercal}\) The units correspond to biosolids on a dry basis.
* INF = ldonitrotetzolium formazan (1-(4-lodophenyl)-5-(4-nitrophenyl)-3 phenyl formazan). ** F = Fluorescein.  
\end{table} 
Table 3: Biological characteristics in biosolids collected and evaluated in the UWWWTP at different season of the year. MBN) can affect natural soil processes, such as the mineralisation of C and N as a consequence of a change in microbial structure [65; 111]. For this reason, it is important to evaluate both MBC and MBN in soils and biosolids as organic amendments [65; 105]. With respect to the C\({}_{\text{mic}}\)/N\({}_{\text{mic}}\) relationship, this has sometimes been used to describe the structure and state of the microbial community [106]. On the other hand, the C\({}_{\text{mic}}\)/N\({}_{\text{mic}}\) ratio of microbial isolates, extracted from soils or obtained from culture collections and cultivated under optimal conditions, varies from 7 to 12 in fungi and from 3 to 6 in bacteria [24]. The results obtained in this study of C\({}_{\text{mic}}\)/N\({}_{\text{mic}}\) varied from 3.82 to 11.66 (Table 3) and presented significant differences (F = 23.377, \(p\) = 0.000) between the seasons of the year. During spring and summer, C\({}_{\text{mic}}\)/N\({}_{\text{mic}}\) values were \(>\)11, with no significant differences (F = 0.019, \(p\) = 0.898) between these 2 seasons of the year. However, in autumn and winter, the C\({}_{\text{mic}}\)/N\({}_{\text{mic}}\) ratio was \(<\)5, and there were also no significant differences (F = 1.992, \(p\) = 0.231) between them. With these results, it was deduced that in spring and summer there was a greater predominance of fungi in the microbiota of biosolids, while in autumn and winter there was a greater predominance of bacteria. The predominance of microbial flora in biosolids can also be attributed to climatic conditions, as in spring and summer 2018 the local ambient temperature ranged from 11.93 to 30.97 \({}^{\circ}\)C and 13.83 to 27.76 \({}^{\circ}\)C, respectively, in autumn and winter 2018 it ranged from 11.70 to 25.83 \({}^{\circ}\)C and 6.27 to 24.27 \({}^{\circ}\)C, respectively [112].