## 3 Results and Discussion
### Agoronomic Potential  
#### 3.1.1 Macronutrients of the Biosolids and Animal Waste  
The average concentration of macronutrients (kg ton\({}^{-1}\)) in the biosolids (Table 2) of the present research, throughout four years of monitoring (2016 until 2019), by and large, is higher than the values for WWTPs in South Africa (also of tropical climate) and of organic residues from animals such as manure of pig, cattle, chicken, and sheep. However, it was lower than in other WWTPs in Brazil. This variability is common and is reported in the literature [8; 9; 10; 14; 15]. This reveals the nutritional and consequently agronomic potential of Brazilian biosolids but also attention that must be given to agronomic projects, taking into consideration and giving due attention to each type of macronutrient of interest. Therefore, studies that provide information on the quality of biosolids from different effluents (domestic, agro-industrial) and processes (anaerobic, aerobic) are necessary. Thus, some details are important. For example, for nitrogen and phosphorus, the present research obtained values similar to those in other WWTP in Brazil and South Africa, considering standard deviation, but the concentrations are significantly higher from WWTP than the organic waste of animals. However, with regard to phosphorus, we highlight that when comparing values of the present research (WWTP--aerobic system with biological removal of phosphorus) with a WWTP in the region that is not by an anaerobic system, the difference is significant considering the standard deviation. On the other hand, the average potassium values are higher for animal waste, especially for residues from chickens and sheep. Refs. [39; 40] also observed that for the N and P macronutrients, WWTP values were higher than for animal waste, which in turn, had a higher quantity of K. Furthermore, the authors also found that aerobic systems with (or without) biological removal of phosphorus showed a higher quantity of P in sludge and/or biosolids. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{3}{*}{**Macronutrients**} & **Present Work** & \multicolumn{3}{c}{**WWTP**} & \multicolumn{3}{c}{**Cantile**} & \multirow{3}{*}{**Pig Slurry**} & \multirow{3}{*}{**Cattle**} & \multirow{3}{*}{**Charome** (**a**)} & \\  & **Sequencing** & & & & & & & \\  & **Batch Reactors** & **(SBR)** & & & & & & \\  & **Study (\({}^{\text{th}}\))** & & & & & & & \\ \hline N & \(33.64\pm 6.08\) & \(31.6\pm 6.72\) & \(42\pm 14\) & \(29.95\pm 7.54\) & \(3.92\pm 0.54\) & \(3.45\pm 1\) & 15 & 7.5 \\ P & \(20.55\pm 3.3\) & \(14.5\pm 1.31\) & \(13\pm 3.6\) & \(18.33\pm 5.89\) & \(1.15\pm 0.21\) & \(1.18\pm 0.2\) & 15 & 3.8 \\ K & \(1.16\pm 1.11\) & \(1.85\pm 0.95\) & \(1.5\pm 1.2\) & \(0.15\pm 0.02\) & \(3.25\pm 1.19\) & \(3.25\pm 2.5\) & 8 & 11.9 \\ Ca & \(3.33\pm 2.59\) & \(13.6\pm 6.32\) & \(31\pm 43\) & \(11.46\pm 1.22\) & \(0.68\pm 0.14\) & \(0.57\pm 0.2\) & 24 & 5.9 \\ Mg & \(0.64\pm 0.37\) & \(6\pm 2.66\) & \(2.6\pm 0.8\) & \(2.61\pm 1.44\) & \(1.93\pm 0.05\) & \(1.7\pm 0.6\) & NF & NF \\ S\({}^{\text{s}}\) & \(11.13\pm 1.76\) & \(11.6\pm 2.66\) & \(17\pm 8.8\) & NF & \(0.2\pm 0.42\pm 0.15\) & NF & NF \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Macronutrient content (kg ton\({}^{-1}\)— nutrient mass per ton of biosolids in wastewater treatment plants (WWTP) biosolids in Brazil and South Africa and other organic residues (pig slurry and manure of cattle, chicken, and sheep). Biosolids in the WWTP of the present research obtained average N (33.64 \(\pm\) 6.08 kgN ton\({}^{-1}\)) and P (20.55 \(\pm\) 3 kgP ton\({}^{-1}\)) concentrations similar to the biosolids of tropical climate WWTPs from Brazil and Africa, considering the standard deviation. However, average values for nitrogen and phosphorus were higher when compared with anaerobic reactors in the same region of the study [15]. [34] found average N and P results in 19 WWTP in Brazil of 42 \(\pm\) 14 kgN ton\({}^{-1}\) and 13 \(\pm\) 3.6 kgP ton\({}^{-1}\).