## 3 Results and Discussion
### Characteristics of Liquid Digestate and Slurry When Used for Ma-B Flocs Growth
#### 3.2.2 Phytoremediation of Liquid Digestate and Slurry: COD and Ammonium Removal  
Ammonium removal occurs through several mechanisms: Nitrification, denitrification through microalgae-bacteria populations, and ammonia volatilization. The pH values affect the ammonium removal process. In our case, the pH was approximately 8 during the 14 days of batch culture, which would have caused the volatilization of some of the ammonia. The ammonium removal efficiency was evaluated for each substrate between day 2 and day 14, as shown in Figure 1a,b. The ammonium removal efficiencies for the two initial substrates DL\({}_{0}\) and SL\({}_{0}\) at the end of the culture were approximately 50.2 \(\pm\) 1.0% and 62.4 \(\pm\) 0.5%, respectively. These values are low compared to the control with synthetic waste products (approximately 69 \(\pm\) 3%) and to what can be read in the literature. This would be due to the high initial concentrations of NH\({}_{4}\)-N varying between 192.6 and 129.1 mg\(\cdot\)L\({}^{-1}\) for DL\({}_{0}\) and SL\({}_{0}\), respectively (Table 3), which could induce an inhibitory or even toxic effect on the growth of Ma-B flocs. Indeed, the thresholds of toxicity for \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Parameter**} & \multicolumn{4}{c}{**Liquid Digestate (D\({}_{\text{L}}\))**} & \multicolumn{4}{c}{**Liquid Slurry (S\({}_{\text{L}}\))**} & \multirow{2}{*}{**Synthetic**} \\ \cline{2-2} \cline{4-9}  & & **D\({}_{\text{L}0}\)** & & **10\%** & & **30\%** & **50\%** \\  & & **D\({}_{\text{L}10\%}\)** & & **D\({}_{\text{L}30\%}\)** & & **D\({}_{\text{L}50\%}\)** & & **S\({}_{\text{L}10\%}\)** & & **S\({}_{\text{L}30\%}\)** \\ \hline \hline \multirow{2}{*}{\
\begin{tabular}{c} **COD\({}_{\text{s}}\)** \\ **(mg-L\({}^{-1}\))** \\ \end{tabular} } & \multirow{2}{*}{1184} & \multirow{2}{*}{137} & \multirow{2}{*}{383.6} & \multirow{2}{*}{550} & \multirow{2}{*}{1337} & \multirow{2}{*}{195} & \multirow{2}{*}{562} & \multirow{2}{*}{1034} & \multirow{2}{*}{601} \\  & & & & & & & & & \\ \hline \hline \multirow{2}{*}{
\begin{tabular}{c} **Total NH\({}_{4}\)-N** \\ **(mg-L\({}^{-1}\))** \\ \end{tabular} } & \multirow{2}{*}{192.6} & \multirow{2}{*}{19.5} & \multirow{2}{*}{51.1} & \multirow{2}{*}{86.2} & \multirow{2}{*}{129.1} & \multirow{2}{*}{14.4} & \multirow{2}{*}{37} & \multirow{2}{*}{58.4} & \multirow{2}{*}{86.7} \\  & & & & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Initial characteristics of liquid digestate and slurry after different dilutions. NH\({}_{4}\)-N depend on the microalgae species. According to [24], different microalgal communities adapt to different ammonium concentrations, such as _Chlorophyceaeae_ (140 mg\(\cdot\) L\({}^{-1}\)), _Cyanophyceaeae_ (45 mg\(\cdot\) L\({}^{-1}\)), and _Diatomophyceaeae_ (6 mg\(\cdot\) L\({}^{-1}\)). The toxicity thresholds for these species are 702, 234, and 65 mg\(\cdot\) L\({}^{-1}\). Further results showed a high capacity of Ma-B flocs to remove ammonium from D\({}_{1,30\%}\), with a removal efficiency of 93 \(\pm\) 1.1% after 14 days starting from an initial NH\({}_{4}\)-N concentration of 51.1 mg\(\cdot\) L\({}^{-1}\) (Figure 1a). Interestingly, the highest removal rate corresponding to day 14 achieved by D\({}_{1,30\%}\) agrees with the work of [PERSON] et al. [13], who worked with nitrates as a nitrogen source. Thus, the dilution of liquid digestate to 30% can be recommended as an effective growth medium for algae provided that initial concentrations are equivalent and that no pollutants or micropollutants are toxic to biological growth. For liquid slurry, the best NH\({}_{4}\)-N removal rate by Ma-B flocs was 84.0 \(\pm\) 2.9% for S\({}_{1,10\%}\) at the end of the culture (Figure 1b). The results suggest that the removal efficiency increases as the nitrogen concentration decreases in the effluent.