## 3 Results and Discussion
### Characteristics of Liquid Digestate and Slurry When Used for Ma-B Flocs Growth
#### 3.2.3 Ma-B Flocs Growth and Biomass Productivity on Liquid Digestate and Slurry  
The culture of Ma-B flocs was tested by monitoring the growth rate measured on day\({}^{-1}\) (d\({}^{-1}\)), as shown in Table 4, for liquid digestate and slurry solutions, considered as growth media. The comparison of Ma-B flocs productivity values, based on the variation of g VSS.L\({}^{-1}\), was performed at different dilutions of DL and SL (10%, 30%, and 50%) during 14 days of batch culture. The lowest productivities were observed for the initial liquid digestate and slurry solutions, without dilution, with values of 0.011 \(\pm\) 0.031 d\({}^{-1}\) and 0.017 \(\pm\) 0.012 d\({}^{-1}\), respectively (Table 4). The high ammonium and COD concentrations (Table 3) could be the main cause of the reduced productivity due to a toxicity effect. \begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{1}{c}{**Media**} & \multicolumn{2}{c}{**Ma-B Flocs Growth Rate (d\({}^{-1}\))**} \\  & \multicolumn{2}{c}{**(Mean Value \(\pm\) SD)**} \\ \hline \multicolumn{2}{c}{Synthetic Wastewater} & 0.032 \(\pm\) 0.021 \\ \hline \multirow{4}{*}{Liquid Digestate} & D\({}_{\text{L}0}\) & 0.011 \(\pm\) 0.031 \\  & D\({}_{\text{L}10\%}\) & 0.015 \(\pm\) 0.042 \\  & D\({}_{\text{L}30\%}\) & 0.024 \(\pm\) 0.021 \\  & D\({}_{\text{L}50\%}\) & 0.018 \(\pm\) 0.014 \\ \hline \multirow{4}{*}{Liquid Slurry} & S\({}_{\text{L}0}\) & 0.017 \(\pm\) 0.012 \\  & S\({}_{\text{L}10\%}\) & 0.028 \(\pm\) 0.022 \\ \cline{1-1}  & S\({}_{\text{L}30\%}\) & 0.021 \(\pm\) 0.031 \\ \cline{1-1}  & S\({}_{\text{L}50\%}\) & 0.018 \(\pm\) 0.043 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Specific growth rate (d\({}^{-1}\), mean value \(\pm\) SD) of batch culture for Ma-B flocs using liquid digestate and slurry (with and without dilution) as culture medium compared to synthetic wastewater. Figure 2: COD removal rates (mean value \(\pm\) SD) evaluated after 2 and 14 days of Ma-B flocs culture for each diluted substrate. (**a**) DL: Liquid Digestate; (**b**) SL: Liquid Slurry. WWS is synthetic wastewater control. According to the data in Table 4, the highest growth rate for liquid digestate effluent corresponds to a 30% dilution and is worth 0.024 \(\pm\) 0.021 d\({}^{-1}\). Indeed, the liquid digestate collected from the anaerobic digestion of agricultural waste would have favored the cultivation of photosynthetic algae (_Tetradesmus obliquus_) and cyanobacteria (_Arthrospina maxima_) due to the availability of nitrogen, as cited by [18]. Another study showed that when using liquid digestate diluted to 30%, the biomass concentration of the microalgae _Chroococcus_ sp. Reaches its optimal value with a value of 0.79 \(\pm\) 0.06 g\(\cdot\)L\({}^{-1}\)[13]. For the case of experiments with slurry, the biomass productivity reached 0.028 \(\pm\) 0.022 d\({}^{-1}\) for SL10%, which is higher than those fed with DL30% and other dilutions. The two dilutions of SL10% and DL30% are therefore the most interesting. Microalgae biomass productivity, as indicated by the change in mg Chl (a)\(\cdot\)g\({}^{-1}\) VSS in the DL30%, SL10%, initial DL0, and SL0 trials and in comparison to synthetic wastewater, is shown in Figure 3a,b. When algae were grown at 51.1 mg NH\({}_{4}\)-N\(\cdot\)L\({}^{-1}\), contained in the D\({}_{130\%}\) test, the total Chl (a) content increased from 1.4 \(\pm\) 0.01 mg Chl (a)\(\cdot\)g\({}^{-1}\) VSS to 2.67 \(\pm\) 0.01 mg Chl (a)\(\cdot\)g\({}^{-1}\) VSS (Figure 2) at the end of the culture. The ammonium concentration of 192.6 mg NH\({}_{4}\)-N\(\cdot\)L\({}^{-1}\) in D\({}_{\text{L0}}\) (Table 4) seems to have resulted in a decrease in biomass productivity and a lower Chlorophyll (a) value of 1.87 \(\pm\) 0.02 mg\(\cdot\)g\({}^{-1}\) VSS, which is also lower than the control test with synthetic wastewater, due to an inhibition effect. Ref. [27] also reports this inhibitory effect of ammonium concentration in pig manure digest on chlorophyll (a) production by algae.