## 3 Results  
Leachate is known for its dark brown color, unpleasant odor, and high nitrogen but low phosphate concentration (Table 2). The measurement of BOD\({}_{5}\) and COD parameters is directly related to organic matter contamination and the age of a landfill, as this factor plays a fundamental role in the leachate composition [46]. For the growth of microalgae, four concentrations of leachate were used: 0.5, 1, 5, and 10% \(v/v\); however, according to the ANOVA analysis, the 10% \(v/v\) of leachate recorded the lowest biomass in comparison with the control (Figure 2). It was also possible to identify that a concentration of 5% favors biomass production in the two strains studied. According to the results, _Chlorella_ sp. increased biomass production up to 0.6 g\(\cdot\)dm\({}^{-3}\), which is due to the increase of nitrate and phosphate content in the medium; on the contrary, there was no significant difference in the biomass produced at different concentrations of leachate using _Scenedesmus_ sp. The removal of nitrate and phosphate is presented in Figure 3. According to the ANOVA analysis, there is a significant difference in the removal of NO\({}_{3}\) and PO\({}_{4}\), in both _Chlorella_ sp and _Scenedesmus_ sp. using 5% \(v/v\) of leachate. _Chlorella_ sp. was able to remove 81.87% and 56.78% of NO\({}_{3}\) and PO\({}_{4}\) respectively. In the case of _Scenedesmus_ sp. this strain was able to remove 90% and 54% of NO\({}_{3}\) and PO\({}_{4}\) respectively. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & **Units** & **Mean Value** \\ \hline Nitrates (NO\({}_{3}\)) & mg\(\cdot\)dm\({}^{-3}\) NO\({}_{3}\) & 71 \(\pm\) 0.04 \\ Phosphates (PO\({}_{4}\)) & mg\(\cdot\)dm\({}^{-3}\) PO\({}_{4}\) & 1.05 \(\pm\) 0.07 \\ pH & pH units & 9.74 \(\pm\) 0.1 \\ Temperature & \({}^{\circ}\)C & 25.10 \(\pm\) 0.5 \\ Conductivity & \(\mu\)S & 35 \(\pm\) 0.5 \\ Total Dissolved Solids (TDS) & mg\(\cdot\)dm\({}^{-3}\) & 2.31 \(\times\) 10\({}^{-5}\) \\ Salinity & mg\(\cdot\)dm\({}^{-3}\) & 1.75 \(\times\) 10\({}^{-5}\) \\ Chemical Oxygen Demand (COD) & mg\(\cdot\)dm\({}^{-3}\) & 630 \(\pm\) 0.02 \\ Biochemical Oxygen Demand (BOD\({}_{5}\)) & mg\(\cdot\)dm\({}^{-3}\) & 2.93 \(\pm\) 0.05 \\ Total solids (TS) & mg\(\cdot\)dm\({}^{-3}\) & 20.73 \(\pm\) 0.1 \\ Total Suspended Solids (TSS) & mg\(\cdot\)dm\({}^{-3}\) & 0.08 \(\pm\) 0.01 \\ Volatile Suspended Solids (VSS) & mg\(\cdot\)dm\({}^{-3}\) & 0.04 \(\pm\) 0.01 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Characterization of landfill leachate. The biomass production using Na\({}_{2}\)CO\({}_{3}\) and NaHCO\({}_{3}\) at different concentrations (0.8, 1.2, and 1.6 g\(\cdot\)dm\({}^{-3}\)), and the removal of NO\({}_{3}\) and PO\({}_{4}\) can be found in Figure 4. In the case of _Chlorella_ sp. NaHCO\({}_{3}\) enhanced the biomass concentration up to 1.23 g\(\cdot\)dm\({}^{-3}\) (using 1.6 g\(\cdot\)dm\({}^{-3}\) of NaHCO\({}_{3}\)), which according to the ANOVA analysis is higher than the other concentrations evaluated. On the other hand, different concentrations of Na\({}_{2}\)CO\({}_{3}\) did not increase the final concentration of biomass compared to the control. In the case of _Scendesmus_ sp., 0.8 g\(\cdot\)dm\({}^{-3}\) of NaHCO\({}_{3}\) was enough to increase the biomass concentration up to 0.77 g\(\cdot\)dm\({}^{-3}\). Higher concentrations of both NaHCO\({}_{3}\) and Na\({}_{2}\)CO\({}_{3}\) reduced the final content of biomass in this alga. Another important result is the removal of NO\({}_{3}\) and PO\({}_{4}\) using different carbon sources. According to the ANOVA analysis, there is not much difference in the removal of either NO\({}_{3}\) or PO\({}_{4}\) when both strains were grown using NaHCO\({}_{3}\) in comparison with the control (alga grown in 5% \(\
u/\
u\) leachate). The only significant difference recorded was found in the removal of NO\({}_{3}\) when _Chlorella_ sp. was grown using different concentrations of NaHCO\({}_{3}\). Figure 3: Removal of N and P in leachates by _Chlorella_ sp. (**a**) and _Scenedesmus_ sp. (**b**).