# Optimization of Microalgae-Bacteria Consortium in the Treatment of Paper Pulp Wastewater
## 3 Results and Discussion
### Assessment of the Biomass Generated in Photogramules and Its Composition  
It is known that the structure of the microalgae-bacteria consortium that is developed in photobioreactors is associated with extracellular polymeric substances (EPS) [61], relatively composed of carbohydrates (polysaccharides), proteins, and lipids. The evaluation of this EPS and its fractions is important because they can act as a \"glue\" for photogranule cell adhesion and their fractions can affect biomass viscosity [62]. Table 3 shows the values and behavior of the biomass found at the end of the photobioreactors operation.  
The protein content in PBR3, PBR4, and PBR5 was \(44.50\pm 4.18\) mg/gVSS, \(49.90\pm 2.06\) a mg/gVSS, and \(49.05\pm 21.18\) mg/gVSS, indicating that biomass has a higher stabilization capacity and that the microalgae-bacteria consortium is mature and structured, as also noted [55]. According to [PERSON] et al. [63], the protein content extracted from the biomass with microalgae could be used to produce animal feed and food supplements.  
Carbohydrate concentrations (EPS-PS) were higher in PBR1 and PBR2, which only used microalgae inoculation or bacterial inoculation, respectively. Concentrations in PBR4, PBR5, and PBR6 were \(9.21\pm 1.66\) mg/gVSS, \(8.16\pm 0.52\) mg/gVSS, and \(12.65\pm 0.37\) mg/gVSS, respectively. Carbohydrate concentrations vary with operating conditions and microalgae species present in the medium [64]. PBR4 and PBR5 were inoculated with \(100\) mg/L of VSS from the microalgae _Scendesmus_ sp., and the polysaccharide values found in these PBRs are similar to the values found by [PERSON] et al. [65], of an algal biomass composed mainly of _Scendesmus_ sp.  
The oil content values for the PBR1, PBR2, PBR3, PBR4, PBR5, and PBR6 were \(19.88\pm 0.96\%\), \(1.76\pm 0.83\%\), \(13.11\pm 0.74\%\), \(7.40\pm 0.45\%\), \(18.69\pm 0.15\%\), and \(22.61\pm 1.01\%\)  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**PBRs** & **EPS-PN (mg/gVSS)** & **EPS-PS (mg/gVSS)** & **PN/PS** \\ \hline PBR1 & 0 & 23.96 \(\pm\) 6.74 & 0 \\ PBR2 & 36.76 \(\pm\) 0.88 & 39.26 \(\pm\) 5.05 & 0.94 \\ PBR3 & 44.50 \(\pm\) 4.18 & 16.79 \(\pm\) 2.94 & 2.65 \\ PBR4 & 49.90 \(\pm\) 2.06 & 9.21 \(\pm\) 1.66 & 5.42 \\ PBR5 & 49.05 \(\pm\) 21.18 & 8.16 \(\pm\) 0.52 & 6.01 \\ PBR6 & 13.09 \(\pm\) 1.56 & 12.65 \(\pm\) 0.37 & 1.03 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Characterization of proteins (EPS-PN) and polysaccharides (EPS-PS) present in the biomass.  
at the end of system operation. Thus, the photobioreactors with the best lipid production performance were PBR1, PBR5, and PBR6, which may be related to a higher final concentration of microalgae in the mixed liquor. The rapid doubling time of microalgae aids in the production and storage of saturated neutral lipids, resulting in a higher biomass yield for biofuel production [66]. PBR2 had the lowest oil content, which can be attributed to the system's initial inoculation with a 0:100 ratio (microalgae:bacteria). The oil content at the end of the batches may be related to the nutritional stress that the species went through during this feeding regime, since organic load did not reach the medium. This fact can be associated with the growth rate of organisms, which increased the cell density until nutrient depletion occurs, as noted in the experiments of [PERSON] et al. [67]. Then, as the growth rate slows, increased storage of high-energy compounds, such as lipids, is possible due to changes in metabolic processes.