## 3 Results and Discussion  
### Microalgal Growth  
The _C. vulgaris_ growth curves in raw and diluted paper industry effluent are shown in Figure 2. These results evidence the inexistence of an adaptation phase for all assays and an exponential growth phase that lasted approximately four days. In addition, no cell decay was observed during the 11-day batch culture, indicating that the experiments could be extended for a longer period. The increase of biomass concentration during the cultivation period, as well as the lack of an adaptation phase, shows that _C. vulgaris_ was able to grow in this effluent. However, biomass concentrations achieved in non-diluted effluent (assay 1) were statistically lower (\(p<0.05\)) than those achieved in more diluted effluents from assays 3-5. Figure 2: _C. vulgaris_ cultures growth curves in raw and diluted secondary-treated paper industry effluent: (**A**) Assay 1——; (**B**) Assay 2——; (**C**) Assay 3——; (**D**) Assay 4—; and (**E**) Assay 5—. Error bars correspond to the standard deviation of the mean obtained from two independent experiments. To complement the analysis from growth curves, microalgal growth parameters, such as specific growth rate, maximum biomass concentration, and maximum and average biomass productivities, were determined and presented in Table 2. From these data, it is possible to see a general increase in growth parameters from assay 1 to assay 5, i.e., from the non-diluted effluent to the more diluted one. Regarding specific growth rates, values ranged from (0.093 \(\pm\) 0.007) d\({}^{-1}\) to (0.16 \(\pm\) 0.02) d\({}^{-1}\) in assays 1 and 5, respectively. The highest values of maximum biomass concentrations were also obtained in more diluted effluents from assays 4 and 5: (249 \(\pm\) 14) mgdw L\({}^{-1}\) and (231 \(\pm\) 31) mgdw L\({}^{-1}\), respectively. Similar behavior was observed for both maximum and average biomass productivities. Maximum biomass productivities/average biomass productivities obtained in assays 4 and 5 were (30 \(\pm\) 3)/(16 \(\pm\) 1) mgdw L\({}^{-1}\) d\({}^{-1}\) and (30 \(\pm\) 6)/(15 \(\pm\) 3) mgdw L\({}^{-1}\) d\({}^{-1}\), respectively. In opposition, maximum and average biomass productivities obtained in assay 1 were (9.8 \(\pm\) 0.2) mgdw L\({}^{-1}\) d\({}^{-1}\) and (6.2 \(\pm\) 0.1) mgdw L\({}^{-1}\) d\({}^{-1}\), respectively. In contrast to what was observed by [PERSON] [13], the increment in nitrogen and phosphorus concentration did not contribute to an increase in kinetic growth parameters. Accordingly, these results may indicate inhibitory effects of the effluent on microalgae, which can influence microalgal cultures in different ways [19; 20; 21]: (i) the effluent color may act as a barrier to light penetration, thus limiting microalgal access to light and photosynthetic activity; and (ii) paper industry effluents are characterized by the presence of lignin, humic acids, furans, and dioxins and by high levels of aluminum and manganese, which exhibit toxic effects on microalgae. Most studies regarding the bioremediation of paper industry effluents with microalgae focus on the removal of contaminants and only a few report biomass production yields. [PERSON], et al. [20] reported that the maximum specific growth rate obtained for _Nannochloropsis couldn_ grown in effluents resulting from pulp and paper industry was 0.405 d\({}^{-1}\). [PERSON], et al. [19] revealed that maximum biomass concentrations achieved by _Scenedesmus acuninatus_ and _C. vulgaris_ grown in paper industry effluents were 291 mg L\({}^{-1}\) and 822 mg L\({}^{-1}\), respectively. Considering the values referred in the literature, microalgal growth parameters obtained in this study were significantly lower, which can be attributed to the inhibitory effects promoted by the effluent used (in assays 1-3) and to the low concentration of some essential nutrients (in more diluted effluents of assays 4 and 5).