## 3 Results  
### Growth Performances: Absorbance at 750 nm and Dry Weight  
_Chlorella vulgaris_ grew better on all three digestates in comparison to the F/2 control medium, both under pHM\({}^{+}\) and pHM\({}^{-}\) conditions (\(p\) < 0.001, Figure 1). Growth under pHM\({}^{-}\) was consistent over the 10 days of experiment, and the highest growth rate was recorded for the SU digestate (0.09 day\({}^{-1}\)). In pHM\({}^{+}\), the growth of _C. vulgaris_ was less linear, and cell clumping was observed in the cultures. The highest absorbance at 750 nm was recorded for the Innolab digestate, reaching 1.26 \(\pm\) 0.15 after 6 days of the experiment; however, this was followed by a decrease until the end of the experiment (Figure 1). The Cooperl digestate showed the second best performance, with an absorbance of 1.08 \(\pm\) 0.05, followed by the SU digestate (0.93 \(\pm\) 0.05) at the end of the experiment. The same growtht trends were observed for the flowcytometry data, which recorded the cell count in the cultures (Supplementary Material, Figure S3). Under pHM\({}^{-}\), _S. obliquus_ showed the best performances in the Cooperl digestate (\(p<0.001\); GR: 0.099 \(\pm\) 0.002 day\({}^{-1}\)), followed by the SU digestate (GR: 0.074 \(\pm\) 0.001 day\({}^{-1}\)), the F/2 control (GR: 0.067 \(\pm\) 0.001 day\({}^{-1}\)), and the Innolab digestate (GR: 0.027 \(\pm\) 0.001 day\({}^{-1}\)). Under pHM\({}^{+}\), growth was more consistent between conditions, and the performances were very similar between digestates (GR: 0.081 \(\pm\) 0.001 day\({}^{-1}\); 0.067 \(\pm\) 0.001 day\({}^{-1}\) and 0.078 \(\pm\) 0.001 day\({}^{-1}\), for SU, Cooperl, and Innolab digestates, respectively). Growth was slightly lower for the F/2 control (GR: 0.059 \(\pm\) 0.002 day\({}^{-1}\)), but no significant differences were found between all of the tested conditions (\(p>0.05\), Figure 1). Additionally, there were no significant differences between the performances of the two strains when the pH was not manipulated (\(p<0.05\)); however, _S. obliquus_ showed significantly better growth under an acidic pH (\(p<0.001\)), overall reaching a higher absorbance at 750 nm at the end of the 10 days of the experiment (Figure 1). The dry weight analysis showed discrepancies at day 0 between the different conditions tested, despite inoculum concentrations being the same for both cultures of _C. vulgaris_ and _S. obliquus_ (Figure 2). Indeed, despite the use of membrane filtration to treat the three different digestates, a significant number of particles can still be found in the filtration permeates, therefore contributing to the dry weights recorded at the start of the experiment. The dry weight significantly increased during the time of the experiment (\(p<0.01\)), and differences observed between conditions after 10 days were mainly related to microalgal growth. Results showed that the dry weight in cultures of _C. vulgaris_ was higher in the Innolab digestate and under pHM\({}^{-}\) (0.28 \(\pm\) 0.025 g L\({}^{-1}\)), whereas, in pHM\({}^{+}\), dry weight was the highest in the Cooperl digestate (0.49 \(\pm\) 0.012 g L\({}^{-1}\)). Overall, the DW was significantly higher in cultures of _C. vulgaris_ in pHM\({}^{+}\) for all digestates tested and the F/2 control (\(p<0.001\)), even doubling in some of the studied conditions (Figure 2). Figure 1: Absorbance at 750 nm for _C. vulgaris_ and _S. obliquus_ grown on three different digestates under pH manipulation and no pH manipulation for 10 days of the experiment. Error bars represent the standard deviation on three replicates. In cultures of _S. obliquus_, the pH manipulation resulted in a higher dry weight in the Innolab digestate and the F/2 control (\(p\) < 0.001); however, no significant changes were observed in the Cooperl and SU digestates, with a DW of around 0.23 \(\pm\) 0.002 g L\({}^{-1}\) in pHM\({}^{-/+}\) and in both digestates (\(p\) > 0.05). Finally, _C. vulgaris_ yielded a higher dry weight at the end of the experiment under pHM\({}^{+}\), in comparison to cultures of _S.